Motor swap.
 

Great input everyone! My g/f has an exchange student that will be doing this and I'm helping her get the parts. If you were to swap out the 12v motor for a 24v or 36v one, what other components would need to change (in MetroMPG's set-up)?

FYI, we just grabbed an old exercise bike from a neighbor. Might use that to save on the woodwork (she's procrastinated and it's due ASAP). Also got a free used battery from a parts store. :)

Thanks!

You might want a diode so current can't flow from the battery to the motor. (Unless you want to do what I did: pedal until above X RPM, then flip the switch.)

Also, are you trying to charge the battery? Or just run electronics? If you're just trying to run electronics, I think people tend to use a large capacitor instead of a battery (in between the motor and the inverter). Probably less resistance taking that route.

Also, I'd go with a larger wheel on the generator, or direct drive. The small dia wheel I needed to use to get enough voltage from my 12v motor generated too much heat and friction and started wearing out the tire sidewall.

Friction v. output.
 

Great suggestions. They'll come in handy for version 2.0. :)

So we went back to the parts store and got a new $15 12v motor (from a 1979 Chevy 2wd 1/2 ton pick-up). The pulley was a hollow cylinder of blades and would have cost another $15, so we opted instead for a short length of free tubing that tightly fits over the shaft as a "roller". The motor only has one electrical prong, so we assumed the ground is through the mounting plate. Got a $3 25A-rated switch and 12-gauge wiring from the electronics store, and a $30 160W inverter from the home improvement center. The exercise bike was free and the battery was made last June! Everything went together perfectly.

We like that this set-up turns the motor a bit more than if we used a larger diameter wheel (aka "roller"). Unfortunately, the tubing on the motor shaft is wearing down after only several minutes of cycling. The shaft is round, but with two opposing flat sides (like your D, but with the curved side also ground down) and it does have a small threaded end. What can we use in place of the tubing? How do we determine the correct diameter?

Thanks again!

My little motor also had a threaded end on the shaft. My wheel is the ground down hub from the squirrel cage/blower that you didn't buy.

Correct diameter will depend on what RPM your motor needs to turn to generate the right voltage, say 14v.

I did mine backward: I ground the hub down first, then tested to find out if it was the right size by pressing it against a moving bike tire while it was on a stand, while reading voltage off a voltmeter.

You should start a new thread with pics. I'm sure others will want to see what you're up to.

Received this query via PM:

Here are some pics of the stand. Hope this helps.

I think the bits that helped me avoid chain issues are the parts I called "chainstay cradles" - the small blocks with the angled top that are screwed to the inside of the main uprights.

Here's my version:
http://i28.tinypic.com/2ibls8n.jpg
I decided to make a dedicated unit since I haven't found a reasonably-priced bicycle stand. Now I just need an oscilloscope so I can work on building my own grid tie inverter.

thats pretty cool, did ya make it from scratch or is that an old weight bench or something?

I agree, looks nice! Tell us more about it.

It used to be a stationary bicycle/video game controller. It had a friction band around the big wheel, with a mechanism containing a potentiometer to sense tension. The potentiometer was connected to a special cable that connected to the joystick port on an old PC and has a passthrough for a normal joystick.

I simply removed the friction band assembly and installed a generator. At first, I had some fun "snapping" the wires together while pedaling and watching the sparks. Next, I connected it to a variety of items, including a car light bulb (lit up very well, wasn't very difficult) and my homemade SMD heat gun (hard to pedal, but it did manage to melt solder!). The main problem is that it is a very variable output just like solar panels or windmills (although it is easier to control), so it won't power a regular inverter or many 12v electronic loads very well. Therefore, I'm going to build my own grid tie inverter, but I'll first need an oscilloscope for debugging.

Hi pat -

Sorry I don't have plans for the one I made. Also, this particular generator might power an x-box, but probably not the display (TV).

You can find some by searching Google though: plans pedal generator bike - Google Search