What the f*ck... R-XSR interfering with 16x16 4in1 ESC


#1

Some random thing happened and I thought it might be good to write this down for the community.
I’ve been working on a 69mm 2S brushless prototype machine for a week now. FrSky R-XSR, TBS Unify Nano, 1.2g camera, 16x16 F4 stack, 1102 11500KV motors.

It had trouble from the beginning - motor 4 was randomly twitching. First we suspected a loose motor wire, so I redid all the wiring. It didn’t help it. I then swapped the 4in1 ESC and the machine started dipping to the right (turns out the replacement ESC had bad FETs). I then moved all 24 FETs from the one ESC to the other and made sure to move the FETs from ESC 4 to another one. After reassembly (new ESC, old FETs) the problem with motor 4 reappeared. Did I mention that I waterproofed everything before? Reflow was a massacre.
So, after reworking this damn thing for something like 3 days - I open the motors tab, spin up motor 4, it twitches - I turn off my transmitter (!) and it runs smoothly - turn the transmitter back on - motor starts twitching again - repeatable. Turns out the antennas of the R-XSR were pretty close to the BusyBee2 of ESC4 (nothing was touching, just too close).

The fix: A small piece of copper-foil covered with kapton-tape between the R-XSR and the 4in1. Seems to work for now.

Lesson learned: Micros/Nanos can be really painful to debug, expect the unexpected.

Edit: Another lesson learned - don’t conformal coat ESCs when not really necessary. Another of these 16x16 ESCs bit the dust, at least on FET burned out - took one trace on the PCB with it, possibly fixable, but only with a bridge-wire.


#2

Thus are FCC testing and licensing requirements born.

First time I’ve heard of this in quadcopter land, but it doesn’t surprise me. I’ve had a couple builds where I thought it might, but most of my RX units don’t do any transmitting like the r-xsr does.

This is why, technically, it’s illegal to run these things in the US without a license that shows you understand RF interference and the consequences.


#3

Sssssssshhhhhh. We don’t want anyone finding out… lol :joy::grin:


#4

This could explain why I had two ‘faulty’ esc’s which in the end were working. Was with a 15mm D8 from BG though. Very interesting observation!


#5

Hadn’t thought about that on the D8 though, forgot it had telemetry.
I must have had a lucky placement with the one I was using!


#6

I still have one of them lying around… let’s see if that was the cause after all.


#7

I just had something similar happen. The video signal would drop out whenever my radio was on - but it wasn’t straight interference from the TX. I thought I was overloading the 5V or getting weird interference or spikes, but couldn’t be…

Then I realized that waving my finger around in the right spots (near the antennas) would make the video come right back. The VTX whip antenna was parallel to one of the RX antennas, so I moved the RX antenna and video was good again.

Finally, I realized that this is my only build where I used the R-XSR instead of XM+(!). Hurray for the ‘best FrSky receiver’!
Any way of completely disabling RF transmission on that thing? I have BF OSD for telemetry, anyway.

Cheers, nice find!

p.s.: I do conformal coat the sh#t out of everything ^^ You should be able to solder right through, right? Maybe try the acrylic type?


#8

The conformal coating works just fine and you can easily solder through it if you use the right stuff. But I suspect it to be the cause for overheating/burn-out of some FETs on the 16x16 ESCs I’m using.


#9

A short update: I had another “incident” where the antennas were too close to a motor signal wire - be careful where you place your R-XSR and its antennas on micro/nano quadcopters! Your (e.g.) ESC might not be the cause of your issues.

I firmware with telemetry disabled would probably be pretty nice…