Another differential swerve

I designed this swerve drivetrain for the recent cadathon; unfortunately after spending a lot of time on the DT (a trap I keep falling into) I didn’t design a super great robot overall (Team 8), but I was proud of the module and wanted to showcase it here.

I think this is perhaps a somewhat new diffy swerve style, at least I haven’t seen one with the same gearing arrangement (correct me if I am wrong). This version of it is kind of silly because cadathon… but I think if one was careful it could be made with mostly cots gears, one of its main advantages. It also builds in a reasonable steering reduction which seems to be an issue with many diffy swerves (If I remember correctly 275rpm steering at 13 or 14 fps). One potential downside is it that it relies on a slightly strange coaxial gear stack up.

Let me know if there are any more Q’s or if how it works is unclear.


Got a grabcad link? its a little hard to see whats going on

The Grabcads a bit of a mess but theirs a step here of the whole bot which you can pull the swerve out of!

Nice, that’s a really compact arrangement!

How do you transfer torque between the two coaxial gears on the idler shaft. Is the smaller one just pressed into the larger one?

What kind of steering gear ratio do you end up with?

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The way the outer gears orbit the larger inner ones is really cool, are the belts supposed to slide on the bronze spacers?

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Thanks, the arrangement initially stemmed from me misunderstanding a diagram I saw on Wikipedia of a differential, which I realized was actually a quite compact arrangement. Took a bit to get all the ratios for the orbiting gear set to work out though…

All of the idler gears are various sized CIM pinions so they are just keyed into the 8mm shaft they ride on.

The modified ultraplanetary (to be thinner but keep the preloaded bearings) is a 5 to 1 stage, which leads into a 15 to 51 belt reduction so overall, a 17 to 1.

@mudpie8 Since I was making this very compact for the Cadathon I used a much smaller pulley then I would feel comfortable to actually put on a robot, so yes I added that middle bronze spacer for the belts to slide against to increase pulley wrap.


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