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.docs/closedLoopDrivetrainControl.md

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+# Closed Loop Drivetrain Control
+
+We achieve smooth control of our drivetrain through a slightly modified [Holonomnic Drivetrain Controller](https://docs.wpilib.org/en/stable/docs/software/advanced-controls/trajectories/holonomic.html)
+
+Swerve Drive has three _independent_ axes of control - Translation (X, Y), and Rotation (Theta). Unlke a tank drive, where side-to-side translation can not be done independently of forward motion, our control startegy may be easier.
+
+Our control logic feeds the drivetrain with desired X, Y, and Rotational Velocity as the sum of two sources:
+
+1) Open Loop velocity command
+2) Closed loop position-correction command
+
+All control starategies (manual, auto-drive, trajectory, etc.) must supply an open loop velocity command for all three axes at all times. Manual control gets these from the joysticks, auto-drive gets them from looking at how we're moving from the current to the next step, trajectories in autonomous pre-calculate the velocity throuhgout the trajectory.
+
+Optionally, a `Pose2d` might be available from the controlling source. Manual control generally will not have this, but auto-drive and trajectory control probably will.
+
+Since we have `odometry` to calculate an estimated `Pose2d` of our robot, we can subtract this from our commanded `Pose2d` to get an error in position. Each axis of the error (3 in total) are run through an independent PID controller, which in turn generates a small additional _corrective_ velocity to get the robot's estiamted pose closer to where we want to be.
+
+Notably, in the past, wpilib's implementation did not have open-loop control of rotation. This was a strage omission. For this reason, we've had our own minimal `HolonomicDriveController` class for quite some time.