Gearbox design advice

As a recent project, both for design practice and to get used to onshape, I made a flat gearbox. As I’m ironing out the final (I think) kinks in the design, I’d like to see if anyone on CD can think of anything that I should take into account.
This gearbox is meant to mount directly to the 2x1 frame of a wcd and direct drive the center wheel. I thought about putting chain in tube, but decided against it and put the chain in the gearbox instead. Feel free to ask for more views if they’re useful.

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Right off the bat, stop using placeholders for your gears. Get the real models from vexpro or WCP.

Also, add your standoffs to the model. You never know what might conflict, such as your chain run and the standoffs (depending what size you use).

Also, technically speaking, you’ve got some extra weight, as one of the gears is unnecessary.

Placeholders for gears were used because it was much easier to change gear ratios throughout the design process if I didn’t have to go and download a new model every time, but now that the ratios are finalized I should switch that.

Or you can use the spur gear featurescript. Then you can go back and change the gears pretty easily.

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As to having the extra gear, when I was looking through some older posts on CD I came across a lot of worries that putting the force of two motors on one pinion could damage the pinion. My team already likes to shove a lot and I didn’t want to risk breaking a pinion if I could avoid it.

Something that I think you need to think through just a little bit more, or maybe I’m just not seeing it: Where does the side rail connect, and how? It’s not particularly obvious–and if it’s supposed to be on the face of the gearbox I’m going to suggest that you change those bolts to countersunk (flat) heads, or plan to put clearance holes for them in the side rail. Also, again if it’s a face mount, that output shaft seems mighty short to get through the shaft and the wheel with enough room to secure the wheel.

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I’m kind of new to onshape and didn’t see this anywhere, is it on mobile and browser or is it just a browser feature?

That’s a reasonable fear. There are other ways of approaching a gearbox like this that could eliminate the gear.

How many teeth do you have on that pinion? If it’s like a 20T I wouldn’t be worried at all. 14T would probably be okay.

The side rail connects with these 4 bolt holes.

The mounting was a main concern of mine: will 4 bolts be strong enough to hold that gearbox on? I don’t know how much the weight of the gearbox would cause it to bend downwards.
The final output shaft is only that short because I haven’t made it longer, I just made it stick out a bit so I could visualize how it would work.
The motor pinions are 14t 20dp

Are there any sensors at all? This constantly gets me into trouble with the electronics team and programming, they need to be added ASAP. Even if this is just practice, it’s not a bad idea to get into the habit.

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One big thing I don’t see is how the shafts are constrained so they don’t slide out.

Not sure since I rarely use mobile, but I assume it would be.

I think this is the FS document link, but not 100% sure it will work:

My understanding was that we would use the built in encoders on the neo motors. What benefit is there to using external encoders?

Fair enough. Might want to CAD that rail in and check for interference.

With your concern of whether the 4 bolts will be strong enough, the answer is “probably”, but that’s contingent on two questions: Size/material of the bolts, and what they’re screwing into/through. I would suggest that larger bolts are better in this application, within reason–1/4-20 steel bolts would be just about perfect, or maybe 10-24 if they’re particularly strong–and I might suggest that you want to insert them from inside the rail into a locknut, using a clearance hole on the far side. Going clear through the rail gets interesting, as does trying to tap into it (or hold a nut inside).

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Make sure you include some encoders, it will make your programming team a lot happier. Also like @ShIfTiNgBoT said, there are ways to make this more compact. Here is an example of a similar low profile gearbox I designed a while back.


Wow, that’s actually a really smart design, putting a sprocket on one shaft and a wheel axle on the other. I dig it.


There isnt any, but make sure to model any sensors. It saves a lot of argument with elex and programming.
For example, you could also have had like a hall effect sensor. Elex and programming get mad if I don’t put it in the CAD. Dunno why it would be on a DT gearbox, but… That’s electronics/programming problem, not mine.

So from what you said it sounds like your process of creating a gearbox may be a bit off. Instead of actually making the 3d models to see if stuff fits you can to it way quicker and more efficiently with a quick sketch.

I start off every single one of my gearboxes with a sketch like this so I know where each gear is, where each standoff is, and where each motor is so that I know they won’t hit each other and everything will mesh together properly. One thing to keep in mind is that these are pitch diameter circles and the actual gear diameter is like .1" wider so give yourself a bit more room around gears.


its probably better if you make the mounting plate of the gearbox around the same size as the mounting plate for the motors. I don’t know for sure bcuz i haven’t seen a gearbox where its not the same size, but theoretically it’ll increase the stress on your bolts and supports cuz the torque transferred from the weight and movement of the motors will result in more force on the mounting bolts due to the decreased radius.
can’t be sure tho, just a thought