Re: [CAD_CAM_EDM_DRO] servo vs stepper

Steve wrote:

> From: "cdoughtynz" <cdoughty@...>
> >
> > Are servo's better then stepper motors? what are the pro's and con's?
>
> Steppers are stronger when they are going slow (strongest when stopped
> and holding), servos are strongest some where close to their top speed.

Servos produce their greatest POWER near the top speed, that is true.
But, they have 100% of their stall torque available from zero to full speed.

> When
> you get a stepper close to it's top speed it doesn't take a lot of force to
> make it loose a few steps, also unless you build a really nice contrler
> there is a solid 200 steps every rotation, where as the servo 'steps'
> smother. When you are trying to move a servo just a little, IE steping over
> .005, or just want it to hold in place as the other axes moves, it can push
> and may even juggle that axes back and forth as it tries to put it self back
> on location.

A properly tuned servo system will not "juggle" or hunt, no matter what the
speed or distance moved. (Certainly, there have been lots of primitive
and sloppy servos built.)

> If you never plan to move fast, and are building a simple controler, then
> steppers are better and cost a lot less. If you are going top rate on the
> controler then a servo is the same or a little less then a stepercontroler.
> For high speed things servos have it over steppers

Small stepper systems are about as cheap as you can go. Large stepper
systems, especially for Bridgeport-sized machines and above get VERY
expensive. 1/2" computer tape drive motors and such similar surplus servo
motors can be had for a song, while giant steppers can go for many hundreds
of $ on the surplus market.

Jon