Upgrading to a BLDC motor

A project log for Rockwell Milling Machine Rebuild

Rebuilding a Rockwell 21-122 Horizontal/Vertical Milling Machine

polyfractalpolyfractal 05/01/2019 at 20:330 Comments

I recently decided to upgrade the motor on my Rockwell mill.  The existing motor is a 3/4hp induction motor and it's OK... but has a bent shaft and mismatched step pulley. I'm upgrading the motor to use a 4kW brushless hobby motor, which is roughly 5hp peak. Realistically, I expect around 1kW continuous (1-1/3hp). I chose a BLDC over VFD induction drive because A) I had the motor on hand, B) they are generally more efficient and power dense...and C) brushless motors are fun :)

In this first part I mill out the motor mounting plates and struggle to drill/tap some stainless pipe. Many broken taps and drills later I have the mount roughed out, ready to start mounting electronics.

The motor is a 192kv Turnigy Aerodrive brushless hobby BLDC. Rated for 48v and 4kW, it's max speed is ~9000 RPM according to the manufacturer.  After running the numbers, it likely comes out a bit closer to 2600W and 7300 RPM.

BLDC torque is theoretically around 3.5 Nm, while the original induction motor is near 2.3 Nm.  So it should, theoretically, be a bit more torque in a smaller package even after a healthy de-rating of the manufacturer specs