Love the comment Klaus!
But is your box the size of a board game dice or is it the bomb bay doors of a B52?
What power source is available, a hearing aid battery or a power station?
Is it in a fixed position or on the move as the door operates?
How fast does it need to open and close?
How heavy is the door?
Is it a single door or two meeting together?
Is it hinged so it drops from one side or should the door slide to one side?
What space is available around it?
Is it in a hostile environment, under liquid, in a vacuum, explosive gas, very hot, very cold...?
What material is the box made from, can it bear weight of an added mechanism?
Is the opener/closer part of the box stucture or a mechanism external to it?
Brian.