Hello,
My current issue is the PWM signal on Pixhawk port is not the same on test run of motors on the ground. What are the options to fix it? Which part of ardupilot software to look for to investigate this behavior?
I built my custom drone and perform 3 test launches. On the 2nd launch I lost control of the drone and it hit the ground from 1.5 meters. On the 3rd launch 1 motor from 4 gives lower revolutions per minute (RPM) which wasn’t the issue on the 1st and 2nd launches. Investigating the issue shown:
- it gives lower RPM rather than others and stops a few earlier rather than others motors
- voltage from PDB on ESC is the same on all 4 motors
- switching engines across ESCs makes a different engine works slowly → it is not the issue with motor itself
- switching signal wire from one port to another on Pixhawk fix an issue on “bad” motors and creates the issue on normal one → it is not an issue with pixhawk itself
This initial investigation shown the issue is in hardware or\and software part of ArduPilot. The next investigation steps shown:
- the oscilloscope everywhere MAIN OUT signal pins shows 3.3 volts at peak and 1.6 volts as an average
- length of “logical one” varies from 1.8 ms to 1.2 ms: when throttle is applied, the length of the logical one of the PWM is extended, and the logical minus - refers to narrows - this is clearly noticeable on the first motor, not bad on the fourth, but on the second and third the changes are ambiguous
- SERVOx parameters in the mission planner show good default values
- I switched the motors to the next four channels – the situation is similar: outputs 1 and 4 give a PWM of 1.5 ms, and 2 and 3 give a PWM of 1 ms. Now the problematic motors is 1 motors instead of 2nd (by the way, they are both CCV motors)
Altogether it gives me an idea unlikely it is a hardware issue: damage all 8 pins where 4 of them wasn’t in use during flight has minor probability. From software part the accel and compass could suffer after a crash, however re-calibration didn’t solve the issue.
Now I need to go deeper into software and understand how mixer (?) behave when adjusting thurst power on different motors.
MissionPlaner should have an option to export logs, but I haven’t found the option to do it yet.
I will appreciate your assistance in tracking down and solving this issue.
Thanks!
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