Problem with KitBot: Motors move at different speeds

[PaulEleven]

Originally Posted by Alan Anderson

Before you calibrate your Talons, make sure your program is telling the roboRIO to send Talon-compatible signals. What programming language are you using? How are you defining your drive motors?

We're using Java and are importing the WPILib's Talon package, we've paired up the talons for each side with Y cable so ultimately we only have two PWM outputs.

[Brian C]

One other item to add. Sorry if I missed it being posted earlier.

Electric motors are designed to be more efficient when operating in a certain direction. The armatures are timed with the magnetic field via the commutator brushes to give more torque/power in the desired rotational direction of operation. When that same motor is operated in reverse it will have less power. Depending on the motor maybe not significantly less but definitely less

When your robot is going forward one set of motors is spinning in their "forward" direction and the other side is going "backwards". When you go in the opposite direction the other side will be less powerful.

This is a common reason to see the issue you're having. Some teams have done a very simple fix to this in software by only allowing one set of motors to go to 85% throttle in one direction and the other set to do the same when in reverse. While not overly scientific it usually does the trick.

[apm4242]

PaulEleven - we are having this exact same issue. Talons from KOP, talons selected in labview, code is right.

Did you ever figure it out? If so, how did you fix it?

[SousVide]

We've seen the same issue every year so far with our kit - pretty much the same thing. Motor spinning in the forward direction will behave a certain way and slightly different when they are spinning in the backward direction. We've seen some gearboxes that would allow both sides to be driven in the same direction and have been considering them... The software solution is still cheaper though.

Originally Posted by Brian C

One other item to add. Sorry if I missed it being posted earlier.

Electric motors are designed to be more efficient when operating in a certain direction. The armatures are timed with the magnetic field via the commutator brushes to give more torque/power in the desired rotational direction of operation. When that same motor is operated in reverse it will have less power. Depending on the motor maybe not significantly less but definitely less

When your robot is going forward one set of motors is spinning in their "forward" direction and the other side is going "backwards". When you go in the opposite direction the other side will be less powerful.

This is a common reason to see the issue you're having. Some teams have done a very simple fix to this in software by only allowing one set of motors to go to 85% throttle in one direction and the other set to do the same when in reverse. While not overly scientific it usually does the trick.

[PAR_WIG1350]

Still beats the drill motors that used to be included in the kit. Those motors had a much more significant directional bias.