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//! PID controllers.
//!
//! PID controllers are first created with [`PidController::new`]
//! and then can be utilized by calling [`PidController::update`] repeatedly.

use core::time::Duration;

/// A proportional–integral–derivative controller.
///
/// This controller is used to smoothly move motors to a certain point,
/// and allows for feedback-based power adjustments. This is desirable
/// over just setting the motor power, as it can be tuned to make the
/// motor stop in exactly the right position without overshooting.
#[derive(Debug, Clone, Copy)]
pub struct PidController {
    /// Proportional constant. This is multiplied by the error to get the
    /// proportional component of the output.
    pub kp: f32,
    /// Integral constant. This accounts for the past values of the error.
    pub ki: f32,
    /// Derivative constant. This allows you to change the motor behavior
    /// based on the rate of change of the error (predicting future values).
    pub kd: f32,

    last_time: vexide_core::time::Instant,
    last_position: f32,
    i: f32,
}

impl PidController {
    /// Create a new PID controller with the given constants.
    pub fn new(kp: f32, ki: f32, kd: f32) -> Self {
        Self {
            kp,
            ki,
            kd,
            last_time: vexide_core::time::Instant::now(),
            last_position: 0.0,
            i: 0.0,
        }
    }

    /// Update the PID controller with the current setpoint and position.
    pub fn update(&mut self, setpoint: f32, position: f32) -> f32 {
        let mut delta_time = self.last_time.elapsed();
        if delta_time.is_zero() {
            delta_time += Duration::from_micros(1);
        }
        let error = setpoint - position;

        self.i += error * delta_time.as_secs_f32();

        let p = self.kp * error;
        let i = self.ki * self.i;

        let mut d = (position - self.last_position) / delta_time.as_secs_f32();
        if d.is_nan() {
            d = 0.0
        }

        let output = p + i + d;

        self.last_position = position;
        self.last_time = vexide_core::time::Instant::now();

        output
    }
}