Re: [CAD_CAM_EDM_DRO] New to servos, please help/advise?

volitan712003 wrote:

>
> Can someone help me with a few things (power supply/encoder)?
>
> My mill is pictured in the "Volitan" folder in the "Photos" section.
> I have 3 of the following servos:
>
> ---------------------------
> Reliance Electric DC Brushed Servo Motors, Model E712
> 37.51 Oz-In/A
> 25.0-30.5 V/KRpm
> Maximum Terminal Voltage 60V
> Maximum Continuous Speed 2100 RPM (No Load)
> Maximum Peak Torque 1500 Oz-In.
> Maximum Peak Current 44.5A
> Maximum Continuous Stall Torque At Max Motor Temp 300 Oz-In.
> Maximum Continuous Current 8.9A
> ---------------------------------
>
> I have 5 TPI ballscrews, and plan on using Gecko 320's and encoders
> from us Digital.

Looks good to me.

> Power supply amperage? I'm confused.
>
> 3 geckos @ 20 amps max each = 60 amps. I've never seen anyone here
> recommend a 60 amp supply.

On my J&L lathe, there was a 1.5KW supply for each 60VDC axis motor
(driven by Gecko G340's). Thats 25 amps * 2 = 50 amps total for X&Z
(not counting the turret motor). So high VA values are not unheard of
for larger machines (the J&L was a 12,000 lb lathe). In fact, the original
peak values of the axis servo motors was 100 amps at 60VDC, but as the Geckos
were only capable of 20 amps, that is what I ran them at, and it worked
really nicely.

> 3 servoes at max continuous - 26.7 amps. So I suppose it should be
> somewhere in between but I'm guessing because I don't really know what
> I'm talking about yet.

I had a look at your 'Volitan' photo, and judging by its size, you won't have the
rigidity and spindle HP to drive those servo motors at their maximum.
***********************

I have a Supermax cnc mill (4500 lb class) which appears to be at least triple
the size of your mill, and I run it quite nicely (with G201's & 1100 oz*in steppers)
with my 1KW 75VDC (14 amps) supply.

Therefore, I would presume a 1KW (60VDC @16.66 amps) power supply (such as I
offer on my website) would be sufficient for your mill (ie stall the spindle).
A bigger 1.5KW supply (60VDC @ 25 amps) might give you more confidence, but I
think it would be overkill on that Volitan mill.

> Encoder resolution. What are the pros/cons to the different
> resolutions? I'd like the ability to thread mill if that means
> anything there.

I would suggest
#1 - figure out how you are going to drive the Step (& Direction) pulses
ie 10-50Khz using DOS & TurboCNC, or 25-45KHz using Master5/Mach1/Mach2
or the various hardware solutions (ie DeskCNC from IMSRV or G2002 from Gecko)

that will give you a peak step rate

#2 - figure out how the step rate would translate through your gearing
to the table, then specify the encoder resoltion to be near your
expected rapid movement rate.

ex: presuming your servos are geared 2:1, and you have 5 TPI leadscrews,
and you want a 120ipm rapid (which is reasonable for that machine):
120 ipm = 2 inch/sec = 10 rev/sec (of the leadscrew) = 20 rev/sec (of the motor)
(now check, will your motor do 20 rev/sec? well 60V/30.5v/krpm =~ 2000rpm = 33 rev/sec
so you are ok there.... that might indicate you want a 3:1 reduction ratio instead)...

continuing with the 2:1 reduction and 20 rev/sec motor rpm, say you are using
a P300-450 class machine under DOS & turbocnc, which should provide ~30,000 steps/sec
(for each axis)

then 30,000steps / 20rps = 1500 steps in quadrature (or 375 CPR cycles per revolution encoder).
if 375 CPR is not available, look for a 350 or 400 CPR encoder.


if instead you pick a 3:1 reduction, and 30 rev/sec motor rpm, then
30,000steps/30 rps = 1000 steps in quadrature, or a 200 CPR encoder,
and this looks better than the 2:1 reduction because of the greater
drive reduction of the motor.

Hope that helps.

Doug Fortune
http://www.cncKITS.com home of the 1KW BEaST power supply kit for Geckos












.

>
> Sorry this is so long, I'm not even asking all the questions I have
> yet :)
>
> Thank you!
> David
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
> Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@..., timg@...
> Moderator: pentam@... indigo_red@... [Moderators]
> URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> bill
> List Mom
> List Owner
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/