Motor cutouts
« on: May 20, 2020, 06:53:59 pm »
Hello everyone,
I tried to build a 3D printed quadcopter and got quite well through the setup, but unfortunately I got a problem while actually operating the craft.

Setup
Remote: Turnigy 5x PWM
FC: CC3D
ESC: Racerstar RS20Ax4
Motors: Racerstar Racing Edition 1806 BR1806 2280KV
Battery: 3S 1500mAh 100C

I know this is a quite cheap setup and there plenty of better controllers outside, but I tried to finish a build with stuff I had laying around.
Flashing and configuring Librepilot went well and basically the copter flies for a short time as it should and is controllable. Unfortunately I'm getting cutouts on random motors and then the copter chrashes into this direction. I debugged this with controlling the motors individually via Librepilot GUI and confirmed the issues happening often above 1650 and sometimes in the range ~1450. Limiting the motors to 1650 makes it better, but then the quad barely hovers and the mentioned crashes also appear (but less often).
Now I'm out of ideas how to investigate further and solve this issue, can anyone point me into a direction? As it happens on random motors, I don't suspect the ESC yet.

Thanks in advance for your help!
Cheers,
Henrik



Re: Motor cutouts
« Reply #1 on: May 21, 2020, 09:42:23 am »
That sounds like the old issue of that ESC doesn't like that motor...

Can you tell if it is always the same ESC/motor?  At least look for bad connections or shorting out.  Factory soldered bullet connectors are sometimes bad.  Give a good tug on each wire going into each side of the connector.

Make sure you are running the correct size prop for that motor / battery combination.  Props that are too big can make the problem worse.

If it's the same ESC/motor, replace.  If it's random, I would flash the ESC's with the latest BLHeli or SimonK.

Re: Motor cutouts
« Reply #2 on: May 24, 2020, 07:49:44 pm »
Thanks for your reply!
The problem is distributed over all 4 motors. Props were recommended for this setup (5040 3 blade).
I'll check for the ESC and flash the new firmware!

Re: Motor cutouts
« Reply #3 on: June 04, 2020, 03:52:44 pm »
Hello again,
I tried everything suggested by did not succeed at all.
I flashed the ESC with the latest available BLHeli for it (16.7) and also resoldered the connections even though i could not spot any faulty points. Additionally I changed one motor where I had the feeling that the cutout would happen the most with no success and switched the receiver to a TGY IA6C with PPM so could talk oneshot/multishot to the ESC (which was not possible with the PWM receiver before).
The behaviour stayed exactly the same.
Any other direction I could head to? Should I change the ESC at all?

Cheers and thanks,
Henrik

Re: Motor cutouts
« Reply #4 on: June 04, 2020, 11:10:37 pm »
Be aware that many things can look like an ESC/motor stopping.

On PWM, I had one signal wire that was intermittent, and when it went open, the quad would fall, but always with a random motor seeming to cut out first (slight tumble).

Enabling Low Voltage Cutoff can cause it.  Due to manufacturing tolerances, one ESC will cut off before the others.

High throttle on old / small battery can cause voltage drop and any of ESC / FC / Rx can reboot.

On either of the previous two, you will notice it much worse if you try to take off without recharging the battery after an incident.  Tell us if this is true.

Props too large.

Do the motors get hot?  Anything that causes the motors to get too hot from just hovering is an issue that can cause this.  Props too large is one such issue.  After just hovering for several minutes you should be able to hold the motor firmly without getting burned.

ESC firmware doesn't like that brand of motor.  Sometimes you can hear a sync failure, sometimes called cogging.  It sounds a bit like a stick being thrown into the spinning prop.  Let us know if you hear that.

Excess vibration at certain throttle but not others (and on banking) can cause bad sensor readings.

Loose motors or damaged arms can have similar effects, but not crashing generally.

Loose props.

Metal parts shorting, like ESC connectors together or FC board touching metal or FC board mounted with metal standoffs.

RC radio glitches, but this is not common on 2.4GHz which generally is digital and has checksums.

Logging can help to tell you what was the cause if the FC caused it, or what was the first thing the FC detected (e.g.bank forward and left if that motor fails), but for you that means buying a pair of OpLinks.

I suggest you make a video of it happening and post it here.

If it's easy to re-create, you could firmly attach the quad to a table, etc. and run it in Rate mode (not Attitude) and recreate it on the table, then try some things, like Output page test mode that bypasses RC Rx and FC sensors, or Manual flight mode (bypass FC sensors and stabilization only) (which you should never do otherwise, uncontrollable for a human without a lot of setup).  Manual might be allowed if you do System->Settings->FlightModeSettings->DisableSanityChecks and press green up arrow at top of window.