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Motor shutdown (protection) in-flight.

Discussion in 'General Discussion' started by Big Ben, Feb 2, 2014.

  1. Big Ben

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    I was wondering about the following. I'm a bit surprised there doesn't seem to be a protection against switching the motors off in-flight. I can imagine people (accidentally) holding the throttle completely down during rapid descent (I know). Imagine the horror when the motors shut down and watching your precious bird falling from the sky. :shock: You need to be very cool headed to realise what has happened and do a CSC to switch them on again and recover. It shouldn't be too difficult to protect against this based on sensor readings before take-off and during flight. The NAZA should be able to 'know' with a considerable amount of probability whether it is in flight or not and at which altitude. Since there may be situations in which such a feature would be unwanted you should be able to switch such a protection feature on and off as you can do with other protective features using the Assistant software.

    In certain situations I can even see a reason to deliberately switch the motors off during flight. I have seen several videos where people send their Phantoms to great heights an then during descent run out of juice causing the poor things to plummet to the earth. If the thing is at great height you can simply calculate how far it will fall for every second with the motors switched off and actually switch them off for let's say 5 seconds in order to lose height rapidly and as a result saving the battery for the final descent.

    If you ignore the drag and calculate the altitude and height loss per second you end up with 'safe' values because the drag will result in the Phantom always being higher than the calculated 'worst scenario' values.

    Code:
    With an initial altitude of 500m.
    
    Time  Alt.  - Meters height loss in previous second.
    00	500,0	
    01	495,1  -  004,9
    02	480,4  -  014,7
    03	455,9  -  024,5
    04	421,6  -  034,3
    05	377,5  -  044,1
    06	323,6  -  053,9
    07	259,9  -  063,7
    08	186,4  -  073,5
    09	103,1  -  083,3
    10	010,0  -  093,1
    11	-92,9  -  102,9
    If you would be higher than 500m with a substantial difference you could even switch the motors off for 10 seconds. You would lose not more than 500m during the fall. Question is how good the Phantom would be at recovering into stable flight after such a fall (if at all) and how much altitude it would lose during recovery.

    Does anyone know how it would behave? Either from own experience or from anecdotal source. A video showing this would be ideal of course.
     
  2. Ton4

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    Yes, please do. Afterall it's your idea.

    If we would be near I would be happy to shoot it for you while you perform the rapid descent maneuver, but I am sure others will be happy to assist. :)
     
  3. iResq

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    Shutting down for an uncontrolled descent?!?! You must start the maneuver by saying "Hey y'all, watch this". Here's your sign.

    Sent from my Nexus 7 using Tapatalk
     
  4. Big Ben

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    Hehe... I'm not into setting altitude records but some people apparently are. They could set even greater records and still land softly IF this would work and they would use it.

    I'm waiting for the first bold (or crazy :p) person to say: "Challenge accepted." :D
     
  5. neil64

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    Instant high torque on the props during a violent death spin at free fall speed sounds like it has the potential to just snap the props off on whichever side is experiencing the most Gs when the motors get power. Sounds fun.
     
  6. djayz

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    I'm pretty sure the "intelligent motor function" in the settings prevents accidental turning off by holding throttle down. That may not apply with CSC manoeuvre.
     
  7. Ton4

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    Of course Big Ben will accept his own challenge, so we will know soon...
     
  8. Big Ben

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    If DJI would provide me with a Phantom (or three :mrgreen:) for flight testing purposes and would supply any replacements if parts get damaged/destroyed during testing then I would happily accept this, and other, challenge(s). There are several unanswered "what would happen if..." questions with regard to the Phantoms. Ideally DJI would have done all testing necessary to answer these questions.

    Airbus and Boeing and the like do extensive testing on their birds to make sure they know how they behave under every circumstance. There are still many unanswered questions about the Phantoms. This is just one of them.