YACDS: small n' light

It’s small, it weighs about 3.3 lbs, what’s not to love.
Free speed: 17.89 fps
Turning ratio: 131:1 (500 deg/sec free speed). Can be reduced more with more stages on the UP.
Footprint: 4.2"x4.2"x8"
Ground Clearance: 3.6" to frame bottom

The steering pinion pulley is interesting: instead of bolting to the provided 16mm bolt circle, I opted to replace the entire output with a 3d printed part. Hopefully, I will have data to show if this actually works soon.

Inventor 2021 files and .x_t here


Any reason you wouldn’t mount the steering motor to the bottom plate, and make the steering pulley part of the forks? That would lower your overall height by ~1 inch, and make for a simpler output from the Ultra Planetary.

No love for the Johnson PLG motor in any of these small swerve designs?


While it might lower the overall height, it would increase the already high ground clearance even more. At a certain point, the moment loads from that much cantilever would overwhelm the poor .25" delrin bushing I’m using in place of a real bearing.

Also, the space that the pulley already occupies is still needed, because of the gears coming off the driving Neo. The space between plates would remain the same and the ground clearance would increase, only netting me a height saving because the N550 + UP is so tall.

Why would it increase the ground clearance? You don’t have to raise the bottom plate at all - there’s lots of room between it and the wheel axle for a pulley. I agree though that you might have to make the pulley a little larger to fit around the bevel gear. You’d be trading off module width for module height.

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Nice looking module!

I like how you integrated the frame corner piece into the module design. Of course the cut-outs in the frame members to clear the module are going to make them pretty weak in lateral bending but you could easily add additional frame support fingers to the module plate and extend that curved bar on top further along the frame members if you were carrying a lot of the frame rigidity through the corner. If you have a belly pan that picks up the frame fairly close to the module, then what you have is probably more than strong enough.

Looks like you are fairly constrained for drive ratio options given how compact the pinion to module gear is packaged. Any idea what the max and min ratios would be for the various COTS pinion and spur gears that would fit?

We had good success in 2020 with a turning ratio of 33.33:1. So, your ratio of 131:1 is more reduction than you need. You might be able to drop one stage of the UP gearbox. Also, make sure you verify the actual gear ratios of the UP gear set slices. They are not exactly 3:1, 4:1 or 5:1.

Nice work Bryce! Very thrifty

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Good point, I was just thinking of sticking it in the stack. However, that would require significant redesign, since the bolts that hold the UP also help mount the top motor plate.

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I don’t do this on my version as I prefer the belt to not be exposed on the underside of the robot.

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Mmmmmm bushing, eh?

I really think,that a bearing for azimuth rotation is the second most important aspect of a swerve module (second only to the bevel gear).

In some of our early in-house designs, we went with bushings and they just never really work out.

I see how you are clamping the main plate between the upper 3D printed part and the machined delrin part. I think it would be relatively easy to integrate a bearing into this design. Instead of clamping the main plate between those two parts, you could clamp the inner race of a bearing with those same two parts and then do something similar to clamp the outer race with the upper part of the clamp being formed by a flanged pocket in the main plate and the other half of the clamp being formed by a 3D printed flanged ring bolted to the main plate.

Bushings are tricky, but if you do the work and dial them in, you won’t have problems. Looks pretty good Bryce!

Edit: (oh no did I just start a bushing war?)

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3.3lbs is crazy light!

Here are a few things I see base on the following cross section:

I suggest putting the bearings under the drive gears beside each other, and completely removing the section outlined in the red box. That should make the whole thing shorter.

It looks like your bevel gears are not meshing correctly.

I think you’re going to want a spacer to the left of the wheel to keep the bevel gears from getting smashed together when you drive around a corner.

I don’t see how you will be able to remove the wheel without disassembly, because the wheel flange will catch on the small bevel gear, and there’s no extra room to right of the wheel.

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Haven’t been in one of those since 2008.


Care to explain for us youngins?

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Last time they let me open an igus bag at kickoff.


I seem to recall there not being enough space to put those two bearings next to each other, but I’ll check on that again.

That’s the spacing that KHK recommends, and if memory serves it’s the same spacing that was found to work with Thrifty Swerve.

Yeah, and I probably need to add the rest of the spacers too lol… I just kept putting off adding them and evidently forgot I hadn’t when it came time to post.

Good catch. This should be easily solvable by cutting into the wheel fork a bit more, as it doesn’t look like it needs that much room.

Thank you for pointing those out!

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At > 3" above the ground, the belts would be safely behind the bumpers.

It’s more a function of being exposed to the debris from the ground.


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