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TWO CHAINZ

Prototype brazed steel full suspension mountain bike

Summary

Much like Dr. Frankenstein in Mary Shelley's book, I learned the hard way that it is possible that in the attempt for perfection, a creator can be both proud and horrified of their own creation. Two Chainz was my Frankenstein's monster.

As a sophomore in college, I decided to challenge myself by building a full suspension mountain bike as my second bike ever. "How hard could it really be?" I told myself, not knowing how to do complicated kinematic analyses (see: Senior Project). I pushed myself to come up with crafty ways of making the frame. I used the conventional Anvil frame jig for the bike's front triangle, then created my own brazing fixtures using whatever I could find around the shop. Instead of using press fit bearings for the main pivot point, I used a second headset, mounted perpendicular to the frame.

The assembly of the frame immediately revealed some parts of the design I had completely overlooked. First and foremost--the chain stretched a significant distance when the suspension compressed. The wheelbase of the bike was already enormous, so upon installing my standard length off-the-shelf chain, I soon learned that when the suspension compressed, the chain stretched so much that it was actually the thing restricting the bike from going through its whole travel. The solution? I bought a second chain and added part of that--and thus, Two Chainz was born.

I'm gonna be honest here--the bike was not good. It had horrible suspension characteristics and the entire rear wheel twisted out of plane with the rest of the bike when you went quickly around a turn. That being said, I was still very proud of it. I rode it very hard down some very technical brutal terrain for over 1.5 years. Plus, the look I got from people when they asked me what the monstrosity of a bike was that I was riding and being able to say "I made it" was worth it. 

After 1.5 years of "testing," Two Chainz developed a small hairline crack on the top tube during the middle of a ride. At this point, I knew it was beyond saving and limping it back would only be delaying the inevitable. As expected, catastrophe struck a little later in the ride. The top tube ripped right in half right where the crack had propagated. Somehow, I was able to still ride it another mile--giving it one last hoorah. 

Two Chainz was a big learning experience for me. It taught me that before I jump headfirst into a project, I need to sit down and gather the scope of what is even needed to design something--AKA reaching the first peak of the Dunning Kruger curve. It also taught me a lot about design. Since I designed Two Chainz before taking a single Statics, Dynamics, or Mechanics of Materials course, I hardly knew what to do besides add a few trusses in some fun places. After the top tube sheared, my Statics professor saw it and mentioned how it had failed in a perfect 45 degree shear plane. Cal Poly's motto is "Learn By Doing" and I cannot think of a better way to learn about shear planes than to make one, then test it, and see the failure in real time. 

I learned an unbelievable amount about design, fabrication, testing, and failure analysis all because I was there to witness every moment of the Two Chainz engineering lifecycle.

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