APM (and all flight controllers) logic with regard to sensors incl. GPS

Discussion in 'Custom Programming' started by Hugh Hemington, Sep 25, 2014.

  1. Hugh Hemington

    Hugh Hemington Well-Known Member

    With regard to the phenomenon known as "Fly-away", where a multi-rotor craft seems to just take off on a strange course and crash or get lost, I think the most likely culprit is the GPS.

    I have seen "fly-away" happen on the bench, using an APM 2.5.2 controller and LEA-6H GPS module. With good GPS signal and 3D position, I saw the real-time indicator in Mission Planner begin moving wildly away from my location. Since it was really just sitting on my bench, I didn't panic and just watched it for a while, and it "flew" nearly a mile away before I got tired of watching.

    I suspect what I watched was the flight controller reading bad input from the GPS, and had the equipment been airborne, my quad would have flown quite a distance in an attempt to correct the false positioning readings I watched.

    I believe that flight controllers place too much weight on GPS data, even to the point of overriding all other sensors, even when those sensors all agree the craft is not moving. The programming of flight controllers that use GPS should be refined such that conflicting instrument readings trigger a pilot confirmation sequence. When the deviation of instrument readings exceeds a preset threshold, I believe the controller should either send a signal back by a telemetry path, or turn on a strobe to alert the pilot that an error condition has been encountered. The pilot could then move a three-position switch down (from center) to indicate that the craft was in fact in a relatively stable hover, and the controller should attempt to resume normal flight, or the pilot could choose the up position to indicate the craft is indeed in "fly-away", and the flight controller should discontinue all stabilization efforts and let the pilot fly it to a safe landing.

    The strobe (if used) could be located where it is visible from an FPV camera as well as the ground.

    Does anyone else have any insight into the fly-away problem?
  2. andy bards

    andy bards Well-Known Member

    while inside the house, I also get glitches which cause the gps to give false readings ,,, my room is full of gadgets wifi Bluetooth and so on,,

    knowing I have all these interferences,, I wil recalibrate gps, compass and so on in the field... IT ALWAYS gives different offsets when outside (which is what I expect)..

    So if you were not to re calibrate outside,,, the actual interference free gps signal will be more of an offset to the indoor calibrated gps on the quad... causing extreme differences in some cases (fly aways)

    I think this is the cause of a few of them fly aways,,

    A second gps is also an option ???
  3. RENOV8R

    RENOV8R Well-Known Member

    I've wondered how many of those "flyaways" were caused by a GPS module not secured properly and shifting position or coming off it's mount. I'm a firm believer that most flyaways are caused by user error. Have you ever noticed that most people who state they've had this happen are new to the hobby?
  4. Chuck

    Chuck Well-Known Member

    The common theme that I see with reported flyaways, is an attempt to exceed the maximum range of the controller at distances where it is difficult to tell the orientation of the drone visually. Even in a wide open area such as a desert terrain, there is a practical limit to flying to "within line of sight". Just because you can see a plateau twenty miles distant, doesn't mean you have flight control for even twenty-five percent of that distance.
  5. RENOV8R

    RENOV8R Well-Known Member

    Maybe with lower priced FCs but any decent one like the Naza-M or ZYX-M should be setup to RTH as the result of a lost signal. It's the first thing I do. And if it were a 250 sized craft with say a Naze32 or CC3D, people ain't gots no biznus flyin much further than you can see it.
    andy bards likes this.

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