Vec3D springTip = new Vec3D(lightTipTraer.position().x(), lightTipTraer.position().y(), lightTipTraer.position().z());
		// spring center, the fixed part
		Vec3D springCenter = new Vec3D(lightCenterTraer.position().x(),lightCenterTraer.position().y(), lightCenterTraer.position().z());

		float angleZ = springTip.headingXY() - springCenter.headingXY();