We built the a test version of a wheeled shooter this summer with Andymark 8" wheels, and VEX clamping gearboxes. See here: https://goo.gl/photos/hjbNw8vYjDLF34nG9. After a bit of iteration (added a second stage, and reduced compression to only about 1") we got it shooting about 75 ft. There’s still a bit of work to do before we can mount it on a robot (and I think we can tweak it to shoot further) but we might use the test version as-is as a “T-shirt mortar” into the stands at this fall’s STEMley Cup
For something like this, it would probably be a lot better and cheaper to buy some Brushless outrunners and brushless ESC’s rather than try to keep to FRC legal parts only. Your spinning a flywheel in one direction at highspeed so it’s basically perfect to be made Brushless.
It really wouldn’t, though. Even assuming they don’t reuse old parts, a CIM is $27 and a Spark is like $45, which together is comparable to or cheaper than a 12V 300W brushless motor. You can get non-reversible PWM speed controllers for brushed motors for less than the cost of common FRC reversible controllers.
Edit: I didn’t see they were feeding the CIM through a VP, which I honestly think they could skip if they wanted and just cantilever the wheels off CIM shafts with hex adapters. Kind of sketchy but it would be fine for an offseason robot.
I’m gonna ignore the cost argument. But I’d have concerns if your shooter wheels had any significant mass. There’d likely be some reconfiguring of the ESC required to get it working without starting a small fire.
DC motors can be abused and, given how students tend to do things, that’s a good thing. I’d stick with maybe some 550 motors and appropriate VP gearboxes if required.
We (the two of us, no longer our team ) have achieved 60-70ft running 6" Colsons directly off MiniCIMs. Compression is a huge factor. Refer to this thread for more information:
Video should be up soon, since we’ll be at Maker Faire NY this weekend.
See you there! Will be very interested to see what you built in action.
Took a bit but here is ours, you cannot see where the t-shirt lands but it is about 115 feet away. The front two wheels are each powered by a CIM and the belts in the back are each powered by a Mini CIM. We couldn’t keep testing because we lost the key to one of the mini-CIMs and don’t have any extras
One of several videos from Maker Faire. We estimate about 70ft in the air. The compression of the shirt is very important (our best shots were made with very tightly rolled shirts).