Modified AndyMark Gearboxes

[Rob2713g]

Hello,

We are having difficulties with our modified AndyMark gearboxes. Each wheel spins at a different speed. The wheel that spins first changes based on which direction we move the joystick.

Our Setup: 1 gearbox on each wheel
The gearbox has been cut to get rid of one half for decreased weight.

Anyone have any ideas why this could be happening?

Thanks!!

[Alan Anderson]

The Victor response is not symmetric around what the RC sends as 127. Are you negating (i.e., subtracting from 254) the pwm commands to one of the speed controllers? Try instead sending the same value to both, and swap the output wires to the motor to make it run in the direction you want.

[Rob2713g]

Yes we are subtracting from 254 on 2 of the motors. I'll make sure that we check that tomorrow. THANKS!!

Could anything else also have an impact? Because the 2 motors that get the same values also spin at different speeds.

[Alan Anderson]

Many things can cause one motor to run faster or slower than another with the same voltage applied. Most of them fit in the category of mechanical load -- a fresh transmission that hasn't yet been broken in, a tight chain, an unlubricated set of gears, a binding shaft, or a wheel rubbing against something can all make a motor run slow.

[Rob2713g]

Hello,

We switched the code and the wires. The robot now behaves as follows:

Front Left Wheel - FL
Front Right Wheel - FR
Back Left Wheel - BL
Back Right Wheel - BR
() - same time

The order that the wheels move in:
When moving forward - BR, FL, (BL FR)
When moving back - (BR BL FR), FL
When strafing/crabbing left - BR, FL, (FR, BL)
When strafing/crabbing right - (BR, FR, BL) FL

We have a mecanum setup identical as shown in this photo: http://www.chiefdelphi.com/media/photos/26582.

Any ideas or help is greatly appreciated.