pic: Flipped CIM Gearbox Attempt #2



This is my second attempt at a two speed flipped CIM WCD gearbox. I like this one much better than the last, mostly because of the improved pneumatic arrangement. Questions and comments are welcome.

I like this. Do you have a mass expectation? Not sure having two motors on the same belt is a good idea. I could be seeing this wrong because you do have two screws next to it but it does look like your shifting bearing isn’t retained properly (unless it’s flanged).

EDIT: Also interested in distance between the plates. Is this with vexpro ball shifting shaft?

Wasn’t 192’s 2014 gearbox with 2 CIMs on a single belt? Or CIM + miniCIM anyway.
This is super neat. I like how the rectangular packaging doesn’t increase the effective volume, but you can still fit the shifter in a clever way.
I can’t tell, but are you using the shifting cylinders as standoffs?
Definitely super solid. You even have a little nub at the bottom for an encoder!

Yes and afterward it was decided separate thinner belts were a better path. 2016 had a different gearbox belt configuration that I believe didn’t have issues. I’m a fan of a 6mm wide GT3 belt for each motor.

The gearbox should weigh about 1.4lbs not including chain sprockets or CIMs.
The shifting bearing is flanged, and captured with the two bolts.
The disatance between the plates is one VEX pneumatic cylinder plus 0.125" plate (or 1.185").
No, it doesn’t use a VEX output shaft, but it could be modified to.

Yes, the shifting cylinders are also acting as standoffs.
I have mixed feelings about putting an encoder on the shifting shaft. Some testing would be required.

What issues did you run into with two motors on a belt?

Sorry for the late response. I was camping out to watch the eclipse.

The belt issues were primarily skipping belts, and then extreme belt wear due to the high tension used to correct the skipping belts. There was also an issue of pulleys comping off of cim shafts which I don’t think was ever diagnosed but I kind of think it could have been the large tracking forces from the high belt tension.

If it’s a custom ball shifting shaft are you using vex inner shaft geometry? Could you go more into what you’re using for ball size, inner shaft diameters, ball ramp angle. Maybe a cross section.

Would you be willing to send the file? My team is interested in recreating one of these without the speed shifter.

Good to know. I think it would be pretty straight forward to make this gearbox use two belts or additional belt wrap if necessary.

If it’s a custom ball shifting shaft are you using vex inner shaft geometry? Could you go more into what you’re using for ball size, inner shaft diameters, ball ramp angle. Maybe a cross section.

Yes the inner shaft or “plunger” as I call it, is exactly the same as the VEX ball shifter’s. The rest of the ball shifting geometry is also identical to the VEX shifter. The only major difference is that this uses a solid 7075 Al output shaft, as opposed to the two piece half steel one that VEX uses.

Here is a google drive link to a folder with the step and native Inventor files.
Let me know if you have trouble opening it or have any questions.