Early on I had a phantom with the Naza flight controller. I had a hard landing with that setup where the phantom all but fell out of the sky during descent.

I have since then been flying professionally for realtors and decided that I wanted a system far more robust than the phantom system.

I opted for an F550 with the A2 controller. I like the smallish frame of the F550 and that it is less obtrusive in crowded neighborhoods than the S900 or S1000 and (I thought) the professional quality of the A2 platform would prevent failures like the one I had with the phantom/Naza..

Two days ago I had the exact same thing happen. I was descending at less than or equal to 1M per second when the f550 started to wobble. I immediately stopped all translation hoping the A2 would get its act together and stabilize the craft. Instead the wobbles increased until the craft got sideways and fell out of the sky and right into the home owners pool. Resulting in a complete loss; GoPro hero 4 black, Zenmuse H43D, motors... everything.

I don't mind losing the craft... If it's my fault. That is a risk that I accept. To watch this supposed 'professional' controller put itself into an ever increasing death wobble was incredibly frustrating and worriesome when flying over houses in the $10,000,000 range. I was glad that it didn't hit the house more than anything else.

The A2 is expensive controller and from my point of view all you get for that expense is an alluminum housing.

IF I decide to continue with DJI does anyone have any idea how to prevent these sort of system failures? Was it my choice of the smaller F550 that was the source of the problem? Would a spreading wings frame be more stable?

Thanks

Doug,

That's a sad story, and other than words of solace the only thing I can say is that I have a Phantom 2 Vision Plus, and when I first bought it, I thought it was the most amazing device I had ever seen for both maneuverability and stability.

I liked it so much I wanted to get into the agricultural imaging business and purchased an S1000+ setup with gangster white-walls... A2, Lightbridge, IOSD Mk II, Datalink 900, and a Zenmuse Z15 gimbal.

After getting everything set up and seeing it fly, I thought the Phantom was old potatoes in terms of stability.

Maybe it's the 8 rotors, maybe it's the increased radius of the rotors, maybe it's the increased lift to weight ratio - I don't know, but its is a very stable flying device.

There is much less normal wobble than on a Phantom, with much less wandering with everything in neutral.

The only wobble I have ever noticed is when I'm at altitude and ready to come down, a full down throttle causes a wobble, but I have always figured that the motors and IMU like up better than down, so when I see the wobble, I just set the throttle to a little less down, and everything evens back to normal.

Everything else flight-wise has always been great. Distances, hovering, spinning, high winds, using the IOC "HOME" mode if I get so far away I loose the Lightbridge image on the monitor, etc.

A DJI forum acquaintance of mine, Gary Francis, has an instability at certain distances from the home point when he's flying in POI, but as I understand, no loss of control yet, and only in POI.

There are many things I wish I could change with the A2, like the fact that if you are headed home and ever accidently have both the throttle and pitch joysticks in the down position, you have just shut down the system and it's a dead weight coming down. For me it was only about 20 feet up, but it was over cement and I ruined a Z15 gimbal and caused so much damage to the S1000+ that I just bought a new body and moved over everything else.

Was that at least partial pilot error? Probably

Do I wish that something inside the A2 said "don't accept a shutdown command until you're either within 1 meter of the altitude your took off at or the motors are in idle with absolutely no movement in any of the 3 directions (landed)" - Yes

My plan is to get the Z15 repaired and to over time fix the crashed body, then buy a second A2 to give me a flyable platform without video feedback.

If your platform is totally inoperative you might never get the chance, but the first things I would look at would be the A2 System definition that says where the IMU is mounted in relation to the platform , and center of gravity. It sounds like what happened to you is a harmonic oscillation that the A2 couldn't overcome, and the only way I can think of that causing a wobble that increases would be a motor failure, which you probably would have noticed if you were looking at it, or center of gravity problem that caused the A2 to try compensating for one motor, then when that didn't move the platform in the correct direction, go back the other way, but a little stronger. Then noticing that pitch/roll problem, re-compensate back to the first motor, but even stronger. I can see where this harmonic oscillation could build to a point where the A2 could no longer react fast enough and over she goes.

Keep in mind that the center of gravity is affected by both battery and camera placement, so even if you were in balance sitting on a table before you mounted the camera, the added weight off-center would cause the A2 to over compensate to make pitch/roll corrections.

Also, the smaller the radius between the rotors and the fewer the rotors, the more pronounced a center of gravity problem would be.

If you still have the craft, and haven't taken it apart, see if holding each pair of opposite arms makes it hang perfectly straight.

I wish I could do more to help

Maybe we could start a "$2500 Zemnuse Boneyard" club of some kind.

Anything else I can do to help, let me know.

Thanks for the response.

It was definitely some kind of harmonic oscillation that the A2 couldn't overcome.

I was descending (not full down but close to 1 meter per second) and the moment it started I centered all the controls and hoped the A2 would know what to do. Once I saw the oscillation getting worse I tried to increase the throttle hoping 'up' would straighten things out, by then it was to late and the F550 went sideways and slipped out from under any lift it still had. Mind you this all happened in about 4 seconds.

I had taken great pains to find the center of gravity. Hanging the F550 by each arm a drawing a line through to the floor. The point where all those lines met was the center of gravity (at least I thought so).

I think it must be that the arms are too narrow to be stable with a heavy load. I'm looking into some solutions like the aericam X6 and the spreading wings family.