Solenoid

From Opendildonics.org

A solenoid is a type of linear actuator. A coil of conductive windings surrounds a ferrous plunger. This plunger is drawn into the center of the magnetic field created by the coil when it is energized.

It is important to note that the plunger cannot be pushed out by reversing the polarity of DC power applied to the coil. In fact, the plunger will be drawn to the center of the coil even when AC power is applied to the coil.

A reciprocating motion can be achieved by using a spring to return the plunger when current is removed, or by alternately energizing two coils which have been offset from each other. (Wire can be shared between the two coils by using a tap).

Content needed: Formula for calculating coil diameter, length, wire gauge, number of turns, power required, etc. for moving a mass of a given size.