//Only read if you care about off topic posting
OK, so I know that by posting what I am about to post I am not following the original intent of the thread BUT this topic was brought up and has enough relevancy for me to justify my single subject post.
//
I have been thinking about the pushing thing for a long time, and I believe it boils down to simple physics. If all robots have the same maximum weight to be pushing on the Normal force, the only other factor affecting a NON STALLING (from lack of torque required to turn wheel(s)) is friction. F=uN if I am not mistaken. To get the greatest force, you must have the greater amount of friction applied to the floor.
*This next part is a really long sentence with many side notes in parenthesis, it is hard to follow, but bear with me.**
I don't care how much horse-power you put into a drive system, as long as there is enough power to not stall the motors (or trip the breakers), which I find is EASILY accomplished with 2 CIMs per side (seeing as how my team doesn't think about stalling with 1 per side), you will win a pushing match with a highest amount of friction with the robot to carpet interface (wheel(s), tread, gum rubber roller
....etc.)
Pretty much
If you don't trip breakers and stall your motors, and you have a higher amount of total friction applied to the floor, you will have the great force in the desired direction, therefor win any pushing match.
Thats my long winded-off topic $.02.
-Henry