Our AM14U5 drivetrain is bouncing when we turn in place, even at low speeds. We have 6" diameter wheels with center blue nitrile tread wheels and outer colson wheels. 4 falcons in stock gearbox geared for ~13 ft/s. Drivetrain is in the default “long” configuration.
Our robot is ~120 lbs, CG is about 3 inches away from the center of the robot’s length and about a foot or two off the ground.
Most robots I’ve seen this happen to have longer wheelbases and shorter track widths. I don’t even see this on other kitbots I’ve watched.
Those are six sticky wheels…
Curious about the chassis torsional stiffness? Is there a nice beefy belly pan holding everything together, or is it pretty much just the stock components? Is there a big bumper cutout at the intake?
Theory: if your chassis would rather flex then allow the coulsons to start slipping, then your chassis will flex a bit, load up, and then hop past the force balance point when the colson slips, and load up again, and hop…
I think we have at least two and possibly four vex 6-in omni’s in our stock in Richmond if you’re at the point of swapping Wheels about it. If you shoot me a DM I might even remember to look tomorrow. You’d still need to send someone up to Oakland, or I could put them in priority mail. There’s likely another team that can help closer.
Fair warning they’re not the same diameter as colsons, you might lose some of the rocking.
In theory the chassis should be stiff? Not 100% sure. Doesn’t seem to flex much under use. There’s a solid 1/4" Baltic birch plywood bellypan adding a fair bit of stiffness.
No cutouts in the frame. I’ve usually seen colsons as less grippy than treaded traction wheels and functional when used in this same configuration so I figured it would be good, but it could be that.
Will look into the omni solution. Would suck to have to modify our drive but we’ll do what we gotta.
Longer tank bots do create a problem with turning the static scrub force is larger in proportion to your rotational force than when your wheels are wider apart. You are also using the nitrile which has a very high traction and creates a large resistance to turn. Is your center wheel any lower than your other two, that can help as you have less contact on either the front or back depending on your bot, a lot of teams do 1/8 lower. If you still have issues you could replace your front (or back) with omni wheels. That will help with your turn.
The other super quick fix, before swapping out to omnis: wrap the outside wheels in duct tape to reduce their coefficient of friction. Should make them slide easier.
Quarter inch Baltic birch actually isn’t that much. We did a bunch of our prototyping in it this year, it flexes noticeably more than even 3/8.
Try wrapping painters tape or gaffers tape around some of the colsons and see how you like the results. If you like it, maybe switch to duct tape or omni. Just make sure it’s wide enough that the edge of the tape doesn’t catch the carpet.