48 SERVO 01.2014
To add three tires to the hub, insert four #4-40 x 1”
machine screws through the hub and then through the
stack of tires (refer to Figures 4A and 4B).
To secure the tires, you need to tap the four holes in
the hub cap with a #4-40 tap. Then, tighten the four
machine screws so they protrude about 1/4” as shown in
Figure 5A. Optionally, you can add four #4-40 lock nuts as
shown in Figure 5B.
The last step in the wheel assembly is to drop the inner
support hub into the center of the wheel so that the four
holes slip over the screws; take a look at Figure 6. Note
that this hub will be held in place with the main mounting
This concludes the wheel construction. I will post the
STL files for the hub parts on the PBOD website. For those
without a 3D printer that want to build the PBOD, I will
offer wheel and tire sets, as well.
Figure 4A. Figure 4B.