Summary
This paper considers an n‐link planar robot moving in the vertical plane with multiple active links. The controllability and observability of the robot around the upright equilibrium point, which are important for the existence of an output‐feedback controller, are investigated in detail. Specific properties of the mechanical parameters are extracted to demonstrate that when there are adjacent active links, the robot is strongly structurally controllable and observable around the upright equilibrium point. When the active links are not adjacent to each other, a necessary and sufficient condition is established to ensure the linear controllability and observability. Finally, the theoretical results are illustrated via several practical examples. Copyright © 2017 John Wiley & Sons, Ltd.