Hi Guys
If someone wants to use the APM to control a fuel driven UAV and wants to go through the trouble of fine tunning the setup what will then need to change in the APM code to operate the servo instead of a ESC?
I know this is not prefered but for people that has petrol engines and doesnt want to spend the cash on new motor and batteries what will they need to change ?
Replies
Well as the servo for petrol throttle is a PWM output and the ESC output for electric is PWM the only difference will be in the APM_Config.h for cruise, min etc.
The only thing that will need to be matched is the throttle movement to the servo movement which is hardware only. I'm not a rc petrol person but I am an engine person so I will make some assumption and try to help.
Throttle bodies usually have a butterfly valve (yes, I know barrel throttes don't but who can affored £600 per opening) and that needs to turn through just shy of 90° (just shy because the butterfly plate will rest against an idle pin which allows just enough air flow for engine to not stop). So lets be nice and say 90 to be nice and round but lets not forget that throttles usually have linkages also which turn the butterfly through the 90°. Lets say the linkage has been sized lovingly to means 5cm of linear movement will do the 90°. The servo you have acquired is a pretty standard servo (120°) with enough beef to pull the cable (VERY important).
Here comes the maths (sorry).
For a linear arrangement so the cable is pulled along a curve (like a normal throttle link but on your servo). The radius of that servo "arm" would need to be:
For a standard arm arrangement (like for ailerons, elevator or rudder) the radius of the servo arm would need to be: