Drive Train
Once I had the gearmotors with the new cast hub and the wheels, I needed to connect them and put them on a axle. The gearbox has a tube thru the middle to cary an axle (inside the tube) and the drive gear (outside the tube), but the tube is made of plastic. Since the tube is plastic and the axle is steel, I did not think that the axle should rotate, so I decided to use a fixed axle, and attach the gearHub directly to the wheel to transfer power.
I started by drilling two holes thru the drive-gear/new-casting inline with the axle hole, but near the outside edge. Next I cut four 3" chunks of 6/32 threaded rod. If I were to do it again, I think that I would pick the next size up.
I inserted the threaded rod into the holes I drilled in the hub/casting and threaded two nuts onto the inside side of the hub and 4 nuts onto the outside of the hub. I used two on the inside to lock them together and the 4 on the outside are to space the wheel away from the hub.
Next I drilled matching holes in the wheels. The hard part here is to align them up such that the holes match the bolts on the hub. My problem was with the drill bit wandering. I got the job done, but ended up with a few extra holes.
Then to the axle. I cut the steel rod to 16 inches, then drilled a hole in one end. I put a pin thru the hole, threaded a washer, the wheel, and another washer (from the other end) and marked the width of the wheel hub on the steel rod. I then drilled another pin hole at the mark.
I turned the rod over and drilled the other end the same way.
Items are stacked on the axle like this:
pin washer washer wheel washer pin washer gearmotor . . . gearmotor washer pin washer wheel washer washer pin
This arangement locks the wheels on the axle and since the drive gear is bolted directly to the wheel, it also blocks the gearmotor from sliding on the axle but does not prevent it from rotating on the axle. Later on, the gearmotor will be connected to the frame in such a way as to allow some movement, but prevent rotation. This will absorb the shock due to rapid direction changes thus reducing the stress on the drive system.