Holonomic drive weirdness

[Levansic]

We've used holonomic drive in several previous robots, but this weekend we saw something that we had not previously seen. Unfortunately, I don't have captures of the code, but we opened up a four-motor drive reference, and passed it to an unmodified WPI cartesian holonomic drive vi. We used X, Y, and Z axes for x and y translation and rotation respectively. We did not hook up a gyro, as we were only looking to use robot-specific rather than field-specific control.

Once the motor directions were properly set, we could correctly rotate left or right. Pushing the stick forward (Y+) gave the expected motor rotations to drive that direction. Pulling the stick backward (Y-) caused the robot to rotate - all wheels turning the same direction, rather than two clockwise and two counter clockwise.

Has anyone else seen this?

Our next moves are to deadband the three axes of the joystick, and to assemble our own holonomic drive vi.

[Greg McKaskle]

I would open the panel of the holonomic VI and verify that the joystick axes are coming in correctly. It may also make sense to look at the dashboard to see if the output values make sense relative to the joystick values. I'd put it on wheels and use small joystick values to determine if there is a left/right or front/back swap that explains the outcome.

Greg McKaskle

[Levansic]

I started this thread a little over a month ago, and will now update with what we found this weekend. We put a deadband on all three of the joystick axes, and that seemed to make this problem go away, as the Z-axis centering of the joystick was poor.

This weekend, this problem came back in spades, which was quite confusing. It did not occur to us that the deadband was not wide enough for our left-handed driver at the regional this weekend, to use the joystick that was contoured for right-handed people like myself or the programmer who worked on that code. Every time our driver moved the stick, a z-axis input was registered, making our robot spin constantly. In fairness, our original deadband was just barely wide enough for right handed people, as letting go of the stick had a ~50% chance of starting an unintentional spin, which we hadn't tested.

Holonomic drive vi is OK.