How are you planning on doing the drive system? I have several ideas on how to do it. Unfortunately I am no artist, so I couldn't get pictures or diagrams. These are very strange to some, but I don't see why they won't work.
Pure Omni Drive:
4 Omni wheel drive.
Omni Hybrid Ver 1:
Pix to come
Omni Hybrid Ver 2:
Pix to come
Omni Hybrid Ver 3:
Pix to come
2 Wheel Drive:
Might not be possible since the wheels must be inside the bumper zone
2 Wheel Alternate Drive:
More plausible, with a caster wheels for stabilization without sensors
Quadruped:
Literally 4 legged robot, like a mammal, legs right under the body mass.
http://www.youtube.com/watch?v=W1czBcnX1Ww
Triped:
Like the Protoss Colossus
Hexaped:
Like the 4 legged robot but with 2 extra legs, 3 legs will always be touching the ground, making it stable
Biped Wheel Hybrid Ver 1:
Biped Wheel Hybrid Ver 2:
Pix to come