An engine controller was built to regulate the speed of a small two-stroke engine intended for use on a small UAV. The controller was developed for the OS160FX engine but it can be adapted to other comparable engines. The controller monitors the temperature of the engine and will alert the ground station if there is a unsafe operating temperature.
It can also monitor altitude but the effects of altitude on the engine performance were not accounted for in the control algorithm. The engine controller was able to reliably regulate the speed of the OS160FX engine through the entire speed range of the engine.
Responses to reference speed steps smaller than 4000 rpm have settling times less than 10 seconds with less than 200 rpm overshoot. Deviations from the reference speed at steady-state are kept under 100 rpm with occasional exceptions. The engine was able to safely idle at speeds as low as 1800 rpm.
The engine controller can prevent the engine from stalling by dropping too far below this speed. The controller provides good rejection of disturbances caused by moderate drops and surges in fuel ow.
The controller performance was found to be sensitive to the carburetor’s fuel valve settings. A poorly tuned carburetor caused instability in the transition region between low and high speeds.