carbon muni musings and impressions

So I had a feeling I would be up through the night working on an assignment and swearing at maple. I was, but I came prepared. At 8:00pm last night I cut a rudimentary seat post clamp out of some scrap and finished off the carbon fiber muni I designed. I worked hard through the night on the assignment (hard cause the muni was done) and finished at about 6:30 this morning. So I did what any sane person would do: I rode my brand new muni in the darkness, cold, and pouring rain until it was light and time for class.

There is nothing like new gear to inspire you. I took tonnes of lines that I used to dream about, sent long standing projects of mine and found dozens more that were right under my nose. The new muni felt rock solid, so I kicked the whole session off with a two foot drop ( which I would normally not consider on a brand spanking new plasic frame, but not a sound was heard. Maybe I’ll run back out right before class and leap sets of stairs for the sorority chicks so I can hear them say “Oh… my… god, did you see that?” Then imagine they said it cause they think I am cool.

Anyway, my first impressions are that the frame is plenty strong. I previously mentioned a new bearing retainer design. It makes assembly an absolute nightmare, but once together looks pretty slick. I don’t think I would do it again that way though. I killed the weight with my impatients by cutting a few pieces out of mild steel instead of cromoly, doa! and by using dang .050 wall for the seat tube, oooffff! Anyway, the frame is right around a pound (the lowers and yoke weigh about 150 grams in total though). If I did it over again with epoxy instead of vynyl ester, and smarter hardware, I think I could make it even stronger and under 1 pound. Anyway, I will start piecing together a gallery to show you all maybe this afternoon, unless the rain quits and my research is done for the day, then I am riding. Whataya suckaz thinka that?
-g

Dis sucka tinks iz kewl.

Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!
Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!
Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!
Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!
Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!
Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!Pictures!

Steve

:smiley: :smiley:

Couldn’t have said it better. I remember riding some “hot-off-the-machines” vehicles in the dark and in the rain. I wonder if those are the only conditions under which projects like these can be finished. Congratulations, gauss, you are your moniker’s prodigy.

Alright I got some pictures up of the new muni. The pictures don’t do it justice, I may take some more. I put descriptions with the pictures of the process to make such a uni. I need to thank Bill Maroun, and my Advisor Joachim Grenestedt for their inputs on design, and for use of materials. Thanks to everyone here for the motivation.
-gauss

Oh, nearly forgot:
http://www.unicyclist.com/gallery/Carbon-Muni-II

Dis sucka wuz rite!

Way cool, Gauss. It’s hard to believe from a layman’s POV that foam wrapped like that is strong, but apparently it is. How strong is it really? If you do a big drop and hit the seat (ouch) will it hold? And what about torquing up a big hill?

It is a special foam for this sort of thing. This stuff is 80 kg/m^3. Whereas they make large ships out of the same foam only 250kg/m^3. Using foam allows the stiffness of a given composite to increase drastically without adding appreciable weight. The important factors are how well the composite skin adheres to the foam in different situations. The foam is a special structure. While it takes relatively little structural load, it is designed to exhibit very close to pure bending when a beam is loaded (very little shear deformation) this allows the skins to see tension and compression loads instead of shearing and bending loads. This is good because they are very stiff in tension and compression.

When composites are done right they are extremly stiff and strong. A strip of unidirectional carbon fiber that is like an inch wide may take 15000 lbs of tension to break in the fiber direction. If you pull the same strip in another direction then a child could break it. Materials that have the same properties in all directions are called isotropic. Materials that don’t are called anisotropic, but there are more specific other names depending on different behaviour. There are all kinds of really neat and nonintuitive properties that result from layering these anisotropic materials. As a result you choose the fiber directions in each layer for the specific application and you get a stiffness to weight ratio that can be very high. Strength to weight ratio is usually pretty good to. Kind of a neat way to think about it is, when you make something from metal it sees a certain combination of compressive and bending and twisting and pulling loads, but the material has the same strength in all directions. It maybe very strong and punishing you with weight in a lot of ways that are unimportant. If you go through your structure and try to figure out just what is going on, you can use composites to make the structure strong in every conceivable way it would ever be loaded, and save weight by not letting it be strong in ways that will never be realized, and cut the weight way down. That is sort of a crude idealization. Sorry if it insults anyone’s intelligence. I have always been facinated with composite materials and since they are all I do all day every day, I sort of have lost track with how much a lay person knows about them.
As for the uni, I don’t know how strong it will be. I will enjoy finding out though!
-gauss

Thanks for the pics :slight_smile:
That is really cool. It will be cool to see how much abuse it can take.

oh yeah, how much does it weigh?

Steve

Re: carbon muni musings and impressions

Very nice. Steve Howard also does a somewhat similar pinching style bearing holder
<http://www.unicyclist.com/gallery/albun23&gt;

I can see how your design would be a nightmare to put together. But it does make for a lightweight design. Is there a lip on the bearing holders to help hold the bearings in place? From my experience with the Steve Howard frames a lip on the outside of the bearing holders helps to keep the bearing holders from wiggling or sliding on the bearings and makes the uni feel more solid especially when pedalling hard uphill.