  The quadruped robot is a versatile mobile platform with potential ability for
high payload carrying. However, most of the existing quadruped robots aim at
high maneuverability, highly dynamic and agile locomotion. In spite of this,
payload carrying is still an indispensable ability for the quadruped robots.
Design of a quadruped robot with high payload capacity is yet deeply explored.
In this study, a 50 kg electrically-actuated quadruped robot, Kirin, is
presented to leverage the payload carrying capability. Kirin is an
characterized with prismatic quasi-direct-drive (QDD) leg. This mechanism
greatly augments the payload carrying capability. This study presents several
design principles for the payload-carrying-oriented quadruped robots, including
the mechanical design, actuator parameters selection, and locomotion control
method. The theoretical analysis implies that the lifting task tends to be a
bottleneck for the existing robots with the articulated knee joints. By using
prismatic QDD leg, the payload carrying capability of Kirin is enhanced
greatly. To demonstrate Kirin's payload carrying capability, in preliminary
experiment, up to 125 kg payload lifting in static stance and 50 kg payload
carrying in dynamic trotting are tested. Whole body compliance with payload
carrying is also demonstrated.
