You may be surprised to know that you can use a DC permanent magnet motor as a DC generator.     This product review covers the  Leeson M1120046 14Amp 12Volt DC PM motor.  This motor is capable of producing energy at a rate of 150 Watts at a 12Volt level.  You will soon see a few graphs here showing you details about how many volts you get at for different RPM speeds.

This is a well designed and manufactured industrial grade Motor.  You can find a DC motor for less money, but it would not have the same feature.  This motor allows you to change the bearings when they wear out.   Other motors do not do this.  Also this motor lets change the brushes when they wear out, another nice feature.  

It has many mounting holes which come in handy when you are trying to invent new ways of fixturing.   You can see the extent of the mounting holes by clicking on the PDF file to the right which will give you the manufacturer's mechanical drawings.

I ordered 2 of these motors.  One through McMaster Carr and the other through Amazon.com.  The shipping container quality was good.  The motors arrived with no damaged and well secured in their boxes.   When I hooked them up to the pedal power bicycle generator they started creating voltage immediately with no problem.   Just by grabbing the shaft of the PM motor with my thumb and middle finger and giving it a quick spin, it would create 5 Volts DC on a voltage meter / DMM. 

I took them to to a 2 day show and let over 300 people ride the bike generators at different speeds and the consistently put out 20Watts to 150 Watts the entire show.   More information about the show HERE.

More Details From the manufacture:

http://www.leeson.com:5000/drawings/frontpage/leeson/M1040247.pdf  

(this is a diagram showing all parts of the motor)

 FEATURES FROM THE MANUFACTURER  (LEESON) 

1. Ball bearings ensure positive shaft alignment, increase reliability, and all-angle mounting flexibility.  Preload spring with washer minimizes end play, reduces vibration and noise
2. 380 Alloy aluminum end shields are high pressure die cast.  Mating surfaces are machined for precise alignment and bearing fit, allowing accurate brush tracking and maximum motor life.
3. Brushes are accessible for easy inspection and replacement, without disassembly of motor.
4. UL recognized insulation system rated Class F or Class H.  Copper magnet resistant winding with environmental resistance and high overload capacity.
5. Brass cartridge-type brush holders with constant pressure stainless steel spring for positive alignment of high current capacity brushes.  Provides for "black band" commutation even if reversing applications.
6. Molded commutator  of silver-bearing copper with high temperature, fusion welded connections for vibration resistance and enhanced reliability.
7. Heavy-gauge, painted steel frame for maximum structural integrity.
8. Dynamically balanced armature/rotor for vibration -free, quite performance.
9. Choice of mounting includes foot, face, flange, or thru-bolt styles.