Make a mutual drivetrain between robots.

Change-Id: I23cc9634d9af5d0482dc5a5501dccc064b7b53d3
diff --git a/frc971/control_loops/drivetrain/drivetrain_config.h b/frc971/control_loops/drivetrain/drivetrain_config.h
new file mode 100644
index 0000000..07fbe93
--- /dev/null
+++ b/frc971/control_loops/drivetrain/drivetrain_config.h
@@ -0,0 +1,54 @@
+#ifndef FRC971_CONTROL_LOOPS_DRIVETRAIN_CONSTANTS_H_
+#define FRC971_CONTROL_LOOPS_DRIVETRAIN_CONSTANTS_H_
+
+#include <functional>
+
+#include "frc971/shifter_hall_effect.h"
+#include "frc971/control_loops/state_feedback_loop.h"
+
+namespace frc971 {
+namespace control_loops {
+namespace drivetrain {
+
+enum class ShifterType : int32_t {
+  HALL_EFFECT_SHIFTER = 0,  // Detect when inbetween gears.
+  SIMPLE_SHIFTER = 1,  // Switch gears without speedmatch logic.
+};
+
+struct DrivetrainConfig {
+  // Shifting method we are using.
+  ShifterType shifter_type;
+
+  // Polydrivetrain functions returning various controller loops with plants.
+  ::std::function<StateFeedbackLoop<4, 2, 2>()> make_drivetrain_loop;
+  ::std::function<StateFeedbackLoop<2, 2, 2>()> make_v_drivetrain_loop;
+  ::std::function<StateFeedbackLoop<7, 2, 3>()> make_kf_drivetrain_loop;
+
+  double dt;  // Control loop time step.
+  double stall_torque;  // Stall torque in N m.
+  double stall_current;  // Stall current in amps.
+  double free_speed_rpm;  // Free speed in rpm.
+  double free_current;  // Free current in amps.
+  double j;  // CIM moment of inertia in kg m^2.
+  double mass;  // Mass of the robot.
+  double robot_radius;  // Robot radius, in meters.
+  double wheel_radius;  // Wheel radius, in meters.
+  double r;  // Motor resistance.
+  double v;  // Motor velocity constant.
+  double t;  // Torque constant.
+
+  double turn_width;  // Robot turn width, in meters.
+  // Gear ratios, from encoder shaft to transmission output.
+  double high_gear_ratio;
+  double low_gear_ratio;
+
+  // Hall effect constants. Unused if not applicable to shifter type.
+  constants::ShifterHallEffect left_drive;
+  constants::ShifterHallEffect right_drive;
+};
+
+}  // namespace drivetrain
+}  // namespace control_loops
+}  // namespace frc971
+
+#endif  // FRC971_CONTROL_LOOPS_DRIVETRAIN_CONSTANTS_H_