A custom PCB to mount MT6835 inside Hoverboard motors - End goal: direct drive Telescope mount

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Hi All!

I have designed a custom sensor PCB that can be mounted inside Hoverboard motors. Some of you might have read about this on the Discord already.

STR_5327
STR_53271920Ă—1282 238 KB

I took inspiration from attemps like here, but wanted to make this a bit more permanent and easier to reproduce by different people. The sensor board I designed uses the 21 Bit MT6835 and breaks out all the pins. You can mount this either on hoverboard motors by removing the disk shaped part, or use the 25*25mm M3 holes to screw it directly to matching motors.

The reason I designed these is that I want to try building a direct-drive telescope mount with hoverboard motors. The angular resolution of the MT6835 is about half an arcsecond, which is on the same order as many telescopes. I don´t expect to get stellar performance (no pun intended…), but instead just want to see how good I can get the tracking.
This idea of using Hoverboard motors is not my own, instead Astroboden built a direct-drive, but open-loop mount and used star guiding successfully.

I have modified one motor already, and am working on a second one. From first tests it looks like the sensor is completely noiseless, at least at zero to slow speeds. I can get following errors of about 5 arcseconds with just some basic PID tuning.

Anyways, I have put all the files and a guide for modifying Hoverboard motors on GitHub here.

I will post some updates here if I make significant progress with the project.

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Pretty neat.

Are you using the existing hall sensor wiring to pull the signal out or you draw separate wires? It’s hard to tell from the pics.

Also when you drill the two holding holes, first you may want to use a center punch instead of directly drilling into the jig holes.

Where is the 8-th pic? I can’t see it.

Cheers,
Valentine

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Thanks!

I completely rewired the connections with 24 AWG wire, because pulling the original wiring out already was a bit cumbersome, and I needed a sixth wire for the SPI anyways.

Didn´t think about this, good idea! I don´t have any centerpunches unfortunately, only the normal, huge punches, that definitely wont fit into a 2mm hole xD

Just added an 8th picture, along with some clarifications based on your comments. I didn´t take any pictures of me marking the center of the rotor unfortunately, so this will have to do.

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