John,
We don't calculate the CoF. If we need to know, we test relative to some other standard (i.e., another robot) by pushing it along carpet and measuring force - sometimes with 'calibrated legs' only.
Your method is valid for static friction, but dynamic friction is also important IMHO, since once you start moving the value is usually quite different from static friction (= Sticktion). To measure that in your test setup, you lift to just below your normal angle, set the robot sliding, then reduce the angle to where it stops. This was very important to us in Lunacy, for example, where the wheels were generally not at rest relative to the surface.
Quote:
Originally Posted by ttldomination
We never did figure out what were causing the variances.
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Probably the 'interlocking' of the soft, rough sponge with the smooth-but-not-as-smooth-as-you-think wood. Get a particularly strong splinter of wood, and it grips more than if you only get weak (or short) ones.