One of the most critical aspects of the rover’s mechanical systems are the drive wheels.  Planetary surface rovers have a long history of using innovative wheel designs to help solve the problem of mobility in an extremely harsh, unforgiving environment with no roadside assistance.  Sojourner, the 10.5kg rover of the Mars Pathfinder Mission, used one-piece aluminum wheels with distinctive stainless steel cleats embedded in the surface.  The Mars Exploration Rovers, Spirit and Opportunity, used crowned aluminum wheels with shaped ridges on the outside, but no cleats.  Their wheels also incorporate thin aluminum spiral spokes to provide a suspension element to help cushion the rover.  Finally, the Mars Science Laboratory/Curiosity rover uses an aluminum wheel rim with zigzag raised tread.  Its hub also has some suspension.

For our wheel system, we decided to base our design on the wheel developed by White Label Space, a competitor in the Google Lunar X-Prize, for their lunar surface rover.  This wheel consists of a narrow (1″ wide) aluminum hub, spoke, and rim system machined from a single plate, a thin wall polycarbonate tube the width of the wheel (4″ wide), and 16 aluminum cleats fabricated from 0.5″x1″x1/8″ aluminum channel.  A piece of silicone rubber bonded to the aluminum rim prevents rocks and soil from getting through the wheel and clogging the drive module.  After several rounds of discussion, we decided that 11″ diameter wheels would be the most suitable.  This enables us to use 10″ diameter polycarbonate tubing, a readily available size.