APM response to catastrophic air frame/wing failure?


All -- what do you believe is an appropriate response of APM (ArduPlane) to a complete air frame failure?

Over Thanksgiving break, I test flew an Experimental Airlines AXON build (in a remote, rural area). The plane was flying fine with default settings, and I flew from FBWA to RTL to Auto. During the Auto mission the main spar (an oak dowel) failed and the wings collapsed at around 300' AGL. The plane, as you might expect, took a nosedive to the ground. If my recollection is correct, I could hear the motor running at full throttle as the plane headed to the ground -- my guess in an attempt to pull itself out of the dive. I didn't have the time (or the reflexes) to switch to manual and cut the throttle myself.

Is there ArduPlane code that could somehow detect such a failure and cut off the throttle?

I certainly don't plan on this happening again -- carbon spar from here on out -- but you never know...



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  • OK. Let us think about how we could detect a lost servo...without adding a wire or two to the current servos on the market having power, return(ground), and signal(position) wires.

    As Jake alluded, there is no direct feedback from the servo to the driver device (RX, APM, Pixhawk, etc). If the servo stopped responding to a change in position, how would the driver know? As Richard mentioned, the x, y, z information *should* have changed on a command. How does the driver know the difference between a command response and a thunderstorm (or prelude to one)?

    It is a classic control system problem.


    Kalman filters, PID loops, and all the other software tools at our disposal, have taken us very far. The red items in my cartoon are the driver/FC, the blue items are outside 'the brains' of the aircraft. In the case of multirotors, the servo and control surface are blended into one with the motor-prop.


  • Lot's of nay-sayers here, but it's pretty damn simple to detect if you lose a wing servo.

    It won't be long before we laugh at the days when there was no feedback on anything.  This is pretty basic stuff and should have at least been added to the pipeline by now.

    Forget about airframe failure for the moment.  Basic detection of lost servos and engine power would lead to much more intelligent operations.

  • Perhaps it could work if the pix detected massive x,y,and z fluctuations all over the map while also seeing a rapid decent it could calculate it's in a very bad way and probably crashing and cut the throttle? Keeping in mind that if it is in any kind of guided mode means it's not a pilot induced acrobatic maneuver. If it was simply in auto or RTL and x,y,and z were suddenly going crazy and also it was falling to the ground well.... I don't think ti would be too far a stretch for it to figure it might want to cut the throttle. No? Then again maybe the poor little guy is trying to make it home through a nasty thunderstorm. ha 

  • Eric,

    That's a super sounding program. I am a 1994 graduate of the Space Life Science Training Program (SLSTP) at KSC. This technology would have been super back then for several of the projects I worked with. GIS was a sub discipline at Canaveral and one of our projects was a 'what if' the sea level rose 3 feet? Could (then) Shuttle operations continue as normal? What impact would it have on other operations at the two facilities? Those kind of questions.

    Yes, it was a Global Warming study project. I've got near IR photos of the two facilities from waaay up there somewhere in my files. (Betcha didn't know the coast line of Florida has changed many times over the centuries - by a lot).

     Another study was leaf area of trees with estimates based on cameras suspended by long poles above the tree. Today? No problem! Just spool up the multirotor over the area of interest and take pictures or FPV the process until you get your image data.

    Your update does put your initial question in perspective now. Thank you.

    All the tech we get to play with today is probably now being used there in some fashion but, alas with Shuttle and other programs de-funded (Shuttle was past due to retire), there is little good press from there today.

    Teach on! Fly more!


  • Chim, Mark, Nathaniel,

    I have a Wisconsin Space Consortium Grant to explore the natural resource application of low-cost drone/UAV aerial photography. Using the AXON as a platform is part of that study. In addition to the AXON, our fleet includes an Event38 E384 (with training from Event38), two APM-laden Bixler 2s, and a Flite Test Blunt-nosed Versa. We also have a flight simulator on campus to train students and myself before they ever touch the controls. In addition, I have quite a few hours of real flight training (alas not a pilot's license), so I'm not new to flying. 

    I just don't have great manual RC flying skills...yet.

    Personally, I see the low-cost platforms as key to expanding the hobby/technology -- an area that should be explored and expanded (with important safety caveats, of course). Working with students with low to no budgets, it may be the only way they'll have access to UAVs.


    P.s. I do plan on teaching UAV technology to others and am interested in hearing more from the community: http://diydrones.com/forum/topics/undergraduate-curriculum-for-dron...

  • Moderator

    As had been said appropriate airframes and training remove the risk. Doing things on the cheap often does not end up cheap. 

  • I think it would be cool if someone found a way to integrate a fiber Bragg grating sensor into the airframe and somehow incorporate that into the APM code. I don't imagine it would be terribly difficult (aside from the costs involved), and could really help in situations like these. This way you could deploy a parachute, or switch to manual. But hey, just my 2 cents.

  • Developer

    Relax. Crashing is the one thing I can absolutely guarantee everybody will do in this hobby. In fact it's just part of the fun. https://www.youtube.com/watch?v=cZlTlDdZfbg&list=UUyw0zM6J3fae6...

  • Moderator

    +1 Mark, Chim you sarcasm is so funny, it reminds me of my little sister....if I had one. Seriously I must ask where did Eric say he was just learning to fly? For all you know he's been flying since he was 4 and just needed a change of pace. Not everyone needs or want's the same mainstream "proven" latest and greatest.

    For your information, the Axon flies surprisingly well and if properly tuned the APM will work just fine with it. How do I know this you ask....because I've built one and flown it with an APM. That said it isn't the best airframe in the world for sure, nobody would argue that. However if you want to experiment with an APM IMHO it's just fine as long as you keep in mind it's limitations and fly it in a safe manner.

    Personally I have flown several of these types of airframes recently, not because they are cheap, but rather because they were different and exposed me to different building techniques. It's all about your life experience and what you allow yourself to be exposed to. Dismissing these airframes limits the possibilities and ignores what can be learned from building and flying them.


    Nathaniel ~KD2DEY

  • Chim, your comment isn't particularly helpful. Eric is just hoping to spark conversation about the possibilities of detecting airframe stress and dealing with airframe failure. I doubt that he is after a condescending put down by you. 

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