Some BLDC motors have hall effect sensors built in and the signals are used by the driver chip to regulate speed, etc. I have a blower from a CPAP machine (from American Science and Surplus) that cost $9 that has a 3 phase BLDC with 3 hall effect sensors. I have seen driver chips for this type of motor that use the hall effect sensor signals as feedback to start up the motor and control the motor speed. I have driven that blower open-loop using a model airplane ESC (about $8 for a 25A Turnigy ESC) and a servo tester (another $5). It seems to me you could grab one of the Hall effect sensor signals and use it to monitor motor revs/speed, and use a uC to provide a PWM signal to the driver chip.
Every cheap BLDC motor I have seen is designed for very high speed (model airplane and helicopter props, fans, etc.). I wonder what happens to torque when you run at the very low speeds 3D printers typically use.
Here is video of an ESC driven blower running open loop at 12V and about 5A (this one has no Hall effect sensors): [vimeo.com]
The blower is 80mm diameter.
Every cheap BLDC motor I have seen is designed for very high speed (model airplane and helicopter props, fans, etc.). I wonder what happens to torque when you run at the very low speeds 3D printers typically use.
Here is video of an ESC driven blower running open loop at 12V and about 5A (this one has no Hall effect sensors): [vimeo.com]
The blower is 80mm diameter.