Motor in Wheel prototype 1 - AKA procrastinating for finals

Today on “How Venkat is procrastinating for his math final,” we have a quite outlandish motor in wheel (non-swerve) module that I’ve been wanting to make since I saw someone do it a couple months back, but I never really got around to it. So then I decided that after taking my Statics final, there’s no better time than the present!

Now usually with my weird CAD ideas, my friends usually ask why and I just answer the how, but even now I have to ask why because this is now begging me to iterate on this design until I can produce something reasonable in packaging, manufacturability, and weight. Whether or not I will be able to achieve that is another story but I can keep trying.

Before we continue, I grossly miscalculated the speeds and size of the module, and looking back it’s really funny but I plan to fix this within a week or so. This is just a proof of concept that the idea works.

6.5" wheel, using blue nitrile tread
Free speed: 28 ft/s
Ratio: 5.25:1 planetary gearbox (18 tooth sun, 34 tooth planet, and 84 tooth ring gear)
Driven off a Falcon 500. Ring gear w/ falcon mounts to a 3"x2" and the wheel is powered around it and rides on silverthin bearings. Another silverthin bearing is set into the ring gear for a secondary plate to cantilever the planet gears.

All comments/criticism is appreciated, as this project is what got me to open inventor after 7 months, and I want to see it through.

GrabCAD link: Click Here


That’s really cool Venkat, I can’t wait to see what your speed-adjusted variation looks like. Hope finals go well!

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I can’t open inventor files.

Is the ring gear integral to the motor mount? Or is it a separate piece bolted on (press fit in?)? The latter may be more manufacturable (as it could be EDM’d separately and then assembled)… or at least, an undercut if you’re going to go the route of gear hobbing.

Your gear teeth don’t add up. 18+34+34 = 86, not 84… I believe there are divisibilities that need to be considered when deciding on number of planets, as well.

Now I want a COTS 20DP ring gear for stuff like this. 84 teeth would work with a 12T sun and 36T planets.

I always like these concepts but they don’t seem to make a lot of “why” sense… In theory I think they could if optimized though.



If you could get them to have enough strength and durability, the packaging helps reduce a chunk of the space claim needed for your drivetrain and associated components.

FWIW, the idea does exist “in the wild”.

A big gap would still be the usual “chain the wheels together” problem, but that’s not unsolvable.

Concept is definitely really sweet though! I also echo: keep pushing as long as you’re willing! If someone came to me with this unit as a reasonably-priced COTS solution and test data to show the robustness, I’d thoroughly consider purchasing!


Thank you! Tuesday’s final went well, so fingers crossed this goes well too.

Ahah the gear teeth is something I messed up. Looking back at my notepad I did the math for a 16 tooth gear and then put an 18 tooth gear in, thank you for picking up on that, I’ll adjust it. As for the ring gear, I made it one piece but it’s definitely possible to make it two, and I’ll probably try that this time around. Honestly probably tonight, but I’ll post an update when I do. I’ll upload a STEP file along with the inventor files as well to make it easier to open for more people.

These mistakes are what I get for trying to rush through a CAD project, but thanks for the help! Hopefully I can justify the why soon enough.

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Thank you! That means a lot, and I’ll keep on pushing with this, I’ll just end up playing R6 or control otherwise. I’ll also try to make a BOM for this next time around, so hopefully it can be gauged as a viable product.

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Just linking this thread in, for any future reference.

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This is looking absolutely amazing!

One question I have though is where you’ll be putting the electronics from the Falcon 500? As the wheel would be spinning, there is a high chance the wires will break or twist unless guided through something else.

We had it where the wires would go onto an aluminum plate so the wires would not tangle but because it was so close to the teeth of the wheel/gear, there would have been a likely chance of the wires breaking.

It also depends on if it would be on a flywheel or intake but just something to keep in mind. And to repeat myself, looks great!


Cim Motor 6 in wheel 8:1 with the bevels

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Ooooh, here’s a fun idea: machine a 5M timing pulley into the outside along with everything else. It may end up being a pretty big pulley … but could work

So I forgot to include a drivebase assembly in the last model, so included that with V2 here. It’s essentially mounted inside the box tubing and wheel, and then the wires come out the top.

Some notable changes:

  • Split the ring gear into 2 parts as @ThaddeusMaximus recommended
  • Changed the gearing to 17 ft/s free speed (Along with that, wheel diameter down from 7 inches to 5.5 inches)
  • Overall manufacturability is much simpler now
  • Still managed to tighten up a lot of the tolerances
  • Got module weight down to about 5 pounds.
  • Now mounts with 8x 8-32’s on a lip to avoid having to cut into the box tubing for bolt head clearance.

Ended up going with this gearing as it was perfect.

Finally, with the drivebase, I went with a 4+2 design because that’d eliminate the need for a drop center, and I’m a firm believer that 4 motors is more than enough for a drive base (though with the new PDP, ports won’t be an issue), but @Drost pointed out that I’m only getting 2/3 of the normal force because the 2 omnis are not powered. I’m tempted to make it a 4 wheel drive, but @krf pointed out that if the motor was mounted through the box tubing instead of inside the wheel, then I could both reduce the width and possibly chain up the omnis and center wheels. It’s something I want to give a try now.

Thank you for all the feedback so far! Glad to be on break now so I can wholeheartedly CAD.

GrabCAD link:


:face_with_monocle: This isn’t a harmonic drive. You can still take this up a level.

(nice work!)


Not EVERYTHING needs to be holonomic…does it?

Harmonic drive is a type of cycloidal-driven gearbox for very dense reductions.

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Aaaand I read it wrong oop. That’s awesome though!

It IS awesome, and sometimes so impractical that it triggers people. It’s fun to design though.

Eh i prefer the term disruptive innovation…

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