Hi !
Thats a long title for my problem :-)
I have 2 Problems:
When i switch to Alt Hold in a relatively windstill environment the copter yaws CW or CCW and then corrects itself back. E.G. in 10 seconds it can do this 2 to 3 times. It also drifts a bit back/forth left/right but thats probably related and due to NOT beeing 100% windstill and the prop backwash i am nut sure that that is a problem...
The frame is very cheap yet very stiff as it is heavy built, its called "Argonaut" and its made of Carbon, see an image attached. There is no noticable arm twist.
Its a small & cheap Platform i wanted for testing the WiDV thingy (blue box, switched off right now, not related to the problem).(I have larger Hexas with 2.6 that fly just fine, did not want those for WiDV)
The frames COG is balanced okay, its using cheap 1806 motors with 5x3 Props.
ACC & Gyro & Compass seem fine to me, GPS is okay but for the tests i just used Stabilize & Alt Hold.
The APM is a bit forward from the COG (5cm), but pretty much in the middle in the other two axis. This did not pose a problem to me before even if the APM was off-COG worse but i better mention that :-) .
ESC are calibrated, Vibrations are okay to my taste.
If you look at the screenshot from MP log view you can see 2 strange things:
The 6 motor outputs are drastically different (something between 1400 <---> 1700 !
And also in the log: the desired yaw stay flat (as i did not yaw on the RC) but the "real" yaw drifts up and down in a smooth curve, exactly what i am experiencing.
I also included the full log, so you can see where i am flying :-)
For the life of me i cannot see how this comes.
As the motor outputs are so drastically different i did a primitive test of the motors.
I fixed the Hexa to a table and did motor test in APM.
(Motor #1 was front right and then the numbers went around the Hexa in CW motion, is that correct, i think so, but i better ask).
I measured RPM at 25% / 50% and 75%.
While they were NOT a perfect match i hope that the variations are in the grren zone and also my RPM-measurung tool is not too precise so allow +-100 RPM for it.
The results i got was:
Motor # (MP) RPM @ 25% RPM @ 50% RPM @ 75%
1 10230 14000 16440 CCW front right
2 10700 14760 16900 CW right
3 10200 14200 16600 CCW back right
4 10600 14600 16900 CW back left
5 10400 14300 16750 CCW left
6 10350 14400 16700 CW front left
Do you guys have any idea whats going on ?
Thanks a lot for helping me out....
Nils
Replies
Hi !
After a much better weigth distribution and several autotuning runs AND adjusting the YAW Gains (increasing them) i have a nice behaviour now !
If i take a look at Yaw vs. desired Yaw i still can see a +- 1 degree "alternating" curve in yaw where desired yaw is a straight line, is this considered normal ? Its not visible in flight.
THANK you so much for helping me !!!!
Nils
To me looking at RCout in your log it looks nose heavy.
Yaw just looks like it needs tuning to me.
This is the Top view, i *assumed* the cog is on the axis of the top and bottom motor (or in APM speech: on the M2-M1 axis).
This is where it is balanced right now.
I guess i have to push the battery further backwards.
Is there a good site explaining CoT & CoG Calculations (especially for Hexas maybe).
Thanks yet again !
Nils
img.JPG
Hi !
Hmm, its my first hexacopter in this "spider" configuration, but the COG should still be in at the intersection of all motor axis, right ?
Because thats how i trimmed it :-) Would be funny if its THAT stupid.
Yaw --> tuning: Do you mean PID Tuning as derived by running autotune ?
THANKS for yout input, i am desperate for a solution...
Nils
P.S. is the chan1...chan8 related to the RCOutput Pins on APM OR the "user friendly" numbering where 1 is front right and then it goes Clockwise around ?!
yeah it should be at the centre, but your front motors outputs are higher than the rear. Being its a small multi it may be particularly sensitive. Thats assuming its not some wierd esc cals.
Unless you have a bewer version of the firmware I have used (3.3?) then yaw isn't tuned during autotune. yours look to be default vals. Try reducing them, my 200mm quad needs lower yaw gains than default.
Oh damn, if the chan corresponds to the RCout pins i can see what you are seeing.
5 & 3 are on high load which are the front ones, 4 & 6 are lazy, geeeez whoever found it funny to have 2 ways of numbering the motors is to blame ;-)
I will check if the COG is NOT where it should be.
Then the Yaw is probably introduced if the frontmost motors cannot cope (maybe ?!)
THANKS,
Nils