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Unread 08-05-2010, 02:11
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VEX Robotics Engineer
AKA: Arthur Dutra IV; NERD #18
FRC #0148 (Robowranglers)
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Re: pic: Prototype Drivetrain

Quote:
Originally Posted by 548swimmer View Post
No, though it does apply to robots. With the simple push of a button, a gyro sensor could be enabled(wrong word) allowing only forward and backward movement. Or you could go with arcade drive, and as long as the joystick stays 1 degree from the y-axis, you only allow straight movement. That number could be tweaked untill it's optimized.
Don't be so quick to assume everything in code will be worked out flawlessly.

When you design mechanically unstable systems, you better have absolute 100% reliable software, otherwise you're a sitting duck.

Putting the main drive wheels right next to each other isn't a smart idea unless you want to implement real-time, closed-loop PD velocity controllers on your drive train. Regardless of physics, putting the drive wheels right next to each other is a bad idea geometrically. Let's assume that since not all motors have identical RPMs (whether due to motor bias or manufacturing tolerances), that one side of your drive train normally operates 5% faster than the other one.

To minimize risk of unpredictably turning with slightly different wheel speeds, you should keep the wheels as far apart as possible. This way, the ICR (instantaneous center of rotation) will be moved much further away from the center of your robot as opposed to a smaller wheelbase. As it is, most existing 6WD drivetrains already turn way too fast at full power to be accurately controllable, with many teams already resorting to smoothing, ramping, or square/cubic response curves.
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Art Dutra IV
Robotics Engineer, VEX Robotics, Inc., a subsidiary of Innovation First International (IFI)
Robowranglers Team 148 | GUS Robotics Team 228 (Alumni) | Rho Beta Epsilon (Alumni) | @arthurdutra

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