• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Help tuning rotor-bones x quad - terrible oscillation

#1
Hey guys,
Wondering if i can get some help. I just scratch build a rotor-bones x quad and am having a terrible time getting the thing PI-edited correct. I set it according to the tuning guide:

Roll/Pitch P-gain: 30 (For a small 25cm size set to 20)
Roll/Pitch P-limit: 100
Roll/Pitch I-gain: 0
Roll/Pitch I-limit: 20

Yaw P-gain: 50
Yaw P-limit: 20
Yaw I-gain: 0
Yaw I-limit: 10


I can't get above 34ish on the roll p-gain before it oscillates terribly. Once set to 35 to elimination the oscillation, the overall control is also terrible. I increased the yaw p-gain to stabilze the tendency to yaw left. (y-pg 75/y-ig 75)

Here is my setup and a pic attached of new rotor-bones X vs H-Quad.
  • kk2.0 v1.6
  • Turnigy D2836/11 750kv motors (attempt to replace the dt750 i had b/c stock was a problem and needed a new motor)
  • 11x4.7 props (leftover from DT750) recommended is 9x6
  • plush 30A ESC
  • 2200 3S


Is the props the problem? I thought i understood a larger prop would still work but may not be best performance.

I have upgraded the booms so that motor-to-motor they are about 25" apart. Reason for this is because i was previously flying an h-quad same dimensions and it flew great but heavy. So i was trying to match the dimensions but lighter center frame to increase overall performance/flite time. 2013-08-09 18.59.35_sm.jpg 2013-06-12 09.59.10_sm.jpg
 
#2
My first thoughts are worried about how you've got the motors mounted to the booms. The torque from those 11" props could be twisting the surface of the motor mount to boom or twisting the whole boom which is longer than your H quad's and has more leverage. The twisting action could exacerbate oscillations as the flight controller makes its corrections.
 
#3
I have since twisted the motor mounts a 1/4 turn and zipped those guys on that way. They are solidly on there now. They were loose before. Even FT recommended boom size of 10 produced the same result. I increased the boom by 1 inch 11 just to test the theory that the props were to close (being 11s). better, but my first post above was with these changes already made.
 

Cyberdactyl

Misfit Multirotor Monkey
#4
One thing I would add, but I sort of doubt is your issue. . .is if your props are slipping slightly. The little DJI 450 clone I lost had that problem when I first put 11" CF on it with the 750's. Larger props can erratically slip a bit since they have more inertia to overcome when attempting to speed up and slow down. It's especially bad with large CF props and smaller shafts because the CF is a relatively hard material and the nut and washer can't "squeeze" the carbon fiber as easily as soft plastic props. But I see you are using plastic, so I'm petty sure it's as you say. . .just props over-sized for the frame and weight, and the FC is over-compensating.