I just posted a Gallery of the new unicycle I have been working on. The frame weighs in a pinch over 2 lbs which I am happy with for the first prototype. I think it could get close to 1.5 and stronger if I give it another go. As of right now I have ridden half a dozen times on south mountain here in Bethlehem. I completed my project trail the first day out with it. I have had numerous wrecks including one monster wreck that involved the uni bouncing as high as my head twice as it bashed rocks and trees. I have taken it off a few drops on the order of 3 feet, ridden it down countless flights of stairs and it is still holding strong.
There are also some pictures of the carbon fiber wheel we built a while back (my apologies to all on just now posting it). The wheel has also seen some serious offroad abuse. It has rimmed rocks and curbs many times and is still very straight. It makes a really cool hollow sound when you hit obstacles with it.
There are a few other unicycle related projects on the horizon. Two notably that I am pretty sure have never been done, both of which may provide a contribution to the sport.
I am very grateful for the help of Joachim Grenestedt and Bill Maroun. Neither of these projects would have been possible without them. Professor Grenestedt is head of the composites lab at Lehigh University and designed both the carbon fiber wheel and the manufacturing process for it. He also helped me with the layup of the frame. Bill Maroun is our lab engineer and helped with all waterjet cutting and with the design of the frame. I would also like to thank Dick Towne for his help.
Originally the goal was to make the aluminum thin enough that it wouldn’t be able to carry the load, but to only be able to transfer the shear to the carbon skins. The upper piece would be empty through on the part that supports the seat. Due to a misunderstanding, the plates were made with a layup that did not allow them to directly support the seat. Also, the aluminum wound up being quite strong, despite removing so much of the material. The foam was added to stiffen the frame. The carbon could probably stop at the break boss bolts. The upper section is supported by the carbon entirely. This is what I would improve on future designs. The carbon would be thicker and the foam core would be eliminated. The aluminum would take less load. Another option that has been considered is to make the whole thing out of sandwich structure which is the ultimate goal once a few issues are worked out. This would likely result in an incredibly light and incredibly stiff frame.
Those are some gorgeous, high-tech projects, Gauss. Are you planning on more iterations before you graduate? Now that the jig is made is it difficult or costly to make additional wheels? Do the wheels remain true laterally? It seems as if the rims would warp on impact without the lateral component of spoke tensioning. Is there a cut in the rim into which the carbon fiber layup is inserted?
To be honest we didn’t know what to expect from the carbon wheel. There was a part of us that thought it might break the instant it was sat on. It has turned out to be very strong. We have done some drops with it and have come closer to getting a pinch flat then to breaking it. If you look at the side view you will see at the thinnest part there is a seam. This seam was wide enough that when we clamped it down and created the wheel dish the gap disappeared. The shape of the three holes allowed the stress concentration associated with warping the plate to be minimal. I grit blasted the rim and suzue hub to aid in the adhesion. We used Hysol 9430 as the adhesive. There weren’t any troughs or edges machined into the rim as the 9430 (aka. Gorilla snot) is pretty tenacious stuff. You can see from the picture that we used mdf glued to steel for the jig. A steel piece in the middle received the hub. The mdf was passed through a jointer so that it would shim to the right height. Initially inspection revealed that the hub was quite straight. Surprisingly it is still very straight even now. If we had not have created wheel dish the wheel probably would have made it about 5 seconds. I suspect of the phenomenal stiffness of the carbon fiber is what’s responsible for making up for the lack of pretension that would have come from spokes. I must admit there are some more projects on the horizon. I would like to go back and make the muni frame stronger and lighter, and to manufacture wheels in other sizes. But I am pretty psyched about the new projects we are considering. It will be a long while before I graduate though so I hope to get a lot done.
Looks cool but I have a question? from the pics you cant really see the rim that you used for the carbon fiber wheel. I was just wondering if you concidered making a rim from carbon fiber and just building the wheel with spokes that traditional way…
I have never sat down to weigh the 2 materials side by side so I guess this all comes down to is what wheighs more spokes or the carbon fiber that is needed to support the wheel. I’m all about a carbon fiber rim though… the wheel looks kickass too way to go.
A little off topic but…
I was cruising the July 2002 issue of mountain bike action and saw a picture of Titus’ new tubes for their high end bikes. Titanium with diamond cut outs. Inside the cut outs carbon fibre was hand layed to add strength and stability.