Questions About Changing From Steppers To Servos

[Brenck]

Hi all,

I currently building another machine,I had steppers before I use KelingINC 640ozin steppers with gecko 203v. This machine I was considering using the same if I was to use steppers. It's a column type, metal working machine, wood or other materials wont even get close to it.

Reading about Steppers vs Servos I've noticed that basically steppers are better for low speed aplications.

Disconsider the advantage that servo are closed loop system for now...

G203v has 10 microsteps so thats 2000 steps per rev, it would be same as a 500 cpr servo encoder, so resolution would be the same...

If steppers work better at low speeds, I am considering using a high lead ballscrew, like 20mm or maybe 16mm. Well lets consider the 20mm for now, at 600 rpm ( witc its low speed for stepper ) I would have plenty of torque left more then 20nm, and a speed of 12000mm/min, resolution will be 0,01mm that is ok for a home machine I don't believe home metal working machines do better then that, thats (0.0004'')

So after all what is better buyng a high lead ballscrew or a servo system? Or I'm just thinking wrong...

Also what servo is equivallent to a 640oz in stepper. Like if I was to change it from one to the other.

Thank You all

[Zappautomation]

While the theoretical resolution of a stepper is 2000 steps per rev running at ten steps per step, it is infact not a good comparison.
First off, a stepper motor is not linear between the full step position, so you can only really rely on the full step position, so i would say it is still only 200 steps per rev, and this would mean a resolution of 0.05mm with a 5mm lead screw.
Also 600 RPM is not considered a slow speed for a stepper and would be at the high end for a nema 34 motor.
Dont forget a stepper motors performance is totally dependant on the driver and the voltage and a 640 Ozinch stepper motor is 640 Oz inch at zero speed (Holding torque)
What you need is the torque curve of the motor that is matched to the driver you are using and same voltage, and this will give you an idea what to compare it to, but servo's and steppers are totally different and a servo will accelerate to max speed very quick, while a stepper will take a lot longer.
If i could i would go servo every time.

Originally Posted by Brenck Hi all, I currently building another machine,I had steppers before I use KelingINC 640ozin steppers with gecko 203v. This machine I was considering using the same if I was to use steppers. It's a column type, metal working machine, wood or other materials wont even get close to it. Reading about Steppers vs Servos I've noticed that basically steppers are better for low speed aplications. Disconsider the advantage that servo are closed loop system for now... G203v has 10 microsteps so thats 2000 steps per rev, it would be same as a 500 cpr servo encoder, so resolution would be the same... If steppers work better at low speeds, I am considering using a high lead ballscrew, like 20mm or maybe 16mm. Well lets consider the 20mm for now, at 600 rpm ( witc its low speed for stepper ) I would have plenty of torque left more then 20nm, and a speed of 12000mm/min, resolution will be 0,01mm that is ok for a home machine I don't believe home metal working machines do better then that, thats (0.0004'') So after all what is better buyng a high lead ballscrew or a servo system? Or I'm just thinking wrong... Also what servo is equivallent to a 640oz in stepper. Like if I was to change it from one to the other. Thank You all

[Brenck]

O so basically the ''fixed'' position on a stepper is just the full step...

What about what servo to choose? If I have a system running a 640ozin stepper, how many watts servo should i choose?

Thank you

[Zappautomation]

It is hard to say without having the details of the motor, but if we presume that the motor is similar to the motors we sell, then at 600 RPM you will get about 2nm, so this works out to be 125W @600 RPM.
So look at a 400W motor and use a 2:1 ratio with a belt and pulley.
That will give you about 2Nm at the 600 RPM, but far better dynamic performance.
Don’t forget the 2Nm that the stepper will give you is the maximum before it will stall, with a servo motor you also have the peak torque that you will use to accelerate and de-accelerate.

Originally Posted by Brenck O so basically the ''fixed'' position on a stepper is just the full step... What about what servo to choose? If I have a system running a 640ozin stepper, how many watts servo should i choose? Thank you

[Al_The_Man]

Originally Posted by Brenck O so basically the ''fixed'' position on a stepper is just the full step... What about what servo to choose? If I have a system running a 640ozin stepper, how many watts servo should i choose? Thank you

Look for a min 640oz-in stall torque servo, you may find it may go into a larger NEMA frame size, however.
Al.

[Brenck]

But everywhere I look servos come in Watts... No oz in = (

[Zappautomation]

Watts is power and Oz inch is torque.
Most servos outside of the US will list the torque as Nm.