# does anyone know the friction Coefficient between the carpet and rubber?

we need the Coefficient to run the numbers
help will be appriciated

You’ll need to be more specific than that. What type of rubber?

It’s pretty easy to do a test yourself if you had a small sample of the carpet/rubber, and an inclined plane.

If you’re looking at tread materials there are a number of commonly used types that people can give you a number for.

The coefficient of friction will vary between different types of rubber. If you are using an Andymark wheel they have the numbers posted on their website for most or all of their wheels on FRC style carpet. Here is the page for the 2010 KOP rubber wheel:

That page lists the CoF as 1.0 static for that wheel.

we are using bicycle wheels i’m not sure what is the type of rubber in those

You’ll have to determine it for yourself. Put a piece of rubber on a piece of carpet mounted on something rigid, and maybe a little weight to make sure the rubber slides instead of rolls. Then lift the section of carpet, keeping one end of it on the ground. The inverse tangent of the angle that the piece of rubber slides down at is your CoF.

We have borrowed a spring force meter from the physics lab at our school to determine coefficient of friction. You would have to rig 4 wheels on a light frame and lock them and try dragging the frame with the force meter. you would have to weight everything to complete the friction calculation. Make you make the frame light because the student force meters don’t read very much force.

Trying to get bicycle wheels to work may not be worth it. It would be much easier and time efficient to order wheels from Andy Mark with a know coefficient friction that already have the proper mountings to the drivetrain.

oh and by the way my school’s team is kinda new so we’re not sure at what speed a fast robot would move can someone give me a estimate? (preferably in km/h)

The fastest “common” speed that I know about is 15-18 ft/sec. It’s much more common to have a 10-12 ft/second robot, though.

If you’re designing in km/h, you may want to look at your orders of magnitude. m/sec is much more applicable to a 54’ long field.

3.3 ft = 1 m

The speedier of robots with shifting gearboxes are usually around 15 to 16 feet per second in high gear. With a single gear anything over about 12 feet per second is probably not a wise choice due to low acceleration (assuming 4 CIMs).

is that so about the same speed i had in mind thanks alot

JVN of team 148 created this great drive train/ mechanical calculator.

http://www.chiefdelphi.com/media/papers/2059

We have gone with a 20:1 total gear reduction (including wheels) in the past with 4 CIM motors. Its more of a medium speed at about 8-9 feet per second. Its kinda nice for newer drivers because its not too fast and has decent pushing. We liked it because it has enough torque spin the andy mark FIRST wheels when it crashes into something. Kinda handy with a run away robot driving into a wall in autonomous because you won’t trip the circuit breaker right before you start a the tele-op part of the match.

This year we are going for a much quicker robot. We will see if our driver likes it. We are keeping extra sprockets handy to tweak with the gear ratio.