Blown Focbox .. ( was Help diagnose cutouts. Dual focbox | can bus | 6384 maytech/lacroix motors | flipshit vx1 | metr logs )

Had some strange cutouts today. I heard that noise from the motor like when it’s doing detection. Like a pop.

Caught some on metr. At 13:38:06 had a cut out then I pulled over and tried to reproduce no load. It did too more times but I didn’t note the time and haven’t picked them out of the log yet.

Not sure if it was remote / receiver or something else yet.

No faults recorded.


Did you hit any sort of bump at that point of the cutout?

If so you may want to check to see if your bluetooth module is loose. @ kevingraehl was getting cutouts on one of his boards and discovered that on a bump or something similar, the module would move and every time it did the ESC would cutout. I believe he said it was resting the throttle position so if you came off the throttle and got back on it would continue to accelerate, but he can chime in.

Edit. I saw focbox and just assumed unity. Not sure this is actually applicable to dual box’s

Edit2. Actually, might also apply here


hmm. I was short course practice racing in a parking lot. there’s a rain gutter I crossed. so yes bump. but lots of back and forth side to side turns too.

note it also did it “on the bench” ( upside down in my lap) …

forgot to mention my VX1 is connected via PPM not UART.


It sounds like an issue with one if the ESCs, but I would think it would be dead if it was phase under/over voltage condition.

Honestly, if I have an issue anything says FlipSky on it start there. That stuff never fails predictably.


yeah that flipsky’s always the suspect. i did just “harden them” though. still could be radio issues though it’d be my first time experiencing them. and the funny noise didn’t happen in my disconnect tests way back when.

does that throw a fault code? i wonder if metr logs show sign of reboot that would have wiped the fault codes… hmm. I didn’t explicitly check the secondary vesc for fault codes now that I think about it. though I think metr captures those now. but it didn’t used to so maybe I missed a fault on the secondary.


I’m not sure but I think a reboot would erase the error. If the error occured and caused a reboot before the metr logged it, you wouldn’t see it.

I don’t know what the error code would be. I had a VESC that created a lot of resistance, intermittently, on a single phase channel (?). Typically it was only under load, but I caught it once on the bench. I sent it off for repair and am still using it. Not clue what the cause was, it’s been a while. I only mention it because it made a weird sound when the issue occurred. It sounded a bit like a duck quacking with James Earl Jones’s deep voice :smile:.


Last time I had something like that happened to me it was a loose phase wire
Bullet connector was barely making contact and I Couldn’t really see because it was under heat shrink and expansion sleeve but spotted a slight spark coming out of the connector while bench testing


Yeah I’d check this too, had this happen on my hub board and I had to look at all the wires to realize one had come out.

Thanks I will definitely check this.

had two other problems on two other boards today. … so haven’t gotten far on this one yet. and now the work week commeth. . [ watch I’ll probably work on it on my lunch break… ]

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That bug applies to all vescs it seems :disappointed:

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By looking at your log I think you had a watch dog reset.
At least your NRFmodule failed to get data points just when you had the fault (between blue lines). Data looks frozen.

Look at the speed, it has not been updated. Sigificant drop when the next valid data was received.

You could trigger a watchdog fault code using vesctool and click reboot. Then check if this code can pop up in your log.


as a testing mechanism to see if metr can catch the faults? interesting.

I didn’t know about triggering a watchdog fault I’ll have to look into what that is about. it sounds like you’re saying I may have triggered one as part of the event but also i can use it as a tool to test?

good observation on the speed. it suggests my vesc was could have been frozen or rebooting. or that BLE module disconnected for that moment. thanks.

Yes exactly. It doesnt say why there could have been a reset… only to see if the fault code is visible in the app. I don’t use
metr so I dont know what it shows regarding faults. The code will be set in vesctool if you read fauls there.

I had watchdog resets (short cutouts) frequently some time ago after having installed a NRFmodule to that esc.

To pin point the problem I swapped the escs to see if the issue followed the esc with the fault code. But since then I have not had any problems. I did position then nrfmodule wires a bit differently so it is possible that it was the module that picked up interference earlier and disturbed the esc in some way.

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So i decided to blame the flipshit VX1. because on inspection it’s wires seemed sketchy despite my previous inspection and hotglue. one wire at the pot was pretty weak and broke off looking at it. :confused:

I redid the wiring. took it out for a test run… and…

the whole thing locked up a wheel. metr and remote disconnected. it’s dead. the one wheel drags the way it feels when you connect to phase wires on an unhooked up motor. I’m guessing I actually do have a phase short or something and i probably just fried my vesc.

I should have opened it up and inspected it depsite suspecting the flipshit.


This is highly unfortunate, I’m assuming all of your phase wire connections were insulated?

sidenote - moving to mr60 on my newest build is a good move bc you can’t mess up wire order or have phase short

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they are bullet connected with heatshrink over the bullets.

really want to ditch work and open it up and inspect. WFH is a lot harder in these circumstances.

Bro I know, that’s why I’m in office (we had the option to wfh or be in office), so I can’t just go work on my board and have less distractions… oh wait

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I see no signs of phase wire issues at the connections and no signs of anything else blown except! …

it did blow a fuse. [ see them in the center on the board with the antispark.

one fuse goes to each vesc. naively swapping the bad fuse with the good fuse… poor detective work. it insta popped the good fuse on power on. so something is shorted somewhere. need to think about how to proceed here.

I will probably disconnect the motor now and do the checks to see if it still works.

Then maybe I extract the vesc open it up an inspect it’s insides?

photo, board is stock lacroix prototipo DSS50

vesc towards top of photo is what blue the fuse. which is middle top side of pic.


I went riding tonight ok. I didn’t fix this thing. I hope this doesn’t make skatan mad.

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so the focbox is foc’d.

question is what caused it? what to do next so I don’t blow another one in it’s place?

  1. With the motor disconnected it spins smoothly. doing the hand tests of shorting phases together it seems to behave as expected.

  2. Plugging any two phase leads from the motor into any phase connectors on the focbox and they drag as if shorted.

  3. testing continuity on the phase connectors on the focbox shows two wires full continuity. between either of the first two and the third wire the other two seem to be charging a capacitor. current flows for a moment. then if i reverse the probes it flows again. on a spare focbox there’s none of this.

  4. The power leads to the focbox also are shorted / have continuity continuously. by contrast on a spare focbox. you get the filling a capacitor effect.

This suggests to me the focbox is foc’d

I think the hand tests of the motor suggest it wasn’t the issue. but how can I be sure? Next I will extract the focbox and open it up see what I can see… what should I see? how can I get to root cause so I don’t blow another one?