We have transitioned through several iterations of of non-tank drives over last four FTC seasons - 4-wheel omni, Kiwi omni and mechanum wheels starting last year and continuing this year.
The mechanum approach has clearly produced the best results.
2014/2015 - VEX wheels again; tested AndyMark and not as good, though easier to attach sprockets onto; gyro control now implemented & more precise autonomous; speed also doubled;
Our first competition is 12-6-15 in Peoria, IL
We are currently focused on autonomous scoring and endgame. We will have three dedicated swing arms; for each goal height; and then, based on partner capabilities, load the best two arms with our two balls. we then select which autonomous program to used, based on our target goals. The mecanum drive with gyro stabilization allows for reasonably fast and complex yet accurate paths
We plan to grab one goal, score large ball in it, then score 2nd ball in closest adjacent goal (moving laterally if needed). and possibly grabbing it too on the way to placing them both into the auto scoring zone.
At end game we will make sure all three goals along with our bot are all up on ramp.
PICs
FTC 2013/14 - Best mecanum drive in state of IL at finals but with no gyro control driving straight was still a problem. Hybrid of Tetrix bearing modules, VEX mecanum wheels on Bosch-Rexroth (or 80/20) slotted frame was super reliable and rugged; Hardened 10-32 SHCS axles (non-driven & polished going through the bronze bearings) are the best.
Chain drive ALWAYS or us.
FTC 2012/13 - Heavy Kiwi bot needed three wheels per axle. with just two, they sunk too deeply into foam surface; still drove poorly (erratically) with no gyro control; rear wheel hooked the plywood scoring platform
-Dick Ledford