Baddeley Mk III dummy hubmotor wheel

In my Michael Baddeley Mk III Astromech droid, I am intending to install the hubmotor variant of the foot drives (which commonly use four inch UUMotor or L-Faster motors), rather than the standard belt/gear/chain drives that many builders use.  As such, I printed Stephane Beaulieu's modified foot drive parts (which are available from the Kyber discord).

When a motor is not installed in the gap in the foot drive housing shown below (which is lying upside down), the outer feet will rest solely on the rear omniwheel, and that foot will tilt forward and drag on the ground.

I was recently assembling the droid as a temporarily static work-in-progress build for Droid Con (the event for Star Wars robots, not the one for cellphones that has the same name), but I didn't yet have hubmotors to put in the feet.

With very little time remaining, I decided to model and print these simple wheels to serve in place of the hubmotors until I can install those. This allows the droid to stand properly and be rolled around by hand.

The wheels themselves are printed entirely in TPU.  I printed at 0.3mm layer height, used about 30% cubic infill, four perimeters (on a 0.5mm nozzle, so 2 mm walls) and 6 top and bottom layers.  They supported the droid's weight just fine.

Mounting the wheels can be done without disassembling the foot drive frames.  The assembly requires (for each wheel):

• two 608zz skate bearings (one on each side of the wheel)

• a roughly 3.5 to 4 inch long x 5/16 inch hex bolt as an axle

• four 5/16 inch hex nuts

• one 5/16 inch nylon locknut.

My bolts were 3.5 inches long and just barely worked.  You may or may not also wish to add 5/16 inch washers.

Installation consists of inserting the bolt from the outboard side of the foot drive unit (you may have to reverse the bolt's direction in order to use a longer bolt), threading two hex nuts onto the bolt once it's inside the drive, then inserting the wheel with its bearings installed, then threading on the remaining hex nuts, before finally the bolt passes through the opposite wall of the foot drive and is secured with the locknut.  I used an appropriate socket to turn the axle bolt, and a crescent wrench for the hex nuts.

The paired hex nuts on either side of the wheel serve as jam nuts, as well as spacers to keep the wheel centered.

With the wheels installed, I was able to get the droid up on its feet and took him to the con.