fly hexacopter with single motor failure?

I know that it is taken as common knowledge that a hexacopter with a single motor failure cannot be flown beyond a controlled crash landing, but this is just plain wrong with our ArduPilot Mega hardware and if we can't do it, it is because of inadequate software.

I have a KK X525 quadcopter which I have flown very successfully for some time with the APM2.

One ESC on it is now progressively failing, continuously reducing power to it's motor after about 2 minutes flight, but all you notice immediately is the need to feed in a little more throttle and eventually it starts descending even at high throttle.

Once it touches the ground you need to switch out of any auto mode to prevent it flipping over (usually too late).

But the moral is that even with one motor failing it tries to maintain level and flight is still controllable.

On a hex if one motor fails all you should have to do is shut off the opposite motor and it should still be completely controllable as long as you have sufficient thrust in the remaining 4 engines to hover the copter.

Auto shutdown of an opposite motor could be handled entirely in software on the APM and control should be fully maintained. as you still have 2 motors turning each way and the lefit points are still symmetrical.

No spinning, no loss of control, no nothing.

If the Arducopter doesn't do this it should and I would definitely like to know what you think.

This could be a tremendous safety and long term cost advantage for a hex and not require an Octo as previously thought.

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  • There is no reason I can think of that you can't reverse the direction of motors.  Maybe you need new esc's but they are already doing it with 3D racing controllers.  So you would just determine which motor failed, turn off th eopposite and reconfig for a quadcopter.  So this shouldn't be a problem at all.

  • All check out this Real Life example of a PIXHAWK HEXACOPTER MOTOR FAILURE. It was not staged.

  • Still have a lot of trouble sending a RED up in one of these.

    Probably what those morons in Aukland New Zealand were using.

  • shoot = chute! sorry.

  • Hi Alberto, some time ago I had an idea for an instant deploying parachute where you basically used 4 fiberglass rods sticking up from 4 corners of your copter (still inside of the prop shadow area) which you bent completely over into a small box on the top middle of your multicopter which had a lid on it which could be released by a servo.

    At the ends, the rods would attach to the corners of a large square shoot.

    When the lid was released the rods would snap out straight and immediately inflate the chute.

    No way to get caught in the props because the rods would be attached to the chute itself and their would be no cords.

    If it were 10 or 20 feet or more above the ground it would even be self righting.

    Could work attached to save only the camera if the camera also had a release.

  • I've benn very interested in this topic... I had an idea, that maybe could be a bit crazy but enough to save the expensive RED cameras: something similar to the ejection seat on the planes with a paragliding... 

    now you solves two problems, the payload and save the camera. Later you can try to land the multicopter. The problem is how to do the separable camara mounting.

  • I've been looking at the hex setup and if you used the motor opposite the dead motor at very low RPM to compensate for undesired yaw it would work fine for one direction of rotation cw or ccw depending on which motor went out, but would not work for the opposite rotation.

    To correct for that direction of rotation you would have to use a combination of pitch which would introduce undesired motion in the direction of the pitch, but it seems to me that a short bobbing motion back and forth in pitch could establish both a stable yaw (compensating with the 5th motor on the off side) and allow for fairly good control.

    Of course, even if you couldn't get enough control this way "Simple" or Super Simple mode could permit a controlled recovery even if the copter was yawing continuously.

  • I thought I remembered that being in the source somewhere, thank you Robert.

    A (auto stabilized limp home mode) for a single motor (failure) certainly seems possible for a hex.

    I think the key issue is a flight mode where the APM is the primary control for maintaining stability and orientation for the copter and transmitter inputs are not allowed to override the APM stability maintenance.

    The off side motor can be used at low RPM to assist in maintaining orientation and pitch stability.

    I know motor reversing would make it easier, but with a little twitchiness, it should be possible to maintain stability and yaw without reversing which would also require that all ESCs be reversible, actually increasing failure proneness and expense considerably.

    It doesn't need to be pretty, but a truly functional limp home mode could greatly increase the safety and utility of these things.

    Little quads like the Parrot and Blade UCMx get over the safety issue by being light and foamy and don't even have a very high terminal velocity.

    Our bigger multicopters have 2 choices, redundant safety measures or some kind of a really fast deploying parachute.

    A stabilized motor out Hex represents one of the cheapest and most satisfactory solutions at this stage of development.

  • No sensors are required for the ESC to detect the motor has stopped.  They already monitor the rotation, and know the RPM.  Yes, they do this through the backEMF.  It's just a matter of getting that info the APM.

  • Re your last input Robert, The people with RED cameras are the ones who can LEAST afford to have them fall out of the sky.

    Personally I was thinking more on the GoPro end of things, where it is easy to end up with a net high thrust to weight.

    The biggest problem we have with these things is zero recovery potential, although as I said, facing progressive single motor failure, the APM has let both myself and a friend with the same KK X525 quads with the same HobbyKing ESC failure land successfully because the APM was doing such a great job of trying to keep itself balanced while the power was going out on one motor.

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