[Marty_Escarcega]

I am going to replace the 140 oz-in stepper motors (driving a 5mm ballscrew with 5:1 reduction) on my Dyna Myte DM 4400 vertical machining center, soon with Baldor MTE3363-BLBCN DC Brush servos. They will be driven by a Flashcut Servo Drive putting out 12Amps continuous with 20Amps peak @ 80VDC

Looking at the specs/torqu chart from the Baldor motors here:
BALDOR DC Servo Motor Tech Specs: Industrial Motion Control, High Continuous Design

The Baldor DC Brush motors have 1000 line encoders.

If I am reading the torque chart correctly, at 80VDC & 12 Amps, the Baldor motors should produce about 27lb-in (or 432 oz-in of torque) @ about 2500rpm.

Since the machine required 900 oz-in of torqe (multiply the original stepper torque of 140 oz-in by 5) then I am wondering if I could get away with a 2:1 reduction?

At 20amps PEAK, the motor should develop about 47 lb.-in (or 752 oz-in) of torque.
Is my math correct? Any thoughts/comments/advice?
Thanks in advance
Marty

[Al_The_Man]

The Continuous torque is 11.25 lb-in at 4.76amps. This is virtually from 0 to 3000rpm.
This is the number you should be looking at, the peak should never be used as a design criteria as you should not go into this area if at all possible, if the peak current is achieved for any lengthy time duration it usually means you have lost control and motor damage can occur.
Al.

[Marty_Escarcega]

The Continuous torque is 11.25 lb-in at 4.76amps. This is virtually from 0 to 3000rpm.
This is the number you should be looking at, the peak should never be used as a design criteria as you should not go into this area if at all possible, if the peak current is achieved for any lengthy time duration it usually means you have lost control and motor damage can occur.
Al.

Al, thanks for the reply, at 11.25lb, the motor develops 180 oz-in. Just a little above the original stepper motor's 140 oz-in. This would still seem to be an ideal servo motor to replace the stepper. And that said, should I leave the 5:1 reduction in place?

Marty

[mike_Kilroy]

....that said, should I leave the 5:1 reduction in place?Marty

by all means YES for not only the torque increase but also for the 25x reduction of machine inertia the motor will see; without it you may have a hard time tuning the servo.

[Marty_Escarcega]

by all means YES for not only the torque increase but also for the 25x reduction of machine inertia the motor will see; without it you may have a hard time tuning the servo.

Thanks Mike. I will retain the 5:1 reduction. Should I expect to see better performance from the servo than the stepper motor?

Marty

[mike_Kilroy]

I didnt pay attention to your servo mfgrs so cannot make guess on if it will be better; most servos will give much better performance than steppers. faster sccel/decels, much higher speed, positioning only limited by the feedback resolution so should be much better than stepper. so yes, should be better unless you got really cheap servo parts, then it may be same as steppers.

[Marty_Escarcega]

I didnt pay attention to your servo mfgrs so cannot make guess on if it will be better; most servos will give much better performance than steppers. faster sccel/decels, much higher speed, positioning only limited by the feedback resolution so should be much better than stepper. so yes, should be better unless you got really cheap servo parts, then it may be same as steppers.

Original post showed them to be Baldor motors with a link to the page. I would appreciate it if you would take a look. I am driving with a Flashcut CNC 12Amp continuous 20A peak Servo drive, 80VDC. The Baldor motor's continuous amperage is 4.7a @ about 2200rpm, peak is 28.5

What I want to make sure of is the pulley ratio. I thought 3:1 was reasonable, but if all we figure is the continuous amperage of 4.7 then the at that current, the motor puts out about 180 oz-in, the original was about 140 oz-in.

Thanks
Marty

[Al_The_Man]

Is there any reason you want to change from the present 5:1?
This would give you 56.25 lb-in continuous torque.
Maximum rpm at the reduction out of 600rpm.
Al.

[Marty_Escarcega]

Is there any reason you want to change from the present 5:1?
This would give you 56.25 lb-in continuous torque.
Maximum rpm at the reduction out of 600rpm.
Al.

Hi Al,
No not really, the machine has an old Dyna Skip control I am wanting to upgrade it. I'm hoping the rapids will increase from the original 100 IPM as well. Most importantly, I want a good reliable machine. Its a quite heavy machine at about 3500lbs, dovetail ways. 14"/10"/14" travels.

Sounds like you and Mike concur and to leave it at 5:1.
Thanks!
Marty

[Al_The_Man]

If it is a 3500lb Gantry, that is a fairly heavy machine for that envelope? If you lower the ratio it will affect your max accel/decel rate.
Your max motion for that motor will be 120"/Min at that ratio.
Al.

[Marty_Escarcega]

Al, it is a CNC Bed mill, like this one:
[ame=http://www.youtube.com/watch?v=x2ZvTu_xF7Q]First run Dyna Mechtronics DM4400 - YouTube[/ame]

[Al_The_Man]

I should have known at that weight!
Were you getting ~3000rpm from the steppers before?
Al.

[Marty_Escarcega]

I should have known at that weight!
Were you getting ~3000rpm from the steppers before?
Al.

Al, I don't know. I got the machine with a dead control. It has 5mm ballscrews. 5:1 reduction. 140 oz-in steppers.I got a nice Flashcut cnc control with 4 axis servo amp. 12amp continuous and 20amp peak. I have 3 of the baldor dc brush servo motors with 1000 line encoders I thought would be a good replacement for the stepper motors.I just want to optimize the reduction for those motors.

Is there a calculation for figuring approximate rapids?

[Al_The_Man]

Have you played around with the Kollmorgen s/w?
Electromate Industrial Sales
The PDF example shows a BP mill.
Al.