Tom Haney explains, in words and pictures, how he engineered his two-part (three if you count the connective rope) tug-of-war-automaton:
The mechanism for this piece is mostly in the base of the woman. However, the piece does not operate unless the 2 bases are at the proper distance from each other. The woman does not pull unless the man is pulling back. There is only a spring in the base of the man, which makes him pull on the rope…. My drawing of Tete. You can see I originally had the figures bent over, but after I tied a piece of rope to a column in my studio and pulled on it, I realized the figures should not be bent over, their bodies should be straight; so I changed my drawing….
Further details on on Haney’s web site.