I had a minor crash recently with my Phantom 1.1.1.  Nothing too bad but now when I fly it 'stutters' and is not stable.  It sounds as though one of the motors slows/stops for a fraction of a second, it will dip and then catch and come back level again.
I had something similar when I bought it (used) and found a motor that was aparently failing which I swapped out and thast fixed it.  On the assumption it was the same I checked and two more motors seems a little rough so I replace both but it is stlil doing it and nothing seems out of place anymore.
A few more details:
a.  It only happens why it is flying - if I run the motors on the bench then all motors appear to run normally
b.  I have performed the advanced calibration several times without any improvement


Any advice?  Is there a way to test the motors so that I can figure out which motor or ESC is causing the problem?


Thanks

Hook it up to the NAZA assistance software and do a motor test, watch the light under the arms if one goes out or flashes could b that one, use different props not the ones you crashed with,if you haven't done so yet open up the phantom and make sure the naza hasn't come off or loss after the crash its only held on my 2 sided tape

Yep, the motor test will tell you.

Yep, the motor test will tell you.

DJI-Dave Posted at 2015-10-15 16:48
Yep, the motor test will tell you.

Unfortunately the motor test doesn't show anything useful.  It only spins the motor for a fraction of a second and all motors do this, so nothing useful there.

I did discover that the situation is worse when using an older battery vs a newer battery so I am assuming that I have a bad connection somewhere.  I'm going to go back and check all the solder joints, esp. where I replaced the motors.  

Yeah hunting down a problem like this can be very difficult. Sounds like you are doing everything I would suggest. If I come up with any other ideas I will post them here.


Dave

Maybe you din't replace the "bad" motor yet?

You replaced two, maybe it was actually one of the other two?
I also suggest you carefully check ALL connectors and ALL solder joints.

Would a strobe light help identify which motor was "stuttering"?  You could do a static test by mounting the phantom to something to keep it from flying, run the motors up to mid speed and then hit it with the strobe.  I would think the props on the faulty motor would stand out from all the others.