incorrect angle for pitch if roll inclination +/-90 degree

[mahowik]

At first it's great and now it's possible to rotate with 360 degree!!! Thanks to ziss_dm!!!

But it seems I have found an issue with new IMU in MultiWii_dev20110607. If you try to tilt/incline the copter for about +/-90 degree for roll (then hold for roll) and then incline for +/-(10-20) degree for pitch it shows/estimate incorrect angle for pitch, about +/-(70-90) degree in GUI...
It's also true for pitch/roll combination, i.e. when pitch is about +/-90 and you will try to incline +/-(10-20) degree for roll it will show about +/-(70-90) degree for roll in GUI.

Probably it's not a bug but feature?!

Pls. let me know if you need more info on this issue.

[mahowik]

Hey,

I can't to see any response on this!
Could anyone reproduce this issue? Probably my description above no so clear?!

[ziss_dm]

Hi,

Sorry, I have missed this post. If you referring "strange" behavior of roll when you pitch 90deg, this is so called singularities or gimbal lock. This is a result of conversion to the Euler angles attitude representation. There lot of articles about this, for example this: http://www.google.com.au/url?sa=t&sourc ... cYVSYHlbuw

The singularities found in the various Euler angle represen-
tations are said to arise from gimbal lock. Two examples
of this phenomenon are presented in Sec's. 5.5.6 and 5.6.6.
Gimbal lock may be understood in several di®erent
ways. Intuitively, it arises from the indistinguishability of
changes in the ¯rst and third Euler angles when the second
Euler angle is at some critical value. Take, for example,
the (1; 2; 3) sequence. When the pitch angle is 90 degrees,
the vehicle is pointing straight up, and roll and yaw are in-
distinguishable. In the case of the (3; 1; 3) sequence, when
the nutation angle is zero, changes in the spin angle are
the same as changes in the precession angle.

I hope this is clarify things..
regards,
ziss_dm

[mahowik]

"strange" behavior of roll when you pitch 90deg

I have reproduced this not only for roll-pitch but also for pitch-roll (i.e. "strange" behavior of pitch when roll 90deg)...
BTW I checked this with MARG adapted by Syberian and this issue true only for roll-pitch (i.e. "strange" behavior of roll when pitch 90deg)..

[ziss_dm]

Hi,
This is small trade-off for efficiency. It should not affect control algorithm.

regards,
ziss_dm

[mahowik]

Clear! Many thanks for comments!