Help! With h-drive holonomic drive.

Help! One my teams is trying to build an h-drive holonomic drive. It tries to work, but it it doesn’t quite. It’s really frustrating them and all of us. I have attached a picture of their drive train and of their robot. Any ideas?

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The code is just the remote control set-up in modkit. They have when they push the right joystick left or right that middle motor spins. It sometimes works, for a few seconds, but then the wheel just spins without moving the robot. It’s like the wheel isn’t quite touching the ground, but it is. They’ve tried putting weight on top of it, but it does the exact same thing. They’ve tried using rubber bands to push the wheel down, but it does the exact same thing. They’ve tried moving the wheel down, so it’s in the bottom holes instead of the center holes. That seems to work, but it makes the robot undriveable, so it’s not a viable solution.

Kind of hard to tell from the picture, but is it possible that the entire drivetrain is bowed upwards from side to side? This could happen if that basket, or something else above the drivetrain, was a notch or two wider than the drivetrain, but the kids were able to force it into place. Was the drivetrain working before the lift and basket were installed? If the drivetrain was not tested by itself, then you might want to go back and do that.

Also, are you sure that the wheel is spinning? Sometimes that motor will make noise, but the wheel is not spinning because the shaft is not pushed all the way in.

@jrp62, I think you’re probably right, from reading your description. Thank you. I’m guessing that the drivetrain is bowed. I know that they really forced that basket in there, because they wanted it to be ‘wide’. The drivetrain was working before the basket was put on it. I was thinking it was a center of gravity problem, but it probably is a bowed drivetrain.

We had a similar issue, what we did was make it a “tricycle” so there was force on all points with two wheel 90 degree to the third. We have another set of wheel; that would normally make up the remaining 2 on the carriage that are chain driven from the identically oriented first ones. However, these 2 are up one hole from level, on purpose. They help on the ramp, but the tricycle does most of the work.