Another 400 miles ended with a shredded tire, burned out servo & cracked rod end.

So the Hextronix died after 394 miles.  It was a motor burnout.

In went the SPT.  

The front tires came up thrashed from old age & going offroad.  

The decision was made to make a helical front tire like the helical rear tires.  Because of the round tread, it couldn't be a simple C program that replicated & rotated an STL file.  This one performed 96 boolean operations in Blender to create individually rotated layers, over 6 minutes.  

Blender has proven useful for final pass booleans, but it doesn't do parametric models, can't import a scene graph from FreeCAD, or have a model history.

It only took 3 tries & $4 of filament to get it close.  They're never the perfect hardness.