FROG-I, Chinese Quadruped Robot Takes Its First Steps

The quadruped robot FROG-I (Four-legged Robot for Optimal Gaits), designed and built by Dr. Wei Wang's group at the Institute of Automation of the Chinese Academy of Sciences. It is about 1150mm long, 700mm wide, and 950mm tall, with a total weight of approximately 55kg. Each leg contains one hip pitch joint and one knee pitch joint, both of which are powered by DC motors. Still, FROG-I possesses one passive compliant prismatic DOF at each toe. An embedded controller performs control, sensing and and communicates with a host computer through a wireless connection.

Images: Institute of Automation/Chinese Academy of Sciences

This research is motivated by the desire to allow the quadruped locomotion on inaccessible or discontinuous terrain. Our current efforts are targeting developing trajectory planning and control techniques to allow capabilities of jumping obstacles and crossing ditches. A recently developed trajectory planning algorithm was examined that enables FROG-I to overstride a wood board.

Video of  FROG-I

Video: Institute of Automation/Chinese Academy of Sciences

It has been learned from experimental studies on the biological locomotion that some mammals show marvelous adaptation capability of locomotion on different environment substrates by regulating ground (substrate) reaction forces (GRF). Although kinematics and dynamics of the quadruped robot are distinct from those of quadruped animals in their mechanisms, actuators, sensors and so on, we try to enhance the ability of the quadruped robot to traverse in a variable geology environment.

In order to improve the real-time control ability, we have developed an embedded controller for FROG-I. The controller includes two parts, the high-level controller and the low-level controller. The high-level controller based on the Intel Xcale PXA270 communicates with the PC operation platform via wireless connection. The low-level controller based on TMS320DM642 and TMS320f2812 controls the actuated joints, and processes signals from cameras, angle sensors, foot contact sensors and gyroscope. In addition, the high-level controller receives the information from the video processor and guides the low-level controller to perform proper actions. With this design of control architecture, the controller can process the signals and control the locomotion effectively.

Quadruped robots are typically high degree-of -freedom systems, inherently under-actuated, and have changing contacts and constraints with respect to the support surface. These features complicate the inverse dynamics computation and control in real time, which are crucial techniques for quadruped locomotion in natural environments.

For preliminary work, see video inverse-dynamics.wmv.

Future Work will address the following issues for quadruped locomotion:

• Presenting the general representation for inverse kinematics and inverse dynamics

• Reducing the computation of the inverse kinematics and inverse dynamics

• Presenting the inverse dynamics control strategy

• Implementing compliant walking control on the real quadruped platform

• Evaluating the inverse dynamics control

Specifications for FROG-I

• L x W x H: 1150 x 700 x950mm
• Weight: 55kg
• DOF: 8 actuated DOFs and 4 passive DOFs
• Sensors: joint angle sensors, 3-axis acceleration sensor, 3-axis gyro sensor, foot-ground contact sensors, ultrasonic sensors.
• Camera: Pan/Tilt camera
• Control Electrics: ARM + DSP + CANOpen
• Control Mode: position control, current control
• OS: RT-Linux
• Communication: wireless LAN
• Power Supply: DC48V 18A, currently tethered

Contacts and sources:

Dr. Wei Wang
Institute of Automation 
Chinese Academy of Sciences 
95 Zhongguancun Donglu Road
Beijing, 100190, China