Gearing for 20 FPS?

[Billfred]

Originally Posted by CNettles11

As hard as it would be to control, would it be possible to gear a normal 120lb FRC robot to travel at 20 feet per second while still having decent acceleration? It wouldn't be practical but it sure would be a fun driving experience.

Most people find 12-14 feet per second to be the upper limit of what is controllable on a regulation field. (And even that is game-dependent; while it was desirable in a game like FIRST Overdrive or LogoMotion, you wouldn't want to think about that in a game like Breakaway with serious obstacles slowing you.)

Now, COULD you build an FRC-legal drivetrain? It's plausible with the right math (I echo the endorsements of JVN's mechanical design spreadsheet) and from parts available on AndyMark's website. As an exercise, try to figure it out before you hit the spoiler:

Spoiler for How I reached it:

AndyMark Shifters (standard gearing) with two CIMs per side, fed through a 12:22 sprocket reduction to an 8" FIRST wheel gives a top-gear speed of 19.64 FPS after accounting for losses--close enough. With a total weight (including battery and bumpers) of 100 pounds on the driven wheels, you'd be facing a worst-case drivetrain current of 148 amps...but once you got in motion, you'd likely dip back below the all-important 120A of the breaker before it tripped. If you wanted to be super-paranoid--nothing wrong with that--then keep the weight on the driven wheels at 80 pounds or below.