diff --git a/y2014/control_loops/drivetrain/drivetrain.q b/y2014/control_loops/drivetrain/drivetrain.q
index ddc2efc..96bd817 100644
--- a/y2014/control_loops/drivetrain/drivetrain.q
+++ b/y2014/control_loops/drivetrain/drivetrain.q
@@ -2,20 +2,37 @@
 
 import "aos/common/controls/control_loops.q";
 
+// For logging information about what the code is doing with the shifters.
 struct GearLogging {
+  // Which controller is being used.
   int8_t controller_index;
+  // Whether the left loop is the high-gear one.
   bool left_loop_high;
+  // Whether the right loop is the high-gear one.
   bool right_loop_high;
+  // The state of the left shifter.
   int8_t left_state;
+  // The state of the right shifter.
   int8_t right_state;
 };
 
+// For logging information about the state of the shifters.
 struct CIMLogging {
+  // Whether the code thinks the left side is currently in gear.
   bool left_in_gear;
+  // Whether the code thinks the right side is currently in gear.
   bool right_in_gear;
+  // The velocity in rad/s (positive forward) the code thinks the left motor
+  // is currently spinning at.
   double left_motor_speed;
+  // The velocity in rad/s (positive forward) the code thinks the right motor
+  // is currently spinning at.
   double right_motor_speed;
+  // The velocity estimate for the left side of the robot in m/s (positive
+  // forward) used for shifting.
   double left_velocity;
+  // The velocity estimate for the right side of the robot in m/s (positive
+  // forward) used for shifting.
   double right_velocity;
 };
 
@@ -23,21 +40,45 @@
   implements aos.control_loops.ControlLoop;
 
   message Goal {
+    // Position of the steering wheel (positive = turning left when going
+    // forwards).
     double steering;
+    // Position of the throttle (positive forwards).
     double throttle;
+    // True to shift into high, false to shift into low.
     bool highgear;
+    // True to activate quickturn.
     bool quickturn;
+    // True to have the closed-loop controller take over.
     bool control_loop_driving;
+    // Position goal for the left side in meters when the closed-loop controller
+    // is active.
     double left_goal;
+    // Velocity goal for the left side in m/s when the closed-loop controller
+    // is active.
     double left_velocity_goal;
+    // Position goal for the right side in meters when the closed-loop
+    // controller is active.
     double right_goal;
+    // Velocity goal for the right side in m/s when the closed-loop controller
+    // is active.
     double right_velocity_goal;
   };
 
   message Position {
+    // Relative position of the left side in meters.
     double left_encoder;
+    // Relative position of the right side in meters.
     double right_encoder;
+    // The speed in m/s of the left side from the most recent encoder pulse,
+    // or 0 if there was no edge within the last 5ms.
+    double left_speed;
+    // The speed in m/s of the right side from the most recent encoder pulse,
+    // or 0 if there was no edge within the last 5ms.
+    double right_speed;
+    // Position of the left shifter (smaller = towards low gear).
     double left_shifter_position;
+    // Position of the right shifter (smaller = towards low gear).
     double right_shifter_position;
     double low_left_hall;
     double high_left_hall;
@@ -46,21 +87,33 @@
   };
 
   message Output {
+    // Voltage to send to the left motor(s).
     double left_voltage;
+    // Voltage to send to the right motor(s).
     double right_voltage;
+    // True to set the left shifter piston for high gear.
     bool left_high;
+    // True to set the right shifter piston for high gear.
     bool right_high;
   };
 
   message Status {
+    // Estimated speed of the center of the robot in m/s (positive forwards).
     double robot_speed;
+    // Estimated relative position of the left side in meters.
     double filtered_left_position;
+    // Estimated relative position of the right side in meters.
     double filtered_right_position;
+    // Estimated velocity of the left side in m/s.
     double filtered_left_velocity;
+    // Estimated velocity of the left side in m/s.
     double filtered_right_velocity;
 
+    // The voltage we wanted to send to the left side last cycle.
     double uncapped_left_voltage;
+    // The voltage we wanted to send to the right side last cycle.
     double uncapped_right_voltage;
+    // True if the output voltage was capped last cycle.
     bool output_was_capped;
   };