Coefficient of Frictions

[Veselin Kolev]

Originally Posted by mzitz2k

I'm not sure that I completely understand your "wheel notches" that your team used. Do you have any pictures or could you expand on this a little for us? Thanks!

Yup, as I said they are all on McMaster, so... I found some pics of the material we used. As for your description of how you attached tred to wheels, we did the exact same thing except that we used high durability epoxy instead of carpet glue. Haha great minds think alike!

The first pic is the notched material, it has a 1/8" groove on 1" centers, fitting right into the wire mesh. The second is the ultra sticky material. It was black gum rubber material, and it had excellent grip on the HDPE. Hope that helps!

[patrickrd]

Here are the results of a test we did for RoboCup. This tested rubber on a felt carpet. It is similar to the FIRST carpet... This data is very good for comparison, but take the values themselves lightly, since the shape of the wheel and the carpet material will be different for FIRST use.

Buna-N: 1.29
Neoprene: 1.60
EPDM: 1.44
Viton: 1.11
Silicone: < 1.29 (not sure of exact value, but it is definately less)

- Patrick

[mzitz2k]

Originally Posted by patrickrd

Here are the results of a test we did for RoboCup. This tested rubber on a felt carpet. It is similar to the FIRST carpet... This data is very good for comparison, but take the values themselves lightly, since the shape of the wheel and the carpet material will be different for FIRST use.

Buna-N: 1.29
Neoprene: 1.60
EPDM: 1.44
Viton: 1.11
Silicone: < 1.29 (not sure of exact value, but it is definately less)

- Patrick

Interesting! What did the neoprene look like? There are so many different types... What was the hardness rating and did it have "teeth" or was it just a flat sheet of material??? If you have a picture of part number, even better!

Thanks again!

[patrickrd]

Originally Posted by mzitz2k

Interesting! What did the neoprene look like? There are so many different types... What was the hardness rating and did it have "teeth" or was it just a flat sheet of material??? If you have a picture of part number, even better!

The neoprene had Durometer = Shore A: 70. We used rubber o-rings as the test specimen, 1/2" outer diameter by 3/32" thickness (purchased from McMaster). This is a much smaller scale than used in FIRST. The o-rings were used for contact with the carpet on each roller of our omni-wheels.Testing each material was simply a matter of replacing the o-rings in the wheel. I've attached photos of the wheel and the test setup. In short, the weight of the setup provided a constant normal force, and a voltage was applied to the motor. The voltage was increased until the wheel slips. From this data it is easy to find out what the coefficient of friction is. The uncertainty is less than 5% for all the data.

- Patrick