Ametek Servo Motors Anyone use them???

[bill south]

I saw in a recent catalog from the surplus center, ametek permanent magnet servo motors for 39.95 each. 38 volts dc, 1150 rpm, 12 amp max, with an auxillary shaft. Seems like a heck of a deal for someone looking for new motors. Strap an encoder on the back (us digital) and you're ready to rock and roll.
Can someone speak to the drawbacks of using such a motor?? Seems like a heck of a deal to me!!!!!!!
Bill from Spartanburg!!!!

[Bubba]

billyjack,
I have a couple of those exact motors that I plan on using on my lathe! I also figure they would be real good candidates for a mill/drill also.

[skip20]

I,m using 3 48V on a large cnc table & they seem to work good.
I got 4 of the 38V motors to use on the beach top mill.

Skip20

[DRD]

I used the amtek motors on my old lagun retro fit 4 years ago. The amtek motors are not true servo motors, the will work, but they just won't run as smooth as a true servo motor. There are more poles inside a true servo motor.
Good luck.

[jdgoguen]

I also have four of these that I plan to use on a small mill and lathe, so I spent time looking into ratings. The 12 amp current is listed as the permanent demagnetization maximum. To get an idea of continuous current rating, I compared the continuous rating for CMC brushed servos with their max rating. The typical ratio is about 9:1, so the Amateks should have a continuous rating of about 1.3 amps. I measure the terminal resistance (room temp) at 4.5 ohms, so the motor should draw about 8.5 amps max at 38 volts. An old C&H Sales catalog that lists the Amatek motors gives a torque constant of 50 oz-in amp, and also reports a current of 2.3 amps at 900 rpm with 100 oz-in load which is reasonably consistent. If this torque constant is correct, the peak torque would be 600 oz-in--a value I've seen given elsewhere for these motors--but 54 volts would be required to get the max 12 amps through the motor when cold and stalled (more when hot or running). At 38 volts, the stalled torque when cold would be about 422 in-oz. These numbers aren't too different from the specs of a CMC model 3509 with a type H winding given here (look at pdf data sheet). [URL="http://www.cmccontrols.com/brush_servo_motor_platform3500.asp"]
The Amatek motors are larger than the 3509, and probably have greater rotor inertia, and longer mechanical and thermal time constants. Conservatively, they should be usable in applications that the 3509 will handle except with respect to agility and speed (the max speed of the 3509 is much higher). The Amatek has a bit higher torque constant.

To be on the safe side and avoid ruining the motor, I wouldn't let the current get above 11 amps. Modern peak torque ratings are usually more conservative than demagnetization current, and are based the current where the torque is 10% below the product of the torque constant and the current drawn.

I read somewhere that the Amatek motors were originally made for large computer tape drives, but don't know if this is correct.

Jon

[H500]

Does anyone know the continuous watt capabilities of these motors? A similarly priced stepper will put out 35 to 50 watts.

[skullworks]

A stated above there was a version of these motors used to drive the old (refrigerator sized) data tape drives.

The following applies to the current model offered by Surplus Center;

This version was made to have the encoder disc mount on the rear shaft and the rear cover was tapped to mount the pickup. A plastic cap with 3 fingers snaps over the entire rear of the motor to enclose the encoder.

There are 3 wires, Black & White which connect to the 2 brushes which contact the armature @ 90 degrees to each other. The Brown wire is a chassis ground. The brush holder mounting plate (fiberboard) shows that it was designed to also be used with a 4 brush configuration.

Applying power from a single AA batt yielded about 50 rpm with NO cogging. The armature is a skewed design.

The rear bearing looks simular to a skate bearing.

( End of Surplus Center model descriptions )

I also have a different Ametek which has a 48V armature, this motor has a entirely different rear cap and both armature bearings are 5/8" I.D. there is no rear shaft, but the cap has about a 3/4" hole and the inner bearing race and armature shaft is exposed in the recess.

I have not opened this unit so I don't know if it is a 4 brush model. It only had 2 wires.

>>> Now There is one IMHO design flaw in the Ametek motors - and that is how the wires exit the rear cover - it is a simple and easy ( from a assembly point of view ) design which uses a cheap plastic strain relief slipped into a notch cast into the cover.

Since I want to use this as a servo on my X3 with full flood - this just won't work for me as is.

So, I have designed a complete replacement rear cover/bearing support to fit the Surplus Center model which provides dual conduit ports and a enclosed "box" that will allow for encoder mounting. The dual conduits allow the encoder data cable to be isolated from the motor drive wires. (you don't have to use 2 conduits, but the option will be there.)

[dgoddard]

Thinking about using the Ametek servo on a 8" rotary table for 4th axis. Looks like it would work and the price is right. Any thoughts from anyone? I would prefer to use a smaller dia. than the 4" on Ametek. Does anyone know of a smaller dia. servo that would work for this application?