Team 159 Robot Tread Testing

Technical Technical Discussion
#1

Team 159 set out to do some testing on wheel tread this offseason. We tested Blue Nitrile Tread (McMaster 5994K9) as that’s what we normally use. We were testing for friction in different situations. I figured I’d share a little of our findings.

First a brief description of our test setup:

We built a jig with an adjustable angle “table”, the table had a piece of the new (2018) field carpet attached to it. The table could shift between 0 and 90 degrees. We attached tread to a block and then set it on the table. Then the angle of the table was adjusted until the tread block slid down the carpet.

Some of our findings:

The field carpet is about as inconsistent than you might think. At an angle on the border of the block slipping it could be placed in one section of the carpet and stick and another section and go sliding quite fast.

Blue Nitrile tread is highly directional. The direction the tread follows on these wheels from AndyMark had a significantly higher coefficient of friction than the tread in the other direction.

The last finding is one that has been widely discussed on CD before and it has to do with whether wider wheels actually gives a robot greater traction. Our testing says that it does not. The 8" square block covered completely with tread slipped at exactly the same angle as the block covered half with tread.

We only got about an hour of testing in so this is not a lot of information, nor was it collected in a highly structured manner. We might do more if people are interested but we’ve got all the information we wanted.

#2

There’s new carpet? Where did you see this?

#3

Wasn’t their a blog post a while back addressing that the “old” carpet was no longer being made and that they were switching to a new carpet? Im on mobile right now and can’t seem to find it, perhaps Op will be of more help.

#4

I can’t seem to find the blog post where they mentioned the old carpet being discontinued. But the new carpet is barely different than the old stuff.

#5

I did some testing of Blue Nitrile when I was with MOE and found rather different results in some aspects, mainly the contact area effects. Two variables you have not given are the weight of the block and the surface area of the block on the carpet. When we did our testing it was with a full weight robot (120+20+13+~7 for a game piece) with 4 1in wide wheels switched to 4 2in wide wheels. We found with the 1in wide wheels they gave about 1 square inch of contact per wheel, so ~40psi vs. The 2in wide which was double the contact area, so ~20psi. At these pressures there is significant mechanical interference between the tread and the carpet not seen at lower pressures. If for example your block is 10lb and has an area of 10 square inches that’s 1psi. If you remove half the tread that’s still only 2psi. At these pressures you will not witness the same mechanical interfaces that generates traction as you would with a setup that replicates full robot weight and contact area. For reference we did find that the 2in wide wheels took about 20% more “force to pull the robot with locked wheels” than the 1in wide wheels. So not double, but not insignificant.

#6