Hi,
I am having some serious with my quad specs are given below.
S500 frame
4s 5200mah lipo battery
DJI Naza Lite with GPS
Naza n2 osd
Gimbal
Racerstar br3508 700kv Motor
Hobbywing 50a ESC

Now, what's happening is when i connect my battery  and start the motors it rotates nice.
But as i stop the motors 4th motor stops quickly, like some opposing force is applied into it.

I tried changing motors but the problem is still there

One day i was flying my drone as i take off, the height was approximately 5 metres, the quad flipped and crashed. This happend two times.

What should i do
   

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Hi,
There could few issues that come to mind
1) how old is this motor?
If it's too old then it could be some bearing problem, spin the motor with hand and see if you feel any resistance, if you do it could be bearing issue. The bearing if it gets dust on it then it can cease up

2) if ESC braking has been activated on your ESC then the motor will stop in a instant of you throttle to 0%. Just recalibrate the ESC

3) swap the 4th motor with any other ESC and see if the problem still exist then it could be issue with the motor like some coil inside is damaged. If the above motor works fine then it's the ESC that's gone bad and change the ESC.

I hope this works out

The motors are new.
And have tried callibrating ESCs but the problem still exist.
I thing the problem is in the ESC

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And yes when i turn the motor with my hand when battery is connected i can feel the resistance but when battery is disconnected there is not resistance.

Prviously i was using some cheap Brushless motor there was still that same problem, then i purchased racerstar motors, but the problem is still therr.

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Looks like ESC issue

What brand ESC are you using? Can you post a picture of it?

 - Try to spin motor with hand when connected to ESC once with ESC powered from battery and once w/o powering. - Note how it feels
 - Once disconnect the motor from ESC and try to spin it. Note again
 - Now try to short the wires by holding them together and try to spin it - Note how it feels.


You can try to compare the similarities b/w each and every step.

Sometimes the ESC firmware tries to stop the motor instead of letting it stop by itself. It does that by pulling down all low side MOSFETS.

I would suggest you to replace the ESC. I think its pre-programmed from factory like that.

The esc are Hobbywing 50a ESC

Here is a programming guide. There is an option for brake mode. Check that once
http://img.banggood.com/file/products/20160303034040SkywalkerV2.pdf

And someone confirm that these ESCs are good for using in multirotors. I mostly saw these ESC being used either in helis or planes