strange screeching/scraping noise

[Grifflyer]

so I took my ft arrow out recently and I was flying just fine with good crisp responses with all controls including the throttle, but when I went to full throttle (progressively) and right as I reached full throttle there was a loud screeching/scraping noise and the motor stopped spinning I brought the plane down and started to inspect everything was cool and I could still control the throttle up until full throttle and it would screech. I was clueless

so I know quite a bit about motors all about bad bearings and loose windings but never heard of this, so can someone chip in and help if the have ever experienced this or knows about it and if you would like to know I am running a emax mt2204 motor 12amp esc with a 6x4 prop.

 

[earthsciteach]

I've experienced this before, but can't remember what the issue was. Maybe try changing the timing on the esc?

 

[Grifflyer]

I've experienced this before, but can't remember what the issue was. Maybe try changing the timing on the esc?

i'll try but I don't think my esc can be calibrated like that

 

[F106DeltaDart]

I've had this happen when a magnet came loose in the motor, and when a C-clip broke off. Check to see if and of the magnets have scooted backwards and are interfering with the backplate, or if there is any play when pulling on the front of the motor can.

 

[Konrad]

This sounds like a classic loss of commutation (the very reason we need a brushless ESC for brushless motors). Many ESCs don't play well with high pole count or high impedance motors. I've had this issue with the ZTW Gecko series of ESC. ZTW has a software fix, finally added to production units.

Also most ESC have an electrical "RPM limit" this is actually a switching limit (not to be confused with the ESC frequency). I just ran into this with a Castle Creation ESC and a high pole count outrunner ( I don't like outrunners).This is what I think is your issue, as the motor and ESC behave well until the very end (full throttle).

"Timing" is another issue. It is the ESC turning on the field winding before the magnets are in the best rotational placement. This is done because a coil (inductor) tries to resist changes in current flow. This resistance to changes in current flow means it takes time for the field (winding) to reach its maximum electrical force. The faster the motor turns or the more windings it has the more time (advance) the winding needs to be at maximum force when the magnet (rotor) finally get into position to help rotate the shaft.

So what brand and model ESC?

All the best,
Konrad

 

[Konrad]

Am I reading this right? You have a 14 pole, 2300Kv motor?

So to see how fast the ESC has to turn on and off we multiply some numbers.
14poles X 4.2v X 3cell X 2300Kv=405,720

Few low cost ESCs can switch past 360,000

Using nominal voltage of 3.7v you are right on the edge at 357,420

Hope this helps,
Konrad

 

[Grifflyer]

konrad i'm using a simonk 12amp esc, if my esc can't handle the switching or winding fast enough could I adjust my throttle end points instead of getting a better more $$ esc?

F106DeltaDart no play in the motor and rock solid, also was cleaned out a few days ago. and C clip intact

 

[Konrad]

Looking at the spec sheet it looks like the max RPM for a 14 pole motor is 30,000 rpm.
http://www.banggood.com/Emax-Simonk...-40A-ESC-For-Quadcopter-QAV-250-p-918126.html

Without an actual tach on your motor I assume you are trying to spin your motor at 4.2V x 2300Kv=29,000 rpm (more like 27,000 in the real world). So it is close to the limits. I'd ask the ESC OEM for a replacement ESC or check for a firmware update.

Just yesterday I had the same kind of problem. Got in contact with Castle Creations and learned that there was an update to firmware for my obsolete Phoenix Ice 2 80HV ESC.

What I'm trying to say is do it right and not try to bandaid the system. In the long run quality pays it does not cost. Or as Keith Shaw (one of the fathers or model electric flight) told me when dealing with our electric toys, buy cheap buy twice! I don't know about you but I can't afford cheap stuff!

But before doing anything make sure your contacts and solder joints are good. I would think based on the spec sheet your set up would work. Work barely but work.

All the best,
Konrad

 

[Konrad]

Looking at this data sheet, the motor is much more inefficient than I thought ( small outrunners usually are).
https://www.emaxmodel.com/emax-multicopter-motor-mt2204-kv2300.html

It looks that with a 6x3 prop the RPM are down in the real world to 16,000 plus rpm. This should be a workable rpm for the esc. BUT, I see with the 6x3 the reseller is claiming the motor is drawing 11.5 amps! I suspect you are over amping your ESC with the 6 x 4 prop. Try dropping down to a 6 x 3. Or if you need to keep the pitch speed up try a 5.7 x 4 prop. Remember it is the velocity that the wing is traveling at that produces lift NOT thrust or worse static thrust.

 

[Konrad]

... also was cleaned out a few days ago. and C clip intact

This is a crashed motor?

 

[Grifflyer]

yep, this has been crashed plenty of times, I've had it for over 8 months just have some sand in it when I crashed into some of our sand/dirt mixture it's happens plenty of times with all my motors just remove the C-clip take off the outer can inspect all the magnets ensure they are held in tight, then go over the all the components (minus the C-clip and washer that sits right in front of the C-clip) with some compressed air through a needle used to blow up balls and your done just reassemble happens all the time and all the motors work fine and run smooth (once found a loose magnet out of the box) so would doing this affect anything?

 

[Konrad]

Just don't air spin the bearing very fast.

So this set up ran fine prior to a crash some time in the past?

Or is this a new set up for you, Motor, ESC, Prop and battery? BTW; I see I've made an assumption that you are using a 3 cell lipo battery.

 

[Hai-Lee]

I have experienced the exact same type of noise and symptoms but most often on a CF2812 1534kV.

The reason for the noise was the grub screws holding the "Bell" onto the motor shaft. The prop had a prop adapter attaching it to the motor shaft.

At high input the bell which rotates around the motor shaft and is driven by the changing magnet fields tries to spin at maximum speed whilst the prop applies an opposing force due to air resistance. At full throttle the poor grub screws could not take the forces involved and began to slip around the motor shaft making a loud and high pitched squeal.

To fix the issue I removed cleaned and refitted the grub screws and added a single drop of CA to where the motor shaft protrudes through the "Bell".

Since doing that all has been OK. To release the CA if you are replacing a motor shaft just remove motor shaft and bell from the stator windings/holders and apply a little heat with a soldering iron.

Have fun!

 

[Grifflyer]

konrad this setup runs fine with no problems and I haven't changed the electronics and I was running a 3S

Hai-Lee thanks for the idea I'll try it and see what happens.

 

[Konrad]

Now that I've learned what all the components are, I too don't think it is an "electrical incapability" issue. If it ran well before a crash or before a maintenance event then I'd look at a mechanical issue, a loose shaft as Hai Lee is suggesting sound highly probable.

I like to use a Loctite product #609 or #290 to aid retention of the shaft to the bell housing rather than CA.

Are the props the same? Did the system perform with the 6x4 prop?

You asked earlier if you could control the electrical RPM limit with the input command signal (end points). The answer is maybe.

But don't use the input signal (throttle) to control the ESC amp limit. The nature of the PWM means that the transistors will see the full amp draw be it at idle of at full throttle. So if your set up is drawing 15amps at full throttle and your ESC is rated at 12amp don't think that cutting back the throttle will help (protect) your ESC. It will help the motor but not the ESC. This has to do with duty cycles (heat)and material breakdown in the mosfet (transistors).

Please let us know what you find as the problem and your solution.