Re: Problem with Euler Angles

Hi Mike,

Many thanks for this new contribution. I will let Muhamed check it out 
and let you know if he finds it works fine.

-Olivier

Mike Jost 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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