Is this realistic?
Hello all! I am a junior in high school, and I am designing a bicycle-powered generator for a science project. The rules of this sub reddit state that I could ask a question about a current engineering project I am working on, so that is what I will be doing.
I've done quite a lot of research on my project, so I hope that this isn't disappointing. Now, I understand that bicycle-powered generators are not new. I want to add something though to my project. In my understanding, no bicycle-powered generator that I've seen is all that efficient. The most efficiency I've seen is 10 watts per second. So, I want to make an extremely efficient bicycle. I know it won't power a house, humans aren't good electricity sources, but I want to create something that, at the very least, isn't laughable. Maybe it could charge a battery. Or a phone. Here is my design. I am currently replacing the back wheel of a bicycle with a flywheel. This flywheel is heavier; thus it contains a lot more inertia. The purpose of this is to keep a steady flow of energy once I've pedaled for about five minutes. Think about it – in the beginning it could be difficult to get the bike going, sure, but after a minute or two keeping the wheel going shouldn't be that difficult. It'll be relatively lightweight. Also, the flywheel helps me got to overall faster speeds. There's only so fast that a regular bicycle wheel can go. A flywheel that is heavier can go much faster once enough energy has been inputted. The generator I am using isn't variable speed, so the flywheel also helps keep a basic speed. I am designing the flywheel so that a chain can be attached. This chain will lead to a sprocket. The sprocket contains 5 teeth. Consequently every time that the flywheel turns one full revolution, the sprocket will turn five revolutions. Because the sprocket is small and directly attached, there shouldn't be much heat lost due to friction. This boosts efficiency. I am also attaching a gearbox that has a 1-7 ratio. Every time the sprocket is turned once, the gearbox is turned 20 times. Thus, every time the flywheel makes one full revolution the gearbox turns 35 times. Pretty simple. I'm attaching this gearbox to a generator, not a motor. You see, if you turn a motor in reverse, that does create electricity. But from some basic research, I have seen that motors are terrible generators. Sure, you can turn them in reverse. However, the design that makes a motor a good motor conversely makes that same motor a bad generator. So I will be using a generator, a pretty powerful one at that. So, here is the math. Let's say that I can only get the flywheel to make 0.5 revolutions per second(worst case). That would mean that the gearbox would turn 17.5 times per second. Multiply by 60(to get rpm, revolutions per minute) and you get 1050 rpm, which is pretty good. My end goal is to charge a battery. Are there any flaws? Am I stupid for trying this? Is this design at the very least commendable and admirable for a high school student?
Submitted July 25, 2017 at 12:43PM by 4tolrman
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