Followup -- How do you test a DC servo motor



Jon, it sounds like you have done a lot of interesting work in the servo drive area. Have you worked with resolvers? I have a couple of new, old stock, modicon brushless servo motors with resolvers. I don't have an application for them right now but I thought I would use them in the future when I find a drive or perhaps a resolver to encoder or resolver to digital (or hall) converter for low $$$. Just to buy the Amphenol bayonet lock plugs for these motors isn't going to be cheap though! If I do an EMC conversion to my Anilam Bridgeport mill I thought it could be interesting to drive the knee when movements are out of quill range.
For an experiment I programmed a PIC for 3 phase sin PWM out and ran the motor like a stepper. Anyway if I come up with an application where I need them perhaps I can find a drive on eBay for reasonable. It looked like some of the Pacific Scientific drives are capable of encoder or resolver feedback and can convert the resolver in and give encoder out.
RogerN
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Do you find it to be great sport in taunting someone whose first language wasn't English?
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Language is not the issue here. Spewing garbage is.
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Outside of the political stuff that I try my best to ignore, Iggy generally has some interesting content. Not that I'm innocent concerning politics. Sometimes I even agree with him.
Iggy is willing to ask questions that some of us are too self conscious to ask ourselves. Learn to lighten up, it is heart healthy. Wes
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I think that it would be fair to say that I goofed, at best, when I called the controller a commutator. I did not realize that commutators can only be mechanical. At the same time, I am glad that I know a lot more about brushless motors now, than I did two days ago. Same about servo motors.
This is not what I do on the job, so I do not feel any shame that I know less about them than someone else. Pointing out that I know very little about brushless motor controllers, aircraft control systems, dough mixers, or any other thing that is outside of my area of competence, cannot possibly embarrass me.
By the way, Wes, so far, you are winning in the Dow prediction contest, so far. If I remember correctly, you predicted 9,000.
i
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I think everyone, including me, would be happier if Ben91932's prediction comes true. I'd rather have Dow 10,300 instead of collecting a few Lincolns.
Wes
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I would rather have Dow 6,600, as I am quite away from retirement.
i
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Oh, you are on the sidelines, I'm all in. Different perspective.
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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Wes, I am also all in. I would estimate that 87% of my money is in stocks. Individual and mutual funds. But, I am a buyer of stocks, as I am saving, and so I would prefer lower prices on what I am buying. I look the same way at, say, steel prices, etc.
i
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you were moaning about languages, not me. Learn to lighten up, it is heart healthy.
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And so is plonking! -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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As a young man, (there were 5 of us kids - 4 years apart) -
The young ones we had a stick and on the end was a loop. The loop had a square top with an indention in the center - coming down to a pair of wires into the stick. The wire was covered in WHITE wire covering. The unit would pull down and push up. Cool to teach young ones to switch the bathroom light on or the bedroom light on all by themselves - and off as well!
Martin
Ignoramus22378 wrote:

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Brushless DC motor has a commutator, and polyphase AC motors do not need one.
i
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Also, in a brushless DC motor, there are permanent magnets on the stator.
i
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wrote:

How do they get power to the windings on the armature without brushes?
RogerN
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Ignoramus22378 wrote:

Ig, A brushless DC motor does not have a commutator, hence the term "brushless". The commutation is done electronically by the controller that drives the motor. That is one of the advantages of them, no brushes to wear out, no carbon dust, etc.
-Al
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wrote:

How does "brushless" and commutator work together? I thought you had to have brushes contacting the commutator.
RogerN
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I chose very unfortunate way to say what I was thinking. I was wrong to call the controller a commutator. I was thinking that because the controller sends current to different windings that I could call it a commutator.
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On Jun 6, 8:54pm, Ignoramus22378 <ignoramus22...@NOSPAM. 22378.invalid> wrote:> I chose very unfortunate way to say what I was thinking. I was wrong

The single phase circuit is called an H bridge, but I haven't heard a standardized English name for the three phase version. At Segway the engineers just call it the motor drive.
jsw
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wrote:

Brushless motors sometimes have hall effect sensors that detect the position of the armature and control the commutation. Some use resolvers, since resolvers are absolute to 1 turn, they can use them for commutation. At work we have some motors that we have to align the resolver to the motor, others we have to run a routine that determines the position of the resolver to motor and stores the position in the drive.
Now if you have a 3 phase brushless motor and put sin of 0, 120, and 240 degrees X the voltage across the three phases, and stepped this at 1 degree at a time (1,121,241 2,122,242 etc.), you would hopefully get 1 degree of rotation per 1 degree of magnetic field rotation. If I'm thinking correctly about it, a DC servo motor might provide linear steps if you provide a linear transition between phases, instead of voltages proportional to Sin of the angle. Maybe like 0% 100%, 1% 99%, 2% 98%... would produce linear sized steps around the commutator.
RogerN
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