  An intuitive control method for the flying trot, which combines offline
trajectory planning with real-time balance control, is presented. The motion
features of running animals in the vertical direction were analysed using the
spring-load-inverted-pendulum (SLIP) model, and the foot trajectory of the
robot was planned, so the robot could run similar to an animal capable of
vertical flight, according to the given height and speed of the trunk. To
improve the robustness of running, a posture control method based on a foot
acceleration adjustment is proposed. A novel kinematic based CoM observation
method and CoM regulation method is present to enhance the stability of
locomotion. To reduce the impact force when the robot interacts with the
environment, the virtual model control method is used in the control of the
foot trajectory to achieve active compliance. By selecting the proper
parameters for the virtual model, the oscillation motion of the virtual model
and the planning motion of the support foot are synchronized to avoid the large
disturbance caused by the oscillation motion of the virtual model in relation
to the robot motion. The simulation and experiment using the quadruped robot
Billy are reported. In the experiment, the maximum speed of the robot could
reach 4.73 times the body length per second, which verified the feasibility of
the control method.
