|Jun 24, 2014, 06:03 PM|
Joined Jun 2014
custom quadcopter randomly shaking
Hope someone can cast a light on my issue I've been having with my custom built quadcopter.
It basically flies as it should but every few seconds it starts to shake quickly like the Kp was too high. I tried to decreasing Kp gain but the shaking does not go away, instead at some low Kp it starts to wobble slowly as the Kp is too low.
Interestingly, the quad only shakes diagonally on "front left - back right" axis. The "front right - back left" axis seems to be rock solid. (The quadcopter is in X configuration). However, the shaking is not continuous. It kicks in randomly and settles down within second or two. It is not related to stick position. The shaking does not really hinder the flight but it will ruin any camera/fpv.
I tried also to put my MPU6050 board on damping foam, but this does not seem to help (http://www.hobbyking.co.uk/hobbyking...dProduct=15214)
What else should I suspect?
frame: HobbyKing Mini Quadcopter Frame V1 - 539mm
motors: turnigy 2209 (980kv)
ecs: afro 20amp with simonk firmware
weight: 650-800g (depending on battery used)
loop frequency: 200hz
This issue is unrelated to flight mode. It is present when flying Rate/Acro or Stab.
My current PID configuration:
However I do not think this is to do with PIDs. It only goes into quick shake every few seconds or so. As mentioned before I went through the entire spectrum of Kp from 300 to 800 and around 800 I see constant high frequency oscillations, and around 400 the quadcopter is not stiff.
I tried to increase Kd but this does not remove the shaking - at high point the motors start to pulsate and at low point I get smoother flight but shaking still is present.
Any advise will be very much appreciated
|Jun 24, 2014, 11:37 PM|
United States, WA, Twisp
Joined Sep 2013
I had a similar issue at one point with my quad. With 9 or 10" 3 blade props it flies great, put a set of 11" 2 blade props on and it bucks like a wild bronc. Later.
|Jun 25, 2014, 12:40 AM|
United States, CA, Azusa
Joined Mar 2014
In order for p to function, you need to turn up d. D stops P.
Try .01 and go up from there.
Then you also need to turn up I. I helps with wind and self leveling
|Jun 25, 2014, 05:15 AM|
Joined Jun 2014
Thanks for all the answers.
Here are a few videos of the copter with Kp being 700, 600, 500 respectively.
Kp set to 700 the quad is stable but does shake with high frequency:
Kp set to 600 the quad is still reasonably stable, shaking is not as strong as with Kp 700:
At Kp 500 the quad is getting unstable and still shakes but with lower frequency:
Ki was set to 1500 (around 3000 I'm getting very bad slow oscillations).
Kd was set to 0.006 (around 0.015 the quad is getting extremely sluggish).
From the videos you can see that the Kp 600 seems the best. If you watch it towards the end (40sec+).
It somehow sounds and looks to me like there is something else going on than PID configuration... maybe really propellers are not right size?
The propellers are balanced (checked them before making the video). The motors sound good to me too.
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