PID speed control#

Tutorial · 12 min read · ESP32, 12 V DC motor, encoder

How I got both wheels to hit their target speed without overshoot, and the graphs that prove it.

Overview#

A speed controller with feedforward and anti-windup
A repeatable step-response test
A live plot of target vs measured speed

The idea#

PID reacts after an error appears. Feedforward predicts the voltage a speed needs. Feedforward does most of the work, PID cleans up the rest.

Step 1: The control loop#

float ff  = kS * sign(target) + kV * target;
float err = target - measured;
integral  = clamp(integral + err * dt, -iMax, iMax);
float pwm = ff + kP * err + kI * integral;

clamp on the integral is the anti-windup. Without it the motor overshoots every time it leaves saturation.

Results#

Metric	Before	After
Overshoot	[X] %	[Y] %
Settling time	[X] ms	[Y] ms
Steady-state error	[X] %	[Y] %

Troubleshooting#

The loop jittered when Wi-Fi was busy#

Moving the web server to the other core fixed it.

Low speeds stuttered#

Static friction. The kS term solved it.