Robotics and Autonomous Systems 40 (2002) 151–162 Innovative design for wheeled locomotion in rough terrain Roland Siegwart ∗ , Pierre Lamon, Thomas Estier, Michel Lauria, Ralph Piguet Swiss Federal Institute of Technology Lausanne, EPFL, Autonomous Systems Lab, CH-1015 Lausanne, Switzerland Abstract In our paper we present an innovative locomotion concept for rough terrain based on six motorized wheels. Using rhombus configuration, the rover named Shrimp has a steering wheel in the front and the rear, and two wheels arranged on a bogie on each side. The front wheel has a spring suspension to guarantee optimal ground contact of all wheels at any time. The steering of the rover is realized by synchronizing the steering of the front and rear wheels and the speed difference of the bogie wheels. This allows for precision maneuvers and even turning on the spot with minimum slippage. The use of parallel articulations for the front wheel and the bogies enables to set a virtual center of rotation at the level of or below the wheel axis. This insures maximum stability and climbing abilities even for very low friction coefficients between the wheel and the ground. A well functioning prototype has been designed and manufactured. It shows excellent performance surpassing our expec- tations. The robot, measuring only about 60 cm in length and 20 cm in height, is able to passively overcome obstacles of up to two times its wheel diameter and can climb stairs with steps of over 20 cm. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Mobile robot; Locomotion; All terrain vehicle; Space rover; Outdoor robot 1. Introduction Recent research in mobile robotics has mainly concentrated on autonomous navigation. These new technologies allow for reliable localization, obstacle avoidance and even autonomous map building in dy- namically changing environment. However, mobility in very rough terrain is often very limited due to the absence of adequate locomotion concepts. Most of the existing surface locomotion concepts are based on wheels, caterpillars or legs and have not much evolved lately. ∗ Corresponding author. Tel.: +41-21-693-38-50; fax: +41-21-693-78-07. E-mail addresses: roland.siegwart@epfl.ch (R. Siegwart), pierre.lamon@epfl.ch (P. Lamon), thomas.estier@epfl.ch (T. Estier), michel.lauria@epfl.ch (M. Lauria), ralph.piguet@epfl.ch (R. Piguet). URL: http://asl.epfl.ch • Walking machines (e.g. [1]) are well adapted to unstructured environment because they can insure their stability in a wide range of situations, but they are mechanically complex and require a lot of con- trol resources. On a plane surface, they demonstrate low speed motion and high power consumption in comparison with the other solutions. • Caterpillars demonstrate good off-road abilities be- cause of their stability and good friction coefficient during motion. Its advantages are simplicity and ro- bustness, but the friction losses between the surface and the caterpillars when the robot is turning are high. • Wheeled rovers are the optimal solutions for well-structured environment like roads or flat and regular terrain. But off-road, their mobility is often very limited and highly depends on the type of environment and the typical size of encountered obstacles [2]. This is well studied for planetary 0921-8890/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0921-8890(02)00240-3