Snake robot to the rescue

Try to picture a snake-like robot that can move into places that are too dangerous for humans to enter. The snake can climb up stairs, force past beams and twist itself round corners. Imagine that it has a built-in advanced water tap that not only can be turned on and off, but can allow the direction of the water flow to be altered.

Valves and water hydraulic motors

This new robot system is now in the development stages at SINTEF. A patent application has been filed and the research scientists have built a demonstrator to prove that the particular research-related challenges have been conquered. The work has so far consumed 18 months and a thesis at SINTEF. A Ph. D study, which is underway at NTNU, is concerned with developing a control strategy for the robot.

The snake contains 20 water hydraulic motors that move the robotic joints – and a similar number of valves to control the water flow to each motor. Each module consists of two hydraulic motors and two valves. The outer layer is comprised of a strong steel skeleton containing the joint modules, which can rotate around two orthogonal axes. The joints are controlled by custom-built electronics.

“It is much like the grab on an excavator where different joints and movements are co-ordinated by the operator. In this instance, the operator is the computer,” says Pål Liljebäck of SINTEF. “There are angle sensors in each joint, and we can decide with conplete accuracy the angle that we want in the joints. A camera in the snake’s head makes operating the snake like driving a remote-controlled car. The operator can tell the snake to move from A to B, and the snake works out on its own how to accomplish this. It knows how to cross a pile of materials, climb down on the back side and twist itself round objects in order to get footing.”

The energy to move the joints comes from 100 bars of hydraulic water pressure. “This pressure is strong enough to lift a car up off the ground, something that again explains how the snake can in principle break through a wall. But both the hydraulic pressure and the use of pure water without additives in the hydraulic system have posed challenges”, Liljebäck says.

At the cutting edge of research

A snake does not rely on any single part of its body to move forward. Instead, it uses its entire body to create co-ordinated movements that move it in the desired direction. Project manager Øyvind Stavdahl says that the project, which is being conducted in co-operation with NTNU Professor Kristin Y. Pettersen, is at the cutting edge of research because of its attempts to recreate a snake’s movement.

The steel skeleton and motors are being custom-built at local workshops in Trondheim, partly because the research scientists needed to take a novel approach in the construction of the water hydraulic valves.

“The lack of space has been a major challenge,” says Liljebäck. “We needed power valves that were small, water tolerant and capable of controlling both the direction and the amount of the water flow. The closest thing we found on the market that met the criteria was valves used in Formula One racing cars, but these cost NOK 100,000 each and didn’t tolerate water. As a result, we decided to manufacture our own valves and, in co-operation with a local workshop, we built a prototype from scratch.”

Applications

The snake has a wide variety of applications: fighting fires where humans can not enter due to heat or the risk of building collapse; underwater operations in connection with maintenance of oil installations on the sea floor; rescue operations in earthquake areas and potentially explosive situations.

“Tunnel fires are explosive and it is extremely dangerous for firefighters to enter the tunnel to extinguish the fire,” says Stavdahl. “In such situations, it is possible to imagine a whole nest of snakes slithering out from a layer in the tunnel. Since the snake has modules, it is possible to design snakes for different functions: snakes can, for example, provide oxygen masks to people trapped in the tunnel, light up the tunnel or carry a camera that provides firefighters outside an overview of the situation without requiring them to enter.”

The research scientists are now talking with American businesses concerning possible sales. Further research is still required until a commercial model is available. But the concept is clear. The project has been financed by Norsk Hydro’s fund for SINTEF