[importon]

So my copter seems to want to drop like a stone periodically.  https://www.youtube.com/watch?v=aFeZTjuw4yE&feature=youtu.be  It almost feels like an esc timing issue or something like that.  You can hear the active breaking going a bit nuts before it hits the ground.  I've tried setting it up as rapid esc and as oneshot in the GCS with the same result.
These are the ESCs I'm using.  http://www.readymaderc.com/store/index.php?main_page=product_info&cPath=505_507_658&products_id=4123  Anyone have an idea of what is happening here?  Thanks! 

[NicholasDavid]

Your issue seems to be like one I had some time ago. I was using DYS bl20 escs. If you get them too hot soldering motor wires direct to the esc the components can move. "Like the little black squares(fets) out by the motor pads."  Just my expirence. Maybe a bad esc

[cato]

I had my Nighthawk dropping out of the sky at irregular occasions. It turned out that the power supply (BEC) powering the FC was to weak. After I exchanged it with a more powerful version, I had no issues anymore so far (not much flying weather since the change).

[NicholasDavid]

Also had a cc3d die after a crash.  Stopped giving reliable power to the RX.

[kennyevo]

My ESC's BEC gave weak power to the FC, I crashed once because of this (only a prop broken), I'm now using a power modul for powering the board (and also for current/voltage sensor), now everything is fine!

[cato]

I have a broken Revo clone, and suspect a bad BEC as the reason. importon, the symptoms you describe look very much like a power issue. My bad BECs would make the Copter fall from the sky like a stone for about one second, then the motors hit in again, but in most cases due to the vortex ring situation I could not catch the copter and it crashed. The motors will make strange noises, trying to stabilize the quad, but the vortex ring will make it almost impossible to catch it, except if you flew at high altitutude, then you can try to escape with high throttle and pitch input.