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Compass calibration question

Discussion in 'General Discussion' started by discv, Mar 18, 2014.

  1. discv

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    It is widely believed that a compass calibration error can lead to a flyaway. DJI support this view.

    Would someone have a stab at explaining this to me?

    I fail to understand why compass calibration error could cause the craft to ignore transmitter input completely.

    I can accept that CL mode and Return Home would be affected. But surely, if for example, you were in manual mode- the compass is effectively disabled. :?
     
  2. Big Ben

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    Very few people fly in manual mode. Many/most probably don't even have it enabled on their right switch.

    It may respond to Tx input, it just could respond wrongly. If you give forward stick and it moves to the rear left you have a problem making it go where you want it to go and that's how flyaways happen. When people have lost adequate control. Quite often simply because of loss of orientation. When a conflict between GPS data and compass data arises RTH is quite possibly affected by that too. Since DJI doesn't inform us about the inner workings of the flight logic in such detail we cannot be certain but have to extrapolate and make educated guesses.
     
  3. ElGuano

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    Most compass errors are cumulative. If it thinks your nose is pointed in a different direction, you get conflicting positioning/directional inputs against the other sensors, all of which are trying to establish stable attitude. If it's bad enough it can spiral out of control in wider and faster arcs. DJI calls this "toilet bowl effect" or TBE. If you're not used to it, it can be very hard to control and look like an uncontrollable flyaway, although you still have full stick control; but because it's changing direction constantly people think they have no control. Flipping to ATTI in this case stabilizes, but it can be going so fast at that point that momentum carries it forward and people still think there is no control.

    In short, a totally boffed compass still doesn't negate stick input, but if you are unused to it, it can feel like it does.
     
  4. discv

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    Thanks guys for the trouble you have gone to in your replies.

    I think what I have learnt is that in a situation where one might think they have a 'flyaway', as a last resort it might be worth pulling back on the left stick only. No other input. In an attempt to force a crash landing. Since this is the likely outcome anyway, perhaps better that the wreckage can be recovered.

    Either way, it reinforces the message with regard to pre-flight check regime.