When I was in my twenties, I biked to the grocery store and to my part time job 3 or 4 times a week, a distance of a mile or more each way with no problem at all.
When I moved back to the country, I turned that old ten speed into a dynamo, with the help of a welder and an old alternator from a Ford Escort. The plan was to never by electricity like a sucker again.
The reality, unfortunately, is that people can't generate much power. Me personally, I can make about 100 watts for about half an hour before I'm wasted. And for every penny I saved on electricity I added twenty dollars to my grocery bill.
Busting my ass for pennies ain't hardly worth it.
Now I'm in my late 40s and I just assembled the second bicycle I've ever bought.
Keep in mind, I walk 5 miles a day without raising my pulse. But today I took the bike for a quick jont to the mailbox about 1/10 a mile away, just to see if I put it together right... and I was so exhausted that I took two aspirins and laid down for fear I was having a stroke!
Biking and walking are Two DIFFERENT THINGS.
20yrs ago, I was looking to make power from pedals.
Today, 25+ yrs later, I'm looking for a way to push pedals with electricity.
The math is compelling.
At my best, I could only produce one or two hundred watts at any given time, an average good workout with the bike was pitifully little, around 50 or 100 watts for an hour. An old car battery holds about 450watts.
Yesterday I pulled a few 12volt motors from the junk cars in my yard (all rednecks have junked cars laying around, don't you know :)
Here's what I came up with.
This is a blower motor out of an old Ford Galaxy.
When hooked up to a 4000rpm drill, this one produced around 10volts, a few volts under 12, meaning that it likely runs at over 4000rpms@12v. Best guess is 4800-5000 if the ratio keeps true (and it should) this is the beefiest of the motors so far, pulling 30watts at no load, suggesting its easily between 250-350watts. Unfortunately, it moves too fast and gearing it down may prove expensive or difficult. One easy solution would be using an worm-gear wench, if I can find one, and hope that it falls into a useful range. They can be made at home by winding wire around a pipe for a screw gear and cutting up a plate, but that's time consuming and if it breaks you're shit out of luck trying to fix it.
Probably the easiest way to go is with belts and pulleys, since wooden pulleys are easy to make and car belts can handle a few horses with no problem. Using a 10" tire to power a cart fixed behind the bike may be ideal, reverse wheelbarrow style . The cart can be made to look like it is being pulled behind the bike and will hide all the potentially illegal 'modifications'.
Math suggests I need a 5" pulley (standard water pump size) for the 10" tire, both of which I already have. That leaves making a pulley for the motor, 3/4". That's too small for a belt to bend around, so it'll have to be 'pinched', which is fine too because it gives me an easy way to add a clutch and gears of my own. I should be able to put 3 to 5 'gears' on a single shaft ranging from 3/4" to 2", giving it a lot of versatility to handle hills and loads. This small, they could be made from fiberglass too.
Pinched, in this use, means putting two tensioner pulleys, before and after, making what electricians call a 3-point saddle if it was made out of pipe. Since we're talking about fractions of a horse, this should be fine.
This is a windshield wiper motor and it turns, after the gearing, at about 12rpm. Ideal for pumping pedals is 60rpm, so, not good but maybe workable. The plan for this one is to bolt on a tall gear from another bike and direct chain it and see what it'll really do. I have my doubts, but you don't know until you know. It also feels under powered, like it might not even be 100 watts which means it may fail all the way around.
By counting the teath in the gear, and knowing that one rev of the screw advances the gear one tooth, the no-load rpm of the motor should be around 700-800rpm. That might put it in a 'direct drive' situation for a 10" tire, but going direct drive is difficult too and would require me to destroy the gear head, something I'm reluctant to do.
Secondly, if I could put its gears on the faster blower motor, it could easily drive the pedals (but I'm not sure it's teeth are strong enough) but that might require a second bike for parts, more expensive and convoluted than is ideal. Simple and basic is usually best, which is why I'm leaning hardest to driving the 10" tire with belts. Belts can slip when things get too tough, instead of breaking, which is a good thing.
My dream is to, step by step, make an RV version of a bicycle for well under a grand, a typical price for a battery bike.
I might be able to pull it off by this fall.