This paper describes the Magnebike robot, a compact robot with two magnetic wheels in a motorbike arrangement, which is intended for inspecting the inner casing of ferromagnetic pipes with complex-shaped structures. The locomotion concept is based on an adapted magnetic wheel unit integrating two lateral lever arms. These arms allow for slight lifting off the wheel in order to locally decrease the magnetic attraction force when passing concave edges, as well as laterally stabilizing the wheel unit. The robot has the main advantage of being compact (180 × 130 × 220 mm) and mechanically simple: it features only five active degrees of freedom (two driven wheels each equipped with an active lifter stabilizer and one steering unit). The paper presents in detail design and implementation issues that are specific to magnetic wheeled robots. Low-level control functionalities are addressed because they are necessary to control the active system. The paper also focuses on characterizing and analyzing the implemented robot. The high mobility • Journal of Field Robotics-2009is shown through experimental results: the robot not only can climb vertical walls and follow circumferential paths inside pipe structures but it is also able to pass complex combinations of 90-deg convex and concave ferromagnetic obstacles with almost any inclination regarding gravity. It requires only limited space to maneuver because turning on the spot around the rear wheel is possible. This high mobility enables the robot to access any location in the specified environment. Finally the paper analyzes the maximum payload for different types of environment complexities because this is a key feature for climbing robots and provides a security factor about the risk of falling and slipping. C 2009 Wiley Periodicals, Inc.

S u m m a r y . This paper describes a novel solution to a mobile climbing robot on magnetic wheels, designed for inspecting the interior surfaces in gas tanks made out of thin metal sheets. These surfaces were inaccessible by previous climbing robots due to the following restrictions: 1. Ridges, where the magnetic force decreases to almost zero 2. Angular transitions between the surfaces (135°) 3. Thin metal sheets that cannot provide high magnetic forces The main optimization criterion for this robot was to design it as light as possible, as the surface was also considered to be very fragile. As the here described type of application is very special and was not examined much in previous publications, this work also stresses on the early analysis phase. This phase mainly consists of tests to optimize magnetic wheels for thin surfaces and mechanical calculations for robots on magnetic wheels. The chosen concept is described in detail, explaining how the robot moves around and passes the obstacles. The analysis of the most critical cases is presented, as well as some details about magnetic wheels and actuators.

Abstract-This paper describes a novel magnetic wheel unit integrating a mechanism that can be used for lifting and stabilizing the unit. The mechanism consists of 2 active lever arms mounted on each side of the wheel and rotating coaxially with the wheel. This mechanism allows slightly lifting the magnetic wheel at any desired position on the wheel circumference and consequently decreasing the magnetic force at this specific location. The same mechanism can also be used to stabilize the wheel, when external forces are unfavorable. This paper also describes the potential of this concept for in-pipe inspection technologies. Indeed it can be used to increase the mobility of magnetic wheels robots which are currently not able to negotiate complex obstacles. At the same time, it allows building smaller robots, since the self stabilizer system allows reducing the amount of required magnetic wheels to only two units.