T960 stability issues - new build - any advice?

[oschefer]

I've been following the forum for a while now and have been flying a DJI 550 for a bit over a year. I bought a T960 about the same time and built it slowly over the last year as I didn't think it was a good idea to go straight to a 960 size. I have flown RC planes for many years so I am not totally new to the hobby but have only been into multi rotors for a bit over a year now. I finally got the 960 together and am having a terrible time getting it stable. The 550 was a very simple build, but the 960 so far .... not so easy. I have a large gimbal ready to go but have not put it on yet (good thing as I doubt it would have survived) I have been very impressed with the strength of the T960 frame, unfortunately, I am testing it a little too often right now. I am hoping someone out there might be able to point me in the right direction.

Basic specs:
Tarot T960
Motors - TMotor 4014 330kv
Props - 17x5.8 Carbon Fiber TMotor
ESC - ZTW spider 40A with Simon K
Battery 6S
Flight Control - DJI Naza V2
Landing Gear - retracts from foxtech the pilot V2 I think they were called
Weight with battery 10.5 lbs (4.7kg) (no camera rig)
Once I add the gimbal with the camera second radio, battery, etc it adds 5 lbs (2.2kg)
unfortunately I have not installed the IOSD Mark 2 yet so do not have logs.

First several attempts to fly, it would tip over on take off. I realized I had not calibrated the ESC so I did that and tried again. Not sure if the lift off issue was the ESC or just trying to go up too slowly but it gets off the ground now...

1st liftoff - tried flying with no gimbal to just get it flying knowing re-tuning would be needed. Then Naza gains were up in the 175 range if I remember. The battery was mounted on top so I think it was top heavy
video is here :

I moved the battery under it and tried again. It was much better but still not stable. I had the gains tied to some dials on the remote to try tuning but it didn't help much.

Second successful flight (kinda) I upgraded the NAZA firmware and also found in the newer DJI manual sample gains for an S900. The S900 is a similar sized frame and in their sample used similar kv motors and similar props. The gains were way down near 100 so I started there. I also added a 5 pound dumbbell to simulate the camera and gimbal. It was much better but still wobbled after making an input. Total weight 15.5lbs (7kg)
video is here -

I did some more reading and watching of videos from others. Found a video online where a guy had changed his ESC then started to have what looked and sounded like a similar wobble/drift. This got me thinking about the ESCs. In the instructions it mentions some low kv motor may need to have the motor timing set vs using the auto mode. I set them all to 2 degrees and tried again. This time I used 2 batteries vs the dumbbell so it was 13 lbs. (5.9kg) This left the power distribution accessible if I was going to make more changes. The results were not good see video
video is here -

Any ideas? Has anyone used these ESC with the TMotors? I am leaning to replacing all the ESC with another brand.

 

[Mediakopter.no]

My tips is following:

First of all, check that the flight controller is mounted correct, with the front facing to the front, etc...

Then:
1: Double and triple check that all motors rotate in the right direction.
2: Make sure you hav mounted correct propellers to all the motors in relation to the motor directions
3: Mount all equipment, (or a dumbbell instead of gimbal) to get the correct weight and center of gravity.
4: Adjust the gains. To me it looks like your gains are way to low. If i remeber corrct my basic gains are about 160 on my 900 X8 multirotor. Adjust your gains up until you get small occilations the the respective axis, then just a bit down again.

If this does not help, pleace update us, and I`m sure someone can help you out.

Do all test flights in atti mode.

I also think the machine might be a bit overpowered, so adding weight, and rise the gains a bit might help.

Good luck.

 

[oschefer]

Thanks for the relpy.

I have the Naza V2 flight control mounted in the correct direction, its in the center of the frame looking down on it but mounted on top of the top plate vs in between the top and bottom plates so it is above the CG. I think that should be ok from what I have seem of other builds.
I have checked the blades and motors many times and had 2 other look at them as well to be sure. I'll double check the weights again and try the gain adjustments and give it another shot. Any ideas if the Naza is ok mounted on top or do I have to get it down in the plates or under them?

 

[Mediakopter.no]

I think you can mount it over the COG, no problem, just make sure you adjust the imu or fc placement values in the naza assist software.

 

[oschefer]

Well it is fixed! I swapped out the ESC and now it is flying very well. I did add some more weight as well to simulate the payload. My thinking is that either
1) There was some mismatch between the ZTW spider 40A esc and the TMotor 4014 330kv (there was some info in the ZTW instructions that motor timing might need to be adjusted with low kv motors)
2) I never got the motor timing set correctly, to be honest I tried the auto setting and the 2 degrees but did not go thru all the others
3) the Simonk firmware didn't like the low kv motors (I did find few threads on that).
All are guesses on my part but it is flying now.

The video is here