Good or bad: back wheels coming off the ground

Technical Technical Discussion
1

During regionals, we discovered an interesting side effect of a super-strong goal grabber; we were being lifted off the ground.

Our goal grabber is T shaped, designed to be pushed out by pneumatics, rotated through a slot, and when pulled back rotate back to pull the goal in. The only thing is, the goal grabber pulls the goal into the chassis, which has a notch cut into it that will perfectly fit the corner of a goal. It’s a very nice mechanism, somewhat self-aligning if the driver screws up, but the angle on the top of the “catcher notch” wasn’t perfectly aligned. Now, when we pull a goal into us, the T goes all the way back into the robot and our back wheels get lifted about a quarter of an inch off the floor.

Mechanism:

During regionals, we manufactured aluminum wheels to replace our front wheels, and now their diameter has increased by 1/4". Is this a good thing or a bad thing? We may get lifted farther off the floor, placing all of our weight on these two new wheels that supposedly have great traction. Is this better or worse than what we had?

-Gui Cavalcanti

“Guess what!?”
“What?”
“Our alliance won the VCU regional!”
“Good lord, how did that happen?”

2

Seems to me that, since your wheels are all chained together, you’d have the same ability to impart force on the ground if two wheels were in the air. Actually, if the wheels you’re on after gripping have more traction than the others, you might just be better off with the other two off the ground.

This all changes if you’re pushing down on the goal, in which case you’re losing normal force on your wheels, and not getting as much traction.

3

We noticed this on Big MO during the Buckeye Regional this last weekend also. We actually have cylinders that lift up our gripper arms. If we do this with only one goal we tip up seriously. And we we accelerate too fast with only one goal we can get up on an angle. However, we have a very aggressive track drive system so it doesn’t affect us much in terms of traction. When we have two goals and lift them up is when we get the real boost in traction. We are about to drive fine with one goal and our robot tipped up but there is really no advantage to it that I can see.