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Advanced Hard acceleration, phantom goes unstable

Discussion in 'Phantom 3 Help' started by rv13, Aug 24, 2015.

  1. rv13

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    My P3A has been running awesome for a couple of months. No crashes, no issues. BUT, these last few flights if I give it hard acceleration, it will go completely unstable for a few seconds (dips hard, off track, loses altitude). There is also a substantial change in the noise from the blades. It acts like one of the motors is crapping out and the others are trying to stabilize it. I have tried a second set of blades, but does the same thing. If I fly calm and cool, no noticeable issues. But if I give it full up and forward throttle it goes nuts. I have to release the controls and then after a couple of seconds it will stabilize. I have to give a little input to keep it elevated. It is making me nervous that a motor is going bad and one of these times it will not recover.

    Any suggestions? Is there a way to test the motors individually?

    Thank you.
     
    #1 rv13, Aug 24, 2015
    Last edited: Aug 24, 2015
  2. III% Streve

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    IMU calibration!
     
  3. rv13

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    Not an IMU issue.
     
  4. III% Streve

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    Ok.. If you know what the problem is then why ask
     
  5. rv13

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    I tried holding the P3A in my hand and gave it full up throttle..... Found the motor that was giving me issue... It started vibrating horribly under power. Upon further inspection it looks like I have a stress crack within one of the screw holes.
     
  6. rv13

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    I didn't know, but in what case would an IMU calibration cause this issue? I appreciate people giving input or suggestions, but just blanket "IMU calibration" responses are not helpful.
     
    Bigfoot_Hunter and bobmyers like this.
  7. rv13

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    This appears to be the problem. Under power this crack is causing this motor to wobble/vibrate. The crack is allowing for 'play' and resulting in the instability.
     

    Attached Files:

  8. III% Streve

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    The IMU is a direct part of stabilization. If its not 100% then it could lead to instability. And it could appear as a temporary instability. Yes, a crack could do it as well. And IMU calibration takes seconds to test. replacing a cracked cast takes weeks or potentially months.
     
  9. bobmyers

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    This has been an ongoing topic of discussion on this forum-- There are several long threads dedicated to these cracks and solutions repairing them as opposed to sending the whole Phantom back to DJI for warranty repair. Check these out from UAV BITs
    http://www.uavbits.net/store/p28/Strong_Arm_reinforcement_plate.html
     
    rv13 likes this.
  10. TedroC

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    Are you running the stock propellers?
    I had a similar issue with some Drone World carbon fiber props with metal hubs (made the same strange sound with hard acceleration and went unstable and crashed). It turns out props have to have composite hubs (like the regular old DJI props).

    It was just a thought...
     
    rv13 likes this.
  11. rv13

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    Yes, still the stock props.
     
  12. Nemmo

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    Seems like a Battery problem (if after hard acceleration) Check with this http://healthydrones.com/
     
  13. zincsoldier

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    What firmware version are you on? Try flying it with VPS off to see if there's any different since you mentioned it loses altitude.
     
  14. kdrak

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    Try to balance props and report back or use another set of props
     
    Pete Leare likes this.
  15. rv13

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    The problem was with the crack in the case on one arm. It was allowing 'play' in the arm/motor and would twist under power enough to cause the instability. I put on a couple of zip-ties and it flies fine now. DJI said to send it in under warranty, but I am not sure i want to be without it for 8-weeks. Boo.
     

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  16. Pete Leare

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    I agree with kdrak.. Try balancing (or at least checking them) the props first to eliminate them as the problem. I've seen other threads where you can check them using the 'wine glass method' if you don't have a balancing rig..