[1.7.10] Problem with animation

Hi! I made a mob model and want to make animations. Every leg have 2 pieces: upper and lower. Parts of code:

    convertToChild(leftleg, leftleg2);

    convertToChild(rightleg, rightleg2);

    this.leftleg.rotateAngleX = -1.3F * this.func_78172_a(f, 9.0F) * f1;

    this.rightleg.rotateAngleX = 1.3F * this.func_78172_a(f, 9.0F) * f1;

    this.leftleg.rotateAngleY = 0.0F;

    this.rightleg.rotateAngleY = 0.0F;

    protected void convertToChild(ModelRenderer parParent, ModelRenderer parChild)

    {

      parChild.rotationPointX -= parParent.rotationPointX;

      parChild.rotationPointY -= parParent.rotationPointY;

      parChild.rotationPointZ -= parParent.rotationPointZ;

      parChild.rotateAngleX -= parParent.rotateAngleX;

      parChild.rotateAngleY -= parParent.rotateAngleY;

      parChild.rotateAngleZ -= parParent.rotateAngleZ;

      parParent.addChild(parChild);

    }

Problem is that upper and lower pieces moving in other directions.