1. Department of Mechanical and Aerospace Engineering and Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Hong Kong, China;
2. Reconfigurable Robotics Laboratory, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland;
3. General Robotics, Automation, Sensing, and Perception (GRASP) Laboratory, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA;