Quote:
Originally Posted by Chris is me
If you want to be able to push indefinitely, your motors can't draw more than 40 amps* each while pushing, or else you'll begin to trip the auto-resetting breakers on the PDB. The 160A total current draw across 4 CIMs is a lot, but not enough to immediately (or even quickly) trip a functional 120A breaker. The speed that roughly correlates with traction limited at 40 amps, for an at weight robot using high traction wheels, is ~5.5 feet per second.
You can definitely still push if your drive isn't geared that slowly for a variety of reasons. For one, circuit breakers don't trip immediately. There are also quite a lot of factors in play during each individual pushing match that affect how successful it will be - wheel traction, pre-existing heat in the motors, chassis rigidity, center of gravity, weight transfer between robots, etc. But if you design a two-speed transmission with a low gear that is traction limited near 40A, you can be confident that you'll always be able to push as well as you're able. This is one of the major selling points of two speed transmissions.
*In reality, the snap-action breakers have a huge safety margin, so there's some wiggle room here.
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Ok, now I understand that you're talking about not tripping breakers. Certainly a slower gearing will draw fewer amps, and there is a cutoff somewhere at which a robot can no longer be driven a certain way for 2 minutes straight without tripping those breakers.
I'm thinking about that, and it seems more complicated than getting traction limited at 40 Amps (or 50 or 55 Amps or whatever won't trip the breakers in 2 minutes). For example, let's say I enter a CoF = 1.1 into the spreadsheet and gear it for 5.5 ft/s and otherwise use the same values as before. With those conditions, the spreadsheet reports that the robot can be traction limited when it's going about 3.5 ft/s while pulling around 40 amps. If that same robot pushes as hard as it can at 1.0 ft/s, it's pulling about 76 amps. So it depends on a few things, including what type of pushing the robot does and under what conditions the wheels actually start to spin out during a shoving match.