Friction coefficients for Omni wheels and Mecanum wheels from AndyMark

Technical Technical Discussion
1

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

2

Correct me if i’m wrong, but doesn’t the mecanum wheel have a theoretical value of .707? (cos45)… Which means you’re doing fairly well.

3

You seem to be thinking of efficiency. The coefficient of friction is independent of this.

4

I don’t think you can have a theoretical coefficient of friction. My engineering professor said that it has to be measured.

5

Andy, what surface were these tested on? Game carpet probably?

6

Yes, thanks. I edited my original note above with this info and also downforce info.

Andy

7

Is there a chance of future testing using other relatively common FIRST field materials like HDPE?

8

Thanks Andy… great info.

As we’re prototyping with the 4" traction wheels from AM, and we’re looking for more traction, does anyone have any thoughts for materials with a higher cof than the rough top?

Any thoughts would be appreciated.

9

the brecoflex stuff… Supergrip green, is it? 1.5-1.7 vs. 1.2-1.3, I think.

10

This is what I see on there site. http://brecoflex.com/images.php?IMGID=82&TBL=submenu2

However, like you said, I thought they had something more grippy.

11

Ignore that. They sent out a message to all teams at the start of the 2006 season, and they reported the findings of their tests of several of their backing material on the carpet, diamond plate, and ramp… Its in the white paper’s section somewhere. That message aside, I don’t think I have ever seen anything grip better than the green brecoflex treads.

edit: http://www.chiefdelphi.com/media/papers/1772

12

Hey Joel…

Thanks for the info… I had searched the white papers and somehow missed this. I’ll give them a call.

On a side note, is your footer up-to-date? If so, I’ll see you in Hartford and on LI.

Regards,