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

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

Postby mahowik » Wed Jun 15, 2011 7:01 pm

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.
Last edited by mahowik on Fri Jun 24, 2011 10:52 am, edited 2 times in total.
mahowik
 
Posts: 331
Joined: Sun Apr 10, 2011 6:26 pm

Re: incorrect angle for pitch if roll inclination +/-90 deg

Postby mahowik » Fri Jun 24, 2011 9:43 am

Hey,

I can't to see any response on this! :)
Could anyone reproduce this issue? Probably my description above no so clear?!
mahowik
 
Posts: 331
Joined: Sun Apr 10, 2011 6:26 pm

Re: incorrect angle for pitch if roll inclination +/-90 degr

Postby ziss_dm » Fri Jun 24, 2011 12:29 pm

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
ziss_dm
 
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Re: incorrect angle for pitch if roll inclination +/-90 degr

Postby mahowik » Fri Jun 24, 2011 3:57 pm

ziss_dm wrote:"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)..
mahowik
 
Posts: 331
Joined: Sun Apr 10, 2011 6:26 pm

Re: incorrect angle for pitch if roll inclination +/-90 degr

Postby ziss_dm » Fri Jun 24, 2011 5:22 pm

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

regards,
ziss_dm
ziss_dm
 
Posts: 529
Joined: Tue Mar 08, 2011 5:26 am

Re: incorrect angle for pitch if roll inclination +/-90 degr

Postby mahowik » Fri Jun 24, 2011 7:12 pm

Clear! Many thanks for comments!
mahowik
 
Posts: 331
Joined: Sun Apr 10, 2011 6:26 pm


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