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Like a baby falling from a hot air balloon...

#1
... a baby holding a tricopter. That's what it looked like as my DIY aircraft plummeted toward the Earth. A moment of shock, the sounds of propellers spinning up and down wildly trying to regain control, then WHAM. From 50 feet up, my tricopter had suddenly tumbled out of the air and bellyflopped onto the highway.

How could this have happened? Where did it go wrong? One minute it was flying just fine, then suddenly... destruction.

My heart was in my stomach as I slowly approached the disaster area in the middle of the two lane road. Thankfully no cars were in sight on the little-traveled highway. As I got closer I could see pieces everywhere. All three Rotor Bones landing gears were completely shattered. The battery - smashed. Rear servo - annihilated. Motors? One was still connected to the airframe with a severely bent mount. One was still zip-tied to its broken Rotor Bones mount and lay a few feet away. The third was gone - disappeared into the nether. The third motor's bell and prop lay in the middle of the road, but the motor itself and its mount were nowhere to be seen.

The airframe itself somehow survived. It consisted of the Anycopter hub and the traditional 1/2" dowels. One dowel had already been broken and glued back together twice from previous crashes; now it seemed to smirk at me from the road as I picked up the pieces of my more expensive broken parts. Luckily the flight controller and ESCs were still right as rain, though two of the zip-tied ESCs had made the 90 degree rotation to come to rest on the bottom of their square dowels.

How did this happen? I will never know for sure, but I did find a couple clues. The most likely cause of this crash... was a crash I had 5 minutes prior. Flying from the steps of a gazebo, I was doing some close low speed passes to test my orientation skills. Right became left and left became right at the wrong time and the copter flew into one of the gazebo poles and plopped on the ground. The only apparent damage was a slight dent in the prop that had hit the pole. I set the copter back up and it took off perfectly. I thought nothing else of it...

After buying a $4 bottle of cabernet at the gas station on the way home (to be consumed entirely) and having a chance to inspect the wreckage more closely on a table, I noticed that the prop that had made contact with the gazebo pole was spinning freely around the motor shaft. The plastic adapter fitting (whatever it's called) appeared to have melted and cored the propeller's hub.

My hypothesis is that it either became loose or was damaged when it hit the pole, and my fool self just put it right back up in the air. It held for a few minutes until the DT700 finally ripped it apart.

Lessons learned:

- Super glue the adapters to the prop hub, use lock washers above and below the prop, and crank down on a lock nut to secure those props in place until I SAY SO

- don't fly above hard things

- CHECK EVERYTHING after every crash, no matter how minor


Since this incident other crashes have come and gone but the copter is still flying as good as ever (with new homemade landing gear). But this was the crash that so far has had the greatest impact on my approaches to building and flying a contraption that has soaked up so many countless hours of my attention.
 
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xuzme720

Dedicated foam bender
Mentor
#2
Wow, that's sad to hear. I'm not sure the lockwashers are completely necessary, but regularly checking props for spin/looseness is. Especially after a crash. Also, checking the props for the telltale white stress marks near the hub can save an innocent copters life!
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#3
Heard a suggestion for Nylon washers on the props recently. They'll compress a bit, so you can really crank down on the prop nut. haven't tried it but seems sound.
 

Tritium

Amateur Extra Class K5TWM
#4
I ALWAYS use nylon insert locking nuts instead of the standard spinner shaped nut. I had your issue early in my Multirotor builds and have not had it since due to the locking nuts.

Thurmond