Manual

www.nexusrobot.com Robot Kits manual

¾ PID Control

¾ What Is PID

From Wikipedia: "A PID controller calculates an 'error' value as the difference between a measured [Input]

and a desired setpoint. The controller attempts to minimize the error by adjusting [an Output]."

So, you tell the PID what to measure (the "Input",) Where you want that measurement to be (the

"Setpoint",) and the variable to adjust that can make that happen (the "Output".) The PID then adjusts the

output trying to make the input equal the setpoint.

For reference, in a car, the Input, Setpoint, and Output would be the speed, desired speed, and gas pedal

angle respectively.

Tuning Parameters

The black magic of PID comes in when we talk about HOW it adjusts the Output to drive the Input

towards Setpoint. There are 3 Tuning Parameters (or "Tunings"): Kp, Ki & Kd. Adjusting these values will

change the way the output is adjusted. Fast? Slow? God-awful? All of these can be achieved depending

on the values of Kp, Ki, and Kd.

So what are the "right" tuning values to use? There isn't one right answer. The values that work for one

application may not work for another, just as the driving style that works for a truck may not work for a

race car. With each new application you will need to try Several Tuning values until you find a set that

gives you what you want.

¾ The Library

Using The PID Library has two benefits in my mind

1. There are many ways to write the PID algorithm. A lot of time was spent making the algorithm in this

library as solid as any found in industry. If you want read more about this, check out this detailed

explanation.

2. When using the library all the PID code is self-contained. This makes your code easier to understand.

It also lets you do more complex stuff, like say having 8 PIDs in the same program.

See: http://www.arduino.cc/playground/Code/PIDLibrary

See: http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-introduction/

Sample code

/********************************************************

* PID Basic Example Reading analog input 0 to control analog PWM output 3

********************************************************/

#include <PID_v1.h>

double Setpoint, Input, Output; //Define Variables we'll be connecting to

PID myPID(&Input, &Output, &Setpoint,2,5,1, DIRECT); //Specify the links and initial tuning parameters

void setup() {