A simple swing propagation mechanism for multi-robot motion coordination is presented. This mechanism is based on local-perception and low-level communication. It is oriented to coordinate situated modular robots. The swing propagation mechanism is divided into two movements: simple following and collective obstacleavoidance. The first movement is executed when the leader of a robot formation is able to move and proposes a movement that is copied by its followers in the formation. The second movement is executed when the leader of a robot formation is unable to move and asks its followers to undo an action. In the first movement, motion is propagated backwards in a robot formation, whereas in the second movement, a request is propagated backwards and motion is propagated forward in a robot formation. Experimental results of multi-robot motion coordination using Mini-trans, a physical homemade modular system, are presented.