Friction, as taught in introductory physics courses, is a macroscopic empirical model. The model does surprisingly well, much better than an empirical model should do, but one should be careful in how far one takes it. One should not assume that the dogma of the empirical model is true for every possible situation.
Your approach of actually measuring the effect of doubling up on the wheel surface area for your given situation is the right one to take. Don't be surprised when the data shows that the empirical model is a little out of step with reality.
There will be those that say that there is a lot more going on than the simple friction when a wedgetop, or roughtop, tread is forced to slide across an industrial carpet, and this is true. There is also something much more complicated than the simple macroscopic empirical friction model going on when two "hard surfaces" are sliding across each other, when you actually look at the microscopic details of what is happening at the atomic level, which you must do to understand the physical process in a predictive manner.
Eugene
Quote:
Originally Posted by 114ManualLabor
This is an interesting thread.
Short disclaimer: I have yet to take physics, so anything I write is a result of observation.
Anywhoo. I think I understand what people here are talking about, yet I'm still confused. If everyone says that the contact area doesn't matter, then can someone explain how this makes sense: I built two robots. Both were with the kitbot chassis. Both were driven off of Banebots transmissions. Both had two driven wheels, and two casters. One bot had two andymark kit wheels per axle for driving, and the other had only one per axle. I added extra weight on each in order to make the weight exactly equal. I wired both motors to a single battery and switch. Then I put the two drive bases head to head, set so they would drive directly into each other, on an area of FIRST carpet. When turned on, the base with 2 wheels per axle could overcome and outpush the other base every time. We did this 12 times, each time changing to a new, fresh battery.
Anyone care to help me out here? I guess that physics and math and stuff say this shouldn't work, but it did. So I'm confused.
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