Me and my wife have tried to used more renewable resources and cut down our use of electricity. The other day I noticed that my elliptical runs on it's own power. So then the next question was: "How much power is it generating?" Turns out it's about 8.8v when actively running, and goes down slowly from there after you stop. Then I remembered that there were many 9v to USB adapters out there, so I figured that 8.8v was probably close enough for it to work. Turns out anything above 7v works great.

I am not going to go over how to create the circuit itself, as there are many great instructables that do a great job. The following are links that I used in putting this together.

Portable USB Charger (Version 2.0)
Another Altoids iPod Charger
USB Adapter schematics
Another USB Grounding Dagram

Step 1: Test the Power

Take off the control unit and try to figure out which ones are for the power. I just looked for the thickest black wire, then the closed red/orange wire.

Step 2: Build Voltage Adapter

This is where you will need to find the parts necessary to build the adapter circuit. Refer to the links for what you will need and how to build them.

Take note that you will not need the 9v adapter, as we will be connecting directly to the Elliptical's power source.

I tested here to make sure that the thing was working correctly. I had someone hold the volt meter to the output wires for the USB, and I held the input wires to 9v and success!

In addition to the parts above, you will need the following:
Wire splices -- I used some from AutoZone. Probably not the most elegant, but they work...
Hot glue -- What good instructable doesn't include some!?
Patience -- duh.
Work out equipment -- (I used my elliptical but I am sure if your equipment doesn't use batteries or plug into the wall, you could do something like this.)

A loving wife -- at least one willing to let you dig into your very expensive elliptical to save a few watts...
Reebok RL 1500 Elliptical

Donor PII motherboard -- I used this to get the usb (was actually the front usb connectors) and a heat sink for the power regulator.

Throw away USB device -- You will need this to test your setup! ( I used my poopy zune!)

Step 3: CUT!

Okay, so you have to make a hole for your USB port to stick out. I used a power drill to first make two holes side by side, and then a Dremel to round out the edges to that it just barely fit through. Sorry I don't have any pictures of this. I figured that if you can't imagine this part in your head, then you probably shouldn't be doing this project at all. Just saying...

Step 4: Insert and Splice!

Luckily my elliptical was full of space, so there was plenty of room to fit all the components.

I recommend doing a dry run, so you can see where everything fits.
Get your hot glue gun out and glue away! I tried to make it look neat, but that isn't a main concern in this, as once it is buttoned up, it will be completely hidden!

Then splice the power from the elliptical to the wires of your regulator. I like this method as if I don't have to do any unnecessary (read: because I suck at) soldering.

Note:
If you use the splices, make sure that you get the right size. The splices I used fit the cables that i had fine, but did not fit the Elliptical's wires very well. This led to a half-hour of wondering why I was only getting very little if any voltage across them. All I did to remedy this situation was to open the splices back up, and use a box cutter to fully cut the insulation down to the wire so the metal could make contact.