Plaction Vs. Banebots Vs. HiGrip friction coefficients

[Madison]

Originally Posted by Dan.Tyler

That being said, we tested the cF of the green material to be nearly 2.5 on FRC carpet. Of course, the material in the green wheels begins to structurally fail at 2.0. The oranges fail structurally around 2.4, but are traction limited at around 2.1. We drop oranges in the center, and use greens on the outers for added pushing force. It works great for us.

When I say "fail structurally", I mean that the rubber is not strong enough to hold the traction force being applied, and will shear away from itself, leaving what looks like pencil eraser shavings on the field after hard pushing matches.

This is a really strange way of talking about coefficient of friction. The CoF between the materials doesn't change -- it's an experimentally derived constant. I understand what you're getting at with respect to the green material -- it's capable of destroying itself. I do not understand at all what you're saying regarding the orange material.

Can you restate your observation in a manner that reconciles with physics? Can you further explain what you intend to convey by listing two coefficients of friction?

[Tungrus]

keeping it simple.... we have opted for high grip rubber wheels:

https://www.andymark.com/product-p/am-0940a.htm

We had miserable time last year with treads peeling off! Rough top will start wearing out after many matches (50 or more, not sure about the number). We use Bane Bot wheels for shooting balls, not confident enough (and no deep pockets) to try them on drive. Whatever you use, make sure you don't have to replace the tread or wheels during matches.

[magnets]

Originally Posted by Madison

This is a really strange way of talking about coefficient of friction. The CoF between the materials doesn't change -- it's an experimentally derived constant. I understand what you're getting at with respect to the green material -- it's capable of destroying itself. I do not understand at all what you're saying regarding the orange material.

Can you restate your observation in a manner that reconciles with physics? Can you further explain what you intend to convey by listing two coefficients of friction?

I agree. The CoF of two materials doesn't change.
Here's my thought-
When they tested the green material on carpet they found the CoF to be 2.5 when not carrying a 150 lb robot. "Of course, the material in the gree wheels begins to structurally fail at 2.0" Then, when an FRC robot is placed on the wheels, and the drive train pushes the robot forward with more than two times the force of gravity on the robot, the robot shouldn't slip due to friction, but instead the wheels fall apart.

As for the comment about orange, he may be saying that his drive is traction limited (what else could be?) so that the orange wheel (which was experimentally determined to be 2.4) could have a CoF of anything at or above 2.1 and because of the limited torque of the drive train, would never slip. That's a really weird way of talking about CoF though...

Also, a CoF of 2.4 sound really, really unreal high.

[JamesCH95]

CoF above 2 is crazy... that's on the order of really serious racing tires at temperature... and that's rubber so soft you can easily rip it up with a finger nail.

I would love to see an experimental report showing how it was measured and recorded.

[Mike Marandola]

Another factor to take in to consideration is the "mechanical grip" (probably not the right term). What I mean by this it that the traction material can have more grip than many other materials because the tread texture is able to dig into the carpet better.

[Dan.Tyler]

Originally Posted by Madison

This is a really strange way of talking about coefficient of friction. The CoF between the materials doesn't change -- it's an experimentally derived constant. I understand what you're getting at with respect to the green material -- it's capable of destroying itself. I do not understand at all what you're saying regarding the orange material.

Can you restate your observation in a manner that reconciles with physics? Can you further explain what you intend to convey by listing two coefficients of friction?

Sorry for the confusion.

What I mean is:

The material has a very high coefficient of friction, but a low physical strength.
Although the material can hold a higher amount of traction, depending on the conditions, it will fall apart.

The friction coefficient in each case is 2.5 for green and 2.1 for orange. Material was removed from a wheel (somewhat used), then weighted down and tested on an incline plane covered in carpet for initial slip/angle to determine CoF.
Specific loading scenarios are required to reach this coefficient without the grip material shredding. Specifically, lightweight bots or lots of wheels (Probably why colsons aren't 0.8" wide...)

In our lightweight bot from last year (sub 100lb with bumpers and battery), we could only realize the lower number (~2.0) on green before the rubber started shaving off, leaving debris similar to what pencil erasers leave behind. We still had tons of traction, but it tore the wheels up some to operate in this regime.

For the orange wheels, if you test it for shear strength, mechanically bonding or restraining the material above its traction limit, it will fail at around 240lb in shear with the cross-section that is on a wheel. The greens will start to fail in shear at about 200lb with the cross-section that is on a wheel.

So... you have more than enough traction available to push people out of the way. But you'll burn up your wheels doing it if you push too much, too often.



Tl;dr i was giving both experimental and real-world coefficients in an extremely confusing manner. If I still don't make sense... sorry.