[kramarczyk]

Another impact of contact area is in turning itself. We all know that the bots turn different on a hard floor like concrete than on the competition carpet.

<speculation>The carpet under the wheel locally acts like a spring. We know that things sitting on carpet sink in some amount (especially obvious when moving furnature) and the the area of carpet engaged affects how far into the carpet the item sinks. Therefore by increasing the size of the wheels contact patch (relative to the other wheels) we can affect the amount the wheel sinks into the carpet. <edit> ...by making the larger carpet patch behave like a stiffer spring</edit></speculation>

How does this impact the friction? By moving changing the normal forces. It won't change the overall pushing capacity of the bot, but it will allow us to change which wheels have the majority of the traction. This is really what we are doing when we drop the center wheel of a 6x6 after all isn't it. So by widening the center wheel we can move the normal forces to the center axle which lessens the normal loads at the corners... reducing skidding forces... making it easier to turn... with less wheel drop (and rock)... without giving up pushing force.

Attached is a crude spreadsheet attempting to explain my point.

p.s. I am working on getting hard data to back-up my point, but until then feel free to roast me.