[Justin Stiltner]

As a long time participant in FIRST (10 years) I think a few of you are "reverse lawyering" the rule about traction. To me it is pretty clear that the intent of that rule is just what most think, the rover wheels are the ONLY thing that can act against the floor to provide motive force. They actually mention legs, other wheels, etc. I think that a robot with a fan would be a great idea, and something I would look into the feasibility of. I am sure this will be settled soon via the Q and A. What you are talking about doing is done in all motor sports (cars anyway) the car uses down force generated from the aerodynamics of the vehicle to provide extra normal force, and the end result is more traction. If it were properly designed, and guarded I would have no problems with a robot that had normal force increasing devices, but be ready for a lengthy inspection, and have your engineering numbers ready if you designed it yourself, or the data sheet of the fan from the mfg.

To go ahead and comment on various other posts ideas, and take these as you will...

WORN WHEELS
If a team came in with worn in wheels I dont see a problem, It is the same as a team that has run in a previous regional and not changed their wheels, If you are going to say that you cannot have worn wheels then you would need to make everyone change their wheels every few matches. However the manual does state that the profile of the wheel may not be modified. But one thing to ponder, if we assume these to be ideal surfaces, then the surface area of the contact patch doesn't matter.

FANS FOR PROPULSION
Dont think of a fan which is normally moving a relatively low volume of air and relatively low velocity. Think of a helicopter rotor, by using this you can get an off the shelf product, that has been tested to certain rpm limits, and the best part, instead of reversing the rotation of your "fan" you only have to change the collective pitch of the rotor blades, (done with a servo on model helicopters). I have not tested the numbers myself, however there are reports that a heli with a 27.6" rotor diameter was lifting itsself as well as generating 5lbs of upward force, this while consuming about 420W via a brushless motor. However you would need casters to turn if this was all you had, which could result in a wild ride when you had a collision.

FAN FOR DOWNFORCE
To me, a fan blowing up alone would help, however you would most likely see more of an effect if you were to use your fan to generate a low pressure area under the robot. The force in this case being pressure differential multiplied by the area of the robot under this low pressure. Assuming you could affect the entire underside of a full legal size robot with a lower pressure you would have 1064in^2 of area, with something this large, the differential would not have to be much to have a rather large increase in force. For instance a random fan mfg. I looked at quoted 50cfm at 2inches of water (.072PSI), this doesn't sound like much, but over the full area of the bottom of the a fore mentioned maximum dimension robot you would achieve an extra 76lb of downward force, assuming a 120lb robot and a coefF of .05 that would be 6lb of linear force before the blower, and another
3.8 if you could establish -2IWG of pressure under the robot meaning you get 63% more force if you can establish the low pressure.

Take all of this with a grain of salt, plenty of off the cuff calculations there, and food for thought. I also think a good traction control system would be worth its weight in gold!!!