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Control Systems ​

Control systems are the most important thing in NextControl. They are what powers everything else. A control system can be nearly any type of controller.

The Four Elements ​

A control system is made up of four "elements": feedback, feedforward, filter, and interpolator. If you don't pass one of them, a sensible default is used.

  • Feedback elements provide feedback (closed-loop) control for your system. For example, PID Control, SquID Control, and Bang-Bang Control.

  • Feedforward elements provide feedforward (open-loop) control. NextControl has three feedforward controllers: basic, elevator, and arm.

  • Filter elements filter your sensor measurements to remove noise. Examples are low-pass filters and Kalman filters.

  • Interpolator elements interpolate the setpoint in order to smooth out setpoint changes. For example, a trapezoidal motion profile or a moving-average setpoint filter.

The control system calculation process involves:

  1. Filtering sensor measurements
  2. Obtaining the current reference from the interpolator
  3. Calculating feedback component based on error
  4. Calculating feedforward component based on reference
  5. Returning the sum of feedback and feedforward

Creating Control Systems ​

It is highly recommended that you use the control system builder to create your control systems. To create a control system, pass the feedback, feedforward, filter, and interpolator elements. All are optional, and sensible defaults will be used if one isn't passed.

kotlin
val controlSystem = controlSystem {
  feedback(/* feedback element */)
  feedforward(/* feedforward element */)
  posFilter { custom(/* position filter */) }
  velFilter { custom(/* velocity filter */) }
  accelFilter { custom(/* acceleration filter */) }
  interpolator(/* interpolator element */)
}

There are also numerous helper methods, outlined in the following pages. Because of these helper methods, you will almost never need to construct your own elements!

Using a Control System ​

To run the control system's calculations, call calculate every loop. Pass a KineticState consisting of the current position and velocity, and optionally, the acceleration. Calling calculate returns the motor power to set.

kotlin
motor.power = controlSystem.calculate(
  KineticState(motor.position, motor.velocity)
);