摘要：For most legged robots the drive-motors are mounted on the joints of legs, which increase leg＇s mass and rotary inertia. When mounted on legs, the drive-motor has to rotate clockwise and anticlockwise periodically to swing a leg back and forth. Larger inertia of the leg, as well as the ever-changing status of frequent acceleration and deceleration of the motors, limits the moving speed of the legged robots. This article proposes an improved mechanical design to overcome such problems. All the drive-motors are installed on the robot body to reduce the rotary inertia of the legs. Then a crank-rocker mechanism is used to transform continuous rotation of motors to back and forth motion of the leg. With this scheme, the motor may reach higher rotation speed since it drives a lighter leg with no change of the rotation direction. In addition, an elastic tendon is attached to the ankle to reduce the pulse stress on the leg. Kinematics and dynamics analysis demonstrates that the new design enlarges end-workspace, reduces driving torque and increases ground reaction force, which means the new robot has lager stride and higher swing frequency of leg to achieve faster moving.