After a great flight all motors shut down.

I turned off myTx before my Quad batter disconnect, I know it went into FailSafe

I know why it may have done that but if the chopper is stopped and on the ground it should not take off again.  Lucky I grabbed it and brought it back but really I think 

A solution could be to always check that the throttle is > 10% before it ever tries to engage RTL to prevent it from taking off and smacking someone in the head like mine almost did if they forget to unplug their battery after a flight.  I don't want to see someone get hurt from a rouge flying quad.


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  • I just happen to read this run across this topic and thought I would throw my "two cents worth'" in. Back in the 1970's, a certain helicopter manufacturer had a similar problem when trying to implement the programing into their  stability augmentation control computer. It did some really quirky things while on the ground. The fix they came up with was to implement a "weight on wheels" switch as a failsafe to let the computer know when it was on the ground and not in any kind of flight mode. Any micro switch that makes contact when the craft is on the ground would work. Just a thought.


  • Developer

    We reworked both throttle failsafe and battery failsafe for 2.9 and the first thing we did was fix this issue so now if your throttle was zero before the failsafe was engaged then it'll instantly disarm the motors instead of going into RTL.


    If you want to see how it's done you can check out radio.pde's read_radio and set_throttle_and_failsafe functions but in summary there is a short moment, as we receive the new radio frame, in which we know both what the previous throttle was and what the new throttle is.  In that moment we can check if the pilot had his/her throttle at zero before the throttle failsafe was engaged.


    2.9 is in testing at the moment and you can follow progress by looking at the end of the 2.8.1 release thread.  There's one important issue that needs to be fixed which is the new inertial nav alt-hold doesn't work well on the APM1 most likely because the noise characteristics of the APM1's accelerometers and baro are different from the APM2 ... hopefully it'll be resolved in the next few days.

  • Ive had this happen, but Ive also had circumstances where the quad landed pretty far off, and I needed to hit RTL to get it to come home. I'm guessing this happens because the first order of failsafe is to proceed to a safe altitude.

    Now I believe once the quad is on the ground for thirty seconds(without additional input) it disarms.Furthermore you must learn to ARM your drone before you can fly it, and the same instructions tell you next how to disarm it. Pilot error is always going to be the weakest link, but the APM cannot be faulted for that. And the road to eliminating Pilot error via code is a long rode with no end. Simply Disarming the quad, and disconnecting the battery before turning off your TX seems to be the easiest and best solution....and the instructions plainly stat this.

    I don't mean to sound callous, but there is already a safe way to disarm the drone in place.

  • I understand your problem, my Quad took by him self inside my garage, 10 minutes after i shutdown the transmitter and i did not disconected the Lipos on it, result... 2 broken props, luck me i wasn´t near it...   Gil

  • While this is an interesting bug that should be looked into, it sounds like you broke two cardinal safety rules:

    1) For any radio controlled vehicle, NEVER EVER EVER shut off the TX before shutting down the vehicle.  You don't know what else is transmitting in your area.  Shutting off the TX is asking for trouble and it's super-bad to get in the habit of this.

    2) For any vehicle with an arm/disarm function, ALWAYS disarm when you don't want the rotors to be spinning.  The arm/disarm function is there for a reason, use it!

    As for how to fix the bug, I can't think of any quick and easy change change that doesn't introduce its own fun and creative in-flight failure modes.  Note that at the moment, there's no way for APM to "know" that it's on the ground.

  • This is why there is an ARM/DISARM function. The copter doesn't understand your intentions (yet).

    I've had a related problem: I tried using the "ARM" button in the Mission Planner, and the controller was off. When I turned the controller on, the motors were already armed and the vehicle went full-throttle. Luckily, it was tied to my test stand so it didn't crash into the ceiling.

  • Always DISARM when you land, then this won't happen :)

    But yes, I've done the same thing.. only once though!

  • Developer
    In ArduPlane the RTL fail safe does not engage unless the plane reports a movement of 10m/s. Though even with this you can get a false positive if the GPS is indoors. There is a big long thread about fail safe started by Monroe... Check that for more info on this.
  • 3D Robotics

    How can it check to see if the throttle is >10% if there's no RC input at all (because the Tx is turned off)? Instead, a better approach might be to not engage failsafe if the quad is on the ground (that's not always easy to detect 100%, but worth considering).  

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