Motor Condition Monitoring

[gstowers]

Is anyone performing periodic acoustic spectrum analysis and temperature monitoring to monitor the health of the motors on their drone(s)? Seems like doing so might be cheap insurance.

I have inexpensive IR thermometer and recently loaded an acoustic spectrum analyzer app into my I-Phone. I'm thinking about establishing a set of standard condition such as fully charged battery running at idle with no props for five minutes then recording the following information:

- Ambient Temprature
- Motor temprature rise above ambient for each motor
- Peak audio frequency and amplitude for each motor

I could then look for:

Trends in motor temperature rise
Differences in motor termpratures between motors
Trends in peak audio frequency and amplitude for each motor
Differences in motor audio spectrums between motors

The intent woud be to look for any changes in the data over time that may indicate a incipient motor failure before failure occurs during flight.

Thoughts/Suggestions?

 

[alokbhargava]

Good and innovative idea.

As you will be running motors with no props, you will miss effects of loads on motors. Motors may behave ok on light loads but might exhibit problems on load.

In my view, motors will last very long unless we props are obstructed and motors get overheated. The most two sensitive elements are motor windings and bearings. Both have extremely long life compared to the expected life of aircraft as accidents do happen.

Even if the windings insulation gets burned, wings may still work at low voltages. We may have to really evaluate the effects of overheating on the mounting parts and the air gaps between stator and rotor. You will notice changes only when you load the motors.


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[Kevin O]

I have a FLIR camera I've used to monitor batteries and have taken a few shots of the P4.
Having been extensively involved with predictive monitoring of machinery for my job I can say it can provide very valuable information.

As alokbkargava mentioned, it's unlikely that propeller-less no load testing of the motors would be a indicator of problems. Unless the problem is quite severe.
It's also very likely to overspend the motors without props.

You could tether the bird or tie it to a table and run it with props. This would provide a realistic motor load.
A good check would be to run a spectrum at a running, on the deck idle. Then again at a steady hover. A full load spectrum would require tethering.

Depending on the range of the spectrum you may see differences as the characteristics of your props change, nicks in the leading edge etc.

If in consistent ambient temp you were to do full throttle pulls for the same duration, say 30-60 sec and perform an immediate IR scan of the motors you may over time see changes or differences between the motors.

If I were going to do this I'd set it up on my kitchen table and note the room temp for each run.




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[RC Madman]

I will 3rd that without a load you may not see much of a issue. I have done a number of static prop tests with the 8 different motors and 15 different props. I have a test only Sunny Sky 980kv that sounds relatively normal (Just ear) without a prop and does not draw any more amps than the good bunch but put a prop on it and it sounds like someone put sand in the bearings and it draws 4-5 more amps than the good ones.

Visually inspecting them and rotating to see if they are smooth is good enough. There are members on here that have 500+ flight miles on original motors. DJI did a good job sourcing these motors as they are not prone to failure.

 

[gstowers]

Good and innovative idea.

As you will be running motors with no props, you will miss effects of loads on motors. Motors may behave ok on light loads but might exhibit problems on load.

In my view, motors will last very long unless we props are obstructed and motors get overheated. The most two sensitive elements are motor windings and bearings. Both have extremely long life compared to the expected life of aircraft as accidents do happen.

Even if the windings insulation gets burned, wings may still work at low voltages. We may have to really evaluate the effects of overheating on the mounting parts and the air gaps between stator and rotor. You will notice changes only when you load the motors.


Sent from my iPhone using PhantomPilots

I agree that taking measurements under load would likely provide more informative data. I just can't think of a safe way to do a test under load. The props are a significant hazard and I need to get pretty close (~1/2") to the motors to get good data. Perhaps I could build a safety cage out heavy gauge screening to go over the drone with opening over the hubs so I can get clear shot at the motor windings with my IR thermometer.

 

[brothers]

Just one thought: collecting peak frequency/peak amplitude data may not really warn you about imminent failure. When a bearing starts to fail, .it's most likely going to signal its distress at a low-amplitude subharmonic of the motor's primary frequency.

 

[N017RW]

The BLDC motors only have one moving/wearing part.
The bearings.
These will fail long before you develop a problem with one or more of the coils assuming you don't stall the motor under power.
So long as all motors have similar post-flight temps you can be sure all is well.
I have BLDC motors with over 600 hours and still no issues.
You wil likely sell, trade, retire, or wreck your Phantom long before a motor fails.

 

[Mark The Droner]

With my limited experience, I have to agree with #17RW and others above. From all the thread reading I've done, motors aren't apt to suddenly fail. It's more likely the ESC will fail. But even before that, something else will likely go wrong - like a compass or a prop or a crack in an electrical connection due to heat and age, or good old pilot error ending in catastrophe. When I first started this hobby, I learned some will use a thermal laser to check the motors after a flight; others will simply feel the motors with their fingers after a flight. But the majority of experienced pilots simply don't worry about it. The motors are solid.