  A robotic platform for mobile manipulation needs to satisfy two contradicting
requirements for many real-world applications: A compact base is required to
navigate through cluttered indoor environments, while the support needs to be
large enough to prevent tumbling or tip over, especially during fast
manipulation operations with heavy payloads or forceful interaction with the
environment. This paper proposes a novel robot design that fulfills both
requirements through a versatile footprint. It can reconfigure its footprint to
a narrow configuration when navigating through tight spaces and to a wide
stance when manipulating heavy objects. Furthermore, its triangular
configuration allows for high-precision tasks on uneven ground by preventing
support switches. A model predictive control strategy is presented that unifies
planning and control for simultaneous navigation, reconfiguration, and
manipulation. It converts task-space goals into whole-body motion plans for the
new robot. The proposed design has been tested extensively with a hardware
prototype. The footprint reconfiguration allows to almost completely remove
manipulation-induced vibrations. The control strategy proves effective in both
lab experiment and during a real-world construction task.
