cnc machine - which motor to use: servo or step?

[adnan_merter]

servo or step motor?

hi all!
i am trying to desig a cnc machine, but i have a problem

my machine will be a little big, i mean i need two powerfull motor,
and also they have to have high speed.

please tell me can i use stepper motor?
i want this bcs they can be drived easy and they are cheaper.

i know servo motors are powerfull, speedy and very reliable however they are expensive.

 

[Peder]

Re: servo or step motor?

If you are going to use a stepper motor, you will need to add encoders for the system to know the position of the motor, as there is no feed back to the system from the stepper motor itself.

 

[FvM]

Re: servo or step motor?

Stepper motors are mostly used with a home position reference only, it has to be assured by operating parameters, that they don't loose steps. High speed operation of stepper motors requires suitable motors and high voltage chopper supply for the motors, the effort isn't much lower than for servo motors, I think. Most cnc machines uses servo drives for main axes as far as I know. They can be expected to have both higher torque and speed than stepper motors.

 

[adnan_merter]

servo or step motor?

do you have any idea about how speedy step motors. i mean rpm?

 

[FvM]

Re: servo or step motor?

In a danahermotion databook, I see speeds up to 3000 rpm for 1.8° step-angle motors, but with considerably reduced torque.

 

[~E3016~]

Re: servo or step motor?

you said that you need a powerfull and speedy motor right? then the constraint is the price. but for your request about functionality, the higher price the more you get.

 

[tvthang]

servo or step motor?

Hi,
FvM may be correct, because stepper motor often use with low speed, if you need powerfull and speedy you must use dc motor with encoder (servo). Every thing depend on your application.

 

[nandhu015]

Re: servo or step motor?

Servo suits best for your application.

Nandhu

 

[freakkaito]

servo or step motor?

yes I think step it's not strong enough, step motor not very different with ordinary dc motor, they just have special timing to rotate. I sugest u to use Servo, the price is depend what kind of servo coz the servo prize is depend on the material, and the power.

if you litle bit creative, u can modif the step motor by adding some gear to get the torque higher

 

[gito]

servo or step motor?

I think stepper motor is not a bad idea. You can make it more powerful with motor driver or add some combination gear like freakkaito said, although it will be produce more heat and reduce the speed. You can increase the motor speed if you make bigger the frequency of the encoder changing step. But, because it is stepper motor, you have to allocate 4 pin output for one motor minimum.

Servo is more simple because you only have to allocate 1 pin output for the encoder, actually PWM (pulse width modulation).

 

[Slayerza]

Re: servo or step motor?

Have a look on the web for some DIY CNC. Mostly those guys just use stepper motors, and some of the manufacturers are selling retrofit kits that use stepper motors and not the more expensive servo motors.

A possible advantage of the servo motors would be the resolution. Since stepper motors have a fixed resolution typically 12 steps, and a servo has 180+ (depending on the encoder).

Cheers
Slayer

 

[Norm]

servo or step motor?

**broken link removed**

 

[artem]

servo or step motor?

max speed your machine should move (m/min)?(usual servo based cnc's accelerates till 5-8 m/min speed)
max cutting force needed (Newtons)?(depends on application - 90 200 Newton is quite OK for wood)
The weight of moving Y and Z axis and required acceleration?