I wanted to share my experience to help & protect you all. No multicopter is worth personal damage & stitches.
Background
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
- land
- disconnect reciver battery -> gimbal levels
- 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.
- Always start FC first, then connect drivebatteries
- Always disconnevt drivebatteries first, then FC
- Multicopters are very dangerous tools. If I continue with multicopters, a mechanical securing is required on startup & disconnect. Errors (hw, sw & user) will happen.
- 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!
Comments
@patrice: The main difference is that arducopter is still armed (10sec or so) if the rotors stop, a NORMAL configured multiwii is disarmed when motors stop, that is safer.
@criro: That was a bad idea. Writing parameters may be different, but keeping the copter fully powered during flashing is something i didn't dare to try yet....
Thanks for support!
Can someone explain how motors can start at full speed when powering FC? How that can be prevented?
My accident scenario is easy to reproduce. What is the propability of my accident? Someone should setup a secured test bench.... That might be my last service to the community.. :)
Hope for a good recovery.
I did have also an unpredictable situation with Arducopter, APM2.0, after I did arm, then I did try to load another set of parameters from a separate file (when it was armed...), and this cause the copter to start at full power and flip on ground, motor spinning... nothing wrong for me, but copter need some rebuilds. Not sure what caused that issue.
this cannot happen with multiwii !
Ouch. I hope you have a smooth and speedy recovery!
Checklist is definitely a must. Can't tell you how many times I've bitten the bullet for trying to get in a quick flight.
+1 Euan on the checklist. In the "heat of the moment" one can easily forget to shut off all necessary components to ensure safety.
I would add that simplifying your craft makes for safer/simplier startup/shotdown procedures, and less chance of human error. Less power systems, better design, better packaging, less components.
If your craft complexity is essential, you need to operate a fkight checklist, and follow it rigidly. Most injuries occur in the panic/rush after a crash or critical inflight incident. I use a checklist, but mainly because I'm a newb and I tend to panic a little if I crash.
From personal experience I would also add: When connecting / disconnecting flight power, do not have the Tx around your neck. It makes it very easy to knock the throttle away from the fully down position.
My best wishes for your restitution. Perhaps thats why i implemented a killswitch in my own copterproject - i really got used to it after landing - killswitch and nothing in the world will rearm this thing unless the next powercycle. Even if i would experience a flyaway the killswitch will stop that immediately (ok 900ms timeout just in case the rc has signalstrength problem and a failsafe should be done instead of a killsw action). I wonder why a killswitch is not safety - standard with every coptercontrol.
Cheers Kraut Rob
Thanks for sharing this with the community Heikki. I'm sure a lot of us can learn something from your experience. I hope your hand heals up with minimal nerve damage!!!
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