I would like to build the three types of JPL Mars rovers (Sojourner, MER and MSL) with the right size ratio relative to each other. For that, finding the right wheels would be the hardest thing. I can build the rest of the robots as long as I know the wheels will have the right look.
Here's a pictures of the three wheel types:
- The overall size doesn't have to be at the scale of the minifigures. Even though this would be really cool, it would turn the Sojourner project into a micro build. This would be much harder.
- The look of the wheel hubs is not relevant. What is important is the look/ratio of the tire's outside dimensions. Note that Sojourner's wheel (the small one) has a flat rolling surface while the others two are rounded.
Edit: The medium wheel is (appropriately) 1.8x the size of the small wheel while the big wheel is (appropriately) 1.7x the size of the medium wheel.