We did an omni bot very similar in 2004 and won Xerox creativity award. You can view pictures at
http://www.team1322.org/robotics_03-04.htm . What we did is put the wheels in the corners so you can push them way out form center. We also used three omni wheels at each drive for more traction. Back then we had to build our own omni wheels
http://www.team1322.org/omni_drive.htm . The front of our robot was your corner. The robot was very fast and turned on a dime. I do believe the Mecanum drives would be more effective for you. It is more stable going straight and dose all that the omni bot does. Nice drawing and a grate design that is fun to drive. We still get ours out and drive it all over.
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If your not dirty than you must be just watching.
Thank's to
http://weberelectric.biz/
FRC Team site
http://team1322.org/
2004 Great Lakes Xerox Creativity Award, 2008 Web Site Excellence Award, 2010 Kettering District and Western Michigan District Excellence in Engineering award, 2011 Kettering District Gracious Professionalism Award. 2011 Ann Arbor and State Cooperation Awards.2013 Kettering Xeroc Creativity Award.2015 Escanaba Chairman's Award.2015 Kettering Spirit Award.2016 Kettering Chairman's Award
FTC Lightining Boltz 5954, Thunder Botz 7032
http://team1322.org/vex.htm