Need your ideas about what has caused crashes

[father_gorry]

Hi there,
For about 20 flights I've been experiencing trouble flights usually ending with rapid, barely controllable landing.
Here's the video of the first and last accidents. I've changed everything - frame and all electronics except ESC, so there's probably something wrong with them.

My suggestions:
1. Too high low battery threshold, maybe it's set for NiMH, not LiPo. Contra: before I was able to fly flawlessly.
2. All six batteries have just lost their power. Contra: it's cut by Occam's razor
3. One or more ESC's suddenly increase power drain, so others get low power signal and enter emergency mode. Contra: everything - motors and ESC - is cold in the crashed copter.
Your suggestions?

 

[jbrumberg]

I would check the LVC (Low Voltage Cutoff) settings on the ESC's. They may be set too high.

BTW: Welcome and nice videos.

 

[maxwelltub]

Sounds like a voltage issue. What's your fail safe voltage cut off?

 

[Bartman]

setting low voltage cut off in standard ESC's (like hobbyking Plush or Blue series) is done by setting the battery type to NiCad/NiMH and then the voltage to low. Doing this makes sure the low voltage cut off point is TOO LOW for your LiPos to ever reach.

Don't set the low voltage cut-off on the ESC's to LiPo, you don't want the ESC's to be able to initiate a low-voltage cut-off or failsafe.

Low voltage on the flight control system is something entirely different.

Bart

 

[maxwelltub]

Ya I'm referring to FC voltage cut off

 

[violetwolf]

I suspect the battery is simply running low. In both crashes the motors were running until it hit the ground.

Father have you tested to see how much the batteries take to recharge? It should never be more than 80% of the total capacity. For instance a 5000mah batt should take about 4000ma to recharge after a flight.

I always run both a timer (on the radio) and battery alarms on the copter.

 

[father_gorry]

I can't check batteries recharge, but there's no difference between flying with 600g load or without, with one 2200mAH 25C battery or with two of them (set in parallel), aggressive flight or just 50cm hover - the copter falls after 10-40 seconds.
Recently I've changed the ESCs, and still got the same crashes.
I've changed firmware and crashed again!