let’s go on here from this topics http://ardupilot.com/forum/viewtopic.php?f=111&t=13057
So the problem is that during YAW in ALTHOLD, I have a strange altitude variace (somethimes I lost altitude, sometimes I gain altitude)
I run fw 3.3rc7 on a X8 and thanks to other’s help this seems not a problem caused by vibrations.
and here below is the screenshot.
From what I could understand seems to be related to baro reading …
The really strange is that after the Autotune, the Yaw is almost uncontrollable or better, I can controll the Yaw but the loss of altitude is huge!
Sorry for the delay, I haven’t been checking the APM Forum as part of the Copter-3.3 beta testing, it’s only now that we’re doing the soft launch that I’m checking in here.
In any case, I’ve had a look at the logs and I agree it’s likely a baro issue so you could try modifying the frame to try and reduce the impact. Is it possible that the airflow over the flight controller changes when some of the motors speed up or slow down?
Some other possibilities:
High vibration levels - your vehicle’s vibes are higher than my IRIS (Z-axis is about 25m/s/s peaking to 40m/s/s) but I think this is still in the acceptable range.
Motor imbalance - doesn’t seem like the issue - when stable the top and bottom motors are within 150pwm of each other
bad throttle curve. When yawing the clockwise motors and counter clockwise motors’ pwm values separate dramatically to generate the rotational force. If the throttle curve (which converts the desired thrust to a pwm value) is incorrect it could cause the overall thrust to be too high or two low. You could try playing around with the MOT_THST_EXPO parameter to see if it helps. I can be any value between 0.25 to 0.8 and the default is 0.65. Try setting it to a very low or high values to see if it makes a difference.
Hi! Thanks a lot for your reply
I’ve modified then frame adding a plastic dome and closing with tape all the carbon plate cut off. This was the main and more appropriate modification to solve the problem.
There still some improvement into the handling I would like to introduce, but definitelly the pressure variance seems to be the problem.
BTW I’ve never noticied anything bad regarding vibration: I will try to better balance propellers and motors
