I need a small dc motor for a momentum wheel. To conserve power the motor will be turned off once the wheel has reached target RPMs and left off until the RPMs fall out of the target range. This will require a motor that coasts with minimal mechanical resistance when off. Brushless DC motors seem like a good fit, but the permanent magnets in most BLDC motors have a small attraction to the solid core in each of the windings. I've considered modifying a computer fan BLDC to have an excited rotor, but i would really prefer to get something off of the shelf.
Here's my setup:
Power will be supplied by four AA batteries(6V) and the momentum wheel will weigh at max 100 grams. The motor and wheel will be mounted vertically and i a am looking for RPMs between 4,000-10,000 (the higher the better). Spin up times aren't critical so i have some flexibility as far as torque is concerned.