A Rocking Chair in Action
At first sight a rocking rocker seams to be something like a swinging Pendulum.
But if you look more thoroughly, we can recognize that this is more like a rolling wheel, which rolls forward and backward and this in a sinus rhythm.

Here a simplified Rocker reduced to a single skid as a macro object.
For the complete Rocker object see the scene file below!

#macro Rocker0( Rocking_Angle ) //--------------------------------- #local D = 0.00001; // just a little bit! #local R_R = 1.20; // rocker skids radius #local R_rotate = 25; // skids angle +/- #local D_feet = 0.055; //--------------------------------------- #local Skid = intersection{ box{<-R_R,-R_R-D,-D_feet/2-2*D>, <0,R_R+D,D_feet/2+2*D> rotate<0,0,-R_rotate> inverse } box{<-R_R,-R_R-D,-D_feet/2-2*D>, <0,R_R+D,D_feet/2+2*D> rotate<0,0,-R_rotate> inverse scale<-1,1,1> } cylinder{<0,0,-D_feet/2>, <0,0,D_feet/2>, R_R} cylinder{<0,0,-D_feet/2-D>, <0,0,D_feet/2+D>, R_R-D_feet inverse } } // end intersection Skid //--------------------------------------- object{ Skid rotate< 0,0,Rocking_Angle> translate< 0, R_R, 0> // move by the // according part of the circumference: translate <-(2*pi*R_R)*(Rocking_Angle/360),0,0> } // end of Skid #end // end of macro Rocker0() ----------

#declare Time =  clock + 0.00;
//---------------------------------------
object{
  Rocker0( 12* sin(Time*2*pi) )
    texture{
      pigment{ color rgb<0.2,0.12,0.08>}
      finish { phong 1 reflection 0}
    } // end of texture
    rotate<0,0,0>
    translate<0,0,0>
} // end of Rocker0 ---------------------

Scene files for the above skid demo in POV-Ray:
"Rocker0.ini" and "Rocker0.pov"