Newbie- Which values are important when choosing the right servo motor?

[Zeta-Phoenix]

I am wondering which torque value is the most important when choosing a servo motor; peak or continuous? How do these compare to Stepper torque ratings?

I am wanting to know if some Panasonic MUMS022A1 servos would be powerful enough for a retrofit to a Sieg X3 or similar.

Short specs:
Cont.torque: .64Nm (~90 oz-in)
100v AC @ 1.6A
3k rpm
2500 cnt encoder.

I ask as for most stepper conversions, they use around 300oz-in steppers. Would these be worth much for my plans?

Thanks!

Update:
According to: http://sysdoc.doors.ch/PANASONIC/AAD1000CE97.pdf
Peak torque: 1.91 Nm (270 oz-in).

[Bubba]

Zeta,
My opinion of "peak" torque is the figure is useless! This is a thou shalt not exceed value that will guarantee letting the magic smoke out! Use continuous torque ratings as your design value. You get the needed torque to do your design by speed reduction of the servo to the shaft by means of timing belts or other recognized means. Remember, the torque value specified for steppers is the "holding" torque at 0 rpm. It drops off after that and you need a spec sheet to know what it will do at the rpm that you need.


In an attempt to ans. your question about those servos, I would say a qualified YES. What is the max rpm you want the lead screw to rotate. Then take 3000 x .8 (Mariss recommends pushing to no more than 80% of max rpm) = 2400 and divide that by the desired max rpm and this will give your reduction factor. There are many variables to consider here such as the pitch of your lead screw, the load you will be required to move etc. This is why I say qualified. Then you can multiply the 90 oz-in by this reduction to see what your effective power will be at the lead screw!

[Xerxes]

Bubba,

Peak torque is very useful and it is really riskless if drive is smart enough not to burn motor with it. It is wasteful and expensive to size motor so that you never use the peak torque range.

For at least 90% of CNCzone machine builds a 100W servo motor would be sufficient. However, for some reason most people want to pay for 500-1000W motors which would make even a machine weighting tons to zip in target positions in a blink of an eye (like the fastest industrial machines).

Zeta: that motor is good for such retrofit. Depending on ball screw pitch, you may use it with direct drive or, say with 1:2 reduction.

[Zeta-Phoenix]

Both of you, thank you very much for your reply's. I had the same feelings, but wanted to hear it from others.

-Jon