davintosh

A couple of weekends ago I bumped into something online that made me dig up some sketches I’d made years ago (1985 or ’86 I think). Back then I was wanting to build a record-breaking human-powered speed machine. I reasoned that the pedaling action on standard bikes was less than efficient, but the rowing action would allow the power of the legs, back and arms to work in unison to generate the horsepower to scoot along at much higher speeds. Of course, in rowing there is a return stroke that nullifies some of the efficiency gains, but I think that putting the back and arms into the mix more than compensates for the momentum loss in the return stroke.

Back then, the incentive for the project was a contest promoted by a magazine (can’t remember which) that offered a $10,000 award to the first person who could hit and sustain 60mph in a human powered vehicle. Being newly married (or about to marry… Can’t remember exactly), and about to quit my job to start college, that cash would’ve been great seed money. Unfortunately, life got in the way, and the prize money was claimed long before my ideas even got off my sketchbook.

I still think the rowing motion has a lot more potential for speed than pedaling, and I’d still like to revive the idea and build a row-powered bike, just for fun. Digging around a bit online led to the realization that my idea is not original, and others have actually built such creatures, some being mass manufactured & marketed. Of course, some embodiments of that idea are better than others, and some are just downright screwy. One of the better ones that Google brought to light for me is the VogaBike. This machine is truly brilliant. The Italian geniuses at VogaBike seemed to have come up with dead-simple solutions to a lot of the problems that I had encountered in trying to design a row-powered bike.

So slick I just might have to borrow a few of their ideas. 😉

One of the biggest problems that I could foresee with a two-wheeled version of a row-powered bike is the moving seat; With rowing machines, sculls & most row bikes, the feet are stationary and the seat slides on a set of rails. I wondered if a two-wheeled bike would be stable with the weight of the rider continually shifting back & forth between the two wheels. The VogaBike eliminates this potential issue by making the seat stationary and putting the footpegs on sliding rails with a pulley at the extreme forward end of the rails. A cable anchored to the frame loops through a pulley on the pull bar, then through a pulley on the foot rails, then back to a reel attached to the left side of the crank; as the cable is pulled from the reel the power is transferred to a standard set of bicycle gears on the right side of the bike. Truly genius.

From looking at the VogaBike design, I think there are some efficiencies that can be gained by creating a mechanism to allow the pulley on the pull bar to be moved further up; that would allow each stroke to pull more cable through the system at a higher speed, spinning the drive train a little faster. Another thing that would allow a faster spin in the drive train is decreasing the size of the cable spool, or increasing the size of the chainring. In the photos available on the VogaBike site, the spool is considerably larger than the chainring; looks to be about a 2:1 ratio between the two. Reducing the spool size or increasing the chainring size would allow a shorter amount of cable to turn the crank one revolution, resulting in a larger length of chain to be drawn across the chainring. In the videos of the VogaBike in action, the riders seem like they’re hardly working at all to keep the thing moving; rework a few of these things and a little effort should yield some good speed.

Another brilliant detail on the VogaBike is the steering mechanism; the handlebars do the steering, using a simple mechanism of a rod connecting the fork to the steerer tub. A small bolt keeps the steerer end of the rod level with the pivot point of the pull bar.

It looks like they used a pair of bungie cords to wind the cable back onto the spool, which explains the unconventional placement of the bottom bracket. Hmmm… And the spool likely has a spiral groove in it to keep the cable from wrapping on top of itself.

Patent Pending? I don’t think they’ll mind me borrowing a few ideas, as long as I don’t put it into production.

I’ve always wanted to ride the RAGBRAI; any bets on whether I can put this together in time for the 2008 ride?

This entry was posted on Tuesday, July 31st, 2007 at 1:20 am and is filed under Bikes, Cool Technology, Fun!. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.