Mark and I did some work last night that has been overdue. We performed a test of friction coefficients on our wheels from
AndyMark, Inc.. We got some interesting results.
Each wheel was tested in 4 ways:
Radial Static Friction
Radial Dynamic Friction
Transverse Static Friction
Transverse Dynamic Friction
Radial friction could also be considered driving friction, as it is the friction involved when the wheel is being driven forward and reverse. Or, it can be applied when the wheel is stationary and it is resisting a force from the front or back.
Transverse Friction is the ability of the wheel to move sideways, or scrub. This is also the friction involved when the wheel is stationary and a force from the side is applied to it.
Static friction is involved when the wheel just begins to move from a stationary position. Dynamic friction is involved when the wheel is already moving.
6 wheels were involved in the testing:
8" and 6" Plastic Omni Wheels
8" and 6" Aluminum Omni Wheels (not on website yet, but VERY soon)
8" Coolie Dualie Wheel (not on website yet, but VERY soon)
8" Mecanum Wheel
Here are results:
8" Plastic Omni Wheel
- Radial Static: 1.07
- Radial Dynamic: 0.9
- Transverse Static: 0.20
- Transverse Dynamic: 0.16
6" Plastic Omni Wheel
- Radial Static: 0.9
- Radial Dynamic: 0.8
- Transverse Static: 0.27
- Transverse Dynamic: 0.20
8" Aluminum Omni Wheel
- Radial Static: 1.15
- Radial Dynamic: 0.9
- Transverse Static: 0.31
- Transverse Dynamic: 0.20
6" Aluminum Omni Wheel
- Radial Static: 0.9
- Radial Dynamic: 0.8
- Transverse Static: 0.26
- Transverse Dynamic: 0.20
8" Coolie Dualie Wheel
- Radial Static: 1.05
- Radial Dynamic: 1.0
- Transverse Static: 0.29
- Transverse Dynamic: 0.20
8" Mecanum Wheel
- Radial Static: 0.7
- Radial Dynamic: 0.6
- Transverse Static: 0.7
- Transverse Dynamic: 0.6
The new Aluminum Omni-Wheels have the same roller geometry and setup as the Plastic Omni-Wheels.
<edit...
These tests were made on FRC-type carpet, with 30 lbs. of downforce on each wheel. The omni wheels were tested individually, while the Mecanums were tested in a right and left pair, with 60 lbs. of downforce.
(thanks for the question, Andrew Blair)
... end edit>
Andy Baker