Hi people,

At the local trash and treasure I spotted two 50v DC motors with 12g
red and black wires. Bought the pair for $8, so no great loss if they
are not useful. However, if I can find some more specs I am hoping
these, encodeers and some gecko drives will be the X-Y part of a
plasma cutter table.

No encoders, but they had a flat-belt pulley that drove a 3" diameter
x 3" long tachometer. I let the guy keep the tachs. g

All they have marked is...

OIA
135-0043-001
50vdc nominal

They have 5/8" diameter shaft, body about 4" diameter and 7" long.

At 50vdc they draw 0.4A free running at 1300rpm.

They only have two brushes but 90-deg apart.

Also the current stays at 0.4A from about 32v to 50v. Below 32v the
current slowly drops but not by much. Even at 20v it is still about
0.35A. Not sure if that helps or not.

Anyone have an idea of what where and who's??

Thanks in advance.

--

Kind regards,
Jenny and her tribe of survivors.

In article ,
wrote:
Hi people,

At the local trash and treasure I spotted two 50v DC motors with 12g
red and black wires. Bought the pair for $8, so no great loss if they
are not useful. However, if I can find some more specs I am hoping
these, encodeers and some gecko drives will be the X-Y part of a
plasma cutter table.

No encoders, but they had a flat-belt pulley that drove a 3" diameter
x 3" long tachometer. I let the guy keep the tachs. g

*That* was a mistake. If you're going to use these as servo
motors, you need speed feedback to the servo amps.

All they have marked is...

OIA
135-0043-001
50vdc nominal

They have 5/8" diameter shaft, body about 4" diameter and 7" long.

At 50vdc they draw 0.4A free running at 1300rpm.

They only have two brushes but 90-deg apart.

Interesting.

Also the current stays at 0.4A from about 32v to 50v. Below 32v the
current slowly drops but not by much. Even at 20v it is still about
0.35A. Not sure if that helps or not.

The current will go a lot higher when the motor is stalled, or
trying to start (or stop) a heavy object. No clues as to what is the
maximum current before the permanent magnet poles get demagnetized?
You'll need to determine this to set the current limit on the Gecko
driver -- or on whatever other servo amplifier you wind up using.

Anyone have an idea of what where and who's??

Mostly -- if you want to use them with speed control, you should
go back and get the tachs. A servo amp compares the voltage fed into it
as a command with the voltage from the tach, and controls the voltage
fed to the motor to produce the commanded speed.

I'm not sure what the Gecko drivers will do -- as most of their
drivers are for steppers, not servo motors, and only one (IIRC) is
intended to drive a servo motor.

In most uses, without the tach generator, it tends to overshoot,
and come back, and spend a lot of time just bouncing around the desired
point (called "hunting").

O.K. -- looking at the PDF manual file for the G340, it seems to
do without the tach feedback, and just use the encoder. But then, it is
making the servo motor pretend to be a stepper motor, so I guess that
what you have will work. But it *will* hunt -- which they describe as
"singing" in the manual.

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 15 Nov 2003 21:29:14 -0500, (DoN. Nichols)
wrote:

In article ,
wrote:
Hi people,

At the local trash and treasure I spotted two 50v DC motors with 12g
red and black wires. Bought the pair for $8, so no great loss if they
are not useful. However, if I can find some more specs I am hoping
these, encodeers and some gecko drives will be the X-Y part of a
plasma cutter table.

No encoders, but they had a flat-belt pulley that drove a 3" diameter
x 3" long tachometer. I let the guy keep the tachs. g

*That* was a mistake. If you're going to use these as servo
motors, you need speed feedback to the servo amps.

All they have marked is...

OIA
135-0043-001
50vdc nominal

They have 5/8" diameter shaft, body about 4" diameter and 7" long.

At 50vdc they draw 0.4A free running at 1300rpm.

They only have two brushes but 90-deg apart.

Interesting.

Also the current stays at 0.4A from about 32v to 50v. Below 32v the
current slowly drops but not by much. Even at 20v it is still about
0.35A. Not sure if that helps or not.

The current will go a lot higher when the motor is stalled, or
trying to start (or stop) a heavy object. No clues as to what is the
maximum current before the permanent magnet poles get demagnetized?
You'll need to determine this to set the current limit on the Gecko
driver -- or on whatever other servo amplifier you wind up using.

Anyone have an idea of what where and who's??

Mostly -- if you want to use them with speed control, you should
go back and get the tachs. A servo amp compares the voltage fed into it
as a command with the voltage from the tach, and controls the voltage
fed to the motor to produce the commanded speed.

I'm not sure what the Gecko drivers will do -- as most of their
drivers are for steppers, not servo motors, and only one (IIRC) is
intended to drive a servo motor.

In most uses, without the tach generator, it tends to overshoot,
and come back, and spend a lot of time just bouncing around the desired
point (called "hunting").

O.K. -- looking at the PDF manual file for the G340, it seems to
do without the tach feedback, and just use the encoder. But then, it is
making the servo motor pretend to be a stepper motor, so I guess that
what you have will work. But it *will* hunt -- which they describe as
"singing" in the manual.

Good Luck,
DoN.
It is Common place now to use DC motors with no tach feedback if you
are using a CNC contoller (Galil, Acrloop etc) with an encoder
feedback, you will need a Servo Amp that has the option of operating
in the current mode of operation ( e.g. AMC or Copley controls )
rather than the speed mode.
The only thing you have to watch is if the power to the controller is
on first then the servo amps and when powering down the servos amps
should be disabled before removing power from the controller or sudden
jumps may occur.
IMHO with the prices you can obtain the servo controllers/amps on ebay
etc, you can have a XY table with superior servo operation rather than
steppers.
Just my 2c (Can)
Al Inness

writes:

At the local trash and treasure I spotted two 50v DC motors with 12g
red and black wires. Bought the pair for $8, so no great loss if they
are not useful. However, if I can find some more specs I am hoping
these, encodeers and some gecko drives will be the X-Y part of a
plasma cutter table.

If they were really "tachometers", not digital quadrature encoders, then
you are correct that they would have been no use with Geckos. Tachometers
are common in speed-control (not position control) applications.

See my page on retrofitting encoders onto PM DC motors:

http://www.truetex.com/servomod.htm

And the resulting CNC motors onto a mill-drill:

http://www.truetex.com/ymount.htm

The best crude measure of "mystery motors" is often the shaft diameter. At
5/8", they must be pretty hefty units, perhaps 1/3 or 1/2 HP continuous.
At label rating of 50 VDC (which you won't want to exceed by much, this
probably characterizes the insulation quality), you might be looking at 5
to 10 amps continuous current under load, and several times that for short
periods.

If you want to get a detailed characterization, you need to be able to
measure speed, torque, voltage, and current. Then you can know everything.
Those can be measured with middling digital VOM, except for torque, which
requires some kind of dynamometer. Improvising a dynamometer has been a
project I've been musing about for some time.

Richard Kinch
Palm Beach County, Florida USA
http://www.truetex.com

On Sun, 16 Nov 2003 12:47:53 -0600, Alan Inness
wrote:


etc, you can have a XY table with superior servo operation rather than
steppers.

Huh???

--

Kind regards,
Jenny and her tribe of survivors.

On Sun, 16 Nov 2003 22:07:37 -0600, Richard J Kinch
wrote:

Thanks Richard,

I'll get a couple of the gecko drives and try ramping the current
control up until they get hot. g The good old brute force approach.

If they were really "tachometers", not digital quadrature encoders, then

They were tachs, as that much at least was on the label but very
little other information and that's why I didn't bother getting them
as I knew I'd need encoders anyway.

See my page on retrofitting encoders onto PM DC motors:

g Like DejaVu, I was looking at the end of the shaft yesterday and
figured I could do pretty much what you outlined on your site. I will
tap the end of the shaft though and couple the encoder with flexible
joint just to make me feel warm and fuzzy.

Thanks again for the input. I had hoped someone might have recognized
the OIA brand on the motor, if that is the brand but the brute force
approach is always a good fall-back.


--

Kind regards,
Jenny and her tribe of survivors.

Those sound like tape drive motors. I think that because I have a
couple of similar 50-volt motors (also O1A but with 1/2" shafts) that
I was told were surplus from large tape drives. Dimensions of mine
are the same as yours (4 x 7) but the leads are 14 gage.

A quick resistance measurement of my motor suggests that stall
torque at 50 volts would be about 18 amps -- which isn't to say that
the motor would take that for any extended length of time without
overheating.

You seem to have a source of variable DC, so if you also have a way
of measuring motor temperature, you could test your motor by locking
the rotor and slowly raising voltage (and current) until the motor is
about 40 degrees C (72F) above ambient. Give it about 15 minutes
for it to reach equilibrium at each current setting and sneak up on
it. Most motors are rated at 40C rise so that should give you a good
estimate of the motor's current rating for continuous service. I'd
expect as first guess that these motors will probably handle about 9
amps without overheating but I'd start lower and sneak up on it.

Then you could clamp a lever arm to the shaft that bears on a scale
and measure stall torque at the rated current you've estimated.

Permanent magnet motors have a torque-speed curve that is quite
linear, so knowing no-load speed and full-load torque will pretty well
characterize the motor.

Feel free to email questions. I'm a retired electrical engineer,
enjoy playing with stuff like this. I claim no expertise on
available controllers, though. I've designed servomotor controllers
but I have no hands-dirty shop experience with available products as
the Gecko you or someone mentioned.

Regards

Don Foreman
Fridley, MN


On Sat, 15 Nov 2003 16:23:40 -0700, wrote:

Hi people,

At the local trash and treasure I spotted two 50v DC motors with 12g
red and black wires. Bought the pair for $8, so no great loss if they
are not useful. However, if I can find some more specs I am hoping
these, encodeers and some gecko drives will be the X-Y part of a
plasma cutter table.

No encoders, but they had a flat-belt pulley that drove a 3" diameter
x 3" long tachometer. I let the guy keep the tachs. g

All they have marked is...

OIA
135-0043-001
50vdc nominal

They have 5/8" diameter shaft, body about 4" diameter and 7" long.

At 50vdc they draw 0.4A free running at 1300rpm.

They only have two brushes but 90-deg apart.

Also the current stays at 0.4A from about 32v to 50v. Below 32v the
current slowly drops but not by much. Even at 20v it is still about
0.35A. Not sure if that helps or not.

Anyone have an idea of what where and who's??

Thanks in advance.