Re: Basic Servo Motor Question...

The circuit board on this suplus servo motor assembly has 8 unmarked
connection pins?!? I attempted to guestimate the number of slots on
the encoder wheel and it looks like there are close to 360. I doubt
I
will be able to use the existing encoder on this motor because there
is no way I can tell what it really is. I assume I could buy a
quadrature encoder and just attach it to this servo motor... is that
correct? If so where could I find one. I also found a new
6v/1000RPM
tach at the suplus store for $5...

Thanks
- Dan


--- In CAD_CAM_EDM_DRO@egroups.com, "Mariss Freimanis"
<geckohall@h...> wrote:

> Dan,
>
> A quadrature encoder gives direction as well as speed information.
> You can recognize them because they need a minimum of 4

connections;

> 2 for power and the channel A and B outputs. Often there is a fifth
> connection which is called an index output.
>
> 1) The best situation is if the stall torque is listed.
> 2) Next is if the stall current or armature resistance is listed.
> 3) Last, no info except fo no-load speed.
>
> For (2) multiply stall current by rated voltage and divide the

result

> by 4. That will be the motor peak power output in Watts. Re-arrange
> Eq. 3 so it reads S=5407*W/N. Make W your above-calculated Watts

and

> N your no-load speed in RPM. S will be your stall torque in oz-in.
>
> For (3) you need to accurately measure the armature resistance.
> Divide the rated voltage by your measured resistance to calculate

the

> stall current. Use it in (2).
>
> Your applied torque would have to be worked out knowing what will

be

> the maximum force you expect you will need at what maximum speed.
> From this calculate the mechanical watts required to do this work.
> This will be what your motor has to deliver as continuous power.
>
> You can use a tachometer to measure a motor's no-load speed. Some

RPM

> ratings are at rated load. It will be less than no-load speed.

Unless

> it explicitly says "no-load RPM", you may wish to check.
>
> For the last question, I have no idea or experience.
>
> Mariss
>
>
> --- In CAD_CAM_EDM_DRO@egroups.com, djr@n... wrote:
> > Mariss,
> >
> > Thanks for the reply. What is a "quadrature" type encoder? How

can

> I
> > tell if the surplus motor has it? The line count (if you mean
> number
> > of slots in the wheel) is about 500 from memory... it has very

fine

> > slots on about a 3" wheel (from memory). I will take a picture or
> > two
> > of the motor/encoder and post them. I looked at post 9342 and

have

> a
> > few questions... You give the following formula:
> >
> > W=(1 – T/S)N*T/1351.8
> >
> > What is the best way to measure torque applied (T) and stall

torque

> > (S)? Is there a device to help me do this? I imagine no-load

RPM

> is
> > the RPM rating on the motor.
> >
> > How many watts should I shoot for when considering the sherline
> mill?
> >
> > Thanks
> > - Dan
> >
> >
> > --- In CAD_CAM_EDM_DRO@egroups.com, "Mariss Freimanis"
> > <geckohall@h...> wrote:
> > > Dan,
> > >
> > > If you are planning to use a STEP and DIRECTION input DC
> servodrive
> > > then a tachometer is not necessary. It will derive all PID
> > > information from the encoder.
> > >
> > > It sounds like you have a good motor there. Make sure the

encoder

> > is
> > > a "quadrature" type. What is the line count?
> > >
> > > Regards to what you can get out of the motor; please refer to
> > message
> > > #9342. It goes into a little detail on that subject.
> > >
> > > Mariss
> > >
> > >
> > > --- In CAD_CAM_EDM_DRO@egroups.com, djr@n... wrote:
> > > > I want to jump in head first in a CNC servo sherline mill
> > > conversion,
> > > > but I am really ignorant when it comes to DC servo motors and
> > > > drivers.
> > > >
> > > > I see that some servos have slotted encoder wheels with

optical

> > > > detectors and/or tachs and/or brakes. I can see what the
> slotted
> > > > wheels and brakes do... the tell position and stop the thing,
> but
> > > > what
> > > > is the need for tachs? Can't you tell position AND speed with
> > the
> > > > optical detectors? What motor stats are important for me if

I

> am
> > > > going to use a servo motor with the sherline? Does stall
> current
> > x
> > > > volts (watts) tell me something? What RPM range is good?
> > > >
> > > > I was browsing a local surplus store this past weekend ran
> across
> > a
> > > > servo motor with one of those slotted wheels and an optical
> > > detector
> > > > circuit board attached still in the anti-static wrap. It was
> > made
> > > by
> > > > Japan Servo and it's rated at 24v 3000 RPM. It is about 3"

in

> > > > diameter and 5" long. I don't have any other data on it. How
> > can
> > > I
> > > > determine if this motor is a good candidate for the sherline?

> At
> > > 12
> > > > volts it really seems to have a good bit or torque.
> > > >
> > > > Thanks in advance for any answers... Pointers to "servo CNC
> > motors
> > > > and drivers for dummies" websites would also be great!
> > > >
> > > > Thanks
> > > > - Dan