Re: [CAD_CAM_EDM_DRO] Re: mill servo conversion ?'s

> >
> >Are the the Ametek motors from Camtronics really a bad deal? I don't
> >mean in terms of the high resistance. I mean in terms of what you get
> >for the money.
> >

> For brand-new motors with encoder already installed, they are not bad.

Jon is correct that these Ametek are not the greatest motors but for the
beginner who doesn't know what to look out for they are great motors. I have
gotten email from people that have bought motors from surplus stores and
from ebay but had one horrible problem. Internally one of the brush wires
was connected directly to the motor frame. It bench test fine then when
installed on a multi axis machine it promply blew $300 worth of Gecko
drives. So unless you are positive of what you are buying I would recommend
getting them from a proven source. I currently have one of those lousy
Ametek motors on my 8X36 mill on the knee. It has a 2.5/1 ratio timing belt
drive and is lifting about 500 lbs via the stock .2 acme leadscrew installed
on the knee. That rotten motor has been raising and lowering the knee
thousands of times and doesn't get warm on my 36VDC supply. I run it at
about 30 IPM. I also have two of those terrible motors running on the XY
axis of my milldrill at better than 30 IPM and silky smooth operation. I
have quite few customers using those lousy motors that make part of their
living with their machines and my motors. I can alway get better motors
but you need to figure about $450 each. On the other hand I have quite a few
customers using them on millddrills and getting excellent performance .

>
> > If they are, where is there a better deal? And why
> >isn't it more widely publicized? Also, why do you recommend a 80-120V
> >power supply for the Ameteks when camtronics only sells a 36V for them?
> >
> >
> For performance. To get full peak torque, you need to deliver 12 A
> to the motor. With a 36 V power supply, you can't deliver 12 A to a 4 Ohm
> motor, even standing still. At 900 RPM, the back EMF of the motor is
> approximately 36 V, so you can produce zero torque! This severely
> limits performance. I have a client in town who has an 800 Lb Grizzly
> style machine with these motors and a 36 V supply, and the performance is
> pretty weak. To get full peak torque at rated speed, you need 36 + 12 *

4=

> 84 V minimum, appled to the MOTOR itself. You need some margin for the
> modulation scheme of the servo amp. too. So, a 120 V supply sounds good,
> but if using Gecko 320 drives, 75 V or so is the limit. With a 5 TPI

screw

> driven directly, you get 180 IPM, which should be plenty for most users.
> But, if belt reduction is used, or if the screw is finer than 5 TPI,
> then the max
> rapid rate goes down, even with the higher voltage.

Jon is techincally correct so if you don't expect 180 IPM performance and
you don't want to spend what it would cost for a really good motor then the
amtek motor should be considered for the price/performance ratio.

>
> >So, all that is in way of asking, what would be a better deal than
> >Camtronics complete setup? I'm not asking how Bridgeport's or your
> >setup is better; I'm sure they both are. I'm asking if I have ~$1250
> >to spend on a servo system, what should I get?
> >
> >
> Look on eBay, or Surplus Center, or C&H sales in Pasadena, or maybe
> Herbach&Rademan

Be careful some of thsoe motors can be disasterous.

> in NJ. $1250 for motors will go a long way!

I think he means $1250 for motors, power supply, case, connections,cables,
breakout box, encoder cables etc. A complete system.
If that is what he means then the complete Camtronics setup may be within
his financial constrainst and while it isn't a great servo system it is
certainly adequate for students.

Dan

>
>