MSC Software Corporation

Shanghai Jiao Tong University researchers including Dr. Gao Feng, Director of the Chinese National Laboratory of Mechanical System and Vibration at SJTU and Dr. Yang Pan, Postdoctoral Research Fellow at SJTU, have designed the Octopus III six-legged robot for moving, searching, detecting, repairing and rescuing in extreme environments such as nuclear radiation, fires, and underwater. The six-legged Octopus III robot takes advantage of the unusual capabilities of legged robots such as traversing uneven terrain, overcoming obstacles, performing vertical climbs, and righting themselves after turning over.

Legged robots are substantially more difficult to design than wheeled robots because they require complex mechanics and control strategies to maintain their equilibrium, orientation, efficiency and speed. The Octopus III’s six legs each have an identical drive mechanism consisting a parallel mechanism with three limbs. Each leg has one UP limb with a universal joint and a prismatic joint connected in series and two UPS limbs with a universal joint, a prismatic joint and spherical joint connected in series.

The robot is controlled by an onboard computer running the Linux operating system that communicates wirelessly with a remote computer running the Windows operating system. Orders such as move forward or turn left can be issued to the robot through a human machine interface (HMI) on the Windows computer. The onboard computer contains optimized kinematics and dynamic models of the robot and controls the robot’s 180 servo motors. The robot weighs about 270 kg, can climb a 20 degree slope and walks at 1.08 km/hr.

The SJTU researchers tested the prototype under a wide range of conditions such as turning valves and switches and carrying loads of up to 500 kilograms in order to evaluate its fitness for proposed missions. The physical experiments showed that the performance of the prototype closely matched the Adams predictions. “If we had not used Adams to optimize the design prior to building the prototype, we would probably have needed five additional prototypes at a cost of $100,000 each to get the design right,” Pan said. “With Adams, the first prototype worked exactly as intended so we did not have to make a single change.”

• The Adams/View command language works well for parametric modeling of robots
• The performance of the prototype closely matched the Adams predictions
• Applying Adams simulation early in their robot design saved five additional prototypes at a cost of $100,000 each