Yes we have changed the wheels, but we are still exploring how to use bigger tires.
Most geared bicycle wheels use a 3:1 reduction, and are designed for high speed. They are inefficient at low speed high torque, burning a lot more energy than something with a higher gear ratio. Not good on a solar powered robot. We found these geared wheelbarrow hubmotors with a 30:1 gear reduction, which are more efficient at low speed high torque operation. Unfortunately they are not designed to fit a bicycle wheel - they fit a wheelbarrow tire directly over the motor with no room for bicycle spokes. So I came up with a modification to put bicycle wheels on the wheelbarrow motors as a stopgap solution. It is a fairly extensive modification mostly because you have to have a bike shop build a wheel on to it. What we found was that bike shops hated doing this. The very first bike shop we went to was happy to do it… until their good wheel guy moved away. Then they refused. I called loads of other shops and they all refused. I finally found one that would build the wheel, but it was expensive. They don’t like the apparent liability from an electric motor and they don’t like that it is weird.
I was recently working with a vendor on alibaba who said they could build us a planetary gear reduction hub motor to fit a 26" wheel. They started working on it and then eventually decided they couldn’t do it, so we are still looking.
In the meantime, the wheelbarrow hubmotors we are already familiar with can be bought with tires onboard, so for now they are a great solution to get our new system up and running. The large tires of the first version were absolutely amazing at off roading. We will see how these smaller tires perform. From a cost perspective they are great, but we will continue to explore other options before release. On the new vehicle the major questions are on the performance of the new steering system and the new electronics, so using the existing motors with small tires will let us get testing ASAP as we look for other possible wheels.
As far as tracks - we will have to see what is needed. In my mind tracks add a lot of cost. But our system is designed to be customizable so if anyone wants to slap tracks on it and share their experience, this will help us as a community gauge their viability. For our initial vehicle release we will use wheels as they are lower complexity and cost, and we want to get out the door as soon as we have a viable system.
Thanks for the questions!