pic: 3 CIM WCD Ball Shifter Second Edition

I was really happy with the gearbox I posted earlier in most ways, but I thought it was tall. This was my attempt to make a shorter version.
As always, questions and comments are welcome. :slight_smile:

It looks like you added in an extra gear, bearing, and shaft in order to make this viable. Do you think there’s a way to keep the two-shaft design like this? I can’t really think of one.
With that i mind, I think I prefer your last gearbox a bit more.
EDIT: Yeah, not a lot you can do without switching to belt combination it looks like.

On the idler gear, you can make that a bearing bore gear instead of a hex bore and make the shaft dead instead of live so it acts like another standoff.

How/where are you mounting the shifting piston?

I was a little worried about this. I planned on this being a trade off between height and weight. Surprisingly, because the gears are smaller, and the plates are more compact, this version only weighs 0.05lbs more than the previous.

I could do that, but I think it’s unnecessary, and it would require modifying the gear.

How/where are you mounting the shifting piston?

It is mounted to an aluminum plate that is stood off of the back of the gearbox, in-between the CIMs. I could post a picture if your interested.

You can buy bearing bore gears? No need to modify the hex ones.

If you still wanna use hex gears you can get some .250" ID x .500" OD Bearings.

That’s crazy good!
On dead axles, they do sell bearing bore gears, and it looks like you have something like a 48t or 50t gear on there. That would probably bump the weight to lower than what you had before.

It’s a 40 tooth gear. I guess I’m not seeing how a dead axle design would add useful strength or shed weight. I might give it a try anyway though, because I could be wrong.

While it seems convenient to use the CIMs as the nuts that hold the standoff through bolts on, having your gearbox fall apart when the CIMs are removed probably isn’t a good idea. Converting that idler shaft to a standoff would help remedy this and save the weight of a bearing.

Also, if you are going for flat try for one where all the CIMs are in a line (or nearly so) recent 341 and 254 gearboxes come to mind.

If it’s 40 tooth then you would have to modify, unfortunately.
You should reconsider the cim removal issue with the through bolts. Making heavy motors part of the frame is really awkward for assembly. Harder to put them in place, in addition to the regular mounting problems.
Maybe just making one of the cims have a different mounting hole pattern would work.

This. A thousand times this. This is my biggest issue with the WCP single-speed gearboxes; it’s incredibly annoying.

I’m not following here, the issue with Bryce’s gearbox is that all 5 standoffs mount to CIMs so you can’t keep the gearbox together without motors. The WCP gearboxes use two bottom bolts and 2 integrated into the CIM so it doesn’t have this issue.

We normally do this (not our robot) and put in CIM’s later. You had the gearbox fall apart in a similar WCD setup?

If you use the bottom two standoff bolts to mount to the frame (non-WCD designs, such as a modified AM14U, are not necessarily compatible with the through-tube bearing block), then taking the gearbox off of the robot and taking the CIMs off of the gearbox does, indeed, cause the gearbox to fall apart.

Past that, simply removing the bolts to the CIMs with the gearbox still on the robot causes the spacers to fall out, which can be a massive pain if they’re not in an easy-to-reach spot.

We normally do this (not our robot) and put in CIM’s later. You had the gearbox fall apart in a similar WCD setup?

Out of curiosity:

Why is doing this useful?
Why couldn’t you do this with the gearbox design that I posted?


Wasn’t thinking of a non-wcd case. We normally leave the bolts in the same spot and that keeps the spacers there, but this again is a WCD case.

We like the ability to do that so we can add CIMs in later/makes wiring a little easier without CIMs in the way. Also much much lighter without the CIMs in so its easier to handle etc…

The reason why I’m not a huge fan of using all bolts connected to CIMs is during assembly you either:

a) Have to assemble with CIMs to hold the gearbox together or
b) Put it together and put nuts in the back, then when putting in CIMs having to take each nut off.

Nothing crazy revolutionary but could make your life easier.

That makes sense. I agree that it would be a slight inconvenience. Although I like the idea of using the CIMs as standoff nuts because most of the forces on the back plate come from the CIM mounts, and because it lightens things.

It would be a pretty big inconvenience IMO. Gearbox assembly is already hard enough, as I learned last week.
It doesn’t hurt that much to add different mounting holes for the cims. Plus, then you can use a system like what 192 used to tension gearbox belts this year to allow for different pinions to be mounted.

We tried assembling WCP gearboxes. It took us around five hours to assemble two gearboxes due to some unforseen issues. It’s a great gearbox design for teams with little manufacturing resources. But some parts, like the sping washers, are really annoying to work with if you have enough machining resources to make it fit properly.
Also, R.C, if you are reading this, there was a slight error in the instuction manual. A 1/32" spacer is explicitly stated to be a 1/16" spacer in the instuctions. Not sure if that’s our problem or something wrong with the manual.

Assembly should take around 20-30 minutes a gearbox, we used 4 3 CIM WCD gearboxes this year.

I’m not a fan of the spring wave either, it’ll be replaced out to a solid washer in the future here soon…

I’ll take a look and your more than welcome to email me here. Please email me what gearbox you were using and which manual etc… That way we can take care of the typo.


In the future I’m sure we could do it faster. First time is the hardest, I think.
I will shoot you an email just as soon as my team has its next meeting.