*VIDEO* Crash Diagnostics Help Please! DJI WKM on Cinestar8

[volans_oculo]

Absolutely. My first thought on watching this. "Yeah buddy, classic SUP, no wind and he tries to elevator it down" If you had flown forward, backward, or sideways, while decending, all would probably have been OK. I will say prime axis gains could be higher, if so, you get a sort of "shudder" when SUP occurs and you can fly out of it. "Drunken sailor" wobbles like these are typically low gains.

We got the heli back up in the air a couple days after the crash, and started playing with the gains. I'm new to the heli (and multi-rotors in general), so i'm still figuring this all out, and had another near disaster. I was about 5 feet off the ground, and was playing with basic gains, I got a bit aggressive on the adjustment, and ended up getting the same oscillating effect when I turned the gains up. When I got the heli hooked back up, we found that the gains were around 300%! I put some new props on it (because we broke 2), reset the gains at 100%, and took it up again yesterday. It flew like a dream. I had 5 great flights, with lots of low hovering and maneuvering, as well as a bunch of high-speed passes, ramping up to high altitude. I was descending really easily on an angle into the wind, without issue... I didn't even get any drunken sailor wobbles. I'm sticking with gains around 110-120%!

Thanks for the help!

 

[volans_oculo]

If you experience settling with power the best thing you can do to escape it is to fly in any other direction quickly to regain control.
Forward/back/left/or right. whichever is safest for your given environment.
Adding more power will only make the situation worse (in real helicopters). This may or may not be the case in these light multi-rotors.
As reference, real helicopter descent rate shouldn't be greater than 300' per minute if flying below effective translational lift airspeed to avoid settling.

Fly safe.

Thanks R6Media. I've tweaked my gains, and learned my lesson. Straight-down descents shall be avoided wherever possible!

 

[volans_oculo]

When I was first starting I would always just descend straight down too. But don't waste that battery time, instead throttle down so you are descending slowly and continue to fly around and get footage. The secret is coming down at an angle and understanding that it takes time to descend. It doesn't have to be a consistent angle in the same direction, just don't come straight down.

As for gains, I've found that using remote gains on a TX knob to dial them in is the most efficient way. I do throttle first, then apply pitch and roll together, then attitude, then pitch and roll again (to fine tune), then attitude again (to fine tune). The best way to find the values is just like the manual states - increase until you get oscillation, then back it down a little until you don't get oscillation. When fine tuning, you'll want the craft flying close around you so you can see any little wobbles as it passes.

Also, I would quadruple check your IMU and GPS measurements from your COG just to make sure they are correct.

Thanks for all your help janoots2! After another minor blip, where I was learning to tweak gains (I've got them set up on Tx knobs), I ended up downing it again. I did some digging, and found that they were set far too high: around 200% for the crash in the video, and the subsequent crash, and around 300% when I was testing. I got it up yesterday, flying in wind gusting to 12kts, with 110% basic and attitude gains and it was perfect! Ready to get shooting again!

 

[Electro 2]

we found that the gains were around 300%!................
I'm sticking with gains around 110-120%!....................

Don't go bananas with the gains, just upward. *Any* adjustment should be in 15% increments, max. Once you see what you're looking for, back off in 10% increments until you're peaked. If you started at 100, and it was close, I can't imagine that 300 would be remotely OK.

 

[jhardway]

Ya Gains I have an octo with 14inch props and weighs in around 6500g's it seems to sit well under 200 and in the 160 - 170 wheel house, The one gain I had to put up some, was the yawl, its sits in the 190 range. I have found that to be a good setting at the time, and also have another person I know also at the same setting for there Octo.

When I was testing the copter I was having problems like that with it flying very unstable, what I figured out the copter was to light (4600g), when I put a 5lbs weight on the bottom of it, all of a sudden I was good. What I found its a very fine line where the copter can handle stable flight, and unstable flight. Not knowing where you were on your props and with your new set, did you step down in size??, what I saw there I would say may be the issue I was seeing. It may have been a matter the copter was on the edge of being to light. Gains 300 I also believe could be a factor also.

I do not think it was settling with power. Settling with power is a situation where any rotor to say, is a decent through its own vortexes at a rate where it fall into its own power. Because the copter is dropping so fast its source of lift ends up being the dirty air, which it just produced. In most helicopters the general rule its a decent greater then 300 ft per min at a speed under ETL (effective Transitional Lift), or around 18 kts in a normal helicopter.


in the past with my copters I have done some very aggressive decents where the copter was well into the settling with power stage and even though I seen the copters fiddle back and forth they seem to handle the event well. Because of the power and the acceleration speed of the motors we use, I believe the our multirotors will demonstrate the effects of settling with power however they have the ability to over come the physic involved with the event, mainly because they can out produce the vortex spinning power

So just breaking that down I believe you might have to much power for the weight of the copter, that can be caused by prop size. or it a combination of prop size and gains.

I would be interested in hearing what your prop size is and where they the same when you were encountering the problems. I you have changed the props then I would say its a good chance that was were you were.