Re: Team 1296 Mecanum Bump Test
 

It was meant as the 'royal you' as every time this topic of polymer load/pressure sensitivity comes up someone inevitably goes: "well that's not what my physics teacher says!" and I might be a little tired of making the same points over and over :)

Re: Team 1296 Mecanum Bump Test
 

As a physics teacher, I use the disclaimer that the line "...but it's really more complicated than that!" is implicit at the end of every explanation.

Re: Team 1296 Mecanum Bump Test
 

While that may be true for "frictional traction", it's not necessarily true on carpet where a considerable amount of the tractive force is actually a normal force between projections on the wheels and fibers on the carpet. The reason brekoflex type belting and some mechanums get such good traction is the amount of embedded overlap when edges on the wheel surface dig down into the carpet, which is a function of weight but more importantly an inverse function of contact area. Our previous testing and data has shown this.

Re: Team 1296 Mecanum Bump Test
 

Some teams have run experiments showing that wider wheels, i.e. ones with more ground contact, get better grip. A big part of this is that the 'embedded overlap' interface you talk about becomes saturated at a certain contact pressure (the carpet and tread have finite depth) and as pressure increases above this threshold the coefficient of friction drops off. Even before the interface is totally saturated the coefficient of friction generally drops off slightly with load because the carpet/tread presses together more firmly, making it more difficult for the tread to embed further.

This analysis is based on my knowledge of tire-road interfaces and what I've learned from reading many CD threads on the subject.

One thread with related discussion is here: http://www.chiefdelphi.com/forums/sh...ad.php?t=98664

Re: Team 1296 Mecanum Bump Test
 

Is that a normal 3.5" thick 4x4? Or is it a special 4" thick 4x4? :)

If I were you, I'd build a short section of "real" barrier, put it on carpet, and try it. You might find that it's a bit harder on the robot than it looks in the video with the 4x4.

Re: Team 1296 Mecanum Bump Test
 

normal, so not quite 4" tall - we are quite worried about a "real" barrier and are looking to build one, the 4x4 test was kind of impromptu - the bot has did well so hopefully things go well with the real barrier

how are teams building a real barrier?

Re: Team 1296 Mecanum Bump Test
 

Ours isnt real, but we put some 2x4's together and fleshed out the remainder with 1/2 inch plywood. I realize it isn't metal, but it gives us the right dimensions.

Re: Team 1296 Mecanum Bump Test
 

We just did the same thing and it still goes over. I am worried about the metal version. We'll try that this weekend.

Re: Team 1296 Mecanum Bump Test
 

So you guys are building a metal one? ;) may have to make a visit then

Re: Team 1296 Mecanum Bump Test
 

Nope, thinking about finding out where LM sets up a complete field.