Quote:
Originally Posted by M. Krass
I've been thinking a lot lately about why some teams use a high traction wheel as the center pair in a 6WD. There may be some benefit -- again with respect to maneuverability -- but such an arrangement does not offer increased pushing force over 6WD with three pairs of identical wheels, so I'm not convinced that accomodating the differing wheels is worth the trouble.
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Should have posted this earlier...
The center axle in a 6WD system carries a disproportionate amount of weight on it. In a uniformly distributed frame the center axle carries about 62.5% of the weight vs. 18.75% for the outer axles. Since traction is proportional to weight, increasing the friction coefficient at the center axles has the biggest bang for the buck in terms of pushing force while minimizing the reduction in turning due to high skidding losses.
Assuming a uniformly distributed 120lb bot with 6 skyways (0.7 CoF) then the pushing force is 84 lbs. Swap the center wheels to a ridgetop material (1.3 CoF I think) and the pushing force jumps to 129 lbs (120*.625*1.3+120*.1875*.7*2), an improvement of over 50%. In reality most bots are not uniformly distributed, but instead biased to the center which makes this change even more significant.
Dear Mr. Lavery,
Congratulations. For the fourth year running, you have successfully ruined my Christmas holiday with your untimely release of a most obfuscating, but no less tantalizing, hint. - dubious elise [more] 
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