Developed at the Delft Biorobotics Lab, Bob is a 3D Walking robot that is equipped with actuated ankles and knees. The passive dynamic biped lacks controls and is known for its 3D dynamic simulation as well as stability analysis.
Bob uses its actuated ankles and knees for movement. At the end of every step, the ankle tends to extend for inputting energy into the cyclic walking movement. The hips and knees are completely passive joints. For the purpose of preventing falling over sideways, a third motor drives the hipmass left-to-right. These motors are commercially available servo's that are controlled by an affordable microprocessor.
The hips serve as passive hinges while the knees are passive hinges and have unilateral constraints for preventing hyperextension. Springs offer negative stiffness to the knee joint, which slows down the shank while the swing knee is bent as the legs pass each other. This results in improved ground-clearance.
During each step’s first part, the ankle serves as a passive joint. As the step ends, the "Achilles" tendon becomes stretched and signals the servomotor in order to pull the tendon while the ankle is extended. This causes the robot to be lifted a few millimeters. This energy input must be sufficient for compensating for the impact losses at both heel strike and knee strike.