Abstract
Nowadays, pipes buried under a road supply houses with water and town gas. Pipes must be periodically inspected in order to prevent the accident caused by leakage of fluid in pipes. We have proposed inspecting pipes using by green caterpillar type in-pipe mobile robot. The robot imitate the prolegs and the waving motion of the green caterpillar. Now, we derive equilibrium of forces using by dynamics models of moving robot. As a result, we identity traction force of the robot.