Question for you engineers:

[garote]

How would I go about building a bicycle-powered usb-charger? The online resources look pretty sparse so far...

Edit: This project looks like almost exactly what I'd want, but I don't really have the electrical engineering talent to build it...

Comments

[robocowboy.livejournal.com]

The great thing about a permanent-magnet motor is that it is also a generator.

Apply a voltage and the motor spins!
Spin the motor and it makes a voltage!

At the bare minimum, all you need to do is hook a motor up to a USB cable... but it's not always quite that simple. Your device probably expects a specific charging voltage and can only handle up to a certain charging current.

So really what you'd need is:

motor -> capacitor -> voltage regulator -> resistor -> usb cable -> device

- the motor makes the juice
- the capacitor smoothes out the voltage and stores charge when you slow down
- the voltage regulator puts out a constant voltage as long as the input exceeds the output
- the resistor limits current (if necessary)
- the usb cable connects to your device and away you go

Looking at that project you linked, it is fairly similar to what I have described...

[robocowboy.livejournal.com]

Looking at that project you linked, it is fairly similar to what I have described...

... but more complete

[thegoodreverend.livejournal.com]

MAKE had a similar project a while back, available here.

[garote]

Yeah, I ran into that earlier, but I didn't like his design... I was/am hoping to find some kind of generator unit that's a little more customized to a bike. Driving the generator by a wheel leaning onto the inside rim of a bike wheel could get complicated if the wheel is even slightly bent, and would also generate additional friction. The belt-drive approach gets around those issues, but it requires that the generator be at a horizontal angle - and that seems harder to place on a bike.

Recently I saw some interesting looking bikes in a bike shop - each had a generator built into a housing on the axle of the front wheel. But those were wired directly to little headlamps, and looked waaay underpowered compared to what I could get with a different design...

[garote]

If I was able to get the parts to do something like this, could you give me some pointers on assembling the circuits? (I'm kind of a slob with a soldering iron...)

[robocowboy.livejournal.com]

Well... it works in my head. Never made anything like it, but I understand the theory.

[headless-chickn.livejournal.com]

There are a number of generator powered bike lights out there, but (afaik) they all work as you described above... a roller mates with the side of a rim & drives the generator spindle. I think these have fallen out of fashion in recent years due to the availability of high output LED lights, but they're prolly still out there. No idea of power output, but splicing in a mini-USB plug oughtta be a 10 second job even for a sloppy solderer.

As you point out... a belt / chain drive off of the crankset would be far more efficient, but how would it work? It would require customization of the drivetrain / frame yesno?