Hi, I am trying to redesign a system thats already avialable. It contains a small metal rod hanging in mid air between 2 magnet(permanent). There is a solenoid that lets it move to and fro when current is passed. And then there is a spring to limit the movement of the metal rod due to solenoid(I guess). Now I want to redesign it and eliminate some of the magnets. So can you please help me with the equations that I need for that. I mean the different force and EMF equations. I also need to take care of reaction time of the solenoid and the metal rod movements due to the reaction of solenoid. Can you also provide equations for reaction time of a solenoid.