What I observed is that arm 2 moves up before arm 1. I want both of them to move towards each other to cause a compression, and away from each other to cause expansion. Is there any way in which that could be achieved using minimal design requirements?
I can think of two options:
1) have the arms connected by gears at the pivot point - when one is moved so will the other, in fact one could be fixed...
2) connect the arms with a threaded rod (needs left & right hand threads) and use a pulley to rotate the rod - then the arms will move according to the pitch of the thread - actually 1 turn will move twice the pitch.