Help! Motor wobble

[arjun21122006]

I have an A2212 1800kV motor with a 30A ESC and 2200mah 3s battery which I plan to put in the simple scout(second plane)...
The problem is that the motor wobbles as soon as I get over 90% throttle even without the prop...
I am using CT6B transmitter with CC3D and even when I remove the CC3D and connect straight to reciever still I get the wobbles...
BTW the motor was in a crash when I built my first plane(Speed-Built Spitfire). I wasn't able to get the hand launch right and it went straight up then into the ground... The motor wasn't smoking and was not hot to the touch either it was just ambient temperature...

 

[CappyAmeric]

Maybe the motor has a bent shaft.

 

[quorneng]

By "wobbles" I assume you mean it stops spinning (with a screech?) and just oscillates or is it something else?
I assume the motor can be spun freely by hand?
I would certainly expect such a motor and ESC to run perfectly off load from zero to max throttle on a 3s.

If the wiring between the motor and ESC is sound, and it has to be really good with no poor connections, then either the ESC or the motor are suspect.
Unfortunately the only way to confirm which it is by substitution. If the motor runs properly using a different ESC then you know the first ESC is suspect. If the motor still misbehaves then the issue is most likely with the motor itself.

 

[Merv]

...The problem is that the motor wobbles as soon as I get over 90% throttle even without the prop...

I agree with quorneng, not sure what you are describing by wobbles.

Could the motor be out of balance? If so you likely have some dirt or other debris inside the motor.
You’ll need to take the motor apart and clean it. I use an old toothbrush and water to clean my motors.

 

[arjun21122006]

I agree with quorneng, not sure what you are describing by wobbles.

Could the motor be out of balance? If so you likely have some dirt or other debris inside the motor.
You’ll need to take the motor apart and clean it. I use an old toothbrush and water to clean my motors.

The wobble is like it just starts to vibrate like hell in hand..
It just shakes my hand up completely and feels super dangerous..

 

[Merv]

...It just shakes my hand up completely and feels super dangerous..

That sure sounds dangerous, I would not recommend running a motor while holding it. I always secure it to a hunk of wood, then secure the wood to a workbench, using a clamp or vice.

Sounds like the motor is out of balance for some reason, could be missing a magnet, could have some debris inside.

 

[skymaster]

maybe the shaft is broken and the magnets are keeping it in place until it get to a certain speed. check the bell to see if there is anything stuck to it.

 

[arjun21122006]

maybe the shaft is broken and the magnets are keeping it in place until it get to a certain speed. check the bell to see if there is anything stuck to it.

Everything seems to be quite ok...
Here's a video of it

 

[CappyAmeric]

Everything seems to be quite ok...
Here's a video of it

It is hard to judge the difference between oscillation and a simple torque response because the motor is not mounted as should be when testing full throttle range. Mount it on a sold piece of wood - then test it.

 

[quorneng]

What you are seeing is sympathetic vibration.
Any motor has a slight out of balance couple. just sitting free with no or little resistance to movement or natural damping then at some point the out of balance forces with match the motors natural frequency and any resulting vibration will rapidly increase until some feature of the system changes.
The motor expects to be rigidly mounted with sufficient inertia and/or damping so it can never achieve a sympathetic vibration state.
No recommended but here is a similar motor, actually 2200 kV so it is spinning slightly faster, on a 3s but held firmly by the motor wires close to the motor.

By no means truly rigid but it is still firm enough to allow it to spin up perfectly.

 

[arjun21122006]

What you are seeing is sympathetic vibration.
Any motor has a slight out of balance couple. just sitting free with no or little resistance to movement or natural damping then at some point the out of balance forces with match the motors natural frequency and any resulting vibration will rapidly increase until some feature of the system changes.
The motor expects to be rigidly mounted with sufficient inertia and/or damping so it can never achieve a sympathetic vibration state.
No recommended but here is a similar motor, actually 2200 kV so it is spinning slightly faster, on a 3s but held firmly by the motor wires close to the motor.

By no means truly rigid but it is still firm enough to allow it to spin up perfectly.

Ohh...
Thanks for the information
Is there a way to dampen the vibrations or anything or it is fine like this?

 

[quorneng]

The motor itself is most likely perfectly well balanced.
The balance issue is likely to be much more of an issue when the prop is added simply because it has a much larger diameter so even a tiny difference between one blade and the opposite one will create a significant vibration. With a good quality prop and properly fitted prop adapter it should be fine but the motor must be rigidly mounted regardless.

 

[Merv]

...Is there a way to dampen the vibrations...

Yes, attach the motor to something. From your video, it looks like you are holding the motor by nothing but the wires. Motors are not intended to operate without being attached to something.

 

[Tench745]

It looks like you have a collet style prop adapter on the shaft when you're running it up. To eliminate variables, I'd suggest removing the adapter completely when testing, and mount the motor solidly like everyone else has suggested.
It's a little hard to tell from the video, but it looks to me like the bell is shaking but the rest of the motor isn't. This suggests something along the lines of the bell is loose on the shaft or the bearings are starting to fail. If you grab the bell and try to pull it off what does it feel like? More testing is in order.

 

[arjun21122006]

It looks like you have a collet style prop adapter on the shaft when you're running it up. To eliminate variables, I'd suggest removing the adapter completely when testing, and mount the motor solidly like everyone else has suggested.
It's a little hard to tell from the video, but it looks to me like the bell is shaking but the rest of the motor isn't. This suggests something along the lines of the bell is loose on the shaft or the bearings are starting to fail. If you grab the bell and try to pull it off what does it feel like? More testing is in order.

I am unable to pull off the adapter and the bell is about 1mm above base normally but when slight force is applied it raise about half mm and the gap doesn't get over 1.5mm even after putting lot of force...
The bell returns to it position as soon as force is removed

 

[Piotrsko]

To pull the adapter, remove prop, grab a tight hold of the rear prop mounting washer/collet and tap the prop shaft towards the motor carefully so as to not distort the prop shaft.

Been my experiences that cheapo chinese prop adapters aren't that concentric

 

[arjun21122006]

To pull the adapter, remove prop, grab a tight hold of the rear prop mounting washer/collet and tap the prop shaft towards the motor carefully so as to not distort the prop shaft.

Been my experiences that cheapo chinese prop adapters aren't that concentric

Do I need to like pry it apart?

 

[quorneng]

Do I need to like pry it apart?

What has happened is the prop adapter has got stuck onto the motor shaft. This can happen as the aluminium of the adapter can 'bond' to the chrome motor shaft when it is under pressure. Without the taper collet squeezing the adapter it should pull off fairly easily.
If you take a fine blade and carefully insert it between the adapter and the front of motor it should prise off.