Motor Problems

[TexasPilot71]

Just ordered a replacement motor for my new (to me) FMS P-51 Snoot's Sniper.  I'm not sure how long the previous owner had it, or how many flights he put on it, but on my second battery yesterday (the first two batteries I put through it since purchase) I noticed an odd, high-pitched grinding sound at higher power settings. I brought it in, landed, looked at it, and put her back up in the air for the remaining 90 seconds of battery. Landed. Came home.

That evening, I turn the prop and I hear a grinding sound. Take off the spinner and prop down to bare shaft. Turn the shaft and the grinding is coming from the motor itself.  Something is making contact.  Keep in mind, this is the stock motor (FMS 4250-KV540).  So I logged on and ordered a replacement motor.

Decided to sit down and tear into the motor to better understand how they're built and what might be the problem.  Turns out, several (6 to 8) of the magnets weren't glued down.  They would simply slide up and down...none turned sideways or anything crazy.  Some local folks said to try re-gluing the loose magnets and see if that was the problem.  I still couldn't really tell what was actually grinding.  So after watching some You Tube videos, I gave it a shot, made matters worse, smeared glue everywhere, and just tossed the motor in the trash.  

Any thoughts on this?  Is this a typical issue?  Everything is stock on the airplane and I'm using a 4S 3000mAh 35C battery.

(Photos attached)

Thanks in advance!

[OV10]

RE: Motor Problems

Just ordered a replacement motor for my new (to me) FMS P-51 Snoot's Sniper. *I'm not sure how long the previous owner had it, or how many flights he put on it, but on my second battery yesterday (the first two batteries I put through it since purchase) I noticed an odd, high-pitched grinding sound at higher power settings. I brought it in, landed, looked at it, and put her back up in the air for the remaining 90 seconds of battery. Landed. Came home.

That evening, I turn the prop and I hear a grinding sound. Take off the spinner and prop down to bare shaft. Turn the shaft and the grinding is coming from the motor itself. *Something is making contact. *Keep in mind, this is the stock motor (FMS 4250-KV540). *So I logged on and ordered a replacement motor.

Decided to sit down and tear into the motor to better understand how they're built and what might be the problem. *Turns out, several (6 to 8) of the magnets weren't glued down. *They would simply slide up and down...none turned sideways or anything crazy. *Some local folks said to try re-gluing the loose magnets and see if that was the problem. *I still couldn't really tell what was actually grinding. *So after watching some You Tube videos, I gave it a shot, made matters worse, smeared glue everywhere, and just tossed the motor in the trash. *

Any thoughts on this? *Is this a typical issue? *Everything is stock on the airplane and I'm using a 4S 3000mAh 35C battery.

(Photos attached)

Thanks in advance!

Hello Tex,
This is not a "typical" issue as you have asked. It is more indicative of an overheating of the motor which caused the adhesive on the magnet(s) to deteriorate. I have 8 birds with FMS motors primarily in the 42 size but also in the 34 and 50. All of them have a lot of time on them and the only thing I have done to them is ensure periodic lubing of the bearings.
If I was to take a stab at your issue my guess would be that the previous owner "could have" tried to increase his/her speed performance by running with a 5 or 6S battery. I hear of this happening quite a bit by people that don't have clue as to what they are doing. So many times it has been suggested/recommended on this forum and others for a person to obtain a watt meter as part of their equipment for build/test/eval/mod purposes.
I wouldn't just garbage the old motor. I would salvage stuff like the bearings and you are going to need the prop shaft adapter because the new motor doesn't come with one.
Good luck,

[TexasPilot71]

RE: Motor Problems

Hello Tex,
This is not a "typical" issue as you have asked. It is more indicative of an overheating of the motor which caused the adhesive on the magnet(s) to deteriorate. I have 8 birds with FMS motors primarily in the 42 size but also in the 34 and 50. All of them have a lot of time on them and the only thing I have done to them is ensure periodic lubing of the bearings.
If I was to take a stab at your issue my guess would be that the previous owner "could have" tried to increase his/her speed performance by running with a 5 or 6S battery. I hear of this happening quite a bit by people that don't have clue as to what they are doing. So many times it has been suggested/recommended on this forum and others for a person to obtain a watt meter as part of their equipment for build/test/eval/mod purposes.
I wouldn't just garbage the old motor. I would salvage stuff like the bearings and you are going to need the prop shaft adapter because the new motor doesn't come with one.
Good luck,

Good stuff! I have indeed salvaged the parts such as prop shaft, screws, etc. I only tossed the part with the magnets, but like you said...not a bad idea to save the bearing.

I was thinking the same thing as far as why the glue would have deteriorated. I have a watt meter, but didn't use it on this one because I would have had to change connectors or build a harness. Plus it was easy to tell there was a mechanical grinding going on.

Glad to know this is not typical. Looking forward to the new motor and knowing exactly how it is operated. I ran into an acquaintance of the previous owner. He has an FMS P-51 as well and tried a 5S battery with disastrous results. Wonder if these guys were experimenting together. Hmmm....

Many thanks!!

[guapoman2000]

RE: Motor Problems

Too bad you could not salvage that motor as there are several compounds that could have re-adhered those lose magnets.  Of course if you suspect that the motor was overheated then, perhaps it was the best thing to do was to toss it as the magnets might have weakened depending on what kind they were.

Speaking of bearings, I have recently changed out my bearings on my Emax motor (BL3526/04) and purchased the required bearings over at BOCA Bearings here in South Florida and it was higher quality than the stock and my motor runs super smooth, better than new.

[Konrad]

RE: Motor Problems

When you re-glued the magnets had you determined their polarity? 


I use epoxy that is rated for 400°F for reattaching magnets. This is not hobby grade epoxy and needs an accurate scale to mix, as I recall the ratio is something like 6 grams to every 100 grams. Vary this ratio much and the epoxy will not cure. 

I know of no CA that can adequately handle the heat.

Yes, de-bonding of the magnets is a typical failure mode for our toy outrunner motors. The typical cause is over heating (bond failure) or impact (glue fracturing). Impact can come from shaft flex (over speed or prop strike) or crash damage.

Some of the better built out runners have better bearing support of the shaft or bell.

[fhhuber]

RE: Motor Problems

Note a "typical" issue for the magnets to come loose, but it happens occasionally with any maker.

Improper glue application when assembling the motor is one possible cause.

If its just a shortage of glue... Pushing the magnets forward then applying a couple of drops of thick followed by a couple of drops of thin CA (need thick for gap filling and the thin to wick it in) can glue them in adequately.

There have been cases (Turnigy) of motors being assembled with glue that melts at 120F... to fix those you have to get all of the magnets out, clean out all of the glue and then reset all of the magnets properly. Getting the spacing can be "entertaining" I use JB Weld (original, not the newer quick set) to set the magnets from a clean bell. Its a very strong and slow curing epoxy rated 600 F.

[Konrad]

RE: Motor Problems

Good to know about JB weld. Per their FAQ 500°F is more like the workable limit. More than adequate for bonding the magnets to the rotor. and a lot easier to mix than what I use.

http://www.jbweld.com/pages/faqs

All the best,
Konard

[shakespear]

Anyone know about the surging on Dynam's motors. Suspecting to be that short wire on the ESC receiver line(guess it's a surge protector). And how to fix. It's not the timing.

[TiredIronGRB]

Anyone know about the surging on Dynam's motors. Suspecting to be that short wire on the ESC receiver line(guess it's a surge protector). And how to fix. It's not the timing.

Yes, do a reset by following the instructions in this video.

[Alpha]

Shakespear, let us know if that video helps you. I know it has for many others, and I've gotten in the habit of going through this ESC calibration procedure for all my Dynam models whether they need it out of the box or not.

[shakespear]

I saw that video before and didn't do anything for surge, just beeped my right retract and killed it, thanks though

[TiredIronGRB]

I saw that video before and didn't do anything for surge, just beeped my right retract and killed it, thanks though

The ESC calibration would have nothing to do with the retract, I have had to do the ESC reset (number 7) twice on a couple to get the surge to stop.

[shakespear]

so when I try to set cut off or timing, and when it cycles to the second or third section, and the right side retract(not just on dynam but also durafly) kind of jumps. That isn't from programming? If not kind of weird, don't you think. Though I believe you, I will check the y-harness and other things. It does go down, just not back up.