TRIK3R is something different. Most Lego vehicles wheeled vehicles use 'wheelchair steering' which steers by turning two wheels at different rates, with neither wheel actually steerable. TRIK3R uses steering more like of a normal car or tricycle, with a (double) driven wheel at the front which is actually steered by a second motor mounted above the brick. It may look odd, but it's the only way I could arrange for the motor to directly drive the vertical steering axis, thereby avoiding the need to use a gear mechanism. My design allows the wheel to be steered through a full 180° and the fact that this is a 'front wheel drive' design means that the full steering range is usable which would not be the case with a 'rear wheel drive' design. I've done all I can to make the steering axis as rigid as possible. This steering technique does not require a castor or fancy wheel at the back, just two simple wheels. On my model, the back wheels do not share the same axle, which makes it easier for the rover to turn. The front wheels DO share the same axle, and it may be sensible to remove one of the front wheels so that the steering can move more freely, but this would make the robot look asymmetric.
Ultimately I don't think tricycle steering is as good as wheelchair steering, but it was fun to make a rover that is so different from most.