Focbox - stuttering when accelerating from slow speeds in FOC mode?

So, Im very very disappointed.

Ive got a 10s4p (currently 9s4p due to a bad pack - still aint figured out what killed it. Been riding on it anyway with no major issue untill now). Single 6374, 200kV, 15T42T gearing, 100 MBS Wheels

Focbox overheated and cut power after just 6.5 miles riding. I was hammering along at 18 - 22 mph but no major hill till mile 6 and then the board just crawled to a stop.

Anyone else getting this? I think these 100mm MBS wheels are just too big and heavy. Motor was very warm. Truck was warm and acted like a heatsink. Enclosure felt a bit warm, meaning battery was probs warm too.

Here is metr data:

You’ve got a battery problem, not a FocBox problem. At least you didn’t have a FocBox problem, you might now if you battery was throwing garbage.


Ive ordered 4 new 30Qs to replace the bad pack. I still dont know why the pack went dead.

What causes that? Bad BMS? (only using it for charging) Leaving on charger too long (Overnight - did it once coz forgot about it)?

All kinds of things…BMS, bad cells, bad weld, shorted balance wire, intermittent switch short, bad charger, etc. It’s impossible to tell without tearing the back down, which would be my next move.


Ive already done that and found a middle pack to be completely dead. Found no burn marks. No bad welds. No shorts. Just a pack in the middle that had zero V.

I would replace the BMS at least.

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Are the balance wires on the BMS in the correct order? Are two of them swapped?

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It has been fine for about 200 miles. This is a new issue.

If you have your focbox’s set for 10s then your hitting the low voltage cutoff, is what it sounds like to me. I’ve had BMS’s kill cells. Namely the cheap white BMS’s. Maybe set your focbox’s for 9s, if you haven’t already.

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This :point_up_2:t3: Voltage goes down to 30.8v at 5:35:12

The focbox is hitting 84c so it may throttle just a little at that temp but no cutoff.

Some focboxes came with a plastic film over the thermal transfer pads, might be worth checking that also.


Thanks, Ill set it to 9s till my new cells and BMS come. 84c seems high though. Maybe ive just never checked Focbox temp after 6 steady miles.

So, I reprogrammed the Focbox and set to 9s. I put conservative settings on it.

The motor stuttered and shut off/on under medium load. I stopped after 200mtrs and the motor was too hot to hold hand on and the VESC was already close to 80deg C.

Im sure having a 10s4p with a dead pack in there and calling it a 9s in settings cant be good!? I know the next step is new BMS and new pack of 4 18650s. Ugh… rewiring that will be a pain.

I just really really really hope that the Focbox isn’t screwed because of dud battery.

I’m pretty sure you are looking at two separate problems here. Overheating should not cut, but only reduce the power. There is a battery issue. But this doesn’t explain the extreme heat of the FOCBOX or the motor. Please post your settings. The last time I saw someone with this issue, the problem was that he had set the motor to “sensored” instead of “hybrid”.

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Yeah, I have mine set to ‘sensored’. I’ve never heard of anyone setting it to ‘hybrid’! Is that a thing if you’re running a sensored motor?

Its weird… before I changed settings to 9s (due to the bad pack in the 10s obviously) it didnt ‘cut’ the motor. It was more like real voltage sag like I used to get from the old 4.x Vesc when going up hill with the big wheels on. It was still hot but I only checked it after 6 miles (when it started sagging). I’d never noticed any heat before when powering off before.

Now that ive changed to 9s in settings, its fine if rolling gradually on flat but if I jam on power it ‘cuts’ and almost throws you forward… and it gets crazy hot in a short time.

Bad charger? Bad Focbox? Bad settings? Bad BMS? Bad Cells?

There is an argument for all of these. For example, when I plug in my charger to my other 10s2p build, it stays green, rather than red even when there is only 50% charge and it refuses to begin charging straight away. It eventually works. I do recall a time when I shorted the charger by testing the polarity on its tip with a multimeter. This was when I was building and wiring the 10s2p board (8 months after the 10s4p… that had no issues prior to this event… I think. Issues certainly began in the same week or two of this event). Could a briefly shorted charger (that still works, eventually) cause a bad pack, therefore a bad Focbox, therefore an overheating motor, therefore a sagging/cutting. Jeez. What a head melt!!

“Sensored” is definitely never the right choice for eskate. What you want is hybrid. This means the VESC uses sensored for increased startup torque and then switches to sensorless at high ERPM. This is the way it should be. This will certainly cause overheating motor and FOCBOX. From the telemetry you posted, it looks like riding that should barely heat the motor or the FOCBOX at all, if everything is configured correctly. The hard cutoff that you fell could be the motor overheating. I don’t know what’s the result of that. But the FOCBOX overheating causes a soft cutoff, meaning a gradual reduction of power.

So please switch to hybrid mode. But it definitely seems like there is some funny-business going on with you battery - even if this is unrelated to your heat issue. Check your balance cables, the individual cell voltages, your charger etc…


Thanks man! I’ll change to hybrid (I dont even recall that option!). Makes sense, what youre saying although it didn’t cause any issue before… unless thats whats caused the problems now! I’ve done a few hundreds miles on sensored with no apparent issue.

I’ve ordered new cells and a BMS. I’ll be rebuilding the battery anyway to rewire the BMS so I should be checking everything. Till then, I guess I’ll just park it up. Don’t wana mess anything up further!.

Well it for sure also caused way more heat than it should before, and therefore wasted a lot of battery power. You probably just didn’t overheat the motor yet. Once you fixed up your battery, have a try in hybrid. The power and the range should be a day and night difference for high speed/high power riding!

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Hey, sorry to hijack your conversation but that really sounds like a great innovation,hybrid mode. I used to experience a flat spot of acceleration with sensored motors as opposed to unsensored. It was smoother yes but felt less powerful so i unplugged the sensors and adjusted the programming to suit but still experienced a little cogging. more power but cogging. i’m just about to start programming my dual focboxes and am using 200kv 6374 motors and as i understand it the hybrid will allow smooth take off but then let go to achieve full motor revolution at top end. Is this the case? Thanks for the heads up!!

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Yes, that’s exactly the point of hybrid mode. Unsensored is more efficient at high ERPM, and sensored mode has good torque at stand-still. Hybrid is meant to give you the best from both worlds. Sensored mode is NEVER a good choice on an eskate!


How do you even setup hybrid mode? I had a look on Vesc Tool and I dont see it as an option!