The magnet draws power and it kind of heavy. I would just use a servo to remove a pin from three eyebolts, one attached to the "bomb" and two to the plane sandwiching the one on the "bomb". I was actually thinking of ways to drop an object, but mine involve doors and complex mechanisms to open the doors and drop the object with one servo (I'm an engineering student so its what I do ). I hope you understand what I'm talking about. If not then let me know and I will draw you one of my high quality MS Paint pictures (I need a face to indicate sarcasm here).