Training: Interpreting Motor Spec Sheets presentation wanted

Technical Motors
1

As part of our preseason newbie member training, I wish to run a session on the basics of Motors, and interpreting Motor Spec Sheets.

Are there any Motor Industry Standard explanation app notes for understanding basic DC PM motor terminology, and interpreting motor Spec Sheet diagrams? Any Powerpoint presentations or PDF files on this which someone has made up for THEIR team? Even something as simple as a GIF of a combined motor curve (the “X and arch”) with EVERYTHING labeled would help.

In essence, my goal is for them to not be freaked out or confused when they see a Motor Spec Sheet. :smiley: I’ve seen a LOT of materials on gear ratios, SELECTING motors, et al, but most of them assume the students have SOME clue about motors already.

I wish to back up one step from all of the “choosing a motor” papers in the CDF Whitepaper area. I need class materials (for a one session class) to cover basic DC PM motor theory, motor spec sheet terminology (stall current, free speed, etc.), HOW industry diagrams motor specs, the basic equations that affect ANY motor, and how to pull the data you need FROM the spec sheet curves when you only have that instead of in tabular form.

IOW, ONLY theory, terminology and reading diagrams, and nothing about CHOOSING a motor for now.

Since this is NOT my area of expertise, I’d rather not try to make up one myself. Any links to materials would be appreciated. I’m sure others would like this too, so please post responses under this thread.

Thanks!

  • Keith
2

You said you looked at the choosing a motor paper in the white paper section, so I am not sure I am being any help by posting this link, but here it is:

http://www.chiefdelphi.com/forums/papers.php?s=&action=single&paperid=197

The paper cover the basics about a DC motor, from the stand point of a beginner assuming the reader doesn’t know anything about the motors. It start with talking about what’s a motor, then move onto the specs and reading the spec curves. If the reader is interested, they can keep going and read about motor power, gear ratio, and eventually applying everything together in one big problem.

I have a feeling the first few pages are what you are looking for. In general, you want to tie everything together so the students have an overall understand of what a motor does, and how to use them properly.

3

*Originally posted by Ken L *
**[See: ] http://www.chiefdelphi.com/forums/papers.php?s=&action=single&paperid=197

I have a feeling the first few pages are what you are looking for. **
Thanks! That’s MUCH closer to what I was searching for. However, I’m still looking for something even simpler. Maybe a one page “Glossary”, and a one page chart with arrows and formulae on it, as a two sided “reference sheet”. Is there anything like THAT already out there?

BTW, regarding the formula for actually PLOTTING the curves, based on the table data… The two lines of course are “straight” forward. :wink: But you say in the paper that the power curve should be “an inverted parabola”. Aren’t there a whole family of parabolic curves that fit three points?

What’s the exact formula for that parabola, based on the known parameters, for plotting the arc perfectly? I’d like to set up a plot routine to actually DO the plots based on the table data, and need the full formula.

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Another motor question regarding stall measurements of an unknown motor (we plan to do this as an experiment): Can you “scale down” a stall measurement experiment for safety, and still get accurate data?

IOW, can we do this experiment with a smaller power supply, and simply multiply the torque and current measured to the full values based on the ratio of the “FULL” voltage vs “USED” voltage, or are there some resistance or force nonlinearities due to motor heating (or other thing) that messes up this technique?

If we CAN do that, it would allow stall parameters to be measured via a lightweight rig, made with a simple motor clamp, a vice grip on the shaft touching a postal scale, and an under 10A benchtop power supply. That would much safer for the students to do. (If forced to run it at full values, we’d have to set up 100A supplies, ammeters, scales, etc, and STRONG clamp setups to insure something doesn’t come loose and hurt something or someone!)

So, will scaling everything down linearly still give valid stall data, or are motors really nonlinear?

Thanks!

  • Keith
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My philosophy has always been: If you want something, do it yourself ;-).

By now you should be able to understand what the paper says. So, why don’t you take the graph, add in lables yourself, and make the description. That way you get whatever you want ;-).

As for the formula for the power curve, very simple. Power = force X velocity. You use the speed torque curve, and you multiply the force and velocity of each coordinate and you get the numbers for a power curve. The power curve is really just used to visualize the amount of power you have at each combination of force and velocity.

For the experiment, you can reduce the amount of voltage to the motor. Since motor’s job is to transform electrical power to mechanical power, in the case if DC motor, it’s proportional. If you give it 1/2 the voltage, the stall torque is 1/2 of the original stall torque at full voltage, and the free speed is 1/2 of the original free speed at full voltage. With those numbers you get a new speed/torque curve.

Then whatever number you measured for stall torque, just multiple by 2 if you used 1/2 of 12v, or multiply by 4 if you use 1/4 of 12v.