Re: Problem with Euler Angles

Hi Mike,

I tried your angle calculation routines in my Kimaita robot for fall
detection. That seemed to work at first, with the initial dive-attack.
But later on in the match it went wrong: falls were detected when
there was none.

This weekend I logged sensor data every 64 msec while the robot was
walking a small circle, and doing some body rotations after every
(about) 90 degrees: tilt forward/back, tilt left/right and rotate ,
each + and -10 degrees.

Near the Z-axis, the angles routines return values that can be related
to the actual robot posture. But when moving away from the Z-axis, I
cannot relate the returned angles to the robot anymore.

I have made a summary of the test rotation values (angletest 01
summaray.txt). You can donwload this file from
www.van-der-klip.demon.nl/webots/angletest01.zip. It also contains the
 sensor data for each of the 4 test movements in the walk (set 1, 2,
3, 4.txt) and the complete sensor and action log files).

You can download the webview file of the test walk from:
www.van-der-klip.demon.nl/webots/angletest01.wva

Are the calculated angles something else then a rotation of the robot
body around its center? If so, could you please axplain what they are?

Regards,  Frans / Kimaita

--- In [email protected], "Mike Jost"
<webotsContest@m...> wrote:
> Olivier,
> 
> I found some problems with the Euler angle calculations this
weekend.  I tested the previous equations by rotating the robot with
the mouse, since I did not have a robot controller capable of turning
on its own.   Apparently the rotation composition used by the mouse in
the Webots program is different than the rotation composition used
when a robot actually moves itself.  The current gps_euler( ) function
in Webots 4.0.17 also returns wrong X and Z angles for some Y
orientations of a robot.
> 
> Solution:
> I looked at the VRML file and used a rotation composition based on
the heirarchy of the robot.  
>    Judoka_Robot {
>       rotation 0 1 0 0 (rot about Y)
>       children {
>          back_1 servo {
>             rotation 1 0 0 0 (rot about X)
>             children {
>                back_2 servo {
>                   rotation 0 0 1 0 (rot about Z)
>                }
>             }
>          }   
>          gps_device
>       }
>    }
> 
> The resulting composition should be  Rgeneral = Ry * Rx * Rz instead
of the previous  Rx * Ry * Rz.
> 
> The routine to compute the euler angles based on this composition is:
>    public static float[] getAngles(float matrix[]) {
>       
>       float[] angles = new float[3];
>       double cosX;
> 
>       angles[0] = (float)Math.asin(-1*matrix[9]); // find X angle
> 
>       cosX = Math.cos(angles[0]);
>       angles[1] = (float)Math.atan2( -1*matrix[8]/cosX,
matrix[10]/cosX  );  // find Y angle
>       angles[2] = (float)Math.atan2( matrix[1]/cosX, matrix[5]/cosX
);       // find Z angle
> 
>       return angles;
>    } // end of getAngles()
> 
> 
> I have generated a Judoka0 test robot that will rotate itself about
Y and stop at 45 Degree intervals and bend forward,backward, left, and
right, and display the computed angles from this new routine.
> The back_1 and back_2 servos are set to a rotation of +/- 0.5 rad at
each test point.
> Hopefully, this routine will work in all cases, such as after Coyote
does a summersalt and rotates X around a full 2*pi radians.
> 
> 
> Judoka0 Test Robot:
>   
http://www.mikejost.com/cyberbotics/RotationMatrix/Judoka0_AngleTest.zip
> 
> HTML version of Maple worksheet of General Rotation Matrix for
R=Ry*Rx*Rz:
>   
http://www.mikejost.com/cyberbotics/RotationMatrix/RotationMatrix.html
> 
> 
> Mike Jost (FreeTIme)


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