I have had a huge problem trying to control a NEMA 23 Unipolar Stepper Motor 3.6 V, 2.8 A. http://www.mpja.com/Stepper-Motor-NEMA-23-36V/productinfo/17456%20MS/ I bought a bipolar stepper motor controller driver to my arduino Mega and I can't seem to find a unipolar driver. Does anybody have any recommendations?
That is a six lead motor, so ignore the center taps (leave them unconnected) and use it as a bipolar motor.
There presently aren't any hobby-type motor drivers than can handle the maximum current of 2.8 amperes/winding. However, you can operate the motor at lower torque by using the DRV8825 motor driver from Pololu.
Carefully follow the directions on the product page to limit the current to 1.5 amperes/winding.
Have a look at stepper motor basics
If you have a 3.6V 6A supply and 4 power MOSFETs you can drive that motor unipolar, but you won't get much speed from it - the torque will drop off with rotation speed very sharply.
For a low impedance motor you normally only see 4 or 8 wire versions since they are driven with a chopper driver (8 wire allows two different impedance configurations).
So a question - what maximum speed are you wanting? If in the 1000's of rpm then you have no choice, chopper driver from high voltage supply (24V or more). If a couple of 100rpm then you may be able to use the motor unipolar.