Abstract
At present there is a limited experience in operating rovers on Mars and an even smaller experience on robotic Moon rovers, while the experience regarding man-carrying vehicles is limited to the Moon and a single case (although with some differences between a mission and another): the LRV (Lunar Roving Vehicle) of the last Apollo Missions, and all these devices used wheels as running gear. In this chapter the behavior of wheeled devices is studied in its various aspects, like longitudinal, lateral and suspension dynamics. The consequences of operating wheeled machines in the various environments are analyzed in some detail. The chapter is concluded by a description of the Apollo Lunar Roving Vehicle.
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- 1.
In the following the term vehicle is always used for any moving machine, be it a human-carrying vehicle, a rover, a moving robot, etc.
- 2.
Strictly speaking such reference frame is not inertial, as it is fixed to the ground and hence it follows the motion of the planet. It is, however, “enough” inertial for the problems here studied and this issue will not be dealt with any further.
- 3.
G. Genta, Motor Vehicle Dynamics, Modelling and Simulation, World Scientific, Singapore, 2005; G. Genta, L. Morello, The Automotive Chassis, Vol. 2, Springer, New York, 2009.
- 4.
In the present section, where the longitudinal dynamics is studied, a complete symmetry with respect to xz plane is assumed.
- 5.
All resistances (aerodynamic drag and rolling resistance) are directed in the figure in forward direction (the direction of the positive x-axis) but their value is negative, so they are, as they must obviously be, directed backwards.
- 6.
See, for instance, G. Genta, L. Morello, The Automotive Chassis, Springer, New York, 2009.
- 7.
Erasmus Darwin had actually this idea in 1758 but the one who applied it first was a German carriage builder, who had his agent in England, Rudolph Ackermann, to patent in 1818 what is now called the Ackerman steering geometry.
- 8.
Sometimes the term skid steering is used instead of slip steering. It should be avoided, since this way of steering is due to longitudinal and lateral slip of the wheels, but only in extreme cases it produces actual skidding (i.e. global slipping) of the wheels on the ground.
- 9.
G. Genta, L. Morello, The Automotive Chassis, Springer, New York, 2009.
- 10.
The term dynamic steering is used here to denote a condition in which the trajectory is determined by the balance of forces acting on the vehicle, as opposed to kinematic steering in which the trajectory is determined by the directions of the midplanes of the wheels. Note that dynamic steering applies to both steady state and unstationary turning.
- 11.
The sliding factor is more commonly defined as the square root of the same quantity considered here. The present definition, which refers directly to the lateral acceleration instead of the speed at which a given radius can be obtained, is here preferred, as in particular conditions it reduces to the side force coefficient.
- 12.
In the present model no account is taken for the presence of the suspensions and the vehicle is assumed to be a rigid body. For symmetry reasons, the camber angles of the two wheels of the same axle can be assumed to be equal and opposite, so that no camber force acts on each axle: this is just an approximation, but holds quite well for small camber angles.
- 13.
Y β can be considered as a sort of cornering stiffness of the vehicle.
- 14.
Sometimes the position of the neutral-steer point and the static margin are defined with different sign conventions: instead of referring to the position of the neutral-steer point with respect to the center of mass, the position of the latter with respect to the former is given. In this case the signs of x N and \({\mathcal{M}}_{s}\) are changed and an understeer vehicle has a positive static margin.
- 15.
L. Segel, Theoretical Prediction and Experimental Substantiation of the Response of the Automobile to Steering Control, Cornell Aer. Lab., Buffalo, N.Y.
- 16.
G. Genta, Study of the Lateral Dynamics of a Large Pressurized Lunar Rover: Comparison Between Conventional and Slip-Steering, 61st Int. Astronautical Congress, Prague, Sept. 2010.
- 17.
H. Kimura, K. Shimizu, S. Hirose, Development of Genbu: Active-Wheel Passive- Joint Snake-Like Mobile Robot, Journal of Robotics and Mechatronics, Vol. 16, No. 3, 2004.
- 18.
A. Ellery, An Introduction to Space Robotics, Springer Praxis, Chichester, 2000.
- 19.
Y.K. Huang, N. Ahuja, A Potential Field Approach to Path Planning, IEEE Trans. on Robotics and Automation, Vol. 8, No. 1, 1992.
- 20.
G. Genta, A. Genta, Preliminary Assessment of a Small Robotic Rover for Titan Exploration, Acta Astronautica, Vol. 68, No. 5–6, 556–566, March–April 2011.
- 21.
In the following the notation (t),z , (t),φ , etc. will be used.
- 22.
The kingpin axis is the axis about which the wheel hub rotates when steering.
- 23.
T.D. Gillespie, Fundamentals of Vehicle Dynamics, SAE, Warrendale, 1992.
- 24.
G.Genta, P.Campanile, An Approximated Approach to the Study of Motor Vehicle Suspensions with Nonlinear Shock Absorbers, Meccanica, Vol. 24, pp. 47–57, 1989.
- 25.
G. Genta, L. Morello, The Automotive Chassis, Springer, New York, 2009.
- 26.
G. Genta, Dynamic Modelling of a Wheeled Lunar Microrover, 61st International Astronautical Congress, Prague, Oct. 2010.
- 27.
A. Ellery, An Introduction to Space Robotics, Springer Praxis, Chichester, 2000; A. Ellery, Lunar Roving Vehicle Operations Handbook, http://www.hq.nasa.gov/office/pao/History/alsj/lrvhand.html.
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Genta, G. (2012). Wheeled Vehicles and Rovers. In: Introduction to the Mechanics of Space Robots. Space Technology Library, vol 26. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-1796-1_5
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DOI: https://doi.org/10.1007/978-94-007-1796-1_5
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