[Guest]

What was the magnet material? My comments are generic, high quality samarium cobalt can go up to 150+C without failure.

What was the temp class of the windings? If you have a low temp class windings and high temp magnets, its no surprise that you failed the windings first....but this is not how most motors are/should be made for our applications.

There are other failure modes, wire failure causing a short in the windings etc. etc. that could/would destroy windings before magnet failure. For instance if a manufacturer did not use PWM rated wire, its possible you failed the wire.

Why are you bench running? There is really no need and its overly stressful on the motor as there is no cooling. With a good logger you can get all the data you need in flight and its much more meaningful anyway.

[eajohnson]

Originally Posted by can773

What was the magnet material? My comments are generic, high quality samarium cobalt can go up to 150+C without failure.

What was the temp class of the windings? If you have a low temp class windings and high temp magnets, its no surprise that you failed the windings first....but this is not how most motors are/should be made for our applications.

There are other failure modes, wire failure causing a short in the windings etc. etc. that could/would destroy windings before magnet failure. For instance if a manufacturer did not use PWM rated wire, its possible you failed the wire.

Why are you bench running? There is really no need and its overly stressful on the motor as there is no cooling. With a good logger you can get all the data you need in flight and its much more meaningful anyway.

I've had this happen with magnets rated at 180C and also with lower rated magnets (prob. 100 to 120 range). There's a bit of cooling on the bench, the motor is open and of course there is prop wash, but this is much less at the very center of the prop of course which is where the motor is. I bench test because failures in flight are much more expensive than failures on the bench. In-flight can sometimes be worse (as I've unhappily discovered) due to cowling. There are lots of variables. My point anyway is that internal temps can get very very high even when the external temp is pretty moderate i.e. no problem touching with bare hands. The windings can be several mm thick and heat dissipation from inside the windings isn't necessarily very good. Some of these motors with high temp magnets will indeed fail the windings first when pushed hard (not necessarily within motor spec, I mean when pushed to failure). Also a motor that works fine with a short motor run may fail in the windings on a longer run or repeated runs (beware putting in a larger capacity battery and taking a flight that is twice as long), even though the magnets may have reached a steady state temperature relatively early on. I don't think we're necessarily disagreeing, I'm just pointing out that it isn't always the magnet, the windings can and do fail as well.

Eric

[Guest]

I would question the magnet rating unless you know the material its based on. Most motors will use Neodymium because of hits high strength, and I don't recall seeing many Neo magnets that are rated for higher than about 100C. To get 180C you need Samarium Cobalt of a very high quality, I doubt many manufacturers will use this unless its industrial and costs big $$$. If you are buying Chinese made motors, I would not trust any spec posted.

Are you recording real time data while bench testing? So you can see current draw in real time?

By the sounds of it you are intentionally running your motors beyond their ratings....you situation is highly specific, and such you cannot use your failures to describe what is going to happen to the majority.

[eajohnson]

Originally Posted by can773

I would question the magnet rating unless you know the material its based on. Most motors will use Neodymium because of hits high strength, and I don't recall seeing many Neo magnets that are rated for higher than about 100C. To get 180C you need Samarium Cobalt of a very high quality, I doubt many manufacturers will use this unless its industrial and costs big $$$. If you are buying Chinese made motors, I would not trust any spec posted.

Are you recording real time data while bench testing? So you can see current draw in real time?

By the sounds of it you are intentionally running your motors beyond their ratings....you situation is highly specific, and such you cannot use your failures to describe what is going to happen to the majority.

Yep I push some (not all) of my motors hard, and I try to test them out on the ground prior to committing to air, and even then I isolate my radio power and motor power systems because for the reason you mentioned earlier, you can get cascading failures that take out everything (magnets>windings>ESC and maybe even damage the batt also).

Just for general interest neodymium magnets are available in a broad array of temp ratings, though higher strength tends to correspond to lower temp rating (there are only a couple places where you can buy what is purported to be an N50 strength magnet in NEH temp rating, and those ratings seem somewhat suspect):

N 80ºC
NM 100ºC
NH 120ºC
NSH 150ºC
NUH 180ºC
NEH 200ºC

When I'm using motors that use high temp magnets (e.g. NSH or better), and particularly outrunner motors where magnet heat is being dissipated through the can as opposed to inrunners where it is the winding heat that goes out through the can, I'm no longer surprised when it's the windings that fail first.

Eric

[Guest]

If you are purchasing off the shelf motors from China, how you are determining materials? Its one thing to know they are out there and maybe available and another to know that is whats going in your motor.

Second, unless you are taking real time high speed DAQ I don't think you can know which went first, magnets or windings. The higher the power setup, the faster its going to happen.

Even very expensive motors are only using Neo magnets in the 100C range. Intelligent outrunner design will have high temp rated windings (class H), such that the magnets fail first.

[eajohnson]

Originally Posted by can773

If you are purchasing off the shelf motors from China, how you are determining materials? Its one thing to know they are out there and maybe available and another to know that is whats going in your motor.

Second, unless you are taking real time high speed DAQ I don't think you can know which went first, magnets or windings. The higher the power setup, the faster its going to happen.

Even very expensive motors are only using Neo magnets in the 100C range. Intelligent outrunner design will have high temp rated windings (class H), such that the magnets fail first.

I'm a little surprised that you're disagreeing, I didn't think my assertion was all that 'out there'. Various motor manufacturers do say what magnets they use and will also tell you if asked e.g. Neu, Hyperion, Scorpion (and these three don''t all use high temp rated magnets). There is enough mass in the can and the magnets in my opinion that if you take a reading 15 or even 30 seconds after the motor self-destructs, and it shows the magnets are still reasonably cool, I feel pretty confident in concluding that wasn't the root cause of failure, unless of course the magnets were actually much lower rated than what they had been advertised to be.

I've been warned my motor manufacturers that the internal winding temps are much higher than what you will get in an external reading.

All our magnets come from China regardless of where the motor is built, China produces something like 85% of the world production of rare earth oxides, it's basically where this stuff comes from.

[Guest]

Of those three companies you listed Neu is the only manufactuer, the others buy from an OEM supplier. Hyperion and Hacker for instance use the same supplier (for outrunners) in Asia...so no I would not trust what they say is in the motors.

Anywho, this is not going anywhere

[eajohnson]

Originally Posted by can773

Of those three companies you listed Neu is the only manufactuer, the others buy from an OEM supplier. Hyperion and Hacker for instance use the same supplier (for outrunners) in Asia...so no I would not trust what they say is in the motors.

Anywho, this is not going anywhere

Definitely a possibility that the rating claims are wrong (e.g. controversy surrounding the Scorpion N50 high temp magnet claims). Most manufacturers seem OEMed through companies in Asia, though the specs do differ between motors (they are not all the same or made of the same materials). Neu outsources too, they just do final assembly in their shop (I know, I've been waiting 5 months on my latest motor that they're putting together for me because they've been waiting for one part after another from their suppliers). Good discussion though, hopefully it served some purpose.