Page 59 - Introduction to Autonomous Mobile Robots

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Figure 2.27 Chapter 2
Shrimp, an all-terrain robot with outstanding passive climbing abilities (EPFL [97, 133]).

The climbing ability of the Shrimp is extraordinary in comparison to most robots of sim-
ilar mechanical complexity, owing much to the specific geometry and thereby the manner
in which the center of mass (COM) of the robot shifts with respect to the wheels over time.
In contrast, the Personal Rover demonstrates active COM shifting to climb ledges that are
also several times the diameter of its wheels, as demonstrated in figure 2.28. A majority of
the weight of the Personal Rover is borne at the upper end of its swinging boom. A dedi-
cated motor drives the boom to change the front/rear weight distribution in order to facili-
tate step-climbing. Because this COM-shifting scheme is active, a control loop must
explicitly decide how to move the boom during a climbing scenario. In this case the Per-
sonal Rover accomplished this closed-loop control by inferring terrain based on measure-
ments of current flowing to each independently driven wheel [66].
As mobile robotics research matures we find ourselves able to design more intricate
mechanical systems. At the same time, the control problems of inverse kinematics and
dynamics are now so readily conquered that these complex mechanics can in general be
controlled. So, in the near future, we can expect to see a great number of unique, hybrid
mobile robots that draw together advantages from several of the underlying locomotion
mechanisms that we have discussed in this chapter. They will each be technologically
impressive, and each will be designed as the expert robot for its particular environmental
niche.