Almost got killed in the office today. Log file attached..

I have a large octo With powerful motors. It's been in the air many times.

I did some work on it today, changing the camera gimbal. I also installed a New 5,8ghz video tx and a trigger Circuit for operating the shutter on the camera. The shutter and video tx were both Connected to the camera. Shutter was Connected to ch6 on the receiver.

I decided to Power it up in the office to adjust the camera shutter channel and test that everything worked. The telemetry system(Frsky Taranis) warned about low RSSI. Since the only new Connection I had made to receiver/apm was the shutter cable, I removed the servocable from the receiver ch6. The telemetry system stopped warning about low RSSI. So, just to check again, I reconnected the servo cable to ch6. I know I should not do this kind of stuff on a live machine With propellers, and luckily I was taking precautions by keeping out of Reach of propellers. Then all hell broke loose...

8 Heavy lift motors With large APC propellers, capable of lifting a total of 20kg went into full throttle. I just let it go and took shelter, while the machine was doing its thing to the ceiling and Office Furnitures, before shutting Down. Most of the propellers and one motor destroyed. Glad to be alive With all my body parts intact. I've been working on multirotors since "the beginning", and had my share of propeller cuts, but thats a long time ago..  It's obvious I needed a reminder again... :)

So... what happened? I'm not concluding With anything, this may not be related to the APM at all. I suspect that the camera shutter in some way made the receiver bring channels high/low. Logfile Attached. Anyone care to do some analyzing?

2014-10-28 17-59-05 6.log

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  • I use two lengths of foam tubing of the sort used to insulate water pipes to protect my quad's props during transport and on the bench. Cheap and available at any hardware store in various diameters it has a lengthwise slit and is easy to put on and take off each pair of props. It's hardly ever in the way when working on the aircraft. What with the negligible starting torque of our motors I'm confident that it will prevent accidental spooling up, though I haven't tested that.

  • I had exact experience with mini quad 250 w/o props. I was messing around soldering (bad job i did) wires from a miniAPM and probably the wires were touching or whatnot... but when i was testing it randomly a motors started spinning full throttle... then a second one... very weird. but yes, the problem was messing with the Receiver connections, not the APM.

  • Developer

    Well, that sounds incredibly scary.

    I don't think this log file is from the incident though or at least it doesn't capture the time of the incident.  Below is the Throttle in (from the pilot) which is raised just three times above min and the output follows it normally.  The vehicle never takes off according to the barometer altitude (scale on the left) because we can see it's just doing it's "random-walk" type behaviour moving from 0 -> -60cm -> +20cm.

    3701864414?profile=originalMy guess of what happened is:

    1. the APM was plugged in and working normally, it sent the regular low pwm values to the ESCs which caused them to arm (i'm talking about the ESC arming now, not the APM arming)

    2. the reconnecting of the receiver wire caused the APM to blackout and a glitch/spike went out on the RC output pins which was of a width that could be interpreted as a high pwm signal.  the vehicle took off at this point

    3. the ESCs didn't receive any further pwm signals so after 2seconds they timed out and shut down the motors.

    •  Even if the reconnecting of the receiver wire caused the APM to blackout and a glitch/spike went out on the RC output pins which was of a width that could be interpreted as a high pwm signal.  But if APM didnt armed , APM should not out put to ESC , the vehicle should not took off.

  • I learned my lesson with several stitches on a small hex with carbon props, and still find myself being silly and testing things props on. 

    I have gotten a little better and provided ways to power all or any individual component on my birds without applying power to the ESC's. Because I find laziness is the man cause of us doing silly things that get us hurt, so if we can make the easy way the safe way we are almost always safe.  Being able to power one or all components and not the actual motor ESC lets you easily test any and everything without taking of props.

  • Incredible service from www.readymaderc.com !  Parts delivered to Norway With Fedex in 2 days!

    Trying out a New shutter switch. Will make a Optical separated relay if necessary.

    3701864452?profile=original

  •   From your diagram, 1st time you connect servor from Frsky ppm receiver, and the power of receiver is from APM via a diode, if the servor draw too much current , the voltage of receiver will drop and cause the ppm receiver send an unkown code to APM, maybe APM interpret it as arm signal.
      2nd time you connect again, maybe this time APM interpet it as failed safe  or full throtle.
      Did you set the armed spin on? If not , maybe it was already armed 1st time.
    Anyway , I suggest you sould use an independent power for the servor, unless you know the current of servor in any position(shutter on/shutter off) is very low.

    tangtl

    • This sounds very plausible. I have not set the motors to spin on arm, so can't be sure if this is what realy happened.

  • I don't understand some of these incidents. If the Pixhawk isn't armed then how can the motors spin up?

    Also, for those of you who find taking your props on/off tedious have a look in to quick release prop mounts. I use them on all my copters now and they are just great. It's very fast to de prop even an octo and you never have to worry about them being secure as they tighten when the motor spins. 

    • I'm waiting for this mounts thank for share your experience I was affraid that they were not good or unbalanced.

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