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.

Remote: Turnigy 5x PWM
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!

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,

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 ( 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.

Re: Motor cutouts
« Reply #5 on: June 07, 2020, 12:14:31 pm »
Thanks, thats a lot of points to work on :)
Meanwhile I also continued debugging this issue and I found an issue, thats hard for me to grasp:
I took every single motor off the quad to a different ESC, tested it manually with a PWM tester and found 2 out of 4 motors having use issues with a fast switch of the PWM rate and start to stutter then, sounds exactly the sam as whats happening while mounted on the quad. The one thing that bothers me is the fault rate with 4 out of 6 motors in total, as I already changed 2 before and they were also affected on the testbench  - it a bit against statistics ;) - but I verified it with other motors on this "test-setup" and all of them worked fine.
So new motors (different model) are on the road and I'll keep you updated.
Thanks again for your effort!

Re: Motor cutouts
« Reply #6 on: June 08, 2020, 09:04:53 am »
One of the signs that this ESC doesn't like that motor is that motor sometime doesn't start or looses sync when it gets an instant change to a significantly higher speed.  In BLHeli and SimonK there may be some settings (e.g. timing?) that can make it run better.

I once had a quad with an old BLHeli on it as I recall, and in Attitude mode, slightly tilted on the ground, the "lower" motor(s) wouldn't start because they were being commanded to a little higher throttle and the jump from zero to there was too much.  I would hand start it by noticing which motor wouldn't start and hold that motor a little higher and then all 4 would start.  The problem went away when I updated to the latest ESC firmware.

Another issue is that if the motor tries to start, but won't start, you should never give it more throttle in an effort to get it to start.  This sometimes will burn out a winding.  From then on, the motor will only jitter back and forth when it tries to start.  Is that what is wrong with several of your motors?  Generally you can ohm out all three motor wires, call them A, B, and C (disconnect from ESC or at least power down and hand spin the prop, if there is a lot of drag, the ESC must be disconnected).  Simply test if each possible pair (AB, AC, BC) has continuity (acts like a straight wire, but actually has very low resistance in the .1 to .2 ohm range that will register the same as leads touching on your meter).  A simple battery and light bulb tester works for this if you don't have an ohm meter.

Re: Motor cutouts
« Reply #7 on: June 17, 2020, 05:31:12 pm »
a little follow up and end of this threat:
the motors were definitely the culprit in this case, I changed all of them with a different model from the same vendor (just 20 KV difference) and out of the sudden everything is working like a charm.
I also followed most of the instructions from TheOtherCliff (Thanks again for all your effort!) and for all measurements the previous motors seemed to be fine (continuity, connection), they even behaved well on the testbench with different esc's as long as you slowly/moderately changed the throttle but for 4 out of 6 motors this changed while doing fast throttle changes (with no difference on different ESC's) - Either I got very bad luck on the batch or the BR1806 sucks at all ;)
Anyway I learned a lot things how to debug such issues and can now fly happy!

Re: Motor cutouts
« Reply #8 on: June 17, 2020, 07:54:53 pm »
For those who may want to buy BR1806, which KV were the good ones and which KV were the bad ones?

Re: Motor cutouts
« Reply #9 on: June 18, 2020, 09:41:26 pm »
Racerstar BR1806 2280KV were the bad guys and BR2204 2300KV the good ones :)

Re: Motor cutouts
« Reply #10 on: June 18, 2020, 10:09:40 pm »
I realize that this is after the fact, and of limited value, but in my experience, there's more than just a 20Kv difference between an 1806 and a 2204. Depending on your quad's size and weight, the 1806's (with their lower power and max. current rating) may not have been appropriate.  Kv alone is not a good way to compare, and most motor manufacturers are overly optimistic when recommending prop sizes.

Anyway, glad you got it sorted out!