Question regarding FLIGHT MOTOR'S PRE-FLIGHT CHECK. How can a PIC determine if a motor is nearing a possible state of failure???

[Don Testme]

I know carrying any extra load on most, if not all mavics, is not recommended by DJI. But sometimes, I do carry a load. I notice sometimes the back or front motors can be excpetionaly hot after the flight. Yeah, you could say, "just don't carry heavy loads or any at all." But besides this, how would any drone operator know if something is wrong with one of the drones motors regardless if they have or have not carried loads on their DJI drones. What about the regular guy, who just does filming without carrying anything on the drone. How or is there any way to check the motors for airworthiness? What if one is going bad, but there are no signs?

Also, just wondering, we have battery sensors, and gimbal motor sensors. Could DJI add a system that could check the flight motors prior to taking off and or while in flight.

 

[Yorkshire_Pud]

Spin the motor slowly with your finger tips and pay attention to what you feel. It may pulse a bit due to magnets approaching and leaving poles but that is sort of smooth, you shouldn't feel any sudden clicks etc. Also check for wobble of the rotor. I had a mavic mini motor feel wobbly but I think that was due to the screws that clamp the motor to the arm having partially undone. Unfortunately I unscrewed them before I checked if they were nippled up.

 

[akdrone]

I just watch for my drone to begin to fly erratically and then dive uncontrollably to the ground. I figure that's a tip off.

 

[Rich QR]

I turn each motor by hand, paying attention to the feel, and comparing each one to the others. If any one of them feels different, that's a problem.

It won't catch everything. But I hope it should catch mechanical issues like failed bearings and such.

 

[cheddar-man]

There is very little to go wrong with these motors, most likely the props that will fail.
Check prop securing screws regularly, they can come lose. Check for defects, nicks etc. Change if found. If you do change a prop, suggest you change them in pairs and make sure you put the right props on the correct motors.
Sensors, what could you "sense"? Temperature, yes. Vibration, yes both of which you can do with your fingers.
If you use the drone as it's designed, very unlikely anything will fail.

 

[LoudThunder]

What about the regular guy, who just does filming without carrying anything on the drone. How or is there any way to check the motors for airworthiness? What if one is going bad, but there are no signs?

Besides the standard prop check and motor rotation prior to starting as others have already written about. I listen while turning the prop/motors over by hand. Everything should sound normal, no squeaks, grinding, etc…

Then I start my motors (just idling), I listen again, everything moral, I lift off about 6-feet, above eye level and hover a moment, listening; then if I'm still satisfied, I perform my flight check (yaw, roll, and pitch-about a foot in each direction to make sure all controls are working properly.

Now, if I suspect there might be an issue with wind, I turn (yaw) my drone to face North, I then rise up to 50' and check the Atti gauge, looking to see if my drone is having to pitch or roll to fight the wind, then to 100', same thing…

 

[KI5RLL]

All of the above. With 2 additions. If you are carrying payload, remember your ESC’s. They will be getting hotter also along with your motors. ESC failure often happens well before motor failure due to heat. Often they will cook before a motor. They haver cooling fans in a Mavic yes, but nothing like the motors under the props. ESC’s fail too. That can happen in a Mavic.
I flew 1700 miles on my MA2 before selling it with never an issue. Next guy already added about another 150 miles no issues. With serious close inspections all the way.
These are brushless motors. So the old failure criteria is very much eliminated. They do fly a very long time. 6000-12000 rpm for 1700+ miles is a LOT of motor turns.
But you can check other things.
A.
1. Remove a prop
2. With a good handheld magnifying glass, look down into the motor housing to the core. Make sure the vinyl coated copper wiring around the poles is clean, not bubbled, not peeling, no blisters, no flakes or soot on them. Excess heat can damage those windings coatings until they short across each other, then they really burn out.
3. Magnifying glass look at the shaft bearing seats. Clean, dry, no warped seals. Not dirt caked. Hold the glass in one hand while looking, other hand gently spin and wobble the shaft to ensure zero woobble in it.
4. Magnifying glass look at the small neodymium magnets cemented out around the field. None loose or loose and magnetic stuck to a neighbor beside itself. No micro pieces of spare metals stuck to any of them. Picked up out of your bag or box or carpet or yard etc. Spare small metal frags are everywhere around people. These small powerful neodymium magnets will pick them up.
B.
See attached Pics. These are around $20 now. Any model, this is just an example of an IR thermometer gun. Walmart or any hardware has them.
Warm by hand is just that. Warm by comparison is what matters a bit more. Warm by IR read is way more accurate. One single motor may be running 20 degrees hotter than the other 3. Possibly a sign of a problem coming.
Find where the ESC’s are on your craft model. After landing, shoot an IR of the motors. Shoot an IR close to ESC’s also along the bottom heat sink and the craft body, as well as cooling ports.
104F is the top ambient flight temperature Mavic shows on my spec. sheet now. Add the sun, battery conduction heat, normal heat production, ESC heat production, plus payload extra heat production, over a few flights, and that may be reducing component life.
If you are heating your ESC’s and motors (IR reading) too hot for too long, yes they can fail.
There are some very smart electronics people on this forum. They know their science and field. They can tell you how hot your ESC or motor running temps can go for how long before they start degrading.
Add flying in hot weather already, and they may not be able to take much more heat anyway.
But these Mavics are very well built and durable craft. I have flown a 27 minute flight at 112F and landed. Hot craft but no warnings. Only did that once.

If you really want to go deep, we can discuss using a field ammeter and voltmeter around an arm of your Mavic with motors turning. High amperage from high impedance to one motor could show a problem. The onboard computer system will trip a fault at some point too high. But Mavic doesn’t publish that info. as a normal operating range. But we can calculate much of it.

Safe Flying,
KI5RLL

 

[cheddar-man]

If you really want to go deep, we can discuss using a field ammeter and voltmeter around an arm of your Mavic with motors turning. High amperage from high impedance to one motor could show a problem.

Safe Flying,
KI5RLL

Sorry, not quite true. These are effectively three phase motors and current can only be measured wire by wire, not around all three at the same time, with a clamp-on type ammeter. Unless the laws of electricity have changed?
Sorry again but high impedance (resistance) will give you lower current, a short circuit will give you high.
Yes keep an eye on motor temperature. They'll soon let you know of overload and potential trouble.
Personally I would never "load" my drone, they are designed to operate as designed and built.

 

[Yorkshire_Pud]

@cheddar-man 's post makes me ask, since a stalled motor has low impedance do ESC's, in general, have over-current protection? If so has it been improved in the Mavic type drones?

From what I have seen it was/is easy to cook a P3's ESC in a crash that stopped the relevant motor.
I have had a warning from a P3 but fortunately once everything 'cooled?' down the warning disappeared, I had CSC'ed the drone as soon as it hit the hedge (my fault) and started to fall so the motor wasn't trying to turn for long before the power was cut.
Mavic type drones seem to be either less likely to cook an ESC or better protected.

 

[DougMcC]

All of the above. With 2 additions. If you are carrying payload, remember your ESC’s. They will be getting hotter also along with your motors. ESC failure often happens well before motor failure due to heat. Often they will cook before a motor. They haver cooling fans in a Mavic yes, but nothing like the motors under the props. ESC’s fail too. That can happen in a Mavic.
I flew 1700 miles on my MA2 before selling it with never an issue. Next guy already added about another 150 miles no issues. With serious close inspections all the way.
These are brushless motors. So the old failure criteria is very much eliminated. They do fly a very long time. 6000-12000 rpm for 1700+ miles is a LOT of motor turns.
But you can check other things.
A.
1. Remove a prop
2. With a good handheld magnifying glass, look down into the motor housing to the core. Make sure the vinyl coated copper wiring around the poles is clean, not bubbled, not peeling, no blisters, no flakes or soot on them. Excess heat can damage those windings coatings until they short across each other, then they really burn out.
3. Magnifying glass look at the shaft bearing seats. Clean, dry, no warped seals. Not dirt caked. Hold the glass in one hand while looking, other hand gently spin and wobble the shaft to ensure zero woobble in it.
4. Magnifying glass look at the small neodymium magnets cemented out around the field. None loose or loose and magnetic stuck to a neighbor beside itself. No micro pieces of spare metals stuck to any of them. Picked up out of your bag or box or carpet or yard etc. Spare small metal frags are everywhere around people. These small powerful neodymium magnets will pick them up.
B.
See attached Pics. These are around $20 now. Any model, this is just an example of an IR thermometer gun. Walmart or any hardware has them.
Warm by hand is just that. Warm by comparison is what matters a bit more. Warm by IR read is way more accurate. One single motor may be running 20 degrees hotter than the other 3. Possibly a sign of a problem coming.
Find where the ESC’s are on your craft model. After landing, shoot an IR of the motors. Shoot an IR close to ESC’s also along the bottom heat sink and the craft body, as well as cooling ports.
104F is the top ambient flight temperature Mavic shows on my spec. sheet now. Add the sun, battery conduction heat, normal heat production, ESC heat production, plus payload extra heat production, over a few flights, and that may be reducing component life.
If you are heating your ESC’s and motors (IR reading) too hot for too long, yes they can fail.
There are some very smart electronics people on this forum. They know their science and field. They can tell you how hot your ESC or motor running temps can go for how long before they start degrading.
Add flying in hot weather already, and they may not be able to take much more heat anyway.
But these Mavics are very well built and durable craft. I have flown a 27 minute flight at 112F and landed. Hot craft but no warnings. Only did that once.

If you really want to go deep, we can discuss using a field ammeter and voltmeter around an arm of your Mavic with motors turning. High amperage from high impedance to one motor could show a problem. The onboard computer system will trip a fault at some point too high. But Mavic doesn’t publish that info. as a normal operating range. But we can calculate much of it.

Safe Flying,
KI5RLL

That was very educational and helpful. Thanks

 

[cheddar-man]

@cheddar-man 's post makes me ask, since a stalled motor has low impedance do ESC's, in general, have over-current protection? If so has it been improved in the Mavic type drones?

From what I have seen it was/is easy to cook a P3's ESC in a crash that stopped the relevant motor.
I have had a warning from a P3 but fortunately once everything 'cooled?' down the warning disappeared, I had CSC'ed the drone as soon as it hit the hedge (my fault) and started to fall so the motor wasn't trying to turn for long before the power was cut.
Mavic type drones seem to be either less likely to cook an ESC or better protecte

Good question YP and to answer we need to know what motors/.ESCs are fitted. I cannot find that answer so anybody stripped say a Mini 2 down and can advise what's in there?
By the way, one of the best articles on drone motors and ESCs for anybody interested in learning.
Just done a bit of a search and it seems the ESCs on the Mini2 are in the body of the drone, not in the arms as is the case with the old Phantoms. From the image it looks as though all four ESCs are on the one board looking at the R, B & W on each corner.

 

[Yorkshire_Pud]

Cheers, one point, in the P3adv/pro the ESC's are not in the arms, I can clearly remember that, it's just wire, from the mainboard to the motors, in the arms. I her don't know about other phantom but separate ESC's would I think be very welcome and far better than my recollection, which is.
The ESC's are on a board and I think it's the mainboard. If so that becomes a complete pain in the 'pass' since it more or less means a blown ESC scraps the mainboard.

 

[Robert Prior]

I just watch for my drone to begin to fly erratically and then dive uncontrollably to the ground. I figure that's a tip off.

Sounds like navigating by potato…

 

[KI5RLL]

Sorry, not quite true. These are effectively three phase motors and current can only be measured wire by wire, not around all three at the same time, with a clamp-on type ammeter. Unless the laws of electricity have changed?
Sorry again but high impedance (resistance) will give you lower current, a short circuit will give you high.
Yes keep an eye on motor temperature. They'll soon let you know of overload and potential trouble.
Personally I would never "load" my drone, they are designed to operate as designed and built.

I didn’t know they are three phase motors. Cool to know! Yes we have smart electronics folks here thank for answering.
I also fly a B25 with big 13” 3-blade props on electric motors and big ESC’s in each wing. Certainly different than DJI stuff. We use field ammeters and other stuff on them also. But the motor wires are much more accessible to the motors from the ESC area.
Thank you.

Safe Flying,
KI5RLL

 

[cheddar-man]

Basic diagram of ESC + MOTOR wiring. As you can see HERE, the ESC converts the incoming battery supply, + & -, (plus input from the flight computer) into either a sine or square wave three phase supply to operate the motor.

 

[KI5RLL]

Basic diagram of ESC + MOTOR wiring. As you can see HERE, the ESC converts the incoming battery supply, + & -, (plus input from the flight computer) into either a sine or square wave three phase supply to operate the motor.

Yep that is it. An induction ammeter works on the power lines to the ESC there of course. Same as in many circuits. We use an induction ammeter to measure power in a 3-phase circuit. The final load could be many things.
Went through a lot of this in learning to get my radio operator license here in US, but the heavier math I had to let go of, and just look it up again when I need it. We just do the math to make sure we get true rms.
Or use it for comparative circuitry.

 

[Meta4]

how would any drone operator know if something is wrong with one of the drones motors ...... carried loads on their DJI drones. What about the regular guy, who just does filming without carrying anything on the drone. How or is there any way to check the motors for airworthiness? What if one is going bad, but there are no signs?

Brushless electric motors are just about bullet proof.
It's unlikely you'll ever have a problem with them.
Motors getting hot is quite normal.

 

[cheddar-man]

Brushless electric motors are just about bullet proof.
It's unlikely you'll ever have a problem with them.
Motors getting hot is quite normal.

True M4. I remember the old days of RC with brushed motors and if you didn't get the anti spark circuit right the commutator sparking would interfere with the old 27Mhz receiver and the plane would be almost uncontrollable.
And even further back with the vibrating reed system!
Yes, I've been RCing since the 1950s!!

 

[LoudThunder]

I've been RCing since the 1950s!!

You have a decade on me so I was not yet into RC in the '50s, but my first set of HO Scale Slot Cars (c1960) used the Vibrating Reed. Since we were were at home, not in the field. Our Reed Motors would ruin the TV reception for all our neighbors...

 

[Sky One Ohio]

All of the above. With 2 additions. If you are carrying payload, remember your ESC’s. They will be getting hotter also along with your motors. ESC failure often happens well before motor failure due to heat. Often they will cook before a motor. They haver cooling fans in a Mavic yes, but nothing like the motors under the props. ESC’s fail too. That can happen in a Mavic.
I flew 1700 miles on my MA2 before selling it with never an issue. Next guy already added about another 150 miles no issues. With serious close inspections all the way.
These are brushless motors. So the old failure criteria is very much eliminated. They do fly a very long time. 6000-12000 rpm for 1700+ miles is a LOT of motor turns.
But you can check other things.
A.
1. Remove a prop
2. With a good handheld magnifying glass, look down into the motor housing to the core. Make sure the vinyl coated copper wiring around the poles is clean, not bubbled, not peeling, no blisters, no flakes or soot on them. Excess heat can damage those windings coatings until they short across each other, then they really burn out.
3. Magnifying glass look at the shaft bearing seats. Clean, dry, no warped seals. Not dirt caked. Hold the glass in one hand while looking, other hand gently spin and wobble the shaft to ensure zero woobble in it.
4. Magnifying glass look at the small neodymium magnets cemented out around the field. None loose or loose and magnetic stuck to a neighbor beside itself. No micro pieces of spare metals stuck to any of them. Picked up out of your bag or box or carpet or yard etc. Spare small metal frags are everywhere around people. These small powerful neodymium magnets will pick them up.
B.
See attached Pics. These are around $20 now. Any model, this is just an example of an IR thermometer gun. Walmart or any hardware has them.
Warm by hand is just that. Warm by comparison is what matters a bit more. Warm by IR read is way more accurate. One single motor may be running 20 degrees hotter than the other 3. Possibly a sign of a problem coming.
Find where the ESC’s are on your craft model. After landing, shoot an IR of the motors. Shoot an IR close to ESC’s also along the bottom heat sink and the craft body, as well as cooling ports.
104F is the top ambient flight temperature Mavic shows on my spec. sheet now. Add the sun, battery conduction heat, normal heat production, ESC heat production, plus payload extra heat production, over a few flights, and that may be reducing component life.
If you are heating your ESC’s and motors (IR reading) too hot for too long, yes they can fail.
There are some very smart electronics people on this forum. They know their science and field. They can tell you how hot your ESC or motor running temps can go for how long before they start degrading.
Add flying in hot weather already, and they may not be able to take much more heat anyway.
But these Mavics are very well built and durable craft. I have flown a 27 minute flight at 112F and landed. Hot craft but no warnings. Only did that once.

If you really want to go deep, we can discuss using a field ammeter and voltmeter around an arm of your Mavic with motors turning. High amperage from high impedance to one motor could show a problem. The onboard computer system will trip a fault at some point too high. But Mavic doesn’t publish that info. as a normal operating range. But we can calculate much of it.

Safe Flying,
KI5RLL

I use a UTi260B thermal imager from amazon. When i bought mine I got it for about $360 bit they are higher now. Its 256x192 IR resolution ( i wouldn't go any lower on resolution tho) and yiu can buy a macro lens for it for circuit boards. I figured what is 3 to 4 hundred when my cheapest drone cost over $900 not counting extras and more batteries etc. It has pretty good specs and its very durable as I have used at my current job as a CNC service engineer and it really got abused at my last job as a well driller/pump Installation technician. That job required alot of skills from 3phase electrical to running drilling rigs, cranes and equipment on sometimes muddy job sites to installing and wiring commercial and municipal pumps for water supply wells or high service booster pumps even sewage booster pumps, rebuilding them, fabricating and repairing equipment and more. Needless to say it got banged around alot and still works like the day i bought it. Basically saying it might not be a Fluke but its worth buying lol.

I use hand warmers on my drone battery when its near zero degrees out and i ised the thermal imager to check how. Well they were working, i fly in cold all the time now with 2 rubberbands and air activated hand warmers. I sometimes but a small insulating material between it and the battery anx if its not real cold i just wrap the battery in that silver emergency blanket material. I know this ia off topic but my wife will tell you, Im bad about changing topics on the fly anf ging way off into other directions. Lol.