I really enjoy hiking, but I do not when my little copter is hiding somewhere out there... in pieces. After many successful flights today I ended up picking up smashed parts again.
Now I need your help. It would be great if someone (with more abilities as me) could have a look at the log (problems start at around 78%, I think) and the youtube video. My theory is that one prop breaks, then only one side of the prop is intact (which explains this massive shaking) any more and also bursts off after some seconds. It's nice to see that redundancy is working in that short time span. But after the whole prop is lost, it falls like a stone.
My copter is a standard jdrones Hexa with 850Kv motors running 2.0.49 with default PIDs. I was using brand new 10x45 composite props. Weight is about 1.8kg.
If the problem really was a breaking prop, this is the second time that I encountered a crash because of that reason. My copter is now a pile of garbage again (the third time!). Because it fell upside down from that tree, upper carrier plate broke into pieces and scratched some $electronic_components_i_have_no_idea_of from the Olipan shield. I can't even connect to it. :-(
Any help in investigating this horrible crash is highly appreciated!
Hi guys, your comments helped me a lot in finding a clue on how this all could happen. So this is the final crash report.
First I need to state: It's all my fault. After many broken acrylic motor mounts I decided to attach the motors directly on the arms, like many other constructors (e.g. MK or Jakub) are doing it.
But the problem is that the thickness of official kit arms is way too thin! Like I said, I had many trouble-free flight hours with that setup, but tension and vibrations did their job well and attacked structure of the arm slowly but powerful. This is what I found after the crash:
I assume that it broke in flight. How do I come to that conclusion? Wires of the motor are twisted heavily, also their insulation is hurt badly. And I cannot believe that the injury on the arm is caused by the crash itself. So I think it happened like CyberCrash stated: At the first cracking noise, the motor broke off, maybe only partially. This could explain why the copter still looks like to be flying stable. But after some seconds it drops out completely. And this leads to the not Hollywood-like ending of the story.
So thanks again for your comments! I'm kind of glad that it was all my fault, this makes me still believe that ArduCopter is a great product. :)
Sorry for your loss.
I noticed how thin the slow flyer props are near the hub and I looked up on APC's site the recommended max prop speeds
for a 10" Slow Flyer prop the max is 6500 rpm (65000/10")
At full throttle a 850 kv motor wants to turn around 10,710 rpm on a 3S lipo at full charge (12.6 volt)
9,520 rpm at 11.2 volt rated voltage of 3s which is still almost 50% over APC's recommend max RPM for a slow fly prop.
I know a copter is not operating at full throttle most of the time but it looks like anything above 6500 rpm would be asking for trouble and operating outside the designed range of a Slow Flyer prop. Even a full throttle static test might over stress the prop causing a later failure in flight.
Perhaps others have measured the actual rpm of the Arducopter setups and can confirm if the recommended rpm limit is being exceeded.
This is interesting. Since I'm using 4S Lipos, maximum rpm would be 14280. Can those props suitable for higher rpm be used on a multicopter?
I'm also highly interested in some really solid props. Maybe we should open another thread for that.
Yes lets. It's a shame to have such a critical part be a weak link in the system.
The best I found so far are these:
Just can't find them anywhere else and prefer to source them from the US if possible.
Maybe these would work also as a 10" replacement? They are not CF but they say:
Suits 750-800kva on 4S
Which equates to about 12,000rpm.
I'm looking forward to see your experiences with that props!
Me too :) We should have more and better options for props. I've spent $100s in replacement parts costs because of props breaking and now seeing their rpm limit, I see they are minimal for what we should be using.
Really seems like metal fatigue to me.
Interesting observations regarding prop types and speeds. I think the electric thin types might be good, but might be difficult to find matching push & pull props.
I share your loss Johannes. Really. Crashed my rather new hexa into my flag pole, yesterday.
Of course I have excuses, but in the end, well... my fault.