Matek H743 servos issue on boot sometimes. Fix exists but needs to be added to ardupilot.

[thespova]

Bug report

Issue details

Servos go to full deflection on boot some times and it damages hardware. @andyp1per has already created a fix that I have tested some and it appears to solve the issue. The code just needs to be merged I think so Matek H743 users can go to new versions of ardupilot.

Version
4.3.7 through 4.5.7 at least. I assume all previous versions

Platform
[x] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Submarine

Airframe type
I discovered this on a Traditional Helicopter.

Hardware type
Matek H743 Mini

Logs

Previous discussion: https://discuss.ardupilot.org/t/servos-some-times-go-crazy-on-start-up/98641/56
Fix already created by @andyp1per that I have tested some already. Seems to fix the issue.

Please add @andyp1per's code to regular ardupilot code so I can use new versions of ardupilot. It looks like just a few lines so I hope this is a pretty simple fix.

[peterbarker]

Link to Andy's branch: https://github.com/andyp1per/ardupilot/tree/pr-gpio-bootloader

@andyp1per - creating a PR for that might make this easier to discuss on DevCall?

[andyp1per]

Thanks @peterbarker - @tridge didn't like my fix, preferring to leave the pins floating - but its clear that doesn't work in this case. Good discussion to have on the devcall I think

[thespova]

What is "floating"? There should be no PWM signal on PWM pins until commanded. This makes the Matek H743 series unusable with ardupilot on anything that uses servos.

Thanks @peterbarker for linking @andyp1per 's code. I forgot to add that.

[thespova]

Not sure if I am looking at this right but just poking around at some other boards some of them seem to do the same pull down but for specific pins. Is it maybe more desirable to only do this to the S marked PWM pins? Is that even possible?

Edit: By marked I mean the ones Matek marks here and on the board screen print https://www.mateksys.com/?portfolio=h743-mini#tab-id-5