public void go_down(){
		if( this.direction != Tank.direction_down)
			this.direction = Tank.direction_down ;
		else{
			if(this.location_y + this.speed <= this.active_area_y - 2*this.getHeight() && ifCanWalkInThisDirection())
			{
				this.location_y += this.speed ;
				ifGetProps();
			}
		}
	}