Re: [CAD_CAM_EDM_DRO] PWM input Servo Amp / Universal Stepper Controller

jess@... wrote:

>Ok I have a question.
>
>Someone posted a link to US Digital on another topic so I surfed over and
>found heaps of stuff about Encoders ie that can be fitted to various shafts
>for motion data.
>
>Here is my question.
>
>Considering the cost of servo motors with encoders is quite astronomical,
>what about a stepper motor say in the hi torque 34 42 NEMA size with encoder
>from US Digital to over come the problem when a stepper loses steps.
>
>

Having an encoder will prevent an undetected loss of position. But, it
won't help a stepper to not LOSE the steps in the first place. When the
stepper
skips a step, it often stalls violently. When a servo gets behind, it just
keeps trying.

Astronomical? I got 2 servo motors with 1000 cycle/rev encoders on eBay
for $27.50, and another one that needed to have a better encoder put on it
for $9.99! My new PWM servo amplifiers will be selling for $100 per
axis. (I may have to come out with a cheaper, lower power servo amp for
the lighter machines.) Note that the torque on stepper motors drops
severely at higher speeds, while the torque on a servo is maintained to the
maximum speed. People use 600 - 1100 Oz-In stepper motors to get
250 Oz-In at rapid traverse speed. A 250 oz-In servo motor will outperform
the 1100 Oz-In stepper in many cases!

>But which controllers and drivers are compatible to accept encoder
>feedbackloop while driving a stepper?
>
>

EMC, using the Dan Mauch encoder card, or my Universal Stepper Controller
are the only way I know of driving steppers with encoder feedback.

Jon