I posted this picture awhile back in another thread......

Here are some motors I have for comparison sake and the continuous torque rating for them. You can see the BLDC motors have much more continuous torque than a similar sized brushed servo. Why do I have so many? Some of these are spares for existing machines and others will be used for not yet completed ones. ALL have been purchased for under $40 each on eBay, most were around $25. The biggest one #12, was only $25 shipped!!! All work and most of them are actually new.

1. Nema17 stepper motor. 76oz-in. Size found in most 3D printers

2. Brushed servo Yaskawa minertia T01l. 13.9oz-in.

3. BLDC servo Parker CM162. 56oz-in

4. Nema23 stepper motor. 286oz-in. Typical stepper size

5. BLDC servo CMC BNL2310. 100oz-in

6. BLDC servo Parker CM231. 46oz-in

7. Brushed servo Clifton. 46oz-in

8. Brushed servo Minertia T06m. 96oz-in

9. Brushed servo Minertia RM-04sa. 59oz-in

10. Brushed servo Electrocraft E661. 140oz-in

11. BLDC servo CMC BNR3312. 198oz-in

12. BLDC servo CMC BMR4445. 722oz-in. Huge motor!!!

Running a servo motor past its continuous torque rating for any length of time will overheat and could damage it, not recommended to do. The 276oz-in stepper motor is pretty small compared to most of the servos and puts out quite a bit more low speed torque than most of these servos do. This is where pulley reduction for servo motors is quite useful. 3:1 or 4:1 reduction will surpass the low speed torque of the stepper motor and give lots more peak torque for machine acceleration.

Most of these motors are rated to spin at 3000rpm or more. Some of the brushless ones go 10k. With 3:1 reduction, you can still spin a leadscrew 1000rpm. A stepper motor torque starts to drop pretty fast when it spins more than a few hundred rpm. Big advantage to servo motors when you need higher leadscrew rpm.