Chapter 2 – It’s never that easy
The first step is to find a cheap used exercycle. I figured our local throwaway paper, the Nashville Scene, would be able to help out, but a quick check of their online classified ads revealed NO exercise gear category and no obvious matches by just browsing likely categories. Not to be deterred I went to the web site of the only local newspaper, the Tennessean, and checked their online offerings. Right off I could see this would be much easier than the Scene, as the Tennessean divides things into many more categories, and they are easily searchable. I found the section for exercise gear… and no bikes. Out of 12 hits there were 11 treadmills and one uber-gym that cost $80,000 but they’d let go for the sacrifice price of just under $10,000. Shit. This may be a lot harder than I thought. While my assertions about exercycles seems valid, i.e. there are untold hundreds of thousands of them sitting in garages waiting to be thrown away, I may have a hell of a time finding them. I am guessing the cheaper models have so little value that they are not even worth advertising. I may have to find another approach to get one.
Hey, Craigslist! While I have heard about it for years I have never once used it. A friend moving out of town recently made an idle comment about an old 32” TV they didn’t want, to the effect that he’d “just put it on craigslist to get rid of it”. Well, maybe someone wants to get rid of an exercycle! The listings on Craigslist can be sorted regionally, and Nashville has a large number of entries, AND I could find a section just for “sporting goods” where I found various exercise gear… but no bike. I grimaced when I saw a “free stepper” (the stair-climber thing) complete with nice photo, but it does me absolutely no good! Why are there no free or cheap (or ANY) exercycles?!? Shit. While I was at Craigslist I placed an ad in the Wanted section asking for an exercycle for a project to make an emergency power generator, and I also signed up for the RSS feeds for “free stuff” and “sporting goods” in case something comes in. Maybe some Woodstock Yuppy will decide he doesn’t need his old 1978 Sears stationary cycle and would like to contribute to a project that might help lessen our dependence on fossil fuels. I don’t care, I just want a bike!
You know you are desperate when you hit eBay for something you know would cost more to ship that the thing was worth. eBay does indeed have a lot of exercise bike systems, but surprisingly few with a large front flywheel. Even more surprising is that exercycles with massive flywheels are still in vogue, and cost up to $400 even on eBay! Worse, the shipping on some of them is pretty dramatic due to the 40+ pound flywheel. I did find two cool distractions; “recumbent”-style exercise bikes, which might be a lot more comfortable for long term power generation, and “mini exercise bikes” that are little more than pedals poking out of a box the size of the front tire on a child’s coaster bicycle (shown to the right). I am not quite sure how I’d adapt one of those “minis”; either gut it and create a custom generator that fits in the housing (we’re talking winding the coils and positioning the magnets on a wooden disc) or create a gearing system using the gear shifter and front sprockets of a real bike, and run the chain out to the generator shaft. These mini-things can be found for under $100, even under $50, but it seems like too many extra variables for now so I may revisit this once the “full size” version is done.
While not my first choice, I have reconsidered “bike trainers” (shown to the left), metal stands that capture the rear axle and allow the tire to spin against a resistive load. The best ones I find on eBay goes for nearly $300, but there are cheaper units that may goes for as little as $50. I have bid and watched a few, so we will see how it goes. If I get stuck with more than one I’ll just send one to my friend David, who admitted he hasn’t taken out his state-of-the-art mountain bike in months, if not years. It’s a shame we don’t still live in the same town, as I suspect we would both be in better physical shape if we could cajole each other into riding more. :) Anyway, these bike trainers are probably the best idea since it gives me the flexibility of tweaking some of the bike’s parameters, like gearing.
Regardless of how the eBay stuff turns out, and regardless of what style of bike I end up with, I still need a generator. I might as well start that search now, while waiting to see what kind of bike system I luck into.
It becomes clear in short order that the easiest solutions are likely the worst. While you certainly can use an automotive alternator to generate electrical power, they are not a very good fit for this project. They are actually AC devices and have internal rectification to DC, so there is some loss there. They have higher RPM requirements than practical for a human-powered machine unless geared at a pretty high ratio. They also typically have a built-in cooling fan which is totally unnecessary for this project and will do nothing but add noise and reduce efficiency. One day I may get a cheap alternator and see just how bad it is, but for now I think I should stick with straight-up DC motors. They are quite a bit more expensive than a junkyard alternator, but my hope is they will provide a bigger bang for the buck.
Oooh, it’s settled! My co-worker, Wally, just volunteered a 3-phase DC motor pulled from an aircraft. I guess that will be the way I go for the first revision! THANKS WALLY! :)
So, the revised plan is to use a bike trainer frame to hold a conventional bicycle, and drive a DC motor with something like a dryer belt. A belt is not the most efficient method of transferring power since it will eat a little energy in the form of flexing and stretching, but it is likely the easiest to deal with. Of course, we just got finished learning that whatever is easiest is also probably not a good idea, so I have in the back of my head a design that uses a bicycle chain and bike sprockets. As soon as I get the DC motor from Wally I will do some rudimentary tests of the power output and probably some experiments in gearing to get the best power transfer given the best rotational speed for the motor at the most comfortable pedaling speed on the bike. Along those lines I should also acquire the test equipment I will need for all of this, like an optical tachometer and a watt meter. In fact, I need to start thinking about what kind of “dashboard” I might want on this thing, since I want to measure various powers (min, max, average, etc) and times (spent pedaling, system online/offline, etc).
Seems like a good time for the next chapter break.
Chapter 3 coming soon, back to the TOC
