Collin's all wooden bicycle
The bike has 6 gears: 2 with 28 teeth, 2 with 72 and 2 with 21. It weights 71 lbs. The total material cost is about $30 and the bike is now on its 6th set of gears after traveling about 20 miles.
Also here is the link to an article on the bike by a local newspaper http://www.ajc.com/news/lifestyles/avondale-teen-builds-wooden-bike/nRMRc/
I noticed the bike in the newspaper article and YouTube video had a different gear train (see picture at left) and asked Collin about that. His reply:
That was the original design when it had bolts, screws and bearings. The middle gear in the drive train had 28 teeth and the bolt that served as an axle was supported on one side by the outside frame and on the other by a small piece of plywood that was inserted between the gear and then wheel. The large gears eliminate the need for the insert. I added the second drive train as a safety precaution after the single drive train (and my only way to brake) tore up on a hill.
You can see remains of some of the paper gear templates still on the gears.