Decelerating a robot arm converts motion into heat. An ingenious spring mechanism, which can store up to 80% of the kinetic energy, is making robots more energy-efficient. The buffering coupling developed by ir. Michiel Plooij and his colleagues in the 3mE faculty is the size of an espresso cup. The patented invention contains a spring in the middle, with the axles of a differential mechanism on either side. By locking one of the axles at the right time, the resilience slows down the motion. When it is time for the robot arm to return – repetitive motion is characteristic of robots – the extended spring sets the arm back in motion, after which the electro-motors resume control.