One of the major problems of powering anything by using a human to turn a crank is not the amount of power produced. Rather, it is the rpm band where that power is produced. This is also an issue with any other recriprocating engine, be it steam, gasoline, or diesel fueled. Each has a specific rpm range in which the engine produces a useful amount of torque (twisting force). In a gasoline car engine, the useful power band ranges from around 1,300 rpm to 6,000 or more. Racing engines and motorcycles can make power at over 10,000 rpm. Diesels are a lot more limited, making useful power from 1,000 to 3,000 rpm. Ever wonder why a semi-truck shifts so many times when accelerating away from an intersection? Its because the driving wheels accelerate and reach a point where the gearing to the motor limits any further acceleration by forcing the motor to try to turn faster than it would like to. Too fast and the torque of the motor diminishes. Therefore, the driver shifts to the next higher gear. The motor can again turn slow enough to remain in its power band.

So what's that got to do with kinetics? Well, humans have an extremely narrow power band. An average-sized man can produce around 200 foot-pounds of torque when pedaling a bicycle. BUT, he can only do so by pushing on the pedals very hard. And we all know that you can pedal hard, or you can pedal fast, but not both. At 60 rpm, a human pedaling a bicycle can make more torque than many car engines. But at 120 rpm, a human is maxed out an produces less torque than a leaf blower. So, in order to take advantage of the narrow power band of a human, some enterprising fellow around 100 years ago started adding additional cogs to his rear wheel. And just like the semi-truck (that copied the bicycle), the rider of a 10-speed (or more if you've got 'em) can shift gears to achieve the best combination of rpm and torque.

Now in kinetics, drivetrains often must be more complex than a bike. Especially when a kineticist is attempting to build a craft that is useful in its own way. Maybe it would have 16 people all pedaling. Maybe two people want to pedal side by side, but are of different abilities and need individual gearing and the ability to coast if they want to. One way solve this type of problem is to add multiple bicycle freewheels to a single shaft (a jack-shaft) which gathers all of the power from the various humans, and then channels it into the driving axle via a single master-chain. But, freewheels are designed to work on bicycles, not jack-shafts. In order to get one part to mate with another, you'll need an adapter.

A freewheel adapter could be made by machining steel in a lathe. That would be the right way. But as kineticists usually aren't machinists, we must improvise. So lets say you cut the axle out of a rear bike wheel. Then you cut off its left side and center with a grinder. Now you've got a chunk of metal that a freewheel will screw onto. Good. Assuming you took out the wheel's axle and bearings before you hacked at it with the grinder (you did, right?) you can now drill out the resulting hole to the correct diameter for your new jackshaft. To keep the chunk from spinning on the shaft, you'll probably need to weld a nut to the side of the chunk where it was cut off. This is the inside edge of the right hub flange, for you bike-geeks. Assume now that you've just done that. Looks good. You bolt it together and try it. After a few minutes, your adapter is slipping on your shaft. It gets worse, and then fails completely. What went wrong?

Tempering. No, not yours, the adapter's. Bike hubs are made of steel that is hardened by heating and rapid cooling. Ditto on nuts and bolts. When you welded one to the other, you heated the metal hot enough to undo that process. And if you didn't retemper the steel, it won't be hard enough to withstand all of the force that will be applied to it. The threads will tear right out of your little adapter and make a real mess of your day. So how to you retemper the steel? Rapid and controlled cooling. With what? How fast? Well, that is subject to reading, learning, and experimentation. Getting it right means your kinetic super-recycled bicycle transmission will withstand the event. Getting it wrong means you're gonna have to get off and push.

So get out there and start experimenting. On kinetics day, we'll see how well you do.

Dr. (scott) Diabolical

Two fanatstic opinions which I have no idea about. I read it and by the end, I have no idea what you guys are talking about. This is what drives me to compete in Kinetics. I have stumbled upon a paddle wheel that works quite well for me and stays within my budget. I am quite limited to my construction abilities, with only 2 power tools to my name. Back in 2002, I made a 4 foot paddle wheel that has stood the test of time and mud. The funny thing is my paddle wheel is a one to one ratio. No Gears, no free wheel, no bearings, no engineering points here. The proudest day of my life (yikes) was in 2003 when my craft was 4th across Boulder Res. Now, I dropped down to 23rd place over the land, but its a start. Since then, I've redesigned a lighter paddle wheel which still needs a little work but holds true to my one to one ratio gearing. Nothing but metal on wood and lots of friction. Now with that in mind, who wants to help me this year.

I was wondering if anybody else thought of doing a similiar theme this year: "WHEN PIGS FLY (OR THE SWINE FLEW). Yuck-yuck !!!

Twinkieman (in pigs clothing)

Elliot,

About those machined adapters... My best info. leads me to believe that they are threaded for a bmx style single-cog freewheel, which I seem to recall has a different thread standard than that used on most 5-7 speed freewheels. Am I right about this? I've been looking at http://www.bikepartsusa.com/cgi-bin/category.cgi?&category=bicycle%2Dtrike%5Fparts&start=0

Assuming you're following me on the design of the jackshaft, which would be from left to right: freewheel, chainring, freewheel, and I want to use 5/6-speed shimano style freewheels, would the 15mm shaft, bearings, and adapters be the way to go? At this point, my weldments are pretty ugly and I'm only using a 1/2" jackshaft made from a threaded rod. Dunno how long this setup is going to last. I'm also planning a much bigger and heavier craft for next year, maybe even to compete in CA. So I'll be looking for a much more robust design for the future.

Thanks,

Dr (scott) Diabolical

PS: Don't sweat it Twinkie. I've already screwed up my best chainring by welding on it. Looks like a Pringle. Shoulda known better. Plan B involves the use of an old circular saw blade and several bolts! Ugly, but I think it'll work.