At what point is compact too complex

I have seen lots of designs about flipped motor and multiple plate gearboxes for the most compact gearboxes. But at what cost is going compact too complex?
I made this gearbox with a middle motor design if that’s the best term for it and there were lots of sacrifices I had to make to it work. It’s a 2 Falcon 500 gearbox with a 9.38-1 gear ratio and a 10.33 ft/s adjusted speed on 4 in wheels. It is also made for an 8 wheel design.




Because I was making a gearbox I was wondering how else you guys calculate gear rations in sketches for custom gearboxes. We use the formula teeth/DP/+ tolerance (which is .0015 per gear)

This looks pretty typical for a “flipped” gearbox IMHO (even though it’s not technically flipped, the same design constraints apply). There’s a lot of design choices that can be made, it’s all a matter of tradeoffs. I personally like to push the limits with off-season designs to understand just how far I can take something before it stops making sense. As far as putting the gear in the middle of the tube…it works just fine. Apex Robotics 5803 ran gearboxes like than since 2017 (And 2046 machined all of those drive rails, thanks!)

Couple of questions: The renders seem to show both bearings on the output shaft are in the gearbox plates. That’s not typical for WCD style since you want the wheel cantilever as short as possible. The downside is then your gearbox can’t be self-contained. However, given how the 1st stage gear is arranged in the tube, it’s not simple to drop in and out regardless, so I’d consider moving that bearing to the outside of the tube.

Also, it’s hard to tell from the side profile, but the chain looks like it will be running very close to the motor casings. I would model the outside of the chain in your layout sketch and make sure it doesn’t have an issue.

As far as complexity goes…if you’re running chain, you’re gaining about 1.75" of internal space going this route vs a more traditional, non-flipped gearbox (0.5" for each gear set plus 0.75" width for the chain run). A traditional gearbox will be easier to install. There are also arrangements of flipped Falcon gearboxes that are similarly compact but have different pros and cons. (Example: https://imgur.com/a/KlH9Ejz). If you need an extra 3.5" of width between the gearboxes, then it might be worthwhile…if not, I personally would probably not bother. I do like how your design keeps the Talon FX towards the inside of the robot and therefore more protected than a normal flipped design would be.

I’ve not usually done a center distance adder on gearboxes and haven’t had an issue, but Teeth/DP+tolerance as your tangent circles is a pretty typical way to do it. Even if I know the dimension, I prefer to type the fraction into the dimension so that when I go back later I know what size gear I used without having to back calculate it.


This is the exact same gear ratio and the same idea yet packaged differently. This one however is approximately 5.75 in compared to 4.5 in for the smaller version. This design is also much more simple and took half the time to CAD though I didn’t flush it out as much as I did the other.

Falcons and NEOs are so short already, that it’s not as huge of a difference vs flipping a full CIM around.

Is there a reason you’re using the single sprockets vs the double sprockets. They’re billed for “chain in tube” but honestly they work great outside of the tube as well and they’re a little more compact since they share the same hub.

Yes this gearbox is meant to not be centered on an axle that is why the bearing is where it is at. Yes I know the chain is close I kinda just threw this gearbox together today for fun after seeing some designs on here. I do the exact same I believe for instance a 20 dp 62 tooth gear would be typed in as 62/20+.0015 and that allows us easily to change the gear size when needed or checked.

There is actually a 1/16 spacer in between the sprockets because we use 25H chain and we have had issues of the pins clicking together so we space the sprockets now.

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