Re: mill servo conversion ?'s

I'm not sure that the model number is E660. These look to be the
motors offered in this auction:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3830503711&indexURL=0#ebayphotohosting

There the moddel number is 0660. Not sure who the error belongs too. I
would also be interested to hear more about these motors if anybody
has any experience with them or other knowledge about them. Namely,
how do these compare to the 600 in oz Ameteks offered at camtronics,
what sort of power supply would they require, and where would one
acquire such a power supply.

I suppose I'm not really interested in the latter questions if the
motors don't compare favorably with the servos from camtronics.

cheers

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
> aschoepp wrote:
>
> >Hello,
> >
> >I have an old knee mill that I'm looking at converting. I've
> >previously converted my Taig mill to steppers using G201's. For this
> >mill I have some servos I'd like to use. I'm looking at either
> >Gecko's or Rutex drives. The Rutex drives are capable of more power
> >but I'm not sure how limiting the Geckos would be. The info I have on
> >the servos;
> >
> >Reliance Electric DC Servo motor
> >NEMA 34 Frame
> >Model E660
> >Back EMF Constant, ke = 65 V/kRPM
> >Torque Constant, kt = 5.5 lb-In/Amp WOW!
> >Nominal Speed Rating: 1750 RPM
> >Nominal Voltage Rating: 120 Volts
> >
> >Encoders;
> >HEDS-5605 A06 (500 cpr from my searching)
> >
> >I don't know if that is all the required info, I've tried to find more
> >on the net with not much luck.
> >
> >
> Maximum peak current would be useful. Ahh, wait, the E660 is an old
> Electro-Craft number. With the 64 V/KRPM, it is the -05 winding option,
> so it has (GASP) 11.42 Ohms winding resistance, and an 8.1 A Max peak
> current. 5.5 In/Lb / amp x 8.1 A = 44 In-Lb or 717 In-Oz. This,
however,
> is the PEAK rating. The continuous rating isn't given simply, but it
> comes to
> about 110 Oz-In, depending a bit on speed. That high armature
resistance
> is troubling, too. The armature temp rise is given as 2.8 C/Watt.
They
> don't
> give a weight for this, but I'm guessing this motor is less than 5 Lbs
> weight.
> To get full continuous torque at 1750 RPM, you'd need 65 V/KRPM * 1.750
> KRPM +
> 1.25 A * 11.42 = 128 V. But, that is only 160 Watts. I'm really
> getting the feeling
> this is too small a motor for this large a machine.
>
> >I like the idea of the Gecko's since the accept TTL where I should
> >convert to differential for the Rutex according to the email I got
> >from Vladimir.
> >
> >Any advice on the Gecko/Rutex question (or info on the servos) would
> >be appreciated.
> >
> >Also on the Taig the steppers were direct. Can you do that or do you
> >have to use some sort of timing belt drive? What's the deciding
> >factors?
> >
> >
> >
> You'd have to use substantial timing belt reduction with these
motors, and
> I think you'd have to overvolt them to get any reasonable speed, too.
> I can't imagine operating, even with ballscrews, with less than
about 20
> In-Lb
> continuous available at the leadscrew (with a 5 TPI screw). I'm using
> 1/8 Hp rated motors, but they have 1.5 Ohm armature resistance, rather
> than 11 Ohms! That really limits how much you can push them.
>
> See my calculations at http://www.timgoldstein.com/cad_cam/motor.htm
where
> I go through it all for the motors I'm using. The specs on my
motors SEEM
> to show them as less powerful than yours, but I think the difference
is that
> I can push mine harder, as they are MUCH larger and heavier motors.
> What this really boils down to is that my motors can probably
deliver peak
> torque for a minute at a time, where yours can do it for 5 seconds, max.
> I think you are going to need at least a 4:1 belt reduction, maybe even
> more.
> with 4:1 reduction from 1750 RPM, you can get 438 RPM to the screw,
which
> comes out to 88 IPM. I never run my machine that fast because I tend to
> break stuff, like running the vise into the end mill!
>
> Jon