TBS Discovery / Pixhawk or APM PID Tuning

[phoanglong]

This is really frustrated, I think there quite a lot of people are having the exact same problem with me . I have tried every single way possible to fix this but non seem to work.. Very strange..

I wonder what happened.

Here is my log, could someone help:

http://www.uploadmb.com/dw.php?id=1408877424

[Big Island Guy]

Originally Posted by phoanglong

This is really frustrated, I think there quite a lot of people are having the exact same problem with me . I have tried every single way possible to fix this but non seem to work.. Very strange..

I wonder what happened.

Here is my log, could someone help:

http://www.uploadmb.com/dw.php?id=1408877424

I know this sounds silly, but when all else fails, one has to turn to the bizarre, and that is, have you checked all your connectors carefully? The erratic kind of behavior you're getting suggests this as a possibility, assuming that changing the motors didn't cause a radical gain setting change to be needed, which I sort of doubt. The little connectors for the Pixhawk are incredibly fragile and it's super, super easy to back one out of its guide channel a bit without it being obvious. The other thing I'd check is that your ESC connectors are perfect. If you're using bullet connectors, make sure none of them are even the slightest bit loose. Keep drilling. You'll find the problem. Good luck!

[phoanglong]

I think it is not the case here, cause i have checked all the connection very careful. solder all the connection carefully. It fly beautiful in Stabilise mode but the problem only occurs when I switch to Loiter and Att-hold.

I have made some research and they said that it is due to the vibration. I have checked my log and it seems to be the case here, but I don't know what cause such vibration. During the stabilise mode the vibration is completely normal and within an acceptable range, but when I switched to Loiter or Att-Hold mode and fly it for like 10s, the vibration start to jump to a really high as you can see in the pictures.

Also my zacc raw_imu_t is arround -1000 (is this bad? cause in the manual it said normally it is around -820 but the range is -800 to -1200)

yacc raw_imu_t is arround -2 to -8 on average.

Could someone help me plz,

Thanks,

Long

[phoanglong]

Just did a quick test fly. The result, much better, no more rocketing up the sky any more.

Problems still facing is loiter mode does not hold position (I will check the log file for more details on what happen).

Alt-hold does hold the altitude but I think I have some problem with my centre of gravity. It is tail heavy as I mount the 4500mah 4S batter at the back and doesn't have any counter weight at the front.

Conclusion for rocketing the sky (or shoot the stars etc) for anybody that face the same problem:

Pixhawk does not do well with vibration, mount it on some anti-vibration damper and as it does have external MAG please also mount the GPS+MAG on some anti-vibration damper as well. Do not put the MinimOSD too close to Pixhawk, it interfere with MAG and also find a way to use less wires, if you have a lot of equipment board like me, please do twist the wires. For the best performance, please make sure that the Pixhawk and GPS+MAG is as close to the centre of gravity as you can. It will make a hell lot of difference.

I think my last setup did not have a lot of vibration and the shooting up the star problem is because the 750kv TBS motors provide less torque compare to 900kv TBS.

I will keep you guys up-to-date.

[vlasv90]

SeanM, tell me please, what do you have PID values now? Show please screenshot of your Mission Planner PID page

[vlasv90]

Originally Posted by SeanM

After spending lots of time trying to get my Disco dialed in, I thought I would share the settings that have proved to work the best on my rig (2216-11 900kV, Afro 20A, 9x5 Graupners, 4S 3300, GoPro, no FPV yet).

At first, I relied on the autotune function to get the roll and pitch PID's where they needed to be.. And that definitely helped with getting closer to the appropriate values, but it still needed some adjustment. I was having some issues with full throttle wobbles on the pitch axis and some wobbles on the roll axis with yaw inputs. I was able to get rid of the yaw issues, but the wobbles on full throttle were proving to be more difficult to dial out... Especially since I have no experience with PID tuning.

So I resorted to google.. After a one minute search using 'TBS Discovery PID' I found screen shots of the PID settings that others had used to get their disco dialed in. Plugged the numbers into mine and the difference is like night and day, super locked in and stable.

Here are the numbers that I found and am using currently. I'll update this thread if I happen to find even better PID values. For now though, these values are an excellent place to start.

Stabilize Roll P - 4.5000

Rate Roll

P - .0900
I - .0800
D - .0030

Stabilize Pitch P - 4.5000

Rate Pitch

P - .1000
I - .0800
D - .0030

Stabilize Yaw P - 3.0000

Rate Yaw

P - .2500
I - .0250
D - 0.000

For anyone trying to better understand how to adjust PID's, checkout this link. This is the best info I have found yet on the subject of PID tuning.

http://diydrones.com/forum/topics/ar...r-tuning-guide

Here's a video from yesterday with this tune. I was having so much fun that I completely discharged the LiPo down to 3.1-3.3v/cell resting! I am so lucky that I noticed the loss in power just seconds before I came in for a rough emergency landing.... Thankfully, there was no damage!

http://youtu.be/r49u7oOxkT8

SeanM, tell me please, what do you have PID values now? Show please screenshot of your Mission Planner PID page