brushless motor RPM?

[supak111]

What controls the RPM of a brushless motor? Like the high rpm R/C car motors or computer fan motors?

I get that computer and RC cars driver can control the speed but whats to prevent the RPM of such a motor from going out of control if you just connect such a motor straight to a power supply?

My understanding is: hall sensor drives a transistor which energies the coil at the right moment. So basically can I get a PC fan that normally runs at 2000 rpm max and make it spin 4000 rpm but just increasing the voltage? (if the transistor & hall sensor are rated for higher voltage that is)

 

[Harald Kapp]

A brushless DC motor is a synchronous motor. you need a controler to generate the right sequence of control signals. The motor will turn in sync with the control signals. That is how the RPM are set.
As long as the motor is not overloaded, of course.

 

[BobK]

If the motor is simply sensing the position with a hall sensor and activating the proper windings that way, it will act just like a brushed motor. The speed will be a function of the voltage applied and the load.

Bob