Perfect Drive?

[Kevin Sevcik]

Originally Posted by Ether

How did you come up with this number?

JVN worked up an Excel spreadsheet drivetrain calculator years ago. It makes some basic assumptions about the physics to estimate the required torque to turn a skid-steer robot. Then it matches it to the motor curves to determine amps. It's not 100% accurate, but it's a good rule of thumb. Especially if it's telling you you're pulling 110 amps in a turn. I'll grant that that's probably an over estimate, since it doesn't account for pesky realities like the battery's internal resistance dropping your volts from 12 to 8 under a 400 amp load.

@MattC, Unless you've screwed up the settings on the wheelbase dimensions, that's a good indicator that you're geared too fast. I'm assuming you're working off 8" wheels, in which case that's something like a 20 fps robot you've got there. That's insanely fast. It's been a few years since we've done a skid steer, so I don't have a great feel for the appropriate top speed, but that seems excessive. You're going to end up with a lack of torque and the huge current draws in turns like you're seeing. I'd think about dropping the gear ratio a hair to get more torque so you're not beating your batteries quite so close to death. Also recall that a competition robot is 120 lbs dry weight. Bumpers and a battery add another 20-25 lbs, which is going to increase your current draw even more.