Problem with pwm signals

I’m working on an aerial robot (a t-copter) and am having problems with Roll-axis stabilization. The PID controller works correctly but when I get the engine speed from 40% starts to destabilize. The problem is not in the PID but FEZ PWM signal or ESC output is not constant. I have measured the FEZ pwm signal with an oscilloscope, from 1 to 2 ms and vice versa and this is the result ( pwm frequency= 400Hz):

Is it normal that the amplitude change? Is it normal not maintained very stable signal?


Disconnect the pin from anything and try again. Does amplitude change?

It might be a power supply issue. Are you running the FEZ on a different power source from the motor?

Seems like the external circuit connected to the pwm output stresses the output. Or a supply issue, idd. Measure supply voltage on second channel and run test again.

What electronics do you use behind the FEZ?

I am using FEZ Domino with PWM for heating in an application at this moment but cannot replicate this behavior.

WimC, you seems to have work a lot on PWM, LS7366 counters,… Would it be possible possible to ask yousome question by email on those subjects?

Yes, sure you can ask…

Maybe open a new thread Packman and let everybody jump in.

Cu Wim.