OctaV: Small accident & key learnings

I wanted to share my experience to help & protect you all. No multicopter is worth personal damage & stitches.


We have been building & testing ardu-based octa-V craft. Part of the challenge has been power usage / high amperage. Orginally we used 3S, but changed motors and went to 6S. Target being lower power losses to increase flight time & max power.

My BEC's man voltage was 3S so I used a separate battery to drive FC & Gimball system. 2 separate 6S batteries were used to drive motors.

What happend?

I tested OctaV on a field alone. On the 2nd flight the gimball (steered with Multiwii) had a tendency to drift. To reset the gimball 3S battery needs to be disconnected. I had already succesfully reseted the gimball once - with drivebatteries connected.

On the 2nd try octaV takes max power for a split second and flips backward. (seen on attaced video) One propeller hits my hand and another my feet. Situation was clear to me and I left OctaV as is and went to seek for medical assistance.

In the video

  1. land
  2. disconnect reciver battery -> gimbal levels
  3. connect reciver battery -> craft shoots at me

A quite big wound was stitched on my hand and one tendon was partly torn & fixed. Recovery should be full after few weeks time.

Key learnings

FC can output at start / disconnect any signal to ESCs --> anything can happen. Arming does not prevent this - unarmed craft can start (as happend to me). 0.2 secs is enough.

  1. Always start FC first, then connect drivebatteries
  2. Always disconnevt drivebatteries first, then FC
  3. Multicopters are very dangerous tools. If I continue with multicopters, a mechanical securing is required on startup & disconnect. Errors (hw, sw & user) will happen.
  4. Tuning is dangerous. Untypical situations occur, shortcuts are applied. Be careful. Do not shortcut.

Spec of octaV

  • 8x Sunnysky V3508-29 380kv with 12x38 APC props
  • 8x F-A 40A esc with Simonk
  • 2x 2600 6s drivebatteries 2200 3s reciever battery
  • FC: RCtimer Arduflyer 2.9.1B Arducopter (I have APM 2.0 on my hexa)

Happy & safe flying to you all!



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  • Thanks Bill.

    I like your approach. Full scale aviation has adopted its practices through more than 100 years of trial and error & continuous improvement. There must be a lot of wisdom in it.

    My hand has recovered fully from the accident. No limitations, pains or any issues. The tattoo is fading, but I have not flown a multicopter since the accident. Some day I will. Currently I fly upto 700 size "normal helis" - they can be pretty nasty as well. Trying to say on the safe side.

  • Moderator

    My 'drone tattoo' isn't as severe as yours, but I learned the same lesson at the same school as you.  I now use checklists for every flight on the bigger stuff I fly (I'm building my second 1.2 meter octo) and always power up and check FC, the connect main, and reverse the process mains, then FC every time.  It can be annoying sometimes, but I just won't take short cuts.  I think the 5010 300KV motors and CF props could easily cut a finger off. 

    I also have experience as a full scale pilot.  To fly drones correct (and to teach others as well) I now try to follow the same methods that have proven to work for decades for pilots around the globe.

  • @oliver - thanks for your comments. Towel is an excellent proposial. I will test it and try to convince my wife on the safety.

  • Now i have a good RC logo idea: http://www.ritterruestung-handgeschmiedet.de/deutscheversion/werdeg...

    Too bad the logo competition is over!

  • Unless the main batteries are physically disconnected you're looking down the barrel of a loaded gun, no matter how many parameters, switches, failsafes etc.are set this way or that. The problem with most every multicopter is that in order to connect or disconnect the mains you need to put your hands into or very close to the arc of the props and thus the rest of your body is also intimately close to the machine. You have no hope of getting clear other than by dumb luck when Mr.Multi suddenly gets full power and decides to chew on your fingers on the way to flying into your face, the props just spool up way too quickly. The good news is that the motors have very little starting torque, so if the props are at all restrained not much can happen. There is available a really high-tech device that can accomplish that reliably. It's called a towel. Toss it over the props. Now you can diddle your pids & gimbals or whatever, or connect/disconnect the mains, with impunity.

    Regarding inadvertent bumping of the Tx throttle stick, this happens all the time around R/C aircraft, and not just to newbies. Most R/C Tx's have a feature called "throttle hold" that will disable the throttle stick via a toggle switch. R/C helicopter pilots commonly use this but others are often unaware of it. It's a great safety feature, though again relying on anything other than physical restraint always carries some risk.

  • Thanks for sharing this.  I'm sorry it happened to you and I wish you a quick recovery, but I'm glad you took the time to remind the rest of us.  I have been developing my own quad for some time, but it was this post that motivated me to add an arm / disarm sequence so it won't attack me on the bench.  My fingers thank you very much.

  • Thanks for sharing. This actually happened to me when I disconnected the APM UBEC while powering the quad. The props started spinning for about 1-2 seconds. I didn't get hurt at all, I'm sorry you suffered damage.

  • @Muhammad Makes sense. And I bet Simonk (=no filtering of signal) does not require long signal to spin motors. In my case it was very high trottle for short period & that was enough.

  • If I'm not mistaken, when you power up the controller, the uC pulses outputs for a very brief moment, not intentionally by software, it just does it for some reason. If your ESCs are armed when this happens and this pulse falls somewhere in the neighborhood of what the ESCs think is high throttle, they will think they're being told to spin up and do so. 

    I've never actually tried this power cycling situation with an AP, but I have had servos and an ESC hooked up to Arduino before (in a plane setup) and when I power cycled the Arduino (which was powered separately from the servos and ESC) the servos all shot to one side and the ESC ran up for a moment. 

  • @Crashpilot1000: Now I know it did a big mistake trying to load a different param file during the copter arming (I did not have any failsafe setup). But I am sure that the majority believe that throttle down means not motors acting (which is not 100% true).

    What I suggest to prevent this kind of accident is to disable the "Load" button when APM is arm.

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