Help identifying motor leads.

Cross Post: sci.electronics.repair, comp.robotics.misc
*****
Hello Groups,
I have recently acquired two heavy duty motors for robotics use. Below
is a link to the picture of one of them.
http://www.mpja.com/prodinfo.asp?number 386+MD
I have both a left hand and a right hand motor. They are about a foot long, half a foot wide, and weigh in at about 40 lbs each (No wonder it cost $40 for shipping...UPS ground even.). The motor also has serviceable brushes too. There are four wires for these motors, colors red, black, white, and yellow. I'm going to assume that red and black are power, but what are the white and yellow for? A built in tachometer? The gearing is bolted on, but there doesn't appear to be any way to dismantle the motor so I can see how it is wired internally. Any thoughts or suggestions?
--
Daniel Rudy

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Two of the wires for the armature, two for the field.
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At about the time of 10/16/2008 5:51 AM, Smitty Two stated the following:

A DC motor that has a field winding? I need to find a way inside these motors...
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Daniel Rudy

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Older car starter motors had field windings - called series wound. Maximum torque at stall. Will also run on AC.
--
*I started out with nothing... and I still have most of it.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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At about the time of 10/16/2008 4:04 PM, Dave Plowman (News) stated the following:

Interesting.
I have some additional information. The black and white wires are connected to brushes. The DC resistance between the two is about 2.7 ohms. The red and yellow wires have a DC resistance of 7.3 ohms. So I guess they can be wires either series or parallel. What I don't understand is if the red and yellow wires are for the field, then why bring them out? Why not just connect them internally?
--
Daniel Rudy

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Think the way they are connected - series or parallel - makes a difference to the motor characteristics. Also separate access to the field can make speed control easier.
--
*Everybody lies, but it doesn't matter since nobody listens*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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At about the time of 10/16/2008 4:41 PM, Dave Plowman (News) stated the following:

Sorry, but I'm not up on that theory. How can the field make speed control easier? For DC motors, I usually use a PWM scheme for speed control.
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Daniel Rudy

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Daniel Rudy wrote:

You cant reverse it if the field connections are internal. Reversing the polarity on both windings will maintain the same rotation direction. You need to reverse one winding relative to the other to reverse the direction.
REDUCING THE FIELD CURRENT *INCREASES* THE NO LOAD SPEED. (dont take it too far, you wont be happy)
Field loss is a critical failure and if unloaded its likely to over-speed till it grenades, otherwise the armature current will increase till it melts. Its therfore advisable to have a contactor with a low impedance coil in series with the field winding to cut power to the armature if the field circuit fails. At the minimum for bench testing, switch the armature to reverse, not the field.
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At about the time of 10/16/2008 6:26 PM, IanM stated the following:

Well, I just finished doing a bench test on this motor. The results that I have are listed below. The power source that I used was 4 standard C alkaline cells wired in series for 6v. I removed the gear reduction and tested just the motor.
field         armature red    yellow        white    black    result ------------------------------------------------------- +    -        open    open    no rotation open    open        +    -    no rotation +    white        yellow    -    CCW rotation, high torque -    white        yellow    -    CCW rotation, high torque +    black        -    yellow    CW rotation, high torque -    black        -    yellow    CW rotation, high torque +    -        +    -    no rotation
Rotation was observed facing the motor. That last one I'm not sure about...maybe I don't have enough power. But this gives me a few ideas on power control. I'm thinking of placing a DPDT relay in series between the armature and field windings for direction reversal, then use a the standard PWM control from a microprocessor to control speed. Plus, this will also protect the motor too in case any winding fails it will open circuit.
There are absolutely no numbers or any other markings on this motor besides a warning about it being hot. But from what I have been able to scrounge up on the web. It seems that this motor was manufactured by Magnetek and is rated at 24v. Stall current is 20. The lead wires are only 16 AWG, so at stall, even the high temp wires would melt...the wires are rated at 200c.
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Daniel Rudy

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On Fri, 17 Oct 2008 04:52:13 -0700, Daniel Rudy wrote:

To observe while facing _away_ from the motor would involve a mirror, I suppose. :-)
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At about the time of 10/17/2008 7:15 AM, Allodoxaphobia stated the following:

hehehe
Or I could look from the side, but then it would be either left hand or right hand, which neither knows what the other is doing. :)
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Daniel Rudy

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wrote:

No, my mother could have done that easily. A few of my teachers as well. All female, so perhaps we men are left out in the cold? <g>
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I have a pair of these motors that I bought for a medium sized bot. They proved not up to the job and were replaced with wheel chair motors. I think that they were made for elevator or subway door operation, several ads I saw a while ago indicated this. 5 years ago, they were bringing $70 each, now I think they are about $20 each.
I am in the process of building an antenna rotator with the pair right now. I am planning on running the field windings on a constant 12V and PWM'ing the armature for control. I don't need a lot of torque, so I will try 12V for the initial input power.
Good Luck, Bob
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Daniel Rudy wrote:

I did some studying on controlling wound field DC motors with the armature and the field windings in parallel and then driving the two from a PWM source results in sort of an odd torque/speed curve that is lacking in low speed torque. Running the field windings on a constant voltage and controlling the armature voltage gives a flatter torque/speed curve. Also, the adds that I remember seeing suggest that the motor can be run on 36-48VDC.
I needed a place to attach encoders for closing the control loop and found that the output shafts are fairly soft steel and drill and tap very nicely. The unused side of the output shaft is exposed and flat, making it an easy place to attach the encoders.
Good Luck, BobH
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