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Originally Posted by Greg Needel
With wider wheels you have a larger surface area touching the ground thus more friction force.
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This is not 100% true.
Frictional force is independent upon wheel width
theoretically. 'Friction' or traction does not increase with a wider wheel since friction = µ · N. The weight of the robot is distributed to a larger area, thus decreasing the frictional force per unit area, and keeping the total friction essentially the same.
This does not take into account the deflection of the carpet, or any tire that 'digs' into it.
If you relate this to the automotive industry, in most cases wider tires do have more traction, but this has little to do with contact patch width (as most wider tires, of the same OD, with the same tire pressure, have the same contact patch as the thin tires). Cars, for example, desire wider tires primarily because of composition, as well as temperature, side wall deflection, pressure allowances etc. It is not as simple as the commercial "wider is better" Wider tires of the same compound do not have more traction, but will usually have stiffer sidewalls which inherently have less roll and give better handling characteristics.
For a robot, in some cases wider is better, but not always in regards to friction (unless there is some sort of protruding element that goes into the carpet, in which case it gets really complicated and testing is the best way to determine what width is desired using a given material). A wider tire (using belting as a traction material) in most cases will wear better. It has less pressure per unit area as the same belting on a smaller width wheel, and as such, also has a larger total area decreasing the frequency of belt replacements.
Again, you must remember that some belting has an optimal deflection at which its friction coefficient is the highest. You have to take this into account as well when talking about wheel width, especially if the belting is deflecting or protruding into the carpet fibers.
In 2002, team 60 had one of the most powerful and "grippiest" robots on the field. But they only had ~1" wide wheels. How is that? They lifted the 2 goals and used that weight to increase the wheels friction by increasing the normal force the robot put on its wheels.
Just remember that "wider isn't always better".
