This is a Parallax Propeller (P8X32A) based experimental small engine speed controller/governor. In this video I’m doing some basic testing using an old lawn tractor engine. The software implements a proportional-integral-derivative controller (PID controller) to maintain a target RPM even if the load on the engine changes. A PID controller is a generic control loop feedback controller. In this video the knob (potentiometer) on the left controls the target RPM, and the potentiometer on the right controls the proportional Gain (Kp) of the PID controller. At this time, the Integral (Ki), and Derivative (Kd) gain are hard-coded in software and can’t be adjusted externally. The engine throttle is controlled with an old Futaba RC servo.