Re: [CAD_CAM_EDM_DRO] Re: GeckoDrives.. Can anyone Help?

cadman@... wrote:

> --- In CAD_CAM_EDM_DRO@y..., "William Scalione" <wscalione@n...>
> wrote:
> >
> >
> > Also, If you have not allready bought the stepper motors, comparable
> > size servo motors with encoders can be had for less than stepper
> motors
> > if you look on ebay. I bought a couple of good size servo motors
> with
> > encoders
> > on ebay for $25.00 each.
>
> I thought that a servo motor was just a stepper with an encoder on it.
> Are you telling me they are different? I have not purchased my
> steppers or servo motors yet.

No. Completely false. A servo motor can be one of three basic types.
The oldest ones were brush-type DC motors (either wound-field or
permanent magnet). Later, there came brushless DC motors, which have
permanent magnets in the rotor and generally a 3-phase stator winding.
These motors are very similar to the ones in DC fans and the spindle
motors on computer disk drives. Finally, there are AC servo motors, which
use an induced rotor field, very similar to AC induction motors. In fact,
these motors are extremely similar in design to a 3-phase AC induction
motor. Mostly, lower rotor inertia and better cooling are the only
differences.

So, steppers are totally not interchangeable with servo motors of any
type, and totally different drivers are needed for the two. There are
some servo drives that can accomodate several types of servo motors,
others will drive only one type.

>
> >
> > I bought 1 Geko G340 and use it on my Z axis. The difference between
> that
> > and
> > the stepper motor that was previously there is amazing. I would
> never go
> > back to
> > stepper motors. I can't wait to get two more for the X and Y axis'.
> IMHO get
> > the
> > G340 drives if you can.
>
> Are you saying that if I purchase the G340 I have to use servo type
> motors?

Yes.

> The only thing that I have from my first project that I will
> use here is "CNC-PRO" software. Will CNC-Pro work with the G340?

If it will work with the stepper versions of the Gecko, it will work
with the servo versions, such as the G340.

> Also what size servo motors should I be looking at to power a
> Drill/Mill on all three axis? Do you also suggest a pulley system or
> to hook them straight to the lead screw? If a pulley system is best,
> what ratio do you use?

This gets complicated. There are concerns with maximum travel speed
required, the leadscrew thread pitch, encoder resolution, maximum
linear force needed to oppose cutting forces, maximum acceleration
required, total mass of machine table, vise and workpieces. A few
hundred Oz-In. peak should be fine. I'm using 1/8 Hp (continuous)
rated servo motors on my system, and it seems fine. (I had worked
out the Oz-In on that, but I don't remember it at the moment.)
The pulley ratios are determined by the rest of the constraints. They are
fairly easy to change later, if you are not satisfied. If you need more
torque, gear it down. If the top speed is too sluggish, but you have
plenty of torque, reduce the reduction ratio. Most servo motors
are designed for high speed operation, so a fairl high beld reduction
ratio matches them well. If you can get low-speed motors (motors
from 1/2" computer tape drives that mount the reels directly on the
motor shafts are good for this) they will need less reduction.

Jon