The goal of this side-quest was to come up with a light-weight solution for a pulleyed wheel hub that can accept the 6mm D-shaft of FingerTech’s Mega Spark motors. The first idea to come to mind would be to of course use FT’s Twist Hubs and Timing Pulleys together, but this solution is heavy and takes up a lot of space.
Enter the Mega Smol Hub! This design was inspired by Charles Guan’s drive solution to his 30lb Sportsman “Susquehanna Boxcar” as well as my own Smol Hub design I used in my antweight, The Highlander. Not only are these hubs lighter than the FT Hubs, but they have a built-in pulley too!
Of course, since this is a Beetleweight, I was able to combine pulley, hex holder, and inserts into 1 piece of 3D printed nylon. The main issue though, is that the flexible nylon would likely just let the D-shaft spin around it once any significant amount of torque is applied. So the solution to this are the 12mm Hex Adapters Pololu sells for 6mm shafts.
However, you might have noticed that the front part of these hubs are tapped. This means we can’t shove our motor shaft all the way through. But this was easily fixed by drilling the entire bore out with a 6mm bit. Then the hex adapter is simply added to our shaft and the setscrews lock it in place.
Now for the tires. These are cut from sheets of gum rubber with a hole saw, then shoved into a 3d printed PLA jig for the slots to be drilled/sliced.
The tire is then shoved into a 3d printed PLA jug to drill out the hub and add the slices. A 5/8 bit is used to drill out the center then I use a 7/64 bit to precisely place the end of the slice. Finally an Exacto knife is used to to cut from that small hole to the center bore.
Once the tire is prepped, it can be super glued onto the nylon hub.
The back wheel can now be slid onto the hex adapter on the Mega Spark. For the front wheel, a different hub with a circular bore is made that a nylon spacer is pressed into. For this version, I used a 3/4″ long spacer with a #8 ID and a 3/8″ OD.
Then there you have it! 1 set of Mega Smol Wheels! Of course this can be modified however you want to suit your wheel thickness, diameter, shaft size, etc.
Download the Mega Smol Hub CAD Files
Foam Rubber From McMaster