pic: WCD 3 CIM PTO Ball Shifter Render

[Bryce2471]

Originally Posted by asid61

Very nice. PTO/shifter for 2.2lbs is really good.
Is there any way to change the gearing to get a free speed under 18fps? Going above 20fps free speeds seems sketchy with 4 cims.

The slowest the gearbox can be configured without significant plate changes is 7.1 ft/s in low and 17.9 ft/s in high (80% of free speed)

Originally Posted by asid61

I continue to amaze myself with my idiocy. Whoops.
Thank you.
In any case, you can't accelerate with 6 cims to above 20fps with the roboRIO anyway without a brownout, especially a low voltage, so is it possible to reduce the gearing for that?

Originally Posted by GeeTwo

Yes, the gearbox shifts, ball shifters based on the subject line, though the mechanism isn't stated. Low gear is around 7:1 (see first post), so with three CIMs per side, you can easily get up to enough speed for the shift, which can then take you to 20 fps.

Given the voltage brownout levels, I now expect that PTOs are much less useful than they may have been in the past. The first roboRIO year with bumpers, defense, or crazy acceleration requirements will likely be the proof/disproof on this point. The bottim line is that the additional weight for shifting may completely override the weight for separate motors, especially for lower-resource teams.

Originally Posted by R.C.

I'm unsure how PTO's are less useful, as they just power another system. I would say 3 CIM drives will be less useful with the brownouts.

Originally Posted by asid61

I'm aware that it shifts, however, the acceleration/current may still be too high for safety even if you start from low gear. Probably need to test that to be sure, because I have no idea, honestly. You'd also need to implement autoshifting for that to work.
The weight cost is on the order of a pound or two for a PTO if you go with the WCP PTO (plus whatever you're using for integration into the system). The alternative for endgame mechanisms is to use discrete motors or pneumatics, both of which usually cost more weight for similar outputs although they are easier and faster to integrate. Of course, the last endgame was in 2013, so maybe they're gone for good (and with them most of the use of PTOs).

This is all interesting conversation, and thank you all for your replies. However, it would be particularly useful if someone could post a personal testament to how the roboRio responds to having a 6 CIM drive train. This way I could walk the new CAD student through the process of reevaluating the gear ratios with some real evidence. Unless that happens, this project will continue to be a test of the new control system's outer limits, as it was originally intended to be.
Hopefully with this gearbox, we will be know what is too fast, so that when next season comes we will be able to pick appropriate speeds.