The 3 leading/3 trailing wheel on the MUni so far hasn’t been subjected to anything worse than me jumping as high as I can off the flat ground, but in comparison to my Torker 24" 36 spoke, it is notably stiffer. Also, I built the wheel so that what I guessed would be the most flex resistant part would be down when I was in neutral position (as a left footer).
As for the MUni:
TSM 202
Welding a Mountain Unicycle
My mountain unicycle, or MUni project, started as so many projects do: over zealous and ill conceived. The plan was to make an aluminum MUni that would be somewhat light, incredibly strong, and most importantly, built entirely by me! I had started making plans to do a finite element analysis on the frame to figure out the exact dimensions and wall thicknesses needed to create the perfect blend of strength and light weight, but I ran into two problems in doing so. The first being I had no time to do a FEA, and the second being I had absolutely no idea how to do a FEA. Therefor, I made the frame out of commonly available sized aluminum rectangular and circular tubing.
I chose to make the MUni out of aluminum, likely for no other reason than my disordered attachment to the metal. I was able to order the 1.5" by .75", .125" walled 6063 rectangular tubing that would become the frame from Mc-Mastercarr, and the 1.25" OD tubing from Wicks Aircraft supply, used to make the seat tube. The bearing holders were machined out of .75" plate 6061 purchased at the ECE Store on campus. I bought a unicycle wheel from a unicycling parts source, and laced the wheel to the hub using a 3 leading, 3 trailing spoke pattern that I thought looked cool, and was probably pretty strong also.
The project started by making friends with the super-cool Industrial Design guys, who would later become invaluable in getting the bearing holders machined. Frankie Flood, a graduate student at the university helped me machine the bearing holders over Thanksgiving break. The rectangular tubing was miter cut to 22.5° to create the crown. I tacked the crown pieces together after fighting with them for a very long time. Oxidation was affecting my welds, and the two pieces of aluminum were refusing to weld together. After a very long and arduous process, I was able to get the entire crown welded together.
To make the fork blades, I first created a platform that would hold the bearing holders flat and square, allowing me to accurately measure off them and also weld to them, once the forks were cut and tacked to the crown. Keeping everything square was of the utmost importance, so I made sure everything was aligned properly after tacking things together, before welding the whole thing together.
Lastly, the seat tube was aligned in the crown, tacked, and welded. It still needs to be cut to an appropriate length, and have a notch cut in it to allow clamping on the seat post, but that is all tantamount to the actual welding project.
What have I learned, and what would I do differently? The first thing I learned is that aluminum is an evil metal. It pretends to play nicely at first, since it is so light, and shiny, and it cuts and machines so readily. But then, when attempting to weld it, aluminum’s true evil nature comes out. Next time, I think I’ll make it out of steel.
There was definitely a need for more jigs and clamps. I could have made a crown pattern that would have allowed me to weld everything perfectly flush without any of the problems I ended up having. Also, I have learned that aluminum cannot be too clean before it is welded. I would consider some sort of chemical cleaning process, if such a thing exists, before welding next time.
I’m not sure how it rides yet. The MUni still needs a seat and cranks. It sure looks mean though!
I’ll let you all know what breaks first on which uni,
-AA