The building of the four-wheeled MER has started

The building of the four-wheeled MER already has started and the temporal result is visualized below:

Now 2 separate motors are used to drive two wheels on each side to make steering easy and fast. The tires are removed from the other (passive) wheels to keep friction to a minimum. Note that after a better inspection, the Mars surface is more even as thought, so a three-wheel design with a caster wheel also seems to be a very good choice. However, this four-wheel design will be used for the moment and when the achieved results in the future are not what we expected, it is easy to change the design without changing the c-code much.
The 'big' wheels are chosen, so a high speed can be achieved. When a lower speed and higher accuracy is demanded, it is possible to reduce the gearbox ratio or even to reduce the wheeldiameter.
The final design will also have a center of gravitiy very close to the two active wheels and not at the passive wheels to keep the friction while steering relatively low.