pic: Short coaxial swerve module



I posted a CIM-in-wheel swerve not too long ago, and it inspired me to design a swerve that had a horizontal CIM motor, but still coaxial.

3.6:1 gear ratio on a 2.25" wheel.
4.4" tall.
Inventor says it should weigh 5.2lbs.

Any questions or comments are welcome.

While I applaud your efforts, I have to ask, what benefits does having the CIM in a horizontal orientation get you? And are those benefits worth the extra complexity, part count, efficiency loss from the extra miter stage, and potentially weight? (not sure if the last one is a factor or not) The only benefit I can think of that might even be measurable is a lower CG, although I don’t foresee that being much of a difference. I would suggest investigating worm gears in the future if you wish to bring this design into reality. You can get a nice, high, relatively efficient reduction in a single stage, and it sets you up nicely to go coaxial. Anyways, I love seeing your designs posted here fairly regularly, you have a tendency to think outside the box which is fantastic. Keep up the good work!

I won’t dispute worm gears high reductions but i wouldn’t describe them as relatively efficient. The highest efficiently you’ll get is 86% with a four lead worm. At best this would be replacing the two stages before the co-axial, a miter stage and a timing belts stage, each around 95% or higher. I too am unsure of the benefits of a horizontal cim for a coaxial swerve but I don’t think a worm gear would be beneficial on the Cim motor. However, using a worm gear for the steering motor is a different issue and has more merits in my opinion.

You are correct, sir. The miter gears I’ve had experience with are in all likelihood far below 95% efficiency, however upon further research I found that good quality miters in rigid and accurate housings can achieve those numbers. And of course belts are highly efficient, if properly tensioned.

This was a design exercise for me to see how short I could make a coaxial swerve drive. In order to make the module shorter than a CIM motor is long, I had to put it sideways. I agree that there is likely not a huge benefit of doing it this way, but it was something I wanted to try out. I do think it is the lightest and most compact swerve I’ve ever designed, although that is likely for reasons other than the horizontal CIM.

There is also the fact that I’m only looking for a 1.5:1 gear ratio out of that section of the powertrain.

Amazing as usual. :slight_smile: Thank you for sharing this on CD.
That weight is interestingly low. What is the thickness of the top plate? ARe you still using 1/4" diameter balls for the 16-style bearing?
EDIT: And which miter gears are those? They don’t look like Vex ones.

Thanks for the kind words.
The weight is a little lower than I expected as well, considering the added complexity. I attribute the lower weight to the caster portion being smaller. It now fits into a 72 tooth 20 dp gear from VEX instead of an 84 tooth.
The top plate is 0.25’’ thick so that the plate that the CIM mounts to can be attached to the side of it with 6 32 bolts.
Yes, the steering gear and the bottom gearbox plate have grooves milled in them for 0.25" delrin balls.
The first set of miter gears are 1 module, 20 tooth because they have 8mm bore, and they’re a little smaller. The later ones, in the caster, are 20 tooth 20 dp, because my team has had success with them in the past. They are both made of steel, and from SDP-SI.

That’d be awesome if it weighed that little. I don’t really trust inventors weight estimates, I’ve gotten burned by that in the past. Not that I don’t trust you or anything. Looks awesome!

Could you release the cad of this on grabcad. If possible in Inventor Format.

The swerve drive looks great