Re: [CAD_CAM_EDM_DRO] Re: step/dir inputs to servo controllers

John Hebel wrote:

>But now may I ask questions for whoever wishes to point me down the
>right path. I want to get good finishes and work to .0002 to .0005
>in boring small engine cylinders using a lathe.
>
>I have been thinking that servos (with their necessary encoders)
>would do the job better because the encoder data could be processed
>and produce DRO data. I felt that having the realtime DRO data would
>help me in keeping the process of boring under better control by
>stoping the machine between passes measuring the cylinder and putting
>in new values of Y axis data as necessary. This is sort of manually
>controlling a CNC machine to get the most possible out of it in
>accuracy.
>
>So here are some questions:
>
># 1 Is there DRO like information available with steppers as well
>as servos?
>
>

There are ways to do this. The Gecko drives normally are the only place the
encoders are connected to, so you get no position feedback under manual
mode.
You need to have encoder counters connected to the computer to also read
the encoder signals and provide them to the computer.

>#2 If so what is the source and how is it displayed if it is
>displayed? Is the answer different with different software packages?
>
>

Yes, very few hobby-level packages allow any position feedback. EMC
is the only one I know of that does.

>#3 Since the DC motors have brushes is their life a lot shorter
>than steppers? Also don't the brushes make a lot of electrical
>noise that must be suppressed and filtered?
>
>

No, to both. I am using the original brushes that came in my servo motors
when I got them. I suspect they will last several times my own lifetime.
But, then I'm not running the machine 24/7. Electrical noise from the
brushes has never been a problem. These motors run on very low voltages
most of the time. Gecko drives will likely play hob with AM radios,
but it is the PWM pulses in the drives that is the source of that.

>#4 If DC servos are "better" than steppers would it not be even
>better to use brushless servos and avoid the sparks of brushed
>motors? Does Gecko have a version that drives brushless DC motors?
>
>
>

Sure, it would be better. You can pick up brush motors for $25 - 50

most of the time. Brushless motors often go over $100 used, and cost a
fortune new. Gecko does not have a drive for brushless at this time.
Also, the encoder needs 3 more signals to tell the drive when to switch
windings. The drive ends up doing the work of the brushes. Rutex does
have some brushless drives. DC motors are simple. There are (generally)
just two wires. No head scratching. The encoders sometimes need to
be figured out, unless manufacturer's info is available. There is a lot
more head scratching to be done when trying to hook manufacturer A's
brushless motors to manufacturer B's servo drive.

Jon