Testing: Brushless Motors

I found the following the other day over at wattflyer (Home Page) and thought I would share. The linkage should be read as what I've posted here is
only a summery per say and/or a review of said information

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[size=1.25em]Testing Brushless Motors[/size]

• wattfly's "Dry Testing" Brushless Motors  "Would you want to connect a suspect motor to an ESC and risk possible damage to your expensive ESC?"

A Multi-Meter w/ it's AC-Volt-Meter and Continuity-Tester are the choice weapons but as you will see after reading through the above link an Oscilloscope can be use. The oscilloscope is teh FUN tool for this testing, besides practicality aside I gotta see for myself ...

It's common knowledge the reverse aspect of any MOTOR is the fact in can also function has a "generator", it will also produce electricity. When a motor is running normally it will ALSO produce some current. In industry they call this "Back EMF or Back Electromotive Force" and can be quite useful in knowing the rotor's position in sensorless motors. Another aspect of this is as the motor's RPM increases so does it's Back EMF ... If and when researching Back EMF you should also find or what this implies is you "can't have HIGH torque and HIGH speed at the SAME time"

Regardless Back EMF is can be very useful and is the principle behind the TEST procedure shown here

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[size=1.25em]The FUN[/size]

I connected my oscilloscope to a small motor being spun with a Dremel, although the wattflyer info recommend a Variable Speed Drill. Now my personal preference is my Dremel as it's easier to maintain a steadier or more constant RPM without any "MacGyver" DIY remedy needed for my Drill. Again I used the SCOPE but for most we use the recommended AC-Volt-Meter

As it would read w/ an AC-Volt-Meter all 3 Phases (leads/wires) should read approximately the same voltage. The limitations of this scope as it only supports 2-Channel's is I can ONLY test any two of the motors phases at any one time! What I'm saying or implying is you need to get a reading from ALL three phases and they must be close to the same voltage w/ very little delta. FYI: When used in this context DELTA in the Greek (Δ or δ) or GEEK equals "difference"

Also assumed is the RPM input to the motor must also show very little delta but NO specific RPM is needed. For safety it's best to keep the RPM low anyway as not to generate too much heat within the motors windings. This would be especially TRUE for a "suspect" motor or for a motor that might have a mechanical issue! ...

... Any "delta" is the indication of a problem within the motor! However it would still be BEST to read the "linkage" as I found after reading many other issues can be found using this test methodology

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[size=1.25em]My Results:[/size]

{HeHe} Yes "it's" certainly AC ... Note: I've intentionally left out the specific readings as this thread is more about the TEST methodology and NOT so much about any specific issue or problem. Safe to say this motor is a perfectly FINE but yeah the TEST certainly DID prove it. Meh, I would have preferred to show y'all what a BUM verses GOOD motor would have looked like but I simply don't have a bad one to show


     

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I found the Dry Testing Brushless Motors thread over at wattflyer a damn good read if not educational.

It's just one of those questions that POP up quite often making it such a good candidate for any good FAQ. Hope it's also FUN for y'all and the next time someone asks "How to test an motor without RISKING the ESC?" you WILL have the answer

      [size=1.25em][shadow=Orange,left]w00d[/shadow][/size]

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[size=1.25em]
Spore Reading:[/size]

• Brushless Motors and ESC's 101
• Electronic Speed Control and Pulse Width Modulation (PDF) University of Utah - ECE 1250 Lab 3
• Oscilloscope Tutorial Learning Center by Tektronix for the True Propeller Head
• Using an Oscilloscope for the beginner
• Virtual Oscilloscope JUST for FUN

 

Thanks w00d.  I wish I had a oscilloscope at home.  In fact my volt meter just failed not long ago...it didn't seem to like living in the trunk of my car in 100 degree to freezing weather over the years.  Last time I was at Radio Shack I was looking for a reasonable unit but the ones they had in stock didn't appeal to me.

Did you do the test methodology with the volt/ohm meter also?  I think more people will have a volt meter than a oscilloscope at home.

Sorry as I should have said more clearly ...

... the wattflyer link did recommend or they specifically talk about doing the TEST w/ an AC-Volt meter ...
Only later did they talk about using the oscilloscope for few in more depth tests which and only out of curiosity is what I did
 
... and I knew I could DO a pretty PIC for my POST by using the Scope, hehe

Yes of course for most their Multi-Meter and w/ it's AC-Volt-Meter is the weapon of choice
Important we remember it's the AC and NOT the DC-Volt-Meter we need 

[size=1.25em]More Electronic Photogenic's for the Curious: Rx and the Throttle Output[/size]

        Answers: "Is there Output from the Rx (Throttle) to the ESC" or if said in Noobish "is my Rx broked" 

       


[size=1.25em]Magnified View:[/size]

        The Oscilloscopes Screen which as you can see is NOT very good quality ... I'll try again

       


[size=1.25em][shadow=Orange,left]w00d[/shadow][/size]