C_alan

I have access to a SkyRC Brushless Motor Analyzer, and I have picked up a few used brushless motors.

Is there any rules of thumb I could use to tell from the results of the analyzer that a motor has been overheated?

King DORK

iTrader: (53)

Never used a motor analyser, but an overheated motor usually has a very distinct smell, even if you disassemble the motor and everything appears fine.

Roelof

- Low magnetism rotor (only to detect with a gauge meter and knowing what it original need to be)
- burning smell
- no rotation at all.
- no equal resistance if you measure the resistance in all possible ways over the 3 wires
- mechanical resistance

And no, not realy to be detected by a motor analyzer.

Cavi Mike

iTrader: (1)

If the stator has been overheated, it will smell like a blown speaker. If the rotor has been overheated, there’s no way to tell whatsoever. The loss in magnetism can only be checked if you knew exactly what its gauss measurement was when the motor was new and if it was checked both times with the exact same meter. But rotors are easy to replace - stators not so much since they’re glued to the can.

Dino_D

The smell is usually from a burnt sensor board or burnt wiring. If it reaches that point, the motor won't work or has some stuttering issues.

However, most people can get it hot enough to over heat the rotor but not enough to burn out the sensor or wiring, hence no visible damage or smell.
And over heated rotor can easily be fixed by replacing it. Generally you can tell if the rotor is overheated by feeling the COG on the motor. You can compare a new one to yours to see. If the rotor is easy to spin without much cog or resistance, then its most likely been overheated or lost its magnetism over time. Perhaps you can find someone who has a rotor checker to check the guass rating. Most of the latest STOCK 12.5 motors will have a guage reading of 1700+ or higher. Modified rotors are in the 2000+ range.

Cavi Mike

iTrader: (1)

Almost everything you said is incorrect. To degauss a rotor enough to feel a difference you would need to heat it up to a few hundred degrees - and the stator would have failed before that could ever happen.



Also - stock rotors come with the highest gauss ratings of all the rotors, not mod rotors. Mod rotors are designed for RPM, not torque - the drag braking effect of high gauss slows them down and prevents them from spinning fast. All mod rotors are lower gauss with smaller OD and/or larger ID magnets to minimize drag braking and maximize RPM. Take a look at any rotor chart from any manufacturer if you don’t believe me.

jasburrito

iTrader: (3)

No. I think your wrong. Dino d is spot on.
pros running spec rotors change them out after a few runs. I see the used ones stuck to metal objects in the Pitts. They get weak after getting hot.
Good magnet wire can handle 220. Good magnet can handle 170-200

mrreet2001

iTrader: (9)

Everywhere I have read 80° Celsius is when magnet quickly lose their magnetism. 176° Fahrenheit at the rotor is hardly "a few hundred degrees" and rather obtainable. If you are geared to the limit on a fan, losing the fan during a race is enough to harm a rotor.

gigaplex

iTrader: (2)

Your own chart shows the mod rotors typically have a higher gauss rating. 8/10 of them are greater than or equal to the strongest stock rotor.

C_alan

This rotor talk is interesting. What got me going on this is I have a 13.5 Team Powers motor that I have been using all season in my 4wd offroad car. That motor has always run hot, and has flirted with 175 degrees a few times. It doesn't have any kind of smell to it.

I put it on the motor analyzer and it runs about 31k rpms at 5.2 amps. However this motor does take a second to spin up compared to my other motors.

I have a brand new 13.5 R1 motor I haven't installed yet, and fresh out of the box it only runs about 29.5 rpms at around 5 amps.

So would dropping a new rotor into my old Team Powers Motor possibly bring it back to life?

trilerian

iTrader: (51)

Nothing about this statement shows that the Team Powers has lost anything. You are using a motor analyser with no load, thus the motor isn't producing torque. You will not be able to tell if your rotor has faded by this way of testing. All I see from the numbers you just posted is that the Team Powers will need different gearing than the R1. As Roelof suggested. Get a gauss meter and a known good rotor for a reference. Or get a dyno... Or try different gearing on the track and see what that does. You would probably be surprised to learn that driving style can affect gearing, and if your driving has changed over the season, it is possible that your gearing needs to change as well.

mrreet2001

iTrader: (9)

The correct way would be to get a gauss checker (either homemade or something like a Facts Machine), check the rating when new ... and then periodically when used. When the numbers get lower, it's (possibly) time to get a new one.

LowDrag

iTrader: (10)

I use to design linear voice coil motors back in the day, along with FEA simulations and high temp testing. You can verify if your rotor magnetic strength is degrading if your KV starts rolling off or get a gauss meter, but as someone said earlier, you have to check it at the beginning to know. The Curie temp for the low grade neodymium magnets is around 310C. We didn't see the flux fields start decaying until about 110C. Your rotor is typically 20-25C cooler than the stator windings due to the airgap and thermal isolation. The biggest issue with running your motor hot is the derated electrical performance. These are the design rules of thumb we still use in our systems and there's a ton of military hardware flying around based on these rules. Just throw it on on the motorlyzer and see if the KV's seem reasonable. There's some guys who test motors and publish the results on youtube for reference.

trilerian

iTrader: (51)

The issue you are going to run into with KV, is you can't trust the SkyRC analyzer's KV reading. The voltage of the SkyRC units vary as wildly as the timing does. Again, this is one of those situations where you need a baseline, and somebody else's baseline isn't going to work because of the variance in the product.

The moral of the story here: Test everything you want to about your motors when they are new, record everything into a spreadsheet or database. Every so often perform tests again with the same equipment and compare.

LowDrag

iTrader: (10)

The guy is just trying to see if his motors are toasted or not. Charge your batter to what the other guy did on his SkyRC unit and see if you're in the ball park on the KV's. That's it...You don't need a 0.1% standard deviation calibrated equipment to tell if you're motor is toast. Or go buy a gauss meter.