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Drive Pipelines.md

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Drive Pipelines

Drive pipelines are an extensible method to create multiple different ways of driving a robot. Since pipelines are just lambdas, they are highly customizable.

Some "stock" classes (inputs, processors, and outputs) are available in the org.team1540.rooster.drive.pipeline package.

What's a Drive Pipeline?

A pipeline can be used for almost any concievable method of drivetrain control, including standard open-loop teleop drive, closed-loop motion profiling, and anywhere in between.

Pipelines consist of three different kinds of stages: inputs, processors, and outputs. Since inputs, processors, and outputs are just Suppliers, Functions, and Consumers respectively, they can be extended easily and flexibly.

  • An input produces target values for processing; for example, an input could get current values from the driver's joysticks, or the currently executing point in a motion profile.

  • A processor, well, processes values: for example, a closed-loop processor might take a desired position, velocity, and/or acceleration and convert them into setpoints, feed-forwards, etc. to send to motors. Note that processors can receive data from things that are not the currently configured input; for example, a gyro.

  • An output turns values from a processor into commands for motors or other things. An output for Talon SRX motors might just pass a setpoint to the Talons' native closed-loop functionality, while an output for PWM motors might perform additional PID logic.

Examples

Hello World

Control two talons in open-loop tank drive:

Executable pipeline = new SimpleJoystickInput(new Joystick(0), 1, 5, false, false)
    .then(new CTREOutput(leftTalon, rightTalon));

Breakdown:

  • SimpleJoystickInput(new Joystick(0), 1, 5, false, false): Takes values from a joystick on port 0, with axis 1 as the left and axis 5 on the right, inverting neither
  • .then(new CTREOutput(leftTalon, rightTalon)): Sends the output of the previous SimpleJoystickInput to your leftTalon and rightTalon. Since the output of SimpleJoystickInput only sets the feed-forward (i.e. raw throttle) term, it'll automatically use PercentOutput output mode.

Execute a Motion Profile

Executable pipeline = new ProfileInput(leftProfile, rightProfile)
    .then(new OpenLoopFeedForward(kV, vIntercept, kA))
    .then(new CTREOutput(leftTalon, rightTalon));

Breakdown:

  • ProfileInput takes values from two provided MotionProfile instances and returns the setpoint for the current time. The timer starts when the pipeline is first executed.
  • OpenLoopFeedForward takes the velocity and acceleration setpoints from the ProfileInput and calculates a suitable feed-forward for them using coefficients you provide, Oblarg-style. It then passes those velocities down.
  • CTREOutput, since it's receiving position setpoints from the ProfileInput, tells the Talon closed-loop to PID to those setpoints while providing the feed-forward from the OpenLoopFeedForward as an additional bump term.

Use in a Command

A properly composed pipeline (i.e. with an input on one end and an output on the other) implements Executable, so it can be used as the argument to a SimpleCommand or SimpleLoopCommand:

// drivePipeline contains your pipeline
Command command = new SimpleLoopCommand("Drive", drivePipeline, Robot.driveTrain);

Custom Logic

Most "stock" pipeline elements pass around TankDriveData instances to encapsulate position, velocity, etc. It's possible to define your own data classes but there's not too much reason to.

Custom Input

An input that returns the same TankDriveData every time:

Executable pipeline = ((Input) () -> new TankDriveData().withVelocities(0, 0))
   .then(new CTREOutput(leftTalon, rightTalon))

Custom Processor

A processor that multiplies the received position by two:

Executable pipeline = new SimpleJoystickInput(new Joystick(0), 1, 5, false, false)
    .then(data -> data.modifyPositions(
        (left) -> left.isPresent() ? left.getAsDouble() * 2 : left,
        (right) -> right.isPresent() ? right.getAsDouble() * 2 : right)
    .then(new CTREOutput(leftTalon, rightTalon))

Custom Output

Here's an output that just prints the data it receives instead of sending it to a motor:

Executable pipeline = new SimpleJoystickInput(new Joystick(0), 1, 5, false, false)
    .then(data -> System.out.println(data))