Quote:
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.