Onewheel Pint with Little FOCer build thread (#focfm)

Starting a thread about putting Little FOCer into a Onewheel Pint.

For future reference, the build should also appear as blog posts on my website: https://riddimrider.one/

Phase one of the project is to plug the Little FOCer as it is, detect the motor, configure balancing somewhat and get the footpad sensors to work.

First thing I had to do is bypass the stock BMS for discharge (I’ll keep the BMS for now to keep the battery balanced and replace it later):

It’s a very tight fit but I managed to cram the extra XT60 connection in there.

I bought a bricked Onewheel controller and BMS pair and extracted the connector board from the controller:


This will make it very easy to connect the motor and footpad sensor using the existing connectors, which is very convenient and keeps the controller box waterproof.

Another great thing about this setup is that the controller box on the Pint can be opened with the box screwed down to the rails, all you need to do is lift the front footpad to get to the cover.

I’ve ground off the stand-offs that were in the middle of the box, that’s the spot where the Little FOCer will be mounted later. I’ve kept the ones that aren’t in the way right now, they may still come handy.

I’ve soldered an antispark XT90s connector to the Little FOCer and made a short adaptor with an 80A car audio fuse to the XT60 that comes from the battery:

Soldering wires to the motor/sensor connector board:

I’ve found the pinout here:
https://community.onewheel.com/topic/9297/reviving-a-destroyed-pint/13

The sensors are wired with a pullup resistor and short to the ground on the Onewheel controller. The ground pin on the connector board is shared with the motor connector. Since on the Little FOCer there are only pulldown resistors, I’ve interrupted the ground trace that goes to the pin on the sensor connector and that stray red wire is soldered to a pad that is connected with that pin. That red wire is connected to 3.3V on the Little FOCer and the two sensor pins are connected to ADC1 and ADC2.

The two 10k pulldown resistors soldered on the Little FOCer:

It wasn’t easy soldering these, in particular one of the pads on each of those, which I assume is connected to the ground was sucking the heat really fast. I’m glad I bought a 110W soldering iron in preparation for de-soldering and flipping the caps and connectors on the FOCer.

Things ready to connect!

Aaand it’s on!

I’ve done the motor detection, set up the IMU for balancing and configured the footpads. I did a test by pressing the footpads and tilt the board around, got the board to activate and jump up as it spun the motor really fast. Enough with this wonky setup.

Next phase is taking off the heatsink of the FOCer, desolder the caps and connectors from it, and soldering them to the other side, so that I can flip the FOCer and mount it straight to the alu box bottom, heatsinking the mosfets into it. Then I’ll be able to actually close the box and put the footpad on properly.

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Rehosting that image in case it’s taken down over there in the future.

Onewheel Pint pinout

edit Jan 2023: good thing we rehosted it!

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Great job!! :sunglasses:

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Cheers, I wasn’t sure I should “straight up steal it” but I did also save it locally :slight_smile:

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I’d hate for someone to find your thread two years from now and the link to the pinout is broken. :rofl:

Been there, done that…

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Yep… tbf I am also planning on making a blog post with more details, but I wated to throw this together quickly as opposed to sitting on it :smiley:

Alright round 2 here we go!

First thing for mounting the FOCer is to remove the heatsink and resolder the caps and connectors to the other side. This was a huge challenge for me. I’m ashamed to admit in the end I just couldn’t get the solder out from the cap holes, so I very gently drilled the holes out with a hand-powered drill and a 1mm drill bit. FTR I’ve used the Sequre SQ-A110 110W soldering iron that goes up to 500C.

Desoldered (solder still in the holes on this pic):

Resoldered, top side. Used new JSTs, the old ones didn’t really survive desoldering. I used a 6-pin connector instead of the 7-pin for the COMM, as I can’t get 7-pins locally and I don’t need the 5V anyway:

Onwards to mounting the FOCer. Here’s a test fit inside the lid. It fits just perfectly snug under the lid. The channel on the left is an indentation for the footpad sensor cable the caps just so so fit, height-wise as well, they seem to just be touching but there’s no pressure.

I printed a template to drill the holes for the standoffs, double-sided taped it to the box for drilling:

The standoffs I got were 5mm tall, I ground them down to 4mm, tapped the holes and here they are in place:

I’ve spent a lot of time figuring out how to get a fuse on the voltage input side, I realized I just need to fit the input side of the cabling up top behind the caps, otherwise it would get unreasonable with the thick cables. Gone through several iterations of how to cram a fuse in there, in the end I decided to solder this sort of automotive fuse directly in line:



Had to do some hardcore cable gymnastics to fit everything in the space behind the FOCer. You’ll see in the final pic, here’s the resulting “adapter” from XT60 to antispark XT90s with the fuse inbetween:

I’ve also resoldered the wires on the motor/sensor connector board so that they go directly to the side:

Silicone pad and fishpaper under the FOCer, along with washers:

When mounted and tightened, the FOCer has a noticeable bow in the PCB:

The standoffs are 4mm tall and the reddish washers are 0.5mm, though they might squish a bit. The silicone pad is 0.5 mm. I’ve already found out before that the mosfets are actually 4.5 mm proud of the board, but with the original heatsink the spacers were also 4.5mm. So not sure where exactly is an error in the calculation, but I don’t think I can leave it this way. For now I’ve loosened the screws and I’ll be replacing the washers, probably use steel ones and pad them with the fish paper on one side until the mosfets sit well.

So here’s the glorious assembled box, it took many hours to fit everything, but I couldn’t be happier with how clean it is. And I think I’ll be able to cram 4 21700 cells in the leftover space, possibly managing to squeeze full 20S into this thing :smiling_imp:

And a detail of how the adapter in the back fits. Still behind it there’s a plastic light channel on the lid for the led bar. It fits behind the adapter just snug (the adapter puts some pressure on the light channel but none on the caps AFAICT). I should be able to put a led bar in there eventually!

And it’s on :smiley: There is a slight pressure from the sensor cable indent on the leftmost cap in the end, I’ve cut a bit of plastic off, will cut some more so that it doesn’t visibly bend when I put the lid on.

I temporarily attached an external BT module (not pictured) and managed to tune the board for a first ride! Obligatory crappy video :nerd_face:

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wow that cap height in the pint case is perfect!

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It is, I was afraid, but I’m super happy with how everything fits!

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Looking very good! What are you going to do with the left over space?

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I’m hoping to put 4 more 21700 cells in there, try to cram 16 cells in the battery box with a BMS flat on top of the battery, for a total of glorious 20S :smiley: We’ll see how it goes…

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I have a Pint that I am looking at for a buddy. He ran the voltage really low and now the BMS won’t discharge or charge.

I am thinking about doing a bypass on his BMS. Howd that work for you? Any special steps?

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he used a vesc allowing him to not use the FM BMS, which is needed for the FM ESC.

Why are you not just manually charging then resetting the Pint BMS?

I charged the battery seperately from the BMS.

I’ve been trying to figure out how to reset the BMS. Do you know how?

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facebook could prob answer that, if you are in the Macgyver group or whatever

Do you know of a specific group?

I’ve joined a few random onewheel groups to try and figure out the reset. I’ve been looking all over the web.

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image

Haha you got me in that last one. Thought people who messed with vescs might have BMS info as well.

Joined the other two

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Sorry, I wasn’t around and haven’t noticed. Interesting problem, so the BMS got out of sync with the state of charge of the battery? But that would be a common issue if you swap one BMS for another or swap the battery? How does it manifest?

I don’t have an answer, but I can ask around if you would happen to still face the issue…

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