Suddenly burning up motors

[Jessek1486]

Heh, seems I am quite prone to unknown changes/parts breaking, as I've posted a few of these threads and have gotten great advice.

So, I went to my usual field only to find some random activity taking place there. I go to a second one I've been to before, and fly. All is well, I land, swap battery and about a minute into the flight I see a puff of smoke from the motor and bring her in for an emergency landing. I swap motor at home, and fly another battery pack.

Similar thing happens, but no smoke, I just notice the sudden loss of power/stuttering of the motor. It smells slightly burnt.

Now, I can't for the life of me figure out HOW this would happen suddenly. I've never burned out a motor using the exact same config I've used, props/ESC and all. The ONLY change I made is the field, but I've also flown here before, so I dunno about that.

It is rainy season now, so while it wasn't raining, it had the night prior, so the landing site was a bit muddy. But again, I've gotten the plane wet/muddy before and never an issue. I do suspect something with the ground, and it's Florida so no "soil" per se, but sand. Everything I can find online about brushless motors says they're not really effected by water/sand other than the bearings. I don't think a bit of sand/dirt would cause motors to quickly smoke themselves, as I've legit flown head first into a dirt mound(imported soil) and no issues, in fact it was great for a crash landing!

I'm stumped.

 

[Merv]

I know I need to carefully watch my setup anytime it gets hot out, for me, that is anything above 95 degrees. When my motors started getting hot, I switched to a smaller prop.

I'm not sure what your temperatures have been like. If it's hotter than normal, you may just need a smaller prop.

 

[Jessek1486]

I know I need to carefully watch my setup anytime it gets hot out, for me, that is anything above 95 degrees. When my motors started getting hot, I switched to a smaller prop.

I'm not sure what your temperatures have been like. If it's hotter than normal, you may just need a smaller prop.

I mean, it's been about 95F everyday since Mid May here, but yesterday wasn't any hotter than usual.

I considered this, but all the sudden in one day, two motors?

If I can't find any other explanations others may have, then I'll have to try this. Or just early AM/post thunderstorm as it'll drop to 80F.

 

[Jessek1486]

I just remembered my first flight yesterday was at 9:30am and it was only 85F so I really doubt it was the heat, both times since they were hours apart.

Plus 85F is a pretty reasonable temp.

 

[Tench745]

You're right that water and dirt don't make a difference to the motor, except if they somehow gum up the bearings and add some load to the system.
Only things I can think of are some variable you maybe didn't notice. Maybe it windier and you had the throttle a little higher than normal, or battery voltage slightly different than usual. But none of these things would be enough to push it over the edge unless your motor was already pushed to the edge of its operating range.
Clearly the windings burnt on the motor you posted a pic of. Could there have been some damage to the windings on both motors that you didn't notice, and it's just coincidence that this was the day they gave up?

 

[Jessek1486]

You're right that water and dirt don't make a difference to the motor, except if they somehow gum up the bearings and add some load to the system.
Only things I can think of are some variable you maybe didn't notice. Maybe it windier and you had the throttle a little higher than normal, or battery voltage slightly different than usual. But none of these things would be enough to push it over the edge unless your motor was already pushed to the edge of its operating range.
Clearly the windings burnt on the motor you posted a pic of. Could there have been some damage to the windings on both motors that you didn't notice, and it's just coincidence that this was the day they gave up?

I mean, it was pretty low wind. I've flown in high winds, like 25mph gusts and all. All the way down to calm as could be and only thermals for wind.

Battery voltage is always the same. 4.20/12.6 to start.

I hadn't noticed any loss of power like it was struggling.

The only thing that I did differently was the field, and I did land in the same spot.

It kicked up a decent amount of that swamp muck, enough that I noticed it, and hada pour her out before chucking it again.

Motors both burned up after landing, too.

I was thinking maybe some metal filings got in the motor from the swamp muck?

 

[quorneng]

I am not sure that a hot motor and then landing in watery conditions is that good a scenario.
The sudden cooling could cause the lacquer insulation on the winding to break down. Next time the motor is used it could lead to a physical short and a motor burnout.
It would pay to know just how close you are to the motor's amp limit.

The first thing I do on any new motor, prop, ESC & battery set up is measure the full power amps with a Watt meter to check it is adequately within the specification of the components.

 

[Jessek1486]

I am not sure that a hot motor and then landing in watery conditions is that good a scenario.
The sudden cooling could cause the lacquer insulation on the winding to break down. Next time the motor is used it could lead to a physical short and a motor burnout.
It would pay to know just how close you are to the motor's amp limit.

The first thing I do on any new motor, prop, ESC & battery set up is measure the full power amps with a Watt meter to check it is adequately within the specification of the components.

Really? I had no idea about that, but it does make sense. Essentially differential thermal expansion(contraction in this case) is what caused that.

Would explain why I haven't had that issue with early AM flights and the morning dew in the grass.

Yeah I'm probs over amp/watt limit tbh, 2212 1400kv with an 8x6 prop on 3s. I think it pulled 22a last time I checked? 250w or so.

Hadn't had any issues with motors burning up, in fact, dunno that I have burned one up before.

 

[Merv]

...It was only 85F so I really doubt it was the heat...

I agree 85 is not that bad. Air temp is just one thing to keep in mind. Especially as you approach 100 or more.

I think quorneng & trench are making valid points.

 

[Jessek1486]

I'm pretty confident that's what it is. I'm living on the edge 😂

Same thing happened with my elevator servos. They started giving up the ghost.

 

[Merv]

...Same thing happened with my elevator servos. They started giving up the ghost.

I've had great results with the cheap metal gear servos from ebay, banggood or aliexpres. I don't use them with any kind of flight controller or stabilization. The constant movement on more or less the same spot wears them out prematurely.

 

[Jessek1486]

I've had great results with the cheap metal gear servos from ebay, banggood or aliexpres. I don't use them with any kind of flight controller or stabilization. The constant movement on more or less the same spot wears them out prematurely.

Oh yes! I've upgraded since then to the cheapy metal gear ones, and it's been fine.

My point was that this was the second time I've found out the hard way I'm redlining my components. Basically by sudden failures.

Any advice on finding a slightly beefier motor?

 

[Merv]

...Any advice on finding a slightly beefier motor?

As someone else mentioned, get a watt meter.

 

[Jessek1486]

As someone else mentioned, get a watt meter.

Oh yeah I have one, I posted the numbers earlier.

I meant in finding one in the sea of bogus metrics or different ways of expressing motor sizes. They're not directly comparable across manufacturers it seems.

 

[Merv]

...They're not directly comparable across manufacturers it seems.

Agreed. I have found watts & Kv to be my best guide. Pick the watts for the size of plane & how you want to fly. Then the Kv for how fast you want to go, if you want speed, pick a higher Kv. Get the watts form the seller, if they don't provide it, pick a different seller.

The amount of thrust needed from the motor & prop depends on how you want to fly. A slow flying trainer, the thrust will need to be 60-80% of the weight of the plane. A typical plane, 80-100%. A war bird or one with a little zip will be 100-150%. A 3D plane will need 150-200% thrust to plane weight.

Watts per pound is another useful guideline. You'll need to weigh the plane and estimate the weight of the motor and battery.

• 50 to 70 watts per pound is the minimum level of power, good for park flyers and lightly loaded slow flyers.
•70 to 90 watts per pound is perfect for trainers and slow-flying aircraft.
•90 to 110 watts per pound is good for fast-flying scale models and some sport aerobatic aircraft.
•110 to 130 watts per pound is what you want for advanced aerobatics and high-speed aircraft.
•130 to 150 watts per pound is needed for lightly loaded 3D models and ducted fans.
•150 to 210+ watts per pound gives unlimited performance for any 3D model.

Here is a FT thread with more information.

Thrust vs Power to Weight Ratios for Prop Planes​

 

[Shurik-1960]

From the photo of the motor, I see a bad winding of the coils and a burnt-out wire. Most likely you have cheap motors with poor quality wire. I will rewind the new motor from China myself, which worked fine before being installed on the aircraft model, and when I turned on the full throttle on the model to check the thrust and current (the watmeter was connected), the motor stopped and began to twitch (one of the phases burned out).

 

[Jessek1486]

Agreed. I have found watts & Kv to be my best guide. Pick the watts for the size of plane & how you want to fly. Then the Kv for how fast you want to go, if you want speed, pick a higher Kv. Get the watts form the seller, if they don't provide it, pick a different seller.

The amount of thrust needed from the motor & prop depends on how you want to fly. A slow flying trainer, the thrust will need to be 60-80% of the weight of the plane. A typical plane, 80-100%. A war bird or one with a little zip will be 100-150%. A 3D plane will need 150-200% thrust to plane weight.

Watts per pound is another useful guideline. You'll need to weigh the plane and estimate the weight of the motor and battery.

• 50 to 70 watts per pound is the minimum level of power, good for park flyers and lightly loaded slow flyers.
•70 to 90 watts per pound is perfect for trainers and slow-flying aircraft.
•90 to 110 watts per pound is good for fast-flying scale models and some sport aerobatic aircraft.
•110 to 130 watts per pound is what you want for advanced aerobatics and high-speed aircraft.
•130 to 150 watts per pound is needed for lightly loaded 3D models and ducted fans.
•150 to 210+ watts per pound gives unlimited performance for any 3D model.

Here is a FT thread with more information.

Thrust vs Power to Weight Ratios for Prop Planes​

Fair enough! I appreciate the info, it's all just finding reputable manufacturers I guess. Maybe I'll try a legit branded motor like sunnysky.

 

[Jessek1486]

From the photo of the motor, I see a bad winding of the coils and a burnt-out wire. Most likely you have cheap motors with poor quality wire. I will rewind the new motor from China myself, which worked fine before being installed on the aircraft model, and when I turned on the full throttle on the model to check the thrust and current (the watmeter was connected), the motor stopped and began to twitch (one of the phases burned out).

Where's the bad winding??

I'm confused, you've rewired the motor, which worked fine, but no longer worked after??

 

[Merv]

...Maybe I'll try a legit branded motor like sunnysky.

I have great results with Racestar & DYS. I can usually get 3 or 4 of these for the price of 1 of the name brand stuff. If I do burn one out, which rarely happens. I just grab another from my box of spares.

My cheap stuff fails at about the same rate as my buddies expensive stuff.

 

[Shurik-1960]

I rewound the first motor 10 years ago: I didn't have a wattmeter and I put in a big screw - the motor burned out in flight. This motor is still running. All my repaired motors are working. You just need a good wire and wind it carefully, turn by turn.Sunny sky has a lot of fakes. Aeolian - I have 6 motors that are 9 years old. There was a very good company, but I haven't seen their motors on Aliexpress for a long time.