Plaction/Traction coefficient of friction?

[JamesCH95]

I was hoping someone had done traction tests on AM plaction or traction wheels and hoping they would be kind enough to share their results of lateral/longitudinal static/dynamic friction coefficients.

I know this an experiment that teams can do themselves, but suffice it to say that my team is in-between homes right now and we're not able to have regular meetings.

[548swimmer]

Wouldn't the latitudinal and longitudinal values be the same?

[Andrew Schreiber]

Originally Posted by 548swimmer

Wouldn't the latitudinal and longitudinal values be the same?

Can you think of any reason they wouldn't be?

[JamesCH95]

Lat/Long traction will be different, I think, for these reasons (and possibly more I haven't thought of):

The tread typically has an asymmetric tread pattern.

Latitudinal tread has an edge exposed that might dig into the carpet.

Longitudinal direction is curved with the wheel, and when pushed in that direction will compress more on the "up-hill" side of the wheel and loose traction in the "down hill" side of the wheel leading to variations in contact pressure which can lead to variations in grip.

I've attached a very quick paint sketch of this, red representing a pushing force and the green lines representing normal force on the wheel, exaggerated for effect.

[548swimmer]

Originally Posted by JamesCH95

Lat/Long traction will be different, I think, for these reasons (and possibly more I haven't thought of):

The tread typically has an asymmetric tread pattern.

Latitudinal tread has an edge exposed that might dig into the carpet.

Longitudinal direction is curved with the wheel, and when pushed in that direction will compress more on the "up-hill" side of the wheel and loose traction in the "down hill" side of the wheel leading to variations in contact pressure which can lead to variations in grip.

I've attached a very quick paint sketch of this, red representing a pushing force and the green lines representing normal force on the wheel, exaggerated for effect.

In that case, wouldn't the thickness of the wheel matter as well?

[JamesCH95]

Originally Posted by 548swimmer

In that case, wouldn't the thickness of the wheel matter as well?

Quite possibly, though any information is better than no information. I highly doubt that a 1" wide wheel will be wildly better or worse than a 2" or 3" wide wheel.

[Chris is me]

For calculation purposes in a drivetrain, I've been told 1.4 is a safe static CoF for roughtop on carpet in the direction of motion (basically, when gearing for traction limited pushing power / acceleration)

If you need more precision than a good estimate, I would experimentally determine this for yourself.