Move 2018 arm code to frc971 and make dynamics adjustable

Signed-off-by: Maxwell Henderson <mxwhenderson@gmail.com>
Change-Id: I16e7bbb0d293aca461abc931f560fb9066b19aaf
diff --git a/frc971/control_loops/double_jointed_arm/BUILD b/frc971/control_loops/double_jointed_arm/BUILD
new file mode 100644
index 0000000..c7fcefc
--- /dev/null
+++ b/frc971/control_loops/double_jointed_arm/BUILD
@@ -0,0 +1,121 @@
+cc_library(
+    name = "trajectory",
+    srcs = [
+        "trajectory.cc",
+    ],
+    hdrs = [
+        "trajectory.h",
+    ],
+    target_compatible_with = ["@platforms//os:linux"],
+    visibility = ["//visibility:public"],
+    deps = [
+        ":dynamics",
+        "//aos/logging",
+        "//frc971/control_loops:dlqr",
+        "//frc971/control_loops:jacobian",
+        "@org_tuxfamily_eigen//:eigen",
+    ],
+)
+
+cc_test(
+    name = "trajectory_test",
+    srcs = [
+        "trajectory_test.cc",
+    ],
+    target_compatible_with = ["@platforms//os:linux"],
+    deps = [
+        ":demo_path",
+        ":dynamics",
+        ":ekf",
+        ":test_constants",
+        ":trajectory",
+        "//aos/testing:googletest",
+        "@org_tuxfamily_eigen//:eigen",
+    ],
+)
+
+cc_library(
+    name = "dynamics",
+    srcs = [
+        "dynamics.cc",
+    ],
+    hdrs = [
+        "dynamics.h",
+    ],
+    target_compatible_with = ["@platforms//os:linux"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//frc971/control_loops:runge_kutta",
+        "@com_github_gflags_gflags//:gflags",
+        "@org_tuxfamily_eigen//:eigen",
+    ],
+)
+
+cc_library(
+    name = "demo_path",
+    srcs = [
+        "demo_path.cc",
+    ],
+    hdrs = ["demo_path.h"],
+    target_compatible_with = ["@platforms//os:linux"],
+    visibility = ["//visibility:public"],
+    deps = [":trajectory"],
+)
+
+cc_test(
+    name = "dynamics_test",
+    srcs = [
+        "dynamics_test.cc",
+    ],
+    target_compatible_with = ["@platforms//os:linux"],
+    deps = [
+        ":dynamics",
+        ":test_constants",
+        "//aos/testing:googletest",
+    ],
+)
+
+cc_library(
+    name = "ekf",
+    srcs = [
+        "ekf.cc",
+    ],
+    hdrs = [
+        "ekf.h",
+    ],
+    target_compatible_with = ["@platforms//os:linux"],
+    visibility = ["//visibility:public"],
+    deps = [
+        ":dynamics",
+        "//frc971/control_loops:jacobian",
+        "@org_tuxfamily_eigen//:eigen",
+    ],
+)
+
+cc_library(
+    name = "graph",
+    srcs = ["graph.cc"],
+    hdrs = ["graph.h"],
+    target_compatible_with = ["@platforms//os:linux"],
+    visibility = ["//visibility:public"],
+)
+
+cc_test(
+    name = "graph_test",
+    srcs = ["graph_test.cc"],
+    target_compatible_with = ["@platforms//os:linux"],
+    deps = [
+        ":graph",
+        "//aos/testing:googletest",
+    ],
+)
+
+cc_library(
+    name = "test_constants",
+    hdrs = ["test_constants.h"],
+    target_compatible_with = ["@platforms//os:linux"],
+    visibility = ["//visibility:public"],
+    deps = [
+        ":dynamics",
+    ],
+)
diff --git a/y2018/control_loops/superstructure/arm/demo_path.cc b/frc971/control_loops/double_jointed_arm/demo_path.cc
similarity index 98%
rename from y2018/control_loops/superstructure/arm/demo_path.cc
rename to frc971/control_loops/double_jointed_arm/demo_path.cc
index 03856c9..8d549d1 100644
--- a/y2018/control_loops/superstructure/arm/demo_path.cc
+++ b/frc971/control_loops/double_jointed_arm/demo_path.cc
@@ -1,12 +1,11 @@
-#include "y2018/control_loops/superstructure/arm/demo_path.h"
+#include "frc971/control_loops/double_jointed_arm/demo_path.h"
 
 #include <array>
 #include <initializer_list>
 #include <memory>
 
-namespace y2018 {
+namespace frc971 {
 namespace control_loops {
-namespace superstructure {
 namespace arm {
 
 ::std::vector<::std::array<double, 6>> FlipPath(
@@ -25,7 +24,6 @@
   return result;
 }
 
-
 ::std::unique_ptr<Path> MakeDemoPath() {
   return ::std::unique_ptr<Path>(new Path(FlipPath(
       {{{1.3583511559969876, 0.99753029519739866, 0.63708920330895369,
@@ -213,6 +211,5 @@
 }
 
 }  // namespace arm
-}  // namespace superstructure
 }  // namespace control_loops
-}  // namespace y2018
+}  // namespace frc971
diff --git a/frc971/control_loops/double_jointed_arm/demo_path.h b/frc971/control_loops/double_jointed_arm/demo_path.h
new file mode 100644
index 0000000..9a9d393
--- /dev/null
+++ b/frc971/control_loops/double_jointed_arm/demo_path.h
@@ -0,0 +1,19 @@
+#ifndef FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_DEMO_PATH_H_
+#define FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_DEMO_PATH_H_
+
+#include <memory>
+
+#include "frc971/control_loops/double_jointed_arm/trajectory.h"
+
+namespace frc971 {
+namespace control_loops {
+namespace arm {
+
+::std::unique_ptr<Path> MakeDemoPath();
+::std::unique_ptr<Path> MakeReversedDemoPath();
+
+}  // namespace arm
+}  // namespace control_loops
+}  // namespace frc971
+
+#endif  // FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_DEMO_PATH_H_
diff --git a/frc971/control_loops/double_jointed_arm/dynamics.cc b/frc971/control_loops/double_jointed_arm/dynamics.cc
new file mode 100644
index 0000000..b5b6c8d
--- /dev/null
+++ b/frc971/control_loops/double_jointed_arm/dynamics.cc
@@ -0,0 +1,37 @@
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
+
+DEFINE_bool(gravity, true, "If true, enable gravity.");
+
+namespace frc971 {
+namespace control_loops {
+namespace arm {
+
+Dynamics::Dynamics(ArmConstants arm_constants)
+    : arm_constants_(arm_constants),
+
+      K3_((::Eigen::Matrix<double, 2, 2>() << arm_constants_.g1 *
+                                                  arm_constants_.Kt /
+                                                  arm_constants_.resistance,
+           0.0, 0.0,
+           arm_constants_.g2 * arm_constants_.num_distal_motors *
+               arm_constants_.Kt / arm_constants_.resistance)
+              .finished()),
+
+      K3_inverse_(K3_.inverse()),
+      K4_((::Eigen::Matrix<double, 2, 2>()
+               << arm_constants_.g1 * arm_constants_.g1 * arm_constants_.Kt /
+                      (arm_constants_.Kv * arm_constants_.resistance),
+           0.0, 0.0,
+           arm_constants_.g2 * arm_constants_.g2 * arm_constants_.Kt *
+               arm_constants_.num_distal_motors /
+               (arm_constants_.Kv * arm_constants_.resistance))
+              .finished()),
+      alpha_(arm_constants_.j1 +
+             arm_constants_.r1 * arm_constants_.r1 * arm_constants_.m1 +
+             arm_constants_.l1 * arm_constants_.l1 * arm_constants_.m2),
+      beta_(arm_constants_.l1 * arm_constants_.r2 * arm_constants_.m2),
+      gamma_(arm_constants_.j2 +
+             arm_constants_.r2 * arm_constants_.r2 * arm_constants_.m2) {}
+}  // namespace arm
+}  // namespace control_loops
+}  // namespace frc971
diff --git a/frc971/control_loops/double_jointed_arm/dynamics.h b/frc971/control_loops/double_jointed_arm/dynamics.h
new file mode 100644
index 0000000..1e934bc
--- /dev/null
+++ b/frc971/control_loops/double_jointed_arm/dynamics.h
@@ -0,0 +1,195 @@
+#ifndef FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_DYNAMICS_H_
+#define FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_DYNAMICS_H_
+
+#include "Eigen/Dense"
+#include "frc971/control_loops/runge_kutta.h"
+#include "gflags/gflags.h"
+
+DECLARE_bool(gravity);
+
+namespace frc971 {
+namespace control_loops {
+namespace arm {
+
+struct ArmConstants {
+  // Below, 1 refers to the proximal joint, and 2 refers to the distal joint.
+  // Length of the joints in meters.
+  double l1;
+  double l2;
+
+  // Mass of the joints in kilograms.
+  double m1;
+  double m2;
+
+  // Moment of inertia of the joints in kg m^2
+  double j1;
+  double j2;
+
+  // Radius of the center of mass of the joints in meters.
+  double r1;
+  double r2;
+
+  // Gear ratios for the two joints.
+  double g1;
+  double g2;
+
+  // motor constants.
+  double efficiency_tweak;
+  double stall_torque;
+  double free_speed;
+  double stall_current;
+  double resistance;
+  double Kv;
+  double Kt;
+
+  // Number of motors on the distal joint.
+  double num_distal_motors;
+};
+
+// This class captures the dynamics of our system.  It doesn't actually need to
+// store state yet, so everything can be constexpr and/or static.
+class Dynamics {
+ public:
+  Dynamics(ArmConstants arm_constants);
+  // Generates K1-2 for the arm ODE.
+  // K1 * d^2 theta / dt^2 + K2 * d theta / dt = K3 * V - K4 * d theta/dt
+  // These matricies are missing the velocity factor for K2[1, 0], and K2[0, 1].
+  // You probbaly want MatriciesForState.
+  void NormilizedMatriciesForState(const ::Eigen::Matrix<double, 4, 1> &X,
+                                   ::Eigen::Matrix<double, 2, 2> *K1_result,
+                                   ::Eigen::Matrix<double, 2, 2> *K2_result) const {
+    const double angle = X(0, 0) - X(2, 0);
+    const double s = ::std::sin(angle);
+    const double c = ::std::cos(angle);
+    *K1_result << alpha_, c * beta_, c * beta_, gamma_;
+    *K2_result << 0.0, s * beta_, -s * beta_, 0.0;
+  }
+
+  // Generates K1-2 for the arm ODE.
+  // K1 * d^2 theta / dt^2 + K2 * d theta / dt = K3 * V - K4 * d theta/dt
+  void MatriciesForState(const ::Eigen::Matrix<double, 4, 1> &X,
+                         ::Eigen::Matrix<double, 2, 2> *K1_result,
+                         ::Eigen::Matrix<double, 2, 2> *K2_result) const {
+    NormilizedMatriciesForState(X, K1_result, K2_result);
+    (*K2_result)(1, 0) *= X(1, 0);
+    (*K2_result)(0, 1) *= X(3, 0);
+  }
+
+  // TODO(austin): We may want a way to provide K1 and K2 to save CPU cycles.
+
+  // Calculates the acceleration given the current state and control input.
+  const ::Eigen::Matrix<double, 4, 1> Acceleration(
+      const ::Eigen::Matrix<double, 4, 1> &X,
+      const ::Eigen::Matrix<double, 2, 1> &U) const {
+    ::Eigen::Matrix<double, 2, 2> K1;
+    ::Eigen::Matrix<double, 2, 2> K2;
+
+    MatriciesForState(X, &K1, &K2);
+
+    const ::Eigen::Matrix<double, 2, 1> velocity =
+        (::Eigen::Matrix<double, 2, 1>() << X(1, 0), X(3, 0)).finished();
+
+    const ::Eigen::Matrix<double, 2, 1> torque = K3_ * U - K4_ * velocity;
+    const ::Eigen::Matrix<double, 2, 1> gravity_torque = GravityTorque(X);
+
+    const ::Eigen::Matrix<double, 2, 1> accel =
+        K1.inverse() * (torque + gravity_torque - K2 * velocity);
+
+    return (::Eigen::Matrix<double, 4, 1>() << X(1, 0), accel(0, 0), X(3, 0),
+            accel(1, 0))
+        .finished();
+  }
+
+  // Calculates the acceleration given the current augmented kalman filter state
+  // and control input.
+  const ::Eigen::Matrix<double, 6, 1> EKFAcceleration(
+      const ::Eigen::Matrix<double, 6, 1> &X,
+      const ::Eigen::Matrix<double, 2, 1> &U) const {
+    ::Eigen::Matrix<double, 2, 2> K1;
+    ::Eigen::Matrix<double, 2, 2> K2;
+
+    MatriciesForState(X.block<4, 1>(0, 0), &K1, &K2);
+
+    const ::Eigen::Matrix<double, 2, 1> velocity =
+        (::Eigen::Matrix<double, 2, 1>() << X(1, 0), X(3, 0)).finished();
+
+    const ::Eigen::Matrix<double, 2, 1> torque =
+        K3_ *
+            (U +
+             (::Eigen::Matrix<double, 2, 1>() << X(4, 0), X(5, 0)).finished()) -
+        K4_ * velocity;
+    const ::Eigen::Matrix<double, 2, 1> gravity_torque =
+        GravityTorque(X.block<4, 1>(0, 0));
+
+    const ::Eigen::Matrix<double, 2, 1> accel =
+        K1.inverse() * (torque + gravity_torque - K2 * velocity);
+
+    return (::Eigen::Matrix<double, 6, 1>() << X(1, 0), accel(0, 0), X(3, 0),
+            accel(1, 0), 0.0, 0.0)
+        .finished();
+  }
+
+  // Calculates the voltage required to follow the trajectory.  This requires
+  // knowing the current state, desired angular velocity and acceleration.
+  const ::Eigen::Matrix<double, 2, 1> FF_U(
+      const ::Eigen::Matrix<double, 4, 1> &X,
+      const ::Eigen::Matrix<double, 2, 1> &omega_t,
+      const ::Eigen::Matrix<double, 2, 1> &alpha_t) const {
+    ::Eigen::Matrix<double, 2, 2> K1;
+    ::Eigen::Matrix<double, 2, 2> K2;
+
+    MatriciesForState(X, &K1, &K2);
+
+    const ::Eigen::Matrix<double, 2, 1> gravity_torque = GravityTorque(X);
+
+    return K3_inverse_ *
+           (K1 * alpha_t + K2 * omega_t + K4_ * omega_t - gravity_torque);
+  }
+
+  const ::Eigen::Matrix<double, 2, 1> GravityTorque(
+      const ::Eigen::Matrix<double, 4, 1> &X) const {
+    const double accel_due_to_gravity = 9.8 * arm_constants_.efficiency_tweak;
+    return (::Eigen::Matrix<double, 2, 1>()
+                << (arm_constants_.r1 * arm_constants_.m1 +
+                    arm_constants_.l1 * arm_constants_.m2) *
+                       ::std::sin(X(0)) * accel_due_to_gravity,
+            arm_constants_.r2 * arm_constants_.m2 * ::std::sin(X(2)) *
+                accel_due_to_gravity)
+               .finished() *
+           (FLAGS_gravity ? 1.0 : 0.0);
+  }
+
+  const ::Eigen::Matrix<double, 4, 1> UnboundedDiscreteDynamics(
+      const ::Eigen::Matrix<double, 4, 1> &X,
+      const ::Eigen::Matrix<double, 2, 1> &U, double dt) const {
+    return ::frc971::control_loops::RungeKuttaU(
+        [this](const auto &X, const auto &U) { return Acceleration(X, U); }, X,
+        U, dt);
+  }
+
+  const ::Eigen::Matrix<double, 6, 1> UnboundedEKFDiscreteDynamics(
+      const ::Eigen::Matrix<double, 6, 1> &X,
+      const ::Eigen::Matrix<double, 2, 1> &U, double dt) const {
+    return ::frc971::control_loops::RungeKuttaU(
+        [this](const auto &X, const auto &U) { return EKFAcceleration(X, U); },
+        X, U, dt);
+  }
+
+  const ArmConstants arm_constants_;
+
+  // K3, K4 matricies described above.
+  const ::Eigen::Matrix<double, 2, 2> K3_;
+  const ::Eigen::Matrix<double, 2, 2> K3_inverse_;
+  const ::Eigen::Matrix<double, 2, 2> K4_;
+
+ private:
+  const double alpha_;
+  const double beta_;
+  const double gamma_;
+};
+
+}  // namespace arm
+}  // namespace control_loops
+}  // namespace frc971
+
+#endif  // FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_DYNAMICS_H_
diff --git a/frc971/control_loops/double_jointed_arm/dynamics_test.cc b/frc971/control_loops/double_jointed_arm/dynamics_test.cc
new file mode 100644
index 0000000..6e12f75
--- /dev/null
+++ b/frc971/control_loops/double_jointed_arm/dynamics_test.cc
@@ -0,0 +1,53 @@
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
+#include "frc971/control_loops/double_jointed_arm/test_constants.h"
+
+#include "gtest/gtest.h"
+
+namespace frc971 {
+namespace control_loops {
+namespace arm {
+namespace testing {
+
+// Tests that zero inputs result in no acceleration and no motion.
+// This isn't all that rigerous, but it's a good start.
+TEST(DynamicsTest, Acceleration) {
+  Dynamics dynamics(kArmConstants);
+
+  EXPECT_TRUE(dynamics
+                  .Acceleration(::Eigen::Matrix<double, 4, 1>::Zero(),
+                                ::Eigen::Matrix<double, 2, 1>::Zero())
+                  .isApprox(::Eigen::Matrix<double, 4, 1>::Zero()));
+
+  EXPECT_TRUE(
+      dynamics
+          .UnboundedDiscreteDynamics(::Eigen::Matrix<double, 4, 1>::Zero(),
+                                     ::Eigen::Matrix<double, 2, 1>::Zero(), 0.1)
+          .isApprox(::Eigen::Matrix<double, 4, 1>::Zero()));
+
+  const ::Eigen::Matrix<double, 4, 1> X =
+      (::Eigen::Matrix<double, 4, 1>() << M_PI / 2.0, 0.0, 0.0, 0.0).finished();
+
+  ::std::cout << dynamics.FF_U(X, ::Eigen::Matrix<double, 2, 1>::Zero(),
+                               ::Eigen::Matrix<double, 2, 1>::Zero())
+              << ::std::endl;
+
+  ::std::cout << dynamics.UnboundedDiscreteDynamics(
+                     X,
+                     dynamics.FF_U(X, ::Eigen::Matrix<double, 2, 1>::Zero(),
+                                   ::Eigen::Matrix<double, 2, 1>::Zero()),
+                     0.01)
+              << ::std::endl;
+
+  EXPECT_TRUE(dynamics
+                  .UnboundedDiscreteDynamics(
+                      X,
+                      dynamics.FF_U(X, ::Eigen::Matrix<double, 2, 1>::Zero(),
+                                    ::Eigen::Matrix<double, 2, 1>::Zero()),
+                      0.01)
+                  .isApprox(X));
+}
+
+}  // namespace testing
+}  // namespace arm
+}  // namespace control_loops
+}  // namespace frc971
diff --git a/y2018/control_loops/superstructure/arm/ekf.cc b/frc971/control_loops/double_jointed_arm/ekf.cc
similarity index 87%
rename from y2018/control_loops/superstructure/arm/ekf.cc
rename to frc971/control_loops/double_jointed_arm/ekf.cc
index 48a71f4..a70e4a6 100644
--- a/y2018/control_loops/superstructure/arm/ekf.cc
+++ b/frc971/control_loops/double_jointed_arm/ekf.cc
@@ -1,19 +1,18 @@
-#include "y2018/control_loops/superstructure/arm/ekf.h"
+#include "frc971/control_loops/double_jointed_arm/ekf.h"
 
-#include "Eigen/Dense"
 #include <iostream>
 
+#include "Eigen/Dense"
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
 #include "frc971/control_loops/jacobian.h"
-#include "y2018/control_loops/superstructure/arm/dynamics.h"
 
 DEFINE_double(proximal_voltage_error_uncertainty, 8.0,
               "Proximal joint voltage error uncertainty.");
 DEFINE_double(distal_voltage_error_uncertainty, 2.0,
               "Distal joint voltage error uncertainty.");
 
-namespace y2018 {
+namespace frc971 {
 namespace control_loops {
-namespace superstructure {
 namespace arm {
 
 namespace {
@@ -29,7 +28,7 @@
         .asDiagonal());
 }  // namespace
 
-EKF::EKF() {
+EKF::EKF(const Dynamics *dynamics) : dynamics_(dynamics) {
   X_hat_.setZero();
   Q_covariance =
       ((::Eigen::DiagonalMatrix<double, 6>().diagonal() << ::std::pow(0.1, 2),
@@ -69,9 +68,12 @@
 void EKF::Predict(const ::Eigen::Matrix<double, 2, 1> &U, double dt) {
   const ::Eigen::Matrix<double, 6, 6> A =
       ::frc971::control_loops::NumericalJacobianX<6, 2>(
-          Dynamics::UnboundedEKFDiscreteDynamics, X_hat_, U, dt);
+          [this](const auto &X_hat_, const auto &U, double dt) {
+            return dynamics_->UnboundedEKFDiscreteDynamics(X_hat_, U, dt);
+          },
+          X_hat_, U, dt);
 
-  X_hat_ = Dynamics::UnboundedEKFDiscreteDynamics(X_hat_, U, dt);
+  X_hat_ = dynamics_->UnboundedEKFDiscreteDynamics(X_hat_, U, dt);
   P_ = A * P_ * A.transpose() + Q_covariance;
 }
 
@@ -83,8 +85,8 @@
           .asDiagonal());
   // H is the jacobian of the h(x) measurement prediction function
   const ::Eigen::Matrix<double, 2, 6> H_jacobian =
-      (::Eigen::Matrix<double, 2, 6>() << 1.0, 0.0, 0.0, 0.0, 0.0, 0.0,
-      0.0, 0.0, 1.0, 0.0, 0.0, 0.0)
+      (::Eigen::Matrix<double, 2, 6>() << 1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
+       0.0, 1.0, 0.0, 0.0, 0.0)
           .finished();
 
   // Update step Measurement residual error of proximal and distal joint
@@ -106,6 +108,5 @@
 }
 
 }  // namespace arm
-}  // namespace superstructure
 }  // namespace control_loops
-}  // namespace y2018
+}  // namespace frc971
diff --git a/y2018/control_loops/superstructure/arm/ekf.h b/frc971/control_loops/double_jointed_arm/ekf.h
similarity index 81%
rename from y2018/control_loops/superstructure/arm/ekf.h
rename to frc971/control_loops/double_jointed_arm/ekf.h
index 9ae8b47..d969e82 100644
--- a/y2018/control_loops/superstructure/arm/ekf.h
+++ b/frc971/control_loops/double_jointed_arm/ekf.h
@@ -1,11 +1,11 @@
-#ifndef Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_EKF_H_
-#define Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_EKF_H_
+#ifndef FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_EKF_H_
+#define FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_EKF_H_
 
 #include "Eigen/Dense"
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
 
-namespace y2018 {
+namespace frc971 {
 namespace control_loops {
-namespace superstructure {
 namespace arm {
 
 // An extended kalman filter for the Arm.
@@ -13,7 +13,7 @@
 //   [theta0, omega0, theta1, omega1, voltage error0, voltage error1]
 class EKF {
  public:
-  EKF();
+  EKF(const Dynamics *dynamics);
 
   // Resets the internal state back to X.  Resets the torque disturbance to 0.
   void Reset(const ::Eigen::Matrix<double, 4, 1> &X);
@@ -43,11 +43,12 @@
   ::Eigen::Matrix<double, 6, 6> P_half_converged_;
   ::Eigen::Matrix<double, 6, 6> P_converged_;
   ::Eigen::Matrix<double, 6, 6> P_reset_;
+
+  const Dynamics *dynamics_;
 };
 
 }  // namespace arm
-}  // namespace superstructure
 }  // namespace control_loops
-}  // namespace y2018
+}  // namespace frc971
 
-#endif  // Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_EKF_H_
+#endif  // FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_EKF_H_
diff --git a/y2018/control_loops/superstructure/arm/graph.cc b/frc971/control_loops/double_jointed_arm/graph.cc
similarity index 92%
rename from y2018/control_loops/superstructure/arm/graph.cc
rename to frc971/control_loops/double_jointed_arm/graph.cc
index ad6f982..b5a70ab 100644
--- a/y2018/control_loops/superstructure/arm/graph.cc
+++ b/frc971/control_loops/double_jointed_arm/graph.cc
@@ -1,11 +1,10 @@
-#include "y2018/control_loops/superstructure/arm/graph.h"
+#include "frc971/control_loops/double_jointed_arm/graph.h"
 
 #include <algorithm>
 #include <cassert>
 
-namespace y2018 {
+namespace frc971 {
 namespace control_loops {
-namespace superstructure {
 namespace arm {
 
 SearchGraph::SearchGraph(size_t num_vertexes, std::initializer_list<Edge> edges)
@@ -68,6 +67,5 @@
 }
 
 }  // namespace arm
-}  // namespace superstructure
 }  // namespace control_loops
-}  // namespace y2018
+}  // namespace frc971
diff --git a/y2018/control_loops/superstructure/arm/graph.h b/frc971/control_loops/double_jointed_arm/graph.h
similarity index 94%
rename from y2018/control_loops/superstructure/arm/graph.h
rename to frc971/control_loops/double_jointed_arm/graph.h
index 2300d6a..06d396c 100644
--- a/y2018/control_loops/superstructure/arm/graph.h
+++ b/frc971/control_loops/double_jointed_arm/graph.h
@@ -1,5 +1,5 @@
-#ifndef Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_GRAPH_H_
-#define Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_GRAPH_H_
+#ifndef FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_GRAPH_H_
+#define FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_GRAPH_H_
 
 #include <algorithm>
 #include <cassert>
@@ -8,9 +8,8 @@
 #include <memory>
 #include <vector>
 
-namespace y2018 {
+namespace frc971 {
 namespace control_loops {
-namespace superstructure {
 namespace arm {
 
 // Grr... normal priority queues don't allow modifying the node cost.
@@ -183,8 +182,7 @@
 };
 
 }  // namespace arm
-}  // namespace superstructure
 }  // namespace control_loops
-}  // namespace y2018
+}  // namespace frc971
 
-#endif  // Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_GRAPH_H_
+#endif  // FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_GRAPH_H_
diff --git a/y2018/control_loops/superstructure/arm/graph_test.cc b/frc971/control_loops/double_jointed_arm/graph_test.cc
similarity index 90%
rename from y2018/control_loops/superstructure/arm/graph_test.cc
rename to frc971/control_loops/double_jointed_arm/graph_test.cc
index 8f246a5..7b14ced 100644
--- a/y2018/control_loops/superstructure/arm/graph_test.cc
+++ b/frc971/control_loops/double_jointed_arm/graph_test.cc
@@ -1,10 +1,9 @@
-#include "y2018/control_loops/superstructure/arm/graph.h"
+#include "frc971/control_loops/double_jointed_arm/graph.h"
 
 #include "gtest/gtest.h"
 
-namespace y2018 {
+namespace frc971 {
 namespace control_loops {
-namespace superstructure {
 namespace arm {
 namespace testing {
 
@@ -68,6 +67,5 @@
 
 }  // namespace testing
 }  // namespace arm
-}  // namespace superstructure
 }  // namespace control_loops
-}  // namespace y2018
+}  // namespace frc971
diff --git a/frc971/control_loops/double_jointed_arm/test_constants.h b/frc971/control_loops/double_jointed_arm/test_constants.h
new file mode 100644
index 0000000..ea1d3b7
--- /dev/null
+++ b/frc971/control_loops/double_jointed_arm/test_constants.h
@@ -0,0 +1,53 @@
+#ifndef FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_TEST_CONSTANTS_H_
+#define FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_TEST_CONSTANTS_H_
+
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
+
+namespace frc971 {
+namespace control_loops {
+namespace arm {
+namespace testing {
+
+constexpr double kEfficiencyTweak = 0.95;
+constexpr double kStallTorque = 1.41 * kEfficiencyTweak;
+constexpr double kFreeSpeed = (5840.0 / 60.0) * 2.0 * M_PI;
+constexpr double kStallCurrent = 89.0;
+
+constexpr ArmConstants kArmConstants = {
+    .l1 = 46.25 * 0.0254,
+    .l2 = 41.80 * 0.0254,
+    .m1 = 9.34 / 2.2,
+    .m2 = 9.77 / 2.2,
+
+    // Moment of inertia of the joints in kg m^2
+    .j1 = 2957.05 * 0.0002932545454545454,
+    .j2 = 2824.70 * 0.0002932545454545454,
+
+    // Radius of the center of mass of the joints in meters.
+    .r1 = 21.64 * 0.0254,
+    .r2 = 26.70 * 0.0254,
+
+    // Gear ratios for the two joints.
+    .g1 = 140.0,
+    .g2 = 90.0,
+
+    // MiniCIM motor constants.
+    .efficiency_tweak = kEfficiencyTweak,
+    .stall_torque = kStallTorque,
+    .free_speed = kFreeSpeed,
+    .stall_current = kStallCurrent,
+    .resistance = 12.0 / kStallCurrent,
+    .Kv = kFreeSpeed / 12.0,
+    .Kt = kStallTorque / kStallCurrent,
+
+    // Number of motors on the distal joint.
+    .num_distal_motors = 2.0,
+};
+
+} // namespace testing
+} // namespace arm
+} // namespace control_loops
+} // namespace frc971
+
+#endif // FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_TEST_CONSTANTS_H_
+
diff --git a/y2018/control_loops/superstructure/arm/trajectory.cc b/frc971/control_loops/double_jointed_arm/trajectory.cc
similarity index 92%
rename from y2018/control_loops/superstructure/arm/trajectory.cc
rename to frc971/control_loops/double_jointed_arm/trajectory.cc
index c6e09dd..d389eee 100644
--- a/y2018/control_loops/superstructure/arm/trajectory.cc
+++ b/frc971/control_loops/double_jointed_arm/trajectory.cc
@@ -1,20 +1,19 @@
-#include "y2018/control_loops/superstructure/arm/trajectory.h"
+#include "frc971/control_loops/double_jointed_arm/trajectory.h"
 
 #include "Eigen/Dense"
 #include "aos/logging/logging.h"
 #include "frc971/control_loops/dlqr.h"
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
 #include "frc971/control_loops/jacobian.h"
 #include "gflags/gflags.h"
-#include "y2018/control_loops/superstructure/arm/dynamics.h"
 
 DEFINE_double(lqr_proximal_pos, 0.15, "Position LQR gain");
 DEFINE_double(lqr_proximal_vel, 4.0, "Velocity LQR gain");
 DEFINE_double(lqr_distal_pos, 0.20, "Position LQR gain");
 DEFINE_double(lqr_distal_vel, 4.0, "Velocity LQR gain");
 
-namespace y2018 {
+namespace frc971 {
 namespace control_loops {
-namespace superstructure {
 namespace arm {
 
 Path Path::Reversed(const Path &p) {
@@ -106,9 +105,9 @@
     ::Eigen::Matrix<double, 2, 2> K2;
 
     const ::Eigen::Matrix<double, 2, 1> gravity_volts =
-        Dynamics::K3_inverse * Dynamics::GravityTorque(X);
+        dynamics_->K3_inverse_ * dynamics_->GravityTorque(X);
 
-    Dynamics::NormilizedMatriciesForState(X, &K1, &K2);
+    dynamics_->NormilizedMatriciesForState(X, &K1, &K2);
 
     const ::Eigen::Matrix<double, 2, 2> omega_square =
         (::Eigen::Matrix<double, 2, 2>() << omega(0, 0), 0.0, 0.0, omega(1, 0))
@@ -123,18 +122,18 @@
         ::std::sqrt(1.0 / ::std::max(0.001, (alpha_unitizer * alpha).norm()));
 
     const ::Eigen::Matrix<double, 2, 1> vk1 =
-        Dynamics::K3_inverse * (K1 * alpha + K2 * omega_square * omega);
+        dynamics_->K3_inverse_ * (K1 * alpha + K2 * omega_square * omega);
     const ::Eigen::Matrix<double, 2, 1> vk2 =
-        Dynamics::K3_inverse * Dynamics::K4 * omega;
+        dynamics_->K3_inverse_ * dynamics_->K4_ * omega;
 
     // Loop through all the various vmin, plan_vmax combinations.
     for (const double c : {-plan_vmax, plan_vmax}) {
       // Also loop through saturating theta0 and theta1
       for (const ::std::tuple<double, double, double> &abgravity :
            {::std::tuple<double, double, double>{vk1(0), vk2(0),
-                                                gravity_volts(0)},
+                                                 gravity_volts(0)},
             ::std::tuple<double, double, double>{vk1(1), vk2(1),
-                                                gravity_volts(1)}}) {
+                                                 gravity_volts(1)}}) {
         const double a = ::std::get<0>(abgravity);
         const double b = ::std::get<1>(abgravity);
         const double gravity = ::std::get<2>(abgravity);
@@ -178,19 +177,19 @@
   ::Eigen::Matrix<double, 2, 2> K1;
   ::Eigen::Matrix<double, 2, 2> K2;
 
-  Dynamics::NormilizedMatriciesForState(X, &K1, &K2);
+  dynamics_->NormilizedMatriciesForState(X, &K1, &K2);
 
   const ::Eigen::Matrix<double, 2, 2> omega_square =
       (::Eigen::Matrix<double, 2, 2>() << omega(0, 0), 0.0, 0.0, omega(1, 0))
           .finished();
 
   const ::Eigen::Matrix<double, 2, 1> k_constant =
-      Dynamics::K3_inverse *
+      dynamics_->K3_inverse_ *
       ((K1 * alpha + K2 * omega_square * omega) * goal_velocity *
            goal_velocity +
-       Dynamics::K4 * omega * goal_velocity - Dynamics::GravityTorque(X));
+       dynamics_->K4_ * omega * goal_velocity - dynamics_->GravityTorque(X));
   const ::Eigen::Matrix<double, 2, 1> k_scalar =
-      Dynamics::K3_inverse * K1 * omega;
+      dynamics_->K3_inverse_ * K1 * omega;
 
   const double constraint_goal_acceleration =
       ::std::sqrt(
@@ -236,19 +235,19 @@
   ::Eigen::Matrix<double, 2, 2> K1;
   ::Eigen::Matrix<double, 2, 2> K2;
 
-  Dynamics::NormilizedMatriciesForState(X, &K1, &K2);
+  dynamics_->NormilizedMatriciesForState(X, &K1, &K2);
 
   const ::Eigen::Matrix<double, 2, 2> omega_square =
       (::Eigen::Matrix<double, 2, 2>() << omega(0, 0), 0.0, 0.0, omega(1, 0))
           .finished();
 
   const ::Eigen::Matrix<double, 2, 1> k_constant =
-      Dynamics::K3_inverse *
+      dynamics_->K3_inverse_ *
       ((K1 * alpha + K2 * omega_square * omega) * goal_velocity *
            goal_velocity +
-       Dynamics::K4 * omega * goal_velocity - Dynamics::GravityTorque(X));
+       dynamics_->K4_ * omega * goal_velocity - dynamics_->GravityTorque(X));
   const ::Eigen::Matrix<double, 2, 1> k_scalar =
-      Dynamics::K3_inverse * K1 * omega;
+      dynamics_->K3_inverse_ * K1 * omega;
 
   const double constraint_goal_acceleration =
       ::std::sqrt(
@@ -390,12 +389,22 @@
           .finished()
           .asDiagonal();
 
+  const auto x_blocked = X.block<4, 1>(0, 0);
+
   const ::Eigen::Matrix<double, 4, 4> final_A =
       ::frc971::control_loops::NumericalJacobianX<4, 2>(
-          Dynamics::UnboundedDiscreteDynamics, X.block<4, 1>(0, 0), U, 0.00505);
+          [this](const auto &x_blocked, const auto &U, double dt) {
+            return this->dynamics_->UnboundedDiscreteDynamics(
+                x_blocked, U, dt);
+          },
+          x_blocked, U, 0.00505);
+
   const ::Eigen::Matrix<double, 4, 2> final_B =
       ::frc971::control_loops::NumericalJacobianU<4, 2>(
-          Dynamics::UnboundedDiscreteDynamics, X.block<4, 1>(0, 0), U, 0.00505);
+          [this](const auto &x_blocked, const auto &U, double dt) {
+            return this->dynamics_->UnboundedDiscreteDynamics(x_blocked, U, dt);
+          },
+          x_blocked, U, 0.00505);
 
   ::Eigen::Matrix<double, 4, 4> S;
   ::Eigen::Matrix<double, 2, 4> sub_K;
@@ -441,7 +450,7 @@
                         *saturation_goal_acceleration);
   const ::Eigen::Matrix<double, 6, 1> R = trajectory.R(theta_t, omega_t);
   const ::Eigen::Matrix<double, 2, 1> U_ff =
-      Dynamics::FF_U(R.block<4, 1>(0, 0), omega_t, alpha_t);
+      dynamics_->FF_U(R.block<4, 1>(0, 0), omega_t, alpha_t);
 
   *U = U_ff + K * (R - X);
 }
@@ -494,11 +503,11 @@
       U_unsaturated_.setZero();
     } else {
       const ::Eigen::Matrix<double, 6, 1> R =
-          trajectory_->R(theta_, ::Eigen::Matrix<double, 2, 1>::Zero());
+          Trajectory::R(theta_, ::Eigen::Matrix<double, 2, 1>::Zero());
 
-      U_ff_ = Dynamics::FF_U(X.block<4, 1>(0, 0),
-                             ::Eigen::Matrix<double, 2, 1>::Zero(),
-                             ::Eigen::Matrix<double, 2, 1>::Zero());
+      U_ff_ = dynamics_->FF_U(
+          X.block<4, 1>(0, 0), ::Eigen::Matrix<double, 2, 1>::Zero(),
+          ::Eigen::Matrix<double, 2, 1>::Zero());
       const ::Eigen::Matrix<double, 2, 6> K = K_at_state(X, U_ff_);
       U_ = U_unsaturated_ = U_ff_ + K * (R - X);
 
@@ -558,7 +567,7 @@
 
   const ::Eigen::Matrix<double, 6, 1> R = trajectory_->R(theta_t, omega_t);
 
-  U_ff_ = Dynamics::FF_U(R.block<4, 1>(0, 0), omega_t, alpha_t);
+  U_ff_ = dynamics_->FF_U(R.block<4, 1>(0, 0), omega_t, alpha_t);
 
   const ::Eigen::Matrix<double, 2, 6> K = K_at_state(X, U_ff_);
   U_ = U_unsaturated_ = U_ff_ + K * (R - X);
@@ -613,6 +622,5 @@
 }
 
 }  // namespace arm
-}  // namespace superstructure
 }  // namespace control_loops
-}  // namespace y2018
+}  // namespace frc971
diff --git a/y2018/control_loops/superstructure/arm/trajectory.h b/frc971/control_loops/double_jointed_arm/trajectory.h
similarity index 93%
rename from y2018/control_loops/superstructure/arm/trajectory.h
rename to frc971/control_loops/double_jointed_arm/trajectory.h
index a3a4246..a194a03 100644
--- a/y2018/control_loops/superstructure/arm/trajectory.h
+++ b/frc971/control_loops/double_jointed_arm/trajectory.h
@@ -1,5 +1,5 @@
-#ifndef Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_TRAJECTORY_H_
-#define Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_TRAJECTORY_H_
+#ifndef FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_TRAJECTORY_H_
+#define FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_TRAJECTORY_H_
 
 #include <array>
 #include <initializer_list>
@@ -7,10 +7,10 @@
 #include <vector>
 
 #include "Eigen/Dense"
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
 
-namespace y2018 {
+namespace frc971 {
 namespace control_loops {
-namespace superstructure {
 namespace arm {
 
 // This class represents a path in theta0, theta1 space.  It also returns the
@@ -90,8 +90,10 @@
  public:
   // Constructs a trajectory (but doesn't calculate it) given a path and a step
   // size.
-  Trajectory(::std::unique_ptr<const Path> path, double gridsize)
-      : path_(::std::move(path)),
+  Trajectory(const Dynamics *dynamics, ::std::unique_ptr<const Path> path,
+             double gridsize)
+      : dynamics_(dynamics),
+        path_(::std::move(path)),
         num_plan_points_(
             static_cast<size_t>(::std::ceil(path_->length() / gridsize) + 1)),
         step_size_(path_->length() /
@@ -220,7 +222,8 @@
   double GetDAcceleration(double distance) const {
     return GetDAcceleration(distance, max_dvelocity_);
   }
-  double GetDAcceleration(double distance, const ::std::vector<double> &plan) const {
+  double GetDAcceleration(double distance,
+                          const ::std::vector<double> &plan) const {
     ::std::pair<size_t, size_t> indices = IndicesForDistance(distance);
     const double v0 = plan[indices.first];
     const double v1 = plan[indices.second];
@@ -276,6 +279,7 @@
 
   const Path &path() const { return *path_; }
 
+
  private:
   friend class testing::TrajectoryTest_IndicesForDistanceTest_Test;
 
@@ -298,6 +302,8 @@
     return ::std::pair<size_t, size_t>(lower_index, lower_index + 1);
   }
 
+  const Dynamics *dynamics_;
+
   // The path to follow.
   ::std::unique_ptr<const Path> path_;
   // The number of points in the plan.
@@ -315,14 +321,16 @@
 // This class tracks the current goal along trajectories and paths.
 class TrajectoryFollower {
  public:
-  TrajectoryFollower(const ::Eigen::Matrix<double, 2, 1> &theta)
-      : trajectory_(nullptr), theta_(theta) {
+  TrajectoryFollower(const Dynamics *dynamics,
+                     const ::Eigen::Matrix<double, 2, 1> &theta)
+      : dynamics_(dynamics), trajectory_(nullptr), theta_(theta) {
     omega_.setZero();
     last_K_.setZero();
     Reset();
   }
 
-  TrajectoryFollower(Trajectory *const trajectory) : trajectory_(trajectory) {
+  TrajectoryFollower(const Dynamics *dynamics, Trajectory *const trajectory)
+      : dynamics_(dynamics), trajectory_(trajectory) {
     last_K_.setZero();
     Reset();
   }
@@ -405,6 +413,7 @@
   int failed_solutions() const { return failed_solutions_; }
 
  private:
+  const Dynamics *dynamics_;
   // The trajectory plan.
   const Trajectory *trajectory_ = nullptr;
 
@@ -431,8 +440,7 @@
 };
 
 }  // namespace arm
-}  // namespace superstructure
 }  // namespace control_loops
-}  // namespace y2018
+}  // namespace frc971
 
-#endif  // Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_TRAJECTORY_H_
+#endif  // FRC971_CONTROL_LOOPS_DOUBLE_JOINTED_ARM_TRAJECTORY_H_
diff --git a/y2018/control_loops/superstructure/arm/trajectory_test.cc b/frc971/control_loops/double_jointed_arm/trajectory_test.cc
similarity index 86%
rename from y2018/control_loops/superstructure/arm/trajectory_test.cc
rename to frc971/control_loops/double_jointed_arm/trajectory_test.cc
index b91c5a4..e700282 100644
--- a/y2018/control_loops/superstructure/arm/trajectory_test.cc
+++ b/frc971/control_loops/double_jointed_arm/trajectory_test.cc
@@ -1,13 +1,13 @@
-#include "y2018/control_loops/superstructure/arm/trajectory.h"
+#include "frc971/control_loops/double_jointed_arm/trajectory.h"
+#include "frc971/control_loops/double_jointed_arm/test_constants.h"
 
+#include "frc971/control_loops/double_jointed_arm/demo_path.h"
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
+#include "frc971/control_loops/double_jointed_arm/ekf.h"
 #include "gtest/gtest.h"
-#include "y2018/control_loops/superstructure/arm/demo_path.h"
-#include "y2018/control_loops/superstructure/arm/dynamics.h"
-#include "y2018/control_loops/superstructure/arm/ekf.h"
 
-namespace y2018 {
+namespace frc971 {
 namespace control_loops {
-namespace superstructure {
 namespace arm {
 namespace testing {
 
@@ -75,20 +75,22 @@
       (::Eigen::Matrix<double, 2, 1>() << 3.0, 0.0).finished()));
 }
 
-
-// Tests that we can compute the indices of the plan for a given distance correctly.
+// Tests that we can compute the indices of the plan for a given distance
+// correctly.
 TEST(TrajectoryTest, IndicesForDistanceTest) {
   // Start with a stupid simple plan.
   Path p({{{0.0, 0.0, 1.0, 0.0, 0.0, 0.0}},
           {{1.0, 0.0, 1.0, 0.0, 0.0, 0.0}},
           {{2.0, 0.0, 1.0, 0.0, 0.0, 0.0}},
           {{3.0, 0.0, 1.0, 0.0, 0.0, 0.0}}});
-  Trajectory t(::std::unique_ptr<Path>(new Path(p)), 0.1);
+  Dynamics dynamics(kArmConstants);
+  Trajectory t(&dynamics, ::std::unique_ptr<Path>(new Path(p)), 0.1);
 
   // 0 - 3.0 every 0.1 should be 31 points.
   EXPECT_EQ(t.num_plan_points(), 31);
 
-  // Verify that something centered in a grid cell returns the points on either side.
+  // Verify that something centered in a grid cell returns the points on either
+  // side.
   EXPECT_EQ(::std::make_pair(static_cast<size_t>(0), static_cast<size_t>(1)),
             t.IndicesForDistance(0.05));
   EXPECT_EQ(::std::make_pair(static_cast<size_t>(1), static_cast<size_t>(2)),
@@ -145,17 +147,21 @@
   EXPECT_NEAR(path->length(), reversed_path->length(), 1e-6);
 
   for (double d = 0; d < path->length(); d += 0.01) {
-    EXPECT_TRUE(path->Theta(d).isApprox(reversed_path->Theta(path->length() - d)));
-    EXPECT_TRUE(path->Omega(d).isApprox(-reversed_path->Omega(path->length() - d)));
-    EXPECT_TRUE(path->Alpha(d).isApprox(reversed_path->Alpha(path->length() - d)));
+    EXPECT_TRUE(
+        path->Theta(d).isApprox(reversed_path->Theta(path->length() - d)));
+    EXPECT_TRUE(
+        path->Omega(d).isApprox(-reversed_path->Omega(path->length() - d)));
+    EXPECT_TRUE(
+        path->Alpha(d).isApprox(reversed_path->Alpha(path->length() - d)));
   }
 }
 
 // Tests that we can follow a path.  Look at :trajectory_plot if you want to see
 // the path.
 TEST(TrajectoryTest, RunTrajectory) {
+  Dynamics dynamics(kArmConstants);
   ::std::unique_ptr<Path> path = MakeDemoPath();
-  Trajectory trajectory(::std::move(path), 0.001);
+  Trajectory trajectory(&dynamics, ::std::move(path), 0.001);
 
   constexpr double kAlpha0Max = 40.0;
   constexpr double kAlpha1Max = 60.0;
@@ -174,16 +180,17 @@
     X << theta_t(0), 0.0, theta_t(1), 0.0;
   }
 
-  EKF arm_ekf;
+  EKF arm_ekf(&dynamics);
   arm_ekf.Reset(X);
 
-  TrajectoryFollower follower(&trajectory);
+  TrajectoryFollower follower(&dynamics, &trajectory);
   constexpr double sim_dt = 0.00505;
   while (t < 1.0) {
     arm_ekf.Correct((::Eigen::Matrix<double, 2, 1>() << X(0), X(2)).finished(),
                     sim_dt);
     follower.Update(arm_ekf.X_hat(), false, sim_dt, vmax, 12.0);
-    X = Dynamics::UnboundedDiscreteDynamics(X, follower.U(), sim_dt);
+
+    X = dynamics.UnboundedDiscreteDynamics(X, follower.U(), sim_dt);
     arm_ekf.Predict(follower.U(), sim_dt);
     t += sim_dt;
   }
@@ -204,6 +211,5 @@
 
 }  // namespace testing
 }  // namespace arm
-}  // namespace superstructure
 }  // namespace control_loops
-}  // namespace y2018
+}  // namespace frc971
diff --git a/y2018/BUILD b/y2018/BUILD
index ac59493..8feaac4 100644
--- a/y2018/BUILD
+++ b/y2018/BUILD
@@ -57,9 +57,10 @@
         "//aos/network:team_number",
         "//aos/stl_mutex",
         "//frc971:constants",
+        "//frc971/control_loops/double_jointed_arm:dynamics",
         "//frc971/shooter_interpolation:interpolation",
         "//y2018/control_loops/drivetrain:polydrivetrain_plants",
-        "//y2018/control_loops/superstructure/arm:dynamics",
+        "//y2018/control_loops/superstructure/arm:arm_constants",
         "//y2018/control_loops/superstructure/intake:intake_plants",
         "@com_github_google_glog//:glog",
     ],
diff --git a/y2018/constants.h b/y2018/constants.h
index 16f1f8c..2a6f0ac 100644
--- a/y2018/constants.h
+++ b/y2018/constants.h
@@ -6,7 +6,8 @@
 
 #include "frc971/constants.h"
 #include "y2018/control_loops/drivetrain/drivetrain_dog_motor_plant.h"
-#include "y2018/control_loops/superstructure/arm/dynamics.h"
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
+#include "y2018/control_loops/superstructure/arm/arm_constants.h"
 #include "y2018/control_loops/superstructure/intake/intake_plant.h"
 
 namespace y2018 {
@@ -49,8 +50,8 @@
     return (12.0 / 60.0) * (18.0 / 84.0);
   }
   static constexpr double kMaxProximalEncoderPulsesPerSecond() {
-    return control_loops::superstructure::arm::Dynamics::kFreeSpeed /
-           (2.0 * M_PI) / control_loops::superstructure::arm::Dynamics::kG1 /
+    return control_loops::superstructure::arm::kArmConstants.free_speed /
+           (2.0 * M_PI) / control_loops::superstructure::arm::kArmConstants.g1 /
            kProximalEncoderRatio() * kProximalEncoderCountsPerRevolution();
   }
   static constexpr double kProximalPotRatio() { return (12.0 / 60.0); }
@@ -58,8 +59,8 @@
   static constexpr double kDistalEncoderCountsPerRevolution() { return 4096.0; }
   static constexpr double kDistalEncoderRatio() { return (12.0 / 60.0); }
   static constexpr double kMaxDistalEncoderPulsesPerSecond() {
-    return control_loops::superstructure::arm::Dynamics::kFreeSpeed /
-           (2.0 * M_PI) / control_loops::superstructure::arm::Dynamics::kG2 /
+    return control_loops::superstructure::arm::kArmConstants.free_speed /
+           (2.0 * M_PI) / control_loops::superstructure::arm::kArmConstants.g2 /
            kDistalEncoderRatio() * kProximalEncoderCountsPerRevolution();
   }
   static constexpr double kDistalPotRatio() {
diff --git a/y2018/control_loops/python/graph_codegen.py b/y2018/control_loops/python/graph_codegen.py
index e7f8ce1..be267de 100644
--- a/y2018/control_loops/python/graph_codegen.py
+++ b/y2018/control_loops/python/graph_codegen.py
@@ -27,12 +27,12 @@
     cc_file.append("                             %s," % (alpha_unitizer))
     if reverse:
         cc_file.append(
-            "                             Trajectory(Path::Reversed(%s()), 0.005));"
+            "                             Trajectory(dynamics, Path::Reversed(%s()), 0.005));"
             % (path_function_name(str(name))))
     else:
         cc_file.append(
-            "                             Trajectory(%s(), 0.005));" %
-            (path_function_name(str(name))))
+            "                             Trajectory(dynamics, %s(), 0.005));"
+            % (path_function_name(str(name))))
 
     start_index = None
     end_index = None
@@ -68,9 +68,14 @@
     cc_file.append("#include <memory>")
     cc_file.append("")
     cc_file.append(
-        "#include \"y2018/control_loops/superstructure/arm/trajectory.h\"")
+        "#include \"frc971/control_loops/double_jointed_arm/trajectory.h\"")
     cc_file.append(
-        "#include \"y2018/control_loops/superstructure/arm/graph.h\"")
+        "#include \"frc971/control_loops/double_jointed_arm/graph.h\"")
+
+    cc_file.append("using frc971::control_loops::arm::Trajectory;")
+    cc_file.append("using frc971::control_loops::arm::Path;")
+    cc_file.append("using frc971::control_loops::arm::SearchGraph;")
+
     cc_file.append("")
     cc_file.append("namespace y2018 {")
     cc_file.append("namespace control_loops {")
@@ -86,15 +91,21 @@
     h_file.append("#include <memory>")
     h_file.append("")
     h_file.append(
-        "#include \"y2018/control_loops/superstructure/arm/trajectory.h\"")
+        "#include \"frc971/control_loops/double_jointed_arm/trajectory.h\"")
     h_file.append(
-        "#include \"y2018/control_loops/superstructure/arm/graph.h\"")
+        "#include \"frc971/control_loops/double_jointed_arm/graph.h\"")
+    h_file.append(
+        "#include \"frc971/control_loops/double_jointed_arm/dynamics.h\"")
     h_file.append("")
     h_file.append("namespace y2018 {")
     h_file.append("namespace control_loops {")
     h_file.append("namespace superstructure {")
     h_file.append("namespace arm {")
 
+    h_file.append("using frc971::control_loops::arm::Trajectory;")
+    h_file.append("using frc971::control_loops::arm::Path;")
+    h_file.append("using frc971::control_loops::arm::SearchGraph;")
+
     h_file.append("")
     h_file.append("struct TrajectoryAndParams {")
     h_file.append("  TrajectoryAndParams(double new_vmax,")
@@ -182,11 +193,13 @@
     h_file.append("")
     h_file.append("// Builds a search graph.")
     h_file.append("SearchGraph MakeSearchGraph("
+                  "const frc971::control_loops::arm::Dynamics *dynamics, "
                   "::std::vector<TrajectoryAndParams> *trajectories,")
     h_file.append("                            "
                   "const ::Eigen::Matrix<double, 2, 2> &alpha_unitizer,")
     h_file.append("                            double vmax);")
     cc_file.append("SearchGraph MakeSearchGraph("
+                   "const frc971::control_loops::arm::Dynamics *dynamics, "
                    "::std::vector<TrajectoryAndParams> *trajectories,")
     cc_file.append("                            "
                    "const ::Eigen::Matrix<double, 2, 2> &alpha_unitizer,")
diff --git a/y2018/control_loops/superstructure/BUILD b/y2018/control_loops/superstructure/BUILD
index 567810d..a3cb808 100644
--- a/y2018/control_loops/superstructure/BUILD
+++ b/y2018/control_loops/superstructure/BUILD
@@ -94,6 +94,7 @@
         "//frc971/control_loops:control_loop_test",
         "//frc971/control_loops:position_sensor_sim",
         "//frc971/control_loops:team_number_test_environment",
+        "//y2018/control_loops/superstructure/arm:arm_constants",
         "//y2018/control_loops/superstructure/intake:intake_plants",
     ],
 )
diff --git a/y2018/control_loops/superstructure/arm/BUILD b/y2018/control_loops/superstructure/arm/BUILD
index f90cc92..9f969ff 100644
--- a/y2018/control_loops/superstructure/arm/BUILD
+++ b/y2018/control_loops/superstructure/arm/BUILD
@@ -1,128 +1,4 @@
 cc_library(
-    name = "trajectory",
-    srcs = [
-        "trajectory.cc",
-    ],
-    hdrs = [
-        "trajectory.h",
-    ],
-    target_compatible_with = ["@platforms//os:linux"],
-    visibility = ["//visibility:public"],
-    deps = [
-        ":dynamics",
-        "//aos/logging",
-        "//frc971/control_loops:dlqr",
-        "//frc971/control_loops:jacobian",
-        "@org_tuxfamily_eigen//:eigen",
-    ],
-)
-
-cc_test(
-    name = "trajectory_test",
-    srcs = [
-        "trajectory_test.cc",
-    ],
-    target_compatible_with = ["@platforms//os:linux"],
-    deps = [
-        ":demo_path",
-        ":dynamics",
-        ":ekf",
-        ":trajectory",
-        "//aos/testing:googletest",
-        "@org_tuxfamily_eigen//:eigen",
-    ],
-)
-
-cc_library(
-    name = "dynamics",
-    srcs = [
-        "dynamics.cc",
-    ],
-    hdrs = [
-        "dynamics.h",
-    ],
-    target_compatible_with = ["@platforms//os:linux"],
-    visibility = ["//visibility:public"],
-    deps = [
-        "//frc971/control_loops:runge_kutta",
-        "@com_github_gflags_gflags//:gflags",
-        "@org_tuxfamily_eigen//:eigen",
-    ],
-)
-
-cc_library(
-    name = "demo_path",
-    srcs = [
-        "demo_path.cc",
-    ],
-    hdrs = ["demo_path.h"],
-    target_compatible_with = ["@platforms//os:linux"],
-    deps = [":trajectory"],
-)
-
-cc_test(
-    name = "dynamics_test",
-    srcs = [
-        "dynamics_test.cc",
-    ],
-    target_compatible_with = ["@platforms//os:linux"],
-    deps = [
-        ":dynamics",
-        "//aos/testing:googletest",
-    ],
-)
-
-cc_binary(
-    name = "trajectory_plot",
-    srcs = [
-        "trajectory_plot.cc",
-    ],
-    target_compatible_with = ["@platforms//cpu:x86_64"],
-    deps = [
-        ":ekf",
-        ":generated_graph",
-        ":trajectory",
-        "//frc971/analysis:in_process_plotter",
-        "@com_github_gflags_gflags//:gflags",
-        "@org_tuxfamily_eigen//:eigen",
-    ],
-)
-
-cc_library(
-    name = "ekf",
-    srcs = [
-        "ekf.cc",
-    ],
-    hdrs = [
-        "ekf.h",
-    ],
-    target_compatible_with = ["@platforms//os:linux"],
-    visibility = ["//visibility:public"],
-    deps = [
-        ":dynamics",
-        "//frc971/control_loops:jacobian",
-        "@org_tuxfamily_eigen//:eigen",
-    ],
-)
-
-cc_library(
-    name = "graph",
-    srcs = ["graph.cc"],
-    hdrs = ["graph.h"],
-    target_compatible_with = ["@platforms//os:linux"],
-)
-
-cc_test(
-    name = "graph_test",
-    srcs = ["graph_test.cc"],
-    target_compatible_with = ["@platforms//os:linux"],
-    deps = [
-        ":graph",
-        "//aos/testing:googletest",
-    ],
-)
-
-cc_library(
     name = "arm",
     srcs = [
         "arm.cc",
@@ -133,15 +9,16 @@
     target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
-        ":demo_path",
-        ":ekf",
         ":generated_graph",
-        ":graph",
-        ":trajectory",
+        "//frc971/control_loops/double_jointed_arm:demo_path",
+        "//frc971/control_loops/double_jointed_arm:ekf",
+        "//frc971/control_loops/double_jointed_arm:graph",
+        "//frc971/control_loops/double_jointed_arm:trajectory",
         "//frc971/zeroing",
         "//y2018:constants",
         "//y2018/control_loops/superstructure:superstructure_position_fbs",
         "//y2018/control_loops/superstructure:superstructure_status_fbs",
+        "//y2018/control_loops/superstructure/arm:arm_constants",
     ],
 )
 
@@ -170,7 +47,35 @@
     target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
-        ":graph",
-        ":trajectory",
+        ":arm_constants",
+        "//frc971/control_loops/double_jointed_arm:graph",
+        "//frc971/control_loops/double_jointed_arm:trajectory",
+    ],
+)
+
+cc_library(
+    name = "arm_constants",
+    hdrs = ["arm_constants.h"],
+    target_compatible_with = ["@platforms//os:linux"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//frc971/control_loops/double_jointed_arm:dynamics",
+    ],
+)
+
+cc_binary(
+    name = "trajectory_plot",
+    srcs = [
+        "trajectory_plot.cc",
+    ],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
+    deps = [
+        ":arm_constants",
+        ":generated_graph",
+        "//frc971/analysis:in_process_plotter",
+        "//frc971/control_loops/double_jointed_arm:ekf",
+        "//frc971/control_loops/double_jointed_arm:trajectory",
+        "@com_github_gflags_gflags//:gflags",
+        "@org_tuxfamily_eigen//:eigen",
     ],
 )
diff --git a/y2018/control_loops/superstructure/arm/arm.cc b/y2018/control_loops/superstructure/arm/arm.cc
index 1c29157..ab5deea 100644
--- a/y2018/control_loops/superstructure/arm/arm.cc
+++ b/y2018/control_loops/superstructure/arm/arm.cc
@@ -5,8 +5,9 @@
 
 #include "aos/logging/logging.h"
 #include "y2018/constants.h"
-#include "y2018/control_loops/superstructure/arm/demo_path.h"
-#include "y2018/control_loops/superstructure/arm/dynamics.h"
+#include "frc971/control_loops/double_jointed_arm/demo_path.h"
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
+#include "y2018/control_loops/superstructure/arm/arm_constants.h"
 #include "y2018/control_loops/superstructure/arm/generated_graph.h"
 
 namespace y2018 {
@@ -29,9 +30,12 @@
       alpha_unitizer_((::Eigen::Matrix<double, 2, 2>() << 1.0 / kAlpha0Max(),
                        0.0, 0.0, 1.0 / kAlpha1Max())
                           .finished()),
-      search_graph_(MakeSearchGraph(&trajectories_, alpha_unitizer_, kVMax())),
+      dynamics_(kArmConstants),
+      search_graph_(MakeSearchGraph(&dynamics_, &trajectories_, alpha_unitizer_,
+                                    kVMax())),
+      arm_ekf_(&dynamics_),
       // Go to the start of the first trajectory.
-      follower_(ReadyAboveBoxPoint()),
+      follower_(&dynamics_, ReadyAboveBoxPoint()),
       points_(PointList()) {
   int i = 0;
   for (const auto &trajectory : trajectories_) {
diff --git a/y2018/control_loops/superstructure/arm/arm.h b/y2018/control_loops/superstructure/arm/arm.h
index 7ceb001..51d6c4d 100644
--- a/y2018/control_loops/superstructure/arm/arm.h
+++ b/y2018/control_loops/superstructure/arm/arm.h
@@ -4,14 +4,17 @@
 #include "aos/time/time.h"
 #include "frc971/zeroing/zeroing.h"
 #include "y2018/constants.h"
-#include "y2018/control_loops/superstructure/arm/dynamics.h"
-#include "y2018/control_loops/superstructure/arm/ekf.h"
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
+#include "frc971/control_loops/double_jointed_arm/ekf.h"
 #include "y2018/control_loops/superstructure/arm/generated_graph.h"
-#include "y2018/control_loops/superstructure/arm/graph.h"
-#include "y2018/control_loops/superstructure/arm/trajectory.h"
+#include "frc971/control_loops/double_jointed_arm/graph.h"
+#include "frc971/control_loops/double_jointed_arm/trajectory.h"
 #include "y2018/control_loops/superstructure/superstructure_position_generated.h"
 #include "y2018/control_loops/superstructure/superstructure_status_generated.h"
 
+using frc971::control_loops::arm::TrajectoryFollower;
+using frc971::control_loops::arm::EKF;
+
 namespace y2018 {
 namespace control_loops {
 namespace superstructure {
@@ -114,6 +117,8 @@
 
   double vmax_ = kVMax();
 
+  frc971::control_loops::arm::Dynamics dynamics_;
+
   ::std::vector<TrajectoryAndParams> trajectories_;
   SearchGraph search_graph_;
 
diff --git a/y2018/control_loops/superstructure/arm/arm_constants.h b/y2018/control_loops/superstructure/arm/arm_constants.h
new file mode 100644
index 0000000..9ac7020
--- /dev/null
+++ b/y2018/control_loops/superstructure/arm/arm_constants.h
@@ -0,0 +1,53 @@
+#ifndef Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_ARM_CONSTANTS_H_
+#define Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_ARM_CONSTANTS_H_
+
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
+
+namespace y2018 {
+namespace control_loops {
+namespace superstructure {
+namespace arm {
+
+constexpr double kEfficiencyTweak = 0.95;
+constexpr double kStallTorque = 1.41 * kEfficiencyTweak;
+constexpr double kFreeSpeed = (5840.0 / 60.0) * 2.0 * M_PI;
+constexpr double kStallCurrent = 89.0;
+
+constexpr ::frc971::control_loops::arm::ArmConstants kArmConstants = {
+    .l1 = 46.25 * 0.0254,
+    .l2 = 41.80 * 0.0254,
+    .m1 = 9.34 / 2.2,
+    .m2 = 9.77 / 2.2,
+
+    // Moment of inertia of the joints in kg m^2
+    .j1 = 2957.05 * 0.0002932545454545454,
+    .j2 = 2824.70 * 0.0002932545454545454,
+
+    // Radius of the center of mass of the joints in meters.
+    .r1 = 21.64 * 0.0254,
+    .r2 = 26.70 * 0.0254,
+
+    // Gear ratios for the two joints.
+    .g1 = 140.0,
+    .g2 = 90.0,
+
+    // MiniCIM motor constants.
+    .efficiency_tweak = kEfficiencyTweak,
+    .stall_torque = kStallTorque,
+    .free_speed = kFreeSpeed,
+    .stall_current = kStallCurrent,
+    .resistance = 12.0 / kStallCurrent,
+    .Kv = kFreeSpeed / 12.0,
+    .Kt = kStallTorque / kStallCurrent,
+
+    // Number of motors on the distal joint.
+    .num_distal_motors = 2.0,
+};
+
+
+} // namespace arm
+} // namespace superstructure
+} // namespace control_loops
+} // namespace y2018
+
+#endif // Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_ARM_CONSTANTS_H_
diff --git a/y2018/control_loops/superstructure/arm/demo_path.h b/y2018/control_loops/superstructure/arm/demo_path.h
deleted file mode 100644
index 0c18103..0000000
--- a/y2018/control_loops/superstructure/arm/demo_path.h
+++ /dev/null
@@ -1,21 +0,0 @@
-#ifndef Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_DEMO_PATH_H_
-#define Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_DEMO_PATH_H_
-
-#include <memory>
-
-#include "y2018/control_loops/superstructure/arm/trajectory.h"
-
-namespace y2018 {
-namespace control_loops {
-namespace superstructure {
-namespace arm {
-
-::std::unique_ptr<Path> MakeDemoPath();
-::std::unique_ptr<Path> MakeReversedDemoPath();
-
-}  // namespace arm
-}  // namespace superstructure
-}  // namespace control_loops
-}  // namespace y2018
-
-#endif  // Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_DEMO_PATH_H_
diff --git a/y2018/control_loops/superstructure/arm/dynamics.cc b/y2018/control_loops/superstructure/arm/dynamics.cc
deleted file mode 100644
index 02a2861..0000000
--- a/y2018/control_loops/superstructure/arm/dynamics.cc
+++ /dev/null
@@ -1,35 +0,0 @@
-#include "y2018/control_loops/superstructure/arm/dynamics.h"
-
-DEFINE_bool(gravity, true, "If true, enable gravity.");
-
-namespace y2018 {
-namespace control_loops {
-namespace superstructure {
-namespace arm {
-
-const ::Eigen::Matrix<double, 2, 2> Dynamics::K3 =
-    (::Eigen::Matrix<double, 2, 2>()
-         << Dynamics::kG1 * Dynamics::Kt / Dynamics::kResistance,
-     0.0, 0.0, Dynamics::kG2 *Dynamics::kNumDistalMotors *Dynamics::Kt /
-                   Dynamics::kResistance)
-        .finished();
-
-const ::Eigen::Matrix<double, 2, 2> Dynamics::K3_inverse = K3.inverse();
-
-const ::Eigen::Matrix<double, 2, 2> Dynamics::K4 =
-    (::Eigen::Matrix<double, 2, 2>()
-         << Dynamics::kG1 * Dynamics::kG1 * Dynamics::Kt /
-                (Dynamics::Kv * Dynamics::kResistance),
-     0.0, 0.0,
-     Dynamics::kG2 *Dynamics::kG2 *Dynamics::Kt *Dynamics::kNumDistalMotors /
-         (Dynamics::Kv * Dynamics::kResistance))
-        .finished();
-
-constexpr double Dynamics::kAlpha;
-constexpr double Dynamics::kBeta;
-constexpr double Dynamics::kGamma;
-
-}  // namespace arm
-}  // namespace superstructure
-}  // namespace control_loops
-}  // namespace y2018
diff --git a/y2018/control_loops/superstructure/arm/dynamics.h b/y2018/control_loops/superstructure/arm/dynamics.h
deleted file mode 100644
index b1ebc97..0000000
--- a/y2018/control_loops/superstructure/arm/dynamics.h
+++ /dev/null
@@ -1,189 +0,0 @@
-#ifndef Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_DYNAMICS_H_
-#define Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_DYNAMICS_H_
-
-#include "Eigen/Dense"
-
-#include "frc971/control_loops/runge_kutta.h"
-#include "gflags/gflags.h"
-
-DECLARE_bool(gravity);
-
-namespace y2018 {
-namespace control_loops {
-namespace superstructure {
-namespace arm {
-
-// This class captures the dynamics of our system.  It doesn't actually need to
-// store state yet, so everything can be constexpr and/or static.
-class Dynamics {
- public:
-  // Below, 1 refers to the proximal joint, and 2 refers to the distal joint.
-  // Length of the joints in meters.
-  static constexpr double kL1 = 46.25 * 0.0254;
-  static constexpr double kL2 = 41.80 * 0.0254;
-
-  // Mass of the joints in kilograms.
-  static constexpr double kM1 = 9.34 / 2.2;
-  static constexpr double kM2 = 9.77 / 2.2;
-
-  // Moment of inertia of the joints in kg m^2
-  static constexpr double kJ1 = 2957.05 * 0.0002932545454545454;
-  static constexpr double kJ2 = 2824.70 * 0.0002932545454545454;
-
-  // Radius of the center of mass of the joints in meters.
-  static constexpr double r1 = 21.64 * 0.0254;
-  static constexpr double r2 = 26.70 * 0.0254;
-
-  // Gear ratios for the two joints.
-  static constexpr double kG1 = 140.0;
-  static constexpr double kG2 = 90.0;
-
-  // MiniCIM motor constants.
-  static constexpr double kEfficiencyTweak = 0.95;
-  static constexpr double kStallTorque = 1.41 * kEfficiencyTweak;
-  static constexpr double kFreeSpeed = (5840.0 / 60.0) * 2.0 * M_PI;
-  static constexpr double kStallCurrent = 89.0;
-  static constexpr double kResistance = 12.0 / kStallCurrent;
-  static constexpr double Kv = kFreeSpeed / 12.0;
-  static constexpr double Kt = kStallTorque / kStallCurrent;
-
-  // Number of motors on the distal joint.
-  static constexpr double kNumDistalMotors = 2.0;
-
-  static constexpr double kAlpha = kJ1 + r1 * r1 * kM1 + kL1 * kL1 * kM2;
-  static constexpr double kBeta = kL1 * r2 * kM2;
-  static constexpr double kGamma = kJ2 + r2 * r2 * kM2;
-
-  // K3, K4 matricies described below.
-  static const ::Eigen::Matrix<double, 2, 2> K3;
-  static const ::Eigen::Matrix<double, 2, 2> K3_inverse;
-  static const ::Eigen::Matrix<double, 2, 2> K4;
-
-  // Generates K1-2 for the arm ODE.
-  // K1 * d^2 theta / dt^2 + K2 * d theta / dt = K3 * V - K4 * d theta/dt
-  // These matricies are missing the velocity factor for K2[1, 0], and K2[0, 1].
-  // You probbaly want MatriciesForState.
-  static void NormilizedMatriciesForState(
-      const ::Eigen::Matrix<double, 4, 1> &X,
-      ::Eigen::Matrix<double, 2, 2> *K1_result,
-      ::Eigen::Matrix<double, 2, 2> *K2_result) {
-    const double angle = X(0, 0) - X(2, 0);
-    const double s = ::std::sin(angle);
-    const double c = ::std::cos(angle);
-    *K1_result << kAlpha, c * kBeta, c * kBeta, kGamma;
-    *K2_result << 0.0, s * kBeta, -s * kBeta, 0.0;
-  }
-
-  // Generates K1-2 for the arm ODE.
-  // K1 * d^2 theta / dt^2 + K2 * d theta / dt = K3 * V - K4 * d theta/dt
-  static void MatriciesForState(const ::Eigen::Matrix<double, 4, 1> &X,
-                                ::Eigen::Matrix<double, 2, 2> *K1_result,
-                                ::Eigen::Matrix<double, 2, 2> *K2_result) {
-    NormilizedMatriciesForState(X, K1_result, K2_result);
-    (*K2_result)(1, 0) *= X(1, 0);
-    (*K2_result)(0, 1) *= X(3, 0);
-  }
-
-  // TODO(austin): We may want a way to provide K1 and K2 to save CPU cycles.
-
-  // Calculates the acceleration given the current state and control input.
-  static const ::Eigen::Matrix<double, 4, 1> Acceleration(
-      const ::Eigen::Matrix<double, 4, 1> &X,
-      const ::Eigen::Matrix<double, 2, 1> &U) {
-    ::Eigen::Matrix<double, 2, 2> K1;
-    ::Eigen::Matrix<double, 2, 2> K2;
-
-    MatriciesForState(X, &K1, &K2);
-
-    const ::Eigen::Matrix<double, 2, 1> velocity =
-        (::Eigen::Matrix<double, 2, 1>() << X(1, 0), X(3, 0)).finished();
-
-    const ::Eigen::Matrix<double, 2, 1> torque = K3 * U - K4 * velocity;
-    const ::Eigen::Matrix<double, 2, 1> gravity_torque = GravityTorque(X);
-
-    const ::Eigen::Matrix<double, 2, 1> accel =
-        K1.inverse() * (torque + gravity_torque - K2 * velocity);
-
-    return (::Eigen::Matrix<double, 4, 1>() << X(1, 0), accel(0, 0), X(3, 0),
-            accel(1, 0))
-        .finished();
-  }
-
-  // Calculates the acceleration given the current augmented kalman filter state
-  // and control input.
-  static const ::Eigen::Matrix<double, 6, 1> EKFAcceleration(
-      const ::Eigen::Matrix<double, 6, 1> &X,
-      const ::Eigen::Matrix<double, 2, 1> &U) {
-    ::Eigen::Matrix<double, 2, 2> K1;
-    ::Eigen::Matrix<double, 2, 2> K2;
-
-    MatriciesForState(X.block<4, 1>(0, 0), &K1, &K2);
-
-    const ::Eigen::Matrix<double, 2, 1> velocity =
-        (::Eigen::Matrix<double, 2, 1>() << X(1, 0), X(3, 0)).finished();
-
-    const ::Eigen::Matrix<double, 2, 1> torque =
-        K3 *
-            (U +
-             (::Eigen::Matrix<double, 2, 1>() << X(4, 0), X(5, 0)).finished()) -
-        K4 * velocity;
-    const ::Eigen::Matrix<double, 2, 1> gravity_torque =
-        GravityTorque(X.block<4, 1>(0, 0));
-
-    const ::Eigen::Matrix<double, 2, 1> accel =
-        K1.inverse() * (torque + gravity_torque - K2 * velocity);
-
-    return (::Eigen::Matrix<double, 6, 1>() << X(1, 0), accel(0, 0), X(3, 0),
-            accel(1, 0), 0.0, 0.0)
-        .finished();
-  }
-
-  // Calculates the voltage required to follow the trajectory.  This requires
-  // knowing the current state, desired angular velocity and acceleration.
-  static const ::Eigen::Matrix<double, 2, 1> FF_U(
-      const ::Eigen::Matrix<double, 4, 1> &X,
-      const ::Eigen::Matrix<double, 2, 1> &omega_t,
-      const ::Eigen::Matrix<double, 2, 1> &alpha_t) {
-    ::Eigen::Matrix<double, 2, 2> K1;
-    ::Eigen::Matrix<double, 2, 2> K2;
-
-    MatriciesForState(X, &K1, &K2);
-
-    const ::Eigen::Matrix<double, 2, 1> gravity_torque = GravityTorque(X);
-
-    return K3_inverse *
-           (K1 * alpha_t + K2 * omega_t + K4 * omega_t - gravity_torque);
-  }
-
-  static ::Eigen::Matrix<double, 2, 1> GravityTorque(
-      const ::Eigen::Matrix<double, 4, 1> &X) {
-    constexpr double kAccelDueToGravity = 9.8 * kEfficiencyTweak;
-    return (::Eigen::Matrix<double, 2, 1>() << (r1 * kM1 + kL1 * kM2) *
-                                                   ::std::sin(X(0)) *
-                                                   kAccelDueToGravity,
-            r2 * kM2 * ::std::sin(X(2)) * kAccelDueToGravity)
-               .finished() *
-           (FLAGS_gravity ? 1.0 : 0.0);
-  }
-
-  static const ::Eigen::Matrix<double, 4, 1> UnboundedDiscreteDynamics(
-      const ::Eigen::Matrix<double, 4, 1> &X,
-      const ::Eigen::Matrix<double, 2, 1> &U, double dt) {
-    return ::frc971::control_loops::RungeKuttaU(Dynamics::Acceleration, X, U,
-                                                dt);
-  }
-
-  static const ::Eigen::Matrix<double, 6, 1> UnboundedEKFDiscreteDynamics(
-      const ::Eigen::Matrix<double, 6, 1> &X,
-      const ::Eigen::Matrix<double, 2, 1> &U, double dt) {
-    return ::frc971::control_loops::RungeKuttaU(Dynamics::EKFAcceleration, X, U,
-                                                dt);
-  }
-};
-
-}  // namespace arm
-}  // namespace superstructure
-}  // namespace control_loops
-}  // namespace y2018
-
-#endif  // Y2018_CONTROL_LOOPS_SUPERSTRUCTURE_ARM_DYNAMICS_H_
diff --git a/y2018/control_loops/superstructure/arm/dynamics_test.cc b/y2018/control_loops/superstructure/arm/dynamics_test.cc
deleted file mode 100644
index 23e5adc..0000000
--- a/y2018/control_loops/superstructure/arm/dynamics_test.cc
+++ /dev/null
@@ -1,52 +0,0 @@
-#include "y2018/control_loops/superstructure/arm/dynamics.h"
-
-#include "gtest/gtest.h"
-
-namespace y2018 {
-namespace control_loops {
-namespace superstructure {
-namespace arm {
-namespace testing {
-
-// Tests that zero inputs result in no acceleration and no motion.
-// This isn't all that rigerous, but it's a good start.
-TEST(DynamicsTest, Acceleration) {
-  Dynamics dynamics;
-
-  EXPECT_TRUE(dynamics
-                  .Acceleration(::Eigen::Matrix<double, 4, 1>::Zero(),
-                                ::Eigen::Matrix<double, 2, 1>::Zero())
-                  .isApprox(::Eigen::Matrix<double, 4, 1>::Zero()));
-
-  EXPECT_TRUE(dynamics
-                  .UnboundedDiscreteDynamics(
-                      ::Eigen::Matrix<double, 4, 1>::Zero(),
-                      ::Eigen::Matrix<double, 2, 1>::Zero(), 0.1)
-                  .isApprox(::Eigen::Matrix<double, 4, 1>::Zero()));
-
-  const ::Eigen::Matrix<double, 4, 1> X =
-      (::Eigen::Matrix<double, 4, 1>() << M_PI / 2.0, 0.0, 0.0, 0.0).finished();
-
-  ::std::cout << dynamics.FF_U(X, ::Eigen::Matrix<double, 2, 1>::Zero(),
-                               ::Eigen::Matrix<double, 2, 1>::Zero())
-              << ::std::endl;
-
-  ::std::cout << dynamics.UnboundedDiscreteDynamics(
-                     X, dynamics.FF_U(X, ::Eigen::Matrix<double, 2, 1>::Zero(),
-                                      ::Eigen::Matrix<double, 2, 1>::Zero()),
-                     0.01)
-              << ::std::endl;
-
-  EXPECT_TRUE(dynamics
-                  .UnboundedDiscreteDynamics(
-                      X, dynamics.FF_U(X, ::Eigen::Matrix<double, 2, 1>::Zero(),
-                                       ::Eigen::Matrix<double, 2, 1>::Zero()),
-                      0.01)
-                  .isApprox(X));
-}
-
-}  // namespace testing
-}  // namespace arm
-}  // namespace superstructure
-}  // namespace control_loops
-}  // namespace y2018
diff --git a/y2018/control_loops/superstructure/arm/trajectory_plot.cc b/y2018/control_loops/superstructure/arm/trajectory_plot.cc
index 10b39bc..0cee664 100644
--- a/y2018/control_loops/superstructure/arm/trajectory_plot.cc
+++ b/y2018/control_loops/superstructure/arm/trajectory_plot.cc
@@ -1,10 +1,11 @@
 #include "aos/init.h"
 #include "frc971/analysis/in_process_plotter.h"
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
+#include "frc971/control_loops/double_jointed_arm/ekf.h"
+#include "frc971/control_loops/double_jointed_arm/trajectory.h"
 #include "gflags/gflags.h"
-#include "y2018/control_loops/superstructure/arm/dynamics.h"
-#include "y2018/control_loops/superstructure/arm/ekf.h"
+#include "y2018/control_loops/superstructure/arm/arm_constants.h"
 #include "y2018/control_loops/superstructure/arm/generated_graph.h"
-#include "y2018/control_loops/superstructure/arm/trajectory.h"
 
 DEFINE_bool(forwards, true, "If true, run the forwards simulation.");
 DEFINE_bool(plot, true, "If true, plot");
@@ -16,10 +17,12 @@
 namespace arm {
 
 void Main() {
-  Trajectory trajectory(FLAGS_forwards
-                            ? MakeNeutralToFrontHighPath()
-                            : Path::Reversed(MakeNeutralToFrontHighPath()),
-                        0.001);
+  frc971::control_loops::arm::Dynamics dynamics(kArmConstants);
+  frc971::control_loops::arm::Trajectory trajectory(
+      &dynamics,
+      FLAGS_forwards ? MakeNeutralToFrontHighPath()
+                     : Path::Reversed(MakeNeutralToFrontHighPath()),
+      0.001);
 
   constexpr double kAlpha0Max = 30.0;
   constexpr double kAlpha1Max = 50.0;
@@ -96,7 +99,7 @@
 
     const ::Eigen::Matrix<double, 6, 1> R = trajectory.R(theta_t, omega_t);
     const ::Eigen::Matrix<double, 2, 1> U =
-        Dynamics::FF_U(R.block<4, 1>(0, 0), omega_t, alpha_t)
+        dynamics.FF_U(R.block<4, 1>(0, 0), omega_t, alpha_t)
             .array()
             .max(-20)
             .min(20);
@@ -118,7 +121,7 @@
 
     const ::Eigen::Matrix<double, 6, 1> R = trajectory.R(theta_t, omega_t);
     const ::Eigen::Matrix<double, 2, 1> U =
-        Dynamics::FF_U(R.block<4, 1>(0, 0), omega_t, alpha_t)
+        dynamics.FF_U(R.block<4, 1>(0, 0), omega_t, alpha_t)
             .array()
             .max(-20)
             .min(20);
@@ -140,7 +143,7 @@
 
     const ::Eigen::Matrix<double, 6, 1> R = trajectory.R(theta_t, omega_t);
     const ::Eigen::Matrix<double, 2, 1> U =
-        Dynamics::FF_U(R.block<4, 1>(0, 0), omega_t, alpha_t)
+        dynamics.FF_U(R.block<4, 1>(0, 0), omega_t, alpha_t)
             .array()
             .max(-20)
             .min(20);
@@ -156,7 +159,8 @@
     X << theta_t(0), 0.0, theta_t(1), 0.0;
   }
 
-  TrajectoryFollower follower(&trajectory);
+  frc971::control_loops::arm::TrajectoryFollower follower(&dynamics,
+                                                          &trajectory);
 
   ::std::vector<double> t_array;
   ::std::vector<double> theta0_goal_t_array;
@@ -187,7 +191,7 @@
   ::std::vector<double> torque0_hat_t_array;
   ::std::vector<double> torque1_hat_t_array;
 
-  EKF arm_ekf;
+  frc971::control_loops::arm::EKF arm_ekf(&dynamics);
   arm_ekf.Reset(X);
   ::std::cout << "Reset P: " << arm_ekf.P_reset() << ::std::endl;
   ::std::cout << "Stabilized P: " << arm_ekf.P_half_converged() << ::std::endl;
@@ -236,9 +240,9 @@
     actual_U(0) += 1.0;
 
     const ::Eigen::Matrix<double, 4, 1> xdot =
-        Dynamics::Acceleration(X, actual_U);
+        dynamics.Acceleration(X, actual_U);
 
-    X = Dynamics::UnboundedDiscreteDynamics(X, actual_U, sim_dt);
+    X = dynamics.UnboundedDiscreteDynamics(X, actual_U, sim_dt);
     arm_ekf.Predict(follower.U(), sim_dt);
 
     alpha0_t_array.push_back(xdot(1));
@@ -270,10 +274,14 @@
     plotter.AddLine(distance_array, alpha0_array, "alpha0");
     plotter.AddLine(distance_array, alpha1_array, "alpha1");
 
-    plotter.AddLine(integrated_distance, integrated_theta0_array, "integrated theta0");
-    plotter.AddLine(integrated_distance, integrated_theta1_array, "integrated theta1");
-    plotter.AddLine(integrated_distance, integrated_omega0_array, "integrated omega0");
-    plotter.AddLine(integrated_distance, integrated_omega1_array, "integrated omega1");
+    plotter.AddLine(integrated_distance, integrated_theta0_array,
+                    "integrated theta0");
+    plotter.AddLine(integrated_distance, integrated_theta1_array,
+                    "integrated theta1");
+    plotter.AddLine(integrated_distance, integrated_omega0_array,
+                    "integrated omega0");
+    plotter.AddLine(integrated_distance, integrated_omega1_array,
+                    "integrated omega1");
     plotter.Publish();
 
     plotter.AddFigure();
diff --git a/y2018/control_loops/superstructure/superstructure_lib_test.cc b/y2018/control_loops/superstructure/superstructure_lib_test.cc
index 285c8c3..54342c5 100644
--- a/y2018/control_loops/superstructure/superstructure_lib_test.cc
+++ b/y2018/control_loops/superstructure/superstructure_lib_test.cc
@@ -8,7 +8,8 @@
 #include "frc971/control_loops/team_number_test_environment.h"
 #include "gtest/gtest.h"
 #include "y2018/constants.h"
-#include "y2018/control_loops/superstructure/arm/dynamics.h"
+#include "frc971/control_loops/double_jointed_arm/dynamics.h"
+#include "y2018/control_loops/superstructure/arm/arm_constants.h"
 #include "y2018/control_loops/superstructure/arm/generated_graph.h"
 #include "y2018/control_loops/superstructure/intake/intake_plant.h"
 #include "y2018/control_loops/superstructure/superstructure.h"
@@ -129,7 +130,8 @@
                               constants::Values::kProximalEncoderRatio()),
         distal_zeroing_constants_(distal_zeroing_constants),
         distal_pot_encoder_(M_PI * 2.0 *
-                            constants::Values::kDistalEncoderRatio()) {
+                            constants::Values::kDistalEncoderRatio()),
+        dynamics_(arm::kArmConstants) {
     X_.setZero();
   }
 
@@ -174,7 +176,7 @@
     AOS_CHECK_LE(::std::abs(U(1)), voltage_check);
 
     if (release_arm_brake) {
-      X_ = arm::Dynamics::UnboundedDiscreteDynamics(X_, U, 0.00505);
+      X_ = dynamics_.UnboundedDiscreteDynamics(X_, U, 0.00505);
     } else {
       // Well, the brake shouldn't stop both joints, but this will get the tests
       // to pass.
@@ -197,6 +199,8 @@
   const ::frc971::constants::PotAndAbsoluteEncoderZeroingConstants
       distal_zeroing_constants_;
   PositionSensorSimulator distal_pot_encoder_;
+
+  ::frc971::control_loops::arm::Dynamics dynamics_;
 };
 
 class SuperstructureSimulation {