1. Dyson School of Design Engineering, Imperial College London, London SW7 2BX, UK
2. Iomech, Ltd., Sutton SM2 5BY, UK
3. Department of Mechanical Engineering and Robotics, Guangdong Technion-Israel Institute of Technology, Shantou 515063, China
4. Guangdong Provincial Key Laboratory of Materials and Technologies for Energy Conversion, Guangdong Technion-Israel Institute of Technology, Shantou 515063, China
5. NCR Corporation, Atlanta, GA 30308, USA