Ok Kai,
I'm using a 24V DC motor with a Mechanical Time constant of 0.15. My driver to the motor is pushing a maximum of 8Amps, more then sufficient for the motor. I'm using an 80C51 micro, generating 11 KHz PWM to the driver. The PWM signal is inverter using a CMOS inverter. My power supply is only 12V; therefore the motor is not running at its maximum velocity. However, it is sufficient for this experiment. In the motor driver, I've used a Darlington MOSFET driven by a NPN transistor. The Collector of my MOSFET is connected to the GND of the motor and the 12V is connected to the +ve end of the motor. When in operation, the motor is drawing 0.04mA from the CMOS inverter. The maximum speed of the motor is approximately 900RPM with the 12v power supply. Since I'm using the compare and capture unit in the 8051 to generate PWM, I have only few frequency selections. I found that 5 KHz is to small for the motor, and 13.3KHz is to fast. So I am currently using 11KHz. I'm just wondering if anyone out there can give me an opinion of what frequency I should run it with.

The above information is to the best of my knowledge. Mr. Taylor has given some ideas of other parameters to look for and I'll try to work them out. I'm sorry Kai if this post have coursed you some annoyance.

jzl