Hi,

If am correct brushless ac is a bigger in size but less torque then brush dc servo motor.
Brushless motors have fixed windings around a permanently magnetized rotor, whereas a brushed motor has windings on the armature (rotor)
connected via brushes to the power supply and permanent magnets around the outside.

Both types produce plenty of torque and both are about the same size.

Brushed motors were very common years ago and still work OK, but brushless motors are taking over. The brushes wear out eventually. Second,
there is high current in the rotating armature in a brushed DC motor with considerable heat build up. In a brushless motor the high current is in the fixed windings
and the heat can be conducted away into the servo housing which cannot be done with a rotating armature. On balance a brushless motor should produce more
power for the same heat loss....but there's not much in it., both types are used for spindles.

If you are interested in getting a more powerful motor then you might consider a DC motor out of a treadmill. They often come up second hand pretty cheaply.
They are not common here in New Zealand but they are popular in the US on Ebay. I believe there are two models which are particularly common, one about 1.5hp and another
about 2.25hp.

dazp1976 has a 1.8kW AC servo, I think Lichuan brand, that was very well priced. A few years ago I bought a second hand 1.8kW Allen Bradley AC servo and drive for $600US
for the pair. I still had to find/buy/make the cables and I paid for the set-up and tuning software, but it has made an excellent spindle motor.
I mostly use it in velocity mode, that is the controller provides a 0-10V PWM signal and the servo responds from 0rpm to 3500rpm, its rated speed. Because the velocity loop is closed
by the servo drive the revs don't change virtually at all with load, very handy. I use it sometimes in position mode and then it makes for a good rigid tapping spindle.
Note that it has a rated torque of 6.2Nm and an overload of about 18Nm, so its pretty limited as to what size taps it can drive into different materials. I find that 8mm in steel
is a safe max and 10mm, sometimes 12mm in aluminum. You also need to be VERY particular about the hole size drilled prior to tapping, if you try to drill a smallish hole
resulting in a high engagement, 65%, or more thread then you are heading for disaster. To do rigid tapping well and reliably requires lots and LOTS of torque, more than you
might imagine otherwise it all turns to s....t!

Depending on where you are you may find a good servo and drive somewhere for cheap...grab it, you won't be disappointed, they make excellent spindle motors.

Craig