Publication
Design and Field Testing of a Rover with an Actively Articulated Suspension System in a Mars Analog Terrain
Florian Cordes; Frank Kirchner; Ajish Babu
In: Journal of Field Robotics (JFR), Vol. 35, No. 7, Pages 1149-1181, Wiley, 10/2018.
Abstract
This article presents the electro-mechanical design, the control approach and the results of a eld
test campaign with the hybrid wheeled-leg rover SherpaTT. The rover ranges in the 150 kg class
and features an actively articulated suspension system comprising four legs with actively driven and
steered wheels at each leg's end. Five active degrees of freedom are present in each of the legs,
resulting in 20 active degrees of freedom for the complete locomotion system. The control approach
is based on force measurements at each wheel mounting point and roll-pitch measurements of the
rover's main body, allowing active adaption to sloping terrain, active shifting of the center of gravity
within the rover's support polygon, active roll-pitch in
uencing and body-ground clearance control.
Exteroceptive sensors such as camera or laser range nder are not required for ground adaption. A
purely reactive approach is employed, rendering a planning algorithm for stability control or force
distribution unnecessary and thus simplifying the control efforts. The control approach was tested
within a four week feld deployment in the desert of Utah, USA. The results presented in this paper
substantiate the feasibility of the chosen approach: The main power requirement for locomotion
is from the drive system, active adaption only plays a minor role in power draw. Active force
distribution between the wheels is successful in different footprints and terrain types, and is not
infuenced by controlling the body's roll-pitch angle in parallel to the force control. Slope climbing
capabilities of the system were successfully tested in slopes of up to 28deg inclination, covered with loose
soil and duricrust. The main contribution of this article is the experimental validation of the actively
articulated suspension of SherpaTT in conjunction with a reactive control approach. Consequently,
hardware and software design as well as experimentation are part of this article.