Hi Sir
           I want to ask a few question. I want to change my old Anilam 3000M CNC machine to Mach3 control machine. I want to use products from Machmotion Mill kits Teco. My anilam has DC brush Servo Motor with rated torque 31 inlb (3.5 Nm). So I consider I will use Teco 30 in/LB Class AC Servo Motor & Drive. The rated torque from machmotion is 30 in/lb Class (3.389 Newton meters) (480.0 oz/lb). So, I think this motor and drive is suitable for me. But I find the specification for this motor from Teco home site. The rated torque is different from machmotion site. The rated torque is only 2.391 Nm. The max torque is the same from both sites. The max torque is 63.4 in/lb (7.164 Newton meters) (1014 oz/lb). Can I use this motor for my CNC machine. I asked machmotion this problem. They reply like this:
        
        "That is a typo on the web site, the motor is rated at 2.391 Nm, but we call it a 30 inlb class because it's performance is much greater than the old DC brush motors.  If you have DC brush motors rated at 3.3 Nm continuous I would replace that with an AC brushless motor rated at 2.3 Nm because the max torque rating is normally much higher on the brushless motors.  The max torque on the 30 inlb class motor is 7.1 Nm which is 62.8 inlb."

         So, I want to know about the different between AC and DC Servo Motor. Is it really AC motor have greater performance than DC? Moreover, can I use this motor for my machine. I can't use larger motor and drive because of price. Please explain and answer my question. I am worried about this problem because I am a newbie in CNC conversion. I worry that I cannot use this motor with my machine after I have already bought. Thank......

                                                                             High Tech Key

What matters in choosing a motor for a job is its continuous stall torque. So if the continuous rated torque is less than required for the given application, the motor is not suitable! Unless you are willing to compromise on the continuous power you axes can deliver I wouldn't choose that motor.

It is true that AC servos outperform DC servos, but NOT in the sense you can operate them continuously at their peak ratings (or anything higher than the continuous ratings). AC servos usually have higher peak ratings than DC ones, and they can operate for longer times at their peak ratings, but by no means continuously!

Daniel

Thank for your reply. Machmotion recommends me it can be use. Is it possible with slow feed rate with this motor while machining?

I don't think I understand your question. Your limit is not the speed, but rather the continuous torque. An AC servo can practically deliver almost constant torque throughout its whole speed range.

I am not saying you can't use that motor, but simply that by using it you'd reduce your machine's axes power rating. You'll still be able to cut most of the things you have been doing so far. But if so far your machine's limit was for instance 30mm diameter face mill with a 5mm depth of cut, with the new motor it is going to be 3.4mm depth of cut. If that's fine for you then I guess you can use that motor.

Daniel

Another factor in the difference between DC Brushed  and AC or DCBL  servo, Torque being equal, is the motor inertia, taking the windings off the rotor and placing them on the stator reduces the rotor inertia considerably, these factors are taken into account when sizing.
http://www.yaskawa.com/site/dmservo.nsf/(DocID)/NKOE-7TKLD2/$file/PR.DN.01.pdf
http://www.ormec.com/Services/ApplicationsEngineering/ApplicationNotes.aspx
Nosmo.

Thank for reply my problem