pic: Fun 3 CIM Shifter Idea

I enjoyed the conversation that the last design I posted here started, so why not post another! It’s a single reduction 2 speed ball shifter, that would use a highly modified VexPro shifter shaft.

What ratios are you using? I’ve toyed with the idea of a 1 stage shifter quite a bit, recently being involved with 1687’s reverted gearing 1 and 3 stage shifter. Low gear has got to still be awfully fast in this configuration.

Yes, this gearbox is somewhat ridiculous. That’s kind of the the reason why I CADed it this summer as an exercise…

The lowish speed is 11t to 65t, using the VEX pinion. The faster speed is 17t to 60t. I designed it to use a 3.6" custom wheel. This means that the 65t gear is dangerously close to the carpet. that’s why its made from steel as apposed to Al. lol

Earlier in the summer I attempted to CAD a Ball shifter with 1 stage for high gear, and 3 stages for low gear, similar to 1687’s. It actually looked like it was feasible, and I was able to get fairly good ratios to run 4 inch wheels. I’ll have to see if I can dig up the files for it.

Keep in mind that tread wears. Unless the wheel is going to have a tread on top of the 3.6" diameter, in which case it will be fine.

Yeah, I though about this quite a bit. Because the wheel would use custom polyurethane tread, and I would really want the low gear to be traction limited, the wheel would have a very hard tread on it. Such as 80A or 90A polyurethane.

So is the 3.6" number with tread or without?

The polyurethane can be lathed down decently far from its initial OD. Since it wears slowly, diameter loss isn’t much of an issue

Are you running both gears on the CIM shaft directly? This will be almost impossible to achieve due to clocking all the gears. Imagine two CIM gears and two shifting gears, no problem the shifter gears will rotate into position. Add one more motor with a single gear and that second motor will be free to rotate into position. Add a second gear on that second motor and now your clocking for that second gear is based on its alignment to the first gear. You now need the second motors gears to align properly to each other to engage the two larger shifting gears without interference. Adding a third motor makes it impossible if you are using luck. We had issues with two motors doing this in 2013, luckily we were using hex shaft adapters coming off the CIM shafts so we had six different alignments to try per motor. I can only imagine the trouble three motors would cause. This could work if you were to wire EDM the gears or fixture the gears while broaching in the key slot or hex shape. In larger applications you could use a taper lock keyless bushing so that you could line up the gear teeth and then lock down the gear to the shaft, but there would be no room for this with an FRC gearbox. I just want to educate everyone about this method of gearbox design where the CIM motor has two gears on it and the potential issues you might encounter.