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Introduction

A feedforward control system improves system performance by taking preemptive action based on known or anticipated disturbances rather than reacting to the system's output. It directly manipulates the system's input based on a model or prediction of how disturbances will impact the output ( Cadence PCB Resources ).

The FeedForward implementation in lightning is based on The Permanent-Magned DC Motor Feedforward Equation, To se more information about the equation , refer to the article written by WPILib.

The Permanent-Magned DC Motor Feedforward Equation is:

Voltage=Ksโˆ—sgn(dห™)+Kvโˆ—dห™+Kaโˆ—dยจVoltage = K_s * sgn(\dot{d}) + K_v * \dot{d} + K_a * \ddot{d}

During the SPIN-UP season our team ITESM1 used a PID combined with a FeedForward Controller to control the Flywheel Velocity. The results were amazing, providing incredible control over the flywheel velocity and increasing the shooting accurancy. To see this in action, check out this Video.

FeedForward Tutorial

Creating a FeedForward controllerโ€‹

Creating a FeedForward controller is matter of using the constructor for the FeedForward class. Check the FeedForward Documentation for more information about it.

main.cpp
lightning::FeedForward speed_controller (
    5, // The velocity constant.
    1000, // The Friction constant.
    350); //Acceleration constant.

Creating the motion functionโ€‹

In the next code we would create a function with the objetive of controlling the velocity on a flywheel using a feedforward controller.

lightning::FeedForward speed_controller (
    5, // The velocity constant.
    1000, // The Friction constant.
    350); //Acceleration constant.

void move_flywheel(int RPM){
    float velocity=0; 
    while(1){
        velocity = get_flywheel_velocity(); 
        controller.update(velocity);
        flywheel.move_voltage(speed_controller.get_output()); 
    }
}

FeedForward Tuningโ€‹

Tuning the feedforward controller is necessary for accurate results. For a comprehensive guide on how to tune your feedforward controller, We recommend the following guide.

Congratulations! ๐Ÿฅณโ€‹

You finished the FeedForward tutorial, now you are able to create and use a FeedForward controller for your routines.

tip

You can combined the FeedForward controller with a PID controller, having a FeedForward FeedBack controller, feel free to experiment ๐Ÿงช.