pic: 3CIM Shifter Idea

A bit of goofing around in CAD yesterday yielded this. The goal was to modify the WCP 3-CIM dog shifter design to allow the CIMs to mount from the wheel-side, high enough up to float over a 4’’ wheel. Ideally, this would save us a fair amount of space for electronics/mechanisms/whatever.

Ultimately accomplished this by mashing together the lower half of their 3CIM dog shifter with the upper half of their 3CIM single-speed. Had to shuffle around the spacers a bit to get it to work, but it seems feasible.

Feedback welcome.

We did something very similar to this for our drive this year, and it saves about 1.5" on each side, which we needed for our shooter. This looks like it could be useful

It’s hard to see in the picture, but the shaft that we use to shift is the one in the middle (with the 56 tooth lightened gear), and the pneumatic cylinder is on the other side.

The only issue with this design is that the final reduction stage for our high gear needs unusual gears because of the additional torque from adding a third CIM. Most 20 DP gears used in FRC gearboxes are 14.5 degree pressure angle and .375 thick, but we needed to use steel 20 degree pressure angle .500 thick gears to prevent shock loading from snapping off teeth on the final 18 tooth gear. Surprisingly, we’ve had no issues with the cantilevered gears, except for cables getting stuck in them.

We also found it really helpful to have our center wheel’s shaft be 3/8" steel hex (we did support this slightly smaller than usual shaft on both sides of the wheel) then weld a hex sleeve onto our output shaft so our gearbox can just slide in and out of the robot. We only have to undo two bolts to pull our gearbox out.


What software do you use for rendering? That’s beautiful

I did this one in Solidworks. Our school’s educational license included PhotoView 360. Solidworks’ rendering tools are so much nicer than Inventor’s. This is with all the default settings and default appearances, and it came out nicely.

Now there’s a good idea; I had been struggling to come up with good ways of allowing for easy removal of the center wheel in a sheet metal 6WD setup (which is ideally what we’d be using this in).

I tried to do something like this last offseason. My goal was to try to attach the CIMs to the inside plate to decrease the amount of overhang into the wheel well.

If you look at 192’s gear box post you would see another design.

In light of Jared’s hex-sleeve-coupler innovation, I’m currently working on a 2’‘x1’’ tube chassis on which to mount these. The 1/2’’ hex shaft from the center wheel will be supported by a press-fit bearing in the side of the 2’‘x1’’ opposite the gearbox, with a hex coupler welded onto the output shaft, completely enclosed inside the tubing.

I’ll post a picture when I’m done. It’s a miraculously simple solution to what I thought would be a really annoying problem. Thanks to everyone for the ideas.

If you look at 192’s 2013 gearbox here
you can see how we solved this problem. The short output shaft goes halfway into our timing belt sprocket in the frame. I explained it a bit more in one of the posts in that thread.

Can you elaborate on how the bearings were set up to support this multi-piece output shaft? Did you encounter any binding issues with 3+ bearings in such a small place, and was anything special done to prevent binding? Or was there sufficient slop in the hex broach to prevent this?

On that gearbox there are actually only two bearings on that shaft, only one in the gearbox, but thats kind of a special situation for the bevel gearbox. We used the same output shaft set up this year and had three bearings on the shaft and didn’t have any problems with binding. I don’t think thats from slop in the pulley hex because it’s fairly tight.

Bearing set up:
There’s a flanged bearing on the outside of the box beam up against the wheel, and the bearings in the gearbox. The end of the gearbox shaft is threaded with a 1/4-20 thread and a bolt through the outer part of the shaft holding the wheel and shaft in.