Don,
This is a coaxial drive, so by that I mean that the wheel is turned by rotating the inner shaft of the CO-Axel. It is turned/pointed/aimed by a sprocket that is not shown as it is part of another assembly in my design. Because there is no motor mounted inside the module there is no need to manage turn limits, it can turn around as many times as the driver would like it to and no wires will ever be tangled.
The fork is not really a fork, it is made from 3"x3" (1/4" Wall) aluminum extrusion with a piece of aluminum plate welded to the top to form a prism with one open end.
If you wanted to make an outdoor friendly design I might already have a version that features a 6" wheel that I could email you if you like
It should give you the ground clearance I think you want. I could also email you a short video that shows how the CO-Axel turns the wheel in this design.
Hope that helps? I would be happy to try and answer again if not...