Coefficient of Restitution for pneumatic wheels

In summary, Semionsemion estimates the coefficient of restitution to be 0.70. Skrambles says that the change of momentum for the whole robot will be different than the change of momentum for just a wheel, because the wheel is not independent of other bodies.f
  • #1
Hello all.
I'm trying to find impact forces acting upon a stare climbing robot.
I'm using the impulse = change of momentum principle. In order to figure out the change in momentum in a pneumatic wheel bouncing off a stare when it hits it, I need the Coefficient of Restitution of a pneumatic (or just rubber) wheel with a 280 mm diameter. Does anybody know of a data table or any source where Coefficient of Restitution for various wheels are estimated?
Also, if there are other ways to calculate the impact force between a wheel and a stare, given the mass of the robot and the speed with which it approaches the stare, I would be thankful.

Thanks in advance,
  • #2
semion: Assuming the tire air pressure is ~240 kPa, I would currently estimate COR = 0.70.
  • #3
You could drop the wheel from a known height onto a hard, level surface and then measure how high it bounces. The ratio of the two heights should give you a good approximation.

If you know the momentum of the robot (mass times velocity), you can divide that by the time it takes to the robot to stop to give you the average impact force.

What sort of measuring instruments do you have available?
  • #4
Thank you for your replies.
nvn, thanks a lot for the estimation. Is there a way to relate this coefficient of restitution to the change of momentum of the whole robot, given that the two front wheels are hitting the stare, and the initial velocity and the total mass of the robot are known?
Skrambles, thanks for your advice. I'm currently at early stages of designing the robot and and don't have any parts of it available yet.
I do know the initial momentum of the robot, but I don't know the time it takes to the robot to stop as a result of the impact - that's another thing I'm trying to figure out.
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  • #5
semion: If v1 is the initial wheel velocity normal to (perpendicular to) the stair surface, then the final normal wheel velocity, v2, is v2 = -e*v1, where e = coefficient of restitution (COR). The initial normal wheel momentum is m*v1, and the final normal wheel momentum is m*v2.
  • #6
nvn, thank you a lot for the helpful guidance. I suppose though that the coefficient of restitution for the whole structure of the robot will be different than the one for just a wheel, therefore v2 for the wheel, which will be the same as for the whole robot, will be different than the one to be found by v2 = -e*v1, because the wheel is not independent of other bodies. I guess I didn't ask the right question in the first place, sorry about that. There is also the fact that the whole motion of the wheel is done by rolling on the ground and not by free fall for example, but I don't know how relevant is that.

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