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robots. Other combinations that work well systems with are
tracked legs such as Chaos [17] and PackBot [43].
Systems of Similar Morphology
One benefit of our method of analysis is that we can quantify how design changes affect a particular robot. For example, consider two tracked systems that are essentially
extensions of a standard skid-steered track design (e.g.,
Talon [69]). An extension to the standard design is exemplified by PackBot, which adds two additional tracked
appendages to the front of the system [43]. Chaos takes this
one step further and uses four additional tracked appendages [17]. Figure 7 shows that there is a significant increase
in versatility between PackBot and Talon. The additional
tracked legs allow PackBot to control its pitch angle, which
greatly improves its obstacle-crossing capabilities. Compare
this with the increase in versatility between PackBot and
Chaos, which is much smaller. We suspect that this trend
would continue for systems with additional tracks-the
versatility would only slightly increase for comparatively
larger increases in complexity.
Versatility in the Scansorial Domain
The Vortex, a wheeled, skid-steered vehicle that uses a
controlled vortex to adhere to vertical surfaces, is the most
versatile scansorial robot that was studied [75]. One possible
reason why it is so versatile may be that the technology it
uses to adhere to vertical surfaces is completely modular
from its locomotion technology. Compare this with other
scansorial systems such as Stickybot [90], whose dry adhesive attachment mechanisms require specific leg locomotion
patterns and are not mechanically robust to different surface
types (i.e., it can only climb smooth surfaces).
Versatility of Robots Operating
in Multiple Domains
Using the term versatility instead of mobility is couched in
the long-term goal of creating mobile robots that can operate
in multiple environmental domains. Currently, very few systems are capable of this, which makes it difficult to gain
insight on useful design features. The robots that can operate
in multiple domains include the amphibious, snakelike
AmphiBot II [8] and ACM-R5 [5]; MMALV [35], a fixedwing aerial system that can also locomote on the ground;
Whegs II [77], a modification of a rotary-leg robot that uses
tape or dry adhesives to climb vertical and inverted surfaces;
and the aforementioned Vortex [75].
As shown in Figure 8, AmphiBot II has minimal versatility, most likely because of its rudimentary locomotion capabilities. ACM-R5 leads in both versatility and complexity. Whegs
II and Vortex both operate in the terrestrial and scansorial
domains, but Vortex is more versatile. Again, this may be due
to Vortex's ability to add scansorial capabilities to a standard
wheeled system. In contrast, Whegs II uses dry adhesives or
pressure-sensitive adhesives to climb vertical walls, neither of
which generate good traction on normal terrain.
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DECEMBER 2013

Conclusions and Future Work
This article presented a novel versatility metric that allowed a
comparison among mobile robot designs. The results highlighted what design features can help create highly versatile
systems without increasing mechanical complexity. Based on
this analysis, several design guidelines can be posited.
1) Tracked systems have the most potential for creating highversatility, low-complexity mobile robots. This is due to
tracked systems' low ground pressure for operation in
deformable terrain and typically low turning radius.
2) Additional appendages (such as the front flippers of PackBot) offer increased versatility, but their advantage quickly
subsides as the number of appendages increases.
3) Wheel-leg combinations (either as rotary legs or wheels
on active leglike suspensions) tend to combine the advantages of both wheels and legs with minimal disadvantages.
4) Wheels, rotary legs, or tracks on scansorial systems tend to
be better than legs, whose limitations on the ground are
also present when climbing.
For future work, we compared animals to mobile systems
to understand how bioinspired design principles can increase
system versatility. This work can also be extended to cover
concepts such as utility, sensing, and robustness.
References
[1] M. Tavakoli, A. Marjovi, L. Marques, and A. de Almeida, "3DCLIMBER: A
climbing robot for inspection of 3D human made structures," in Proc. IEEE/
RSJ Int. Conf. Intelligent Robots Systems, 2008, pp. 4130-4135.
[2] Y. Umetani and S. Hirose, "Biomechanical study of active cord mechanism
with tactile sensors," in Proc. Int. Symp. Industrial Robots, 1976, pp. 1-10.
[3] M. Mori and S. Hirose, "Locomotion of 3D snake-like robots-shifting and
rolling control of active cord mechanism ACM-R3," J. Robot. Mechatron., vol.
18, no. 5, pp. 521-528, 2006.
[4] S. Takaoka, H. Yamada, and S. Hirose, "Snake-like active wheel robot
ACM-R4.1 with joint torque sensor and limiter," in Proc. IEEE/RSJ Int. Conf.
Intelligent Robots Systems, 2011, pp. 1081-1086.
[5] H. Yamada, S. Chigisaki, M. Mori, K. Takita, K. Ogami, and S. Hirose,
"Development of amphibious snake-like robot ACM-R5," in Proc. 36th Int.
Symp. Robotics, 2005, p. 133.
[6] M. Zhang, "AM18 all-terrain UGV," M.S. thesis, Dept. Mech. Eng.,
National Univ., Singapore, 2008.
[7] L. Jun, "AM24 enhanced mobility robot," M.S. thesis, Dept. Mech. Eng.,
National Univ., Singapore, 2007.
[8] A. Crespi and A. Ijspeert, "AmphiBot II: An amphibious snake robot that
crawls and swims using a central pattern generator," in Proc. Int. Conf. Climbing Walking Robots, 2006, pp. 19-27.
[9] O. E. L. Botello, M. L. B. Garcí, P. del C. Z. Robledo, and A. R. R.
Velázquez, "Design of a hexapod robot based on insects," in Proc. Electronics,
Robotics Automotive Mechanics Conf., 2010, pp. 347-354.
[10] G. Dudek, P. Giguere, C. Prahacs, S. Saunderson, J. Sattar, L.-A. TorresMendez, M. Jenkin, A. German, A. Hogue, A. Ripsman, J. Zacher, E. Milios,
H. Liu, P. Zhang, M. Buehler, and C. Georgiades, "AQUA: An amphibious
autonomous robot," Computer, vol. 40, no. 1, pp. 46-53, 2007.
[11] M. Eich, F. Grimminger, and F. Kirchner, "A versatile stair-climbing robot
for search and rescue applications," in Proc. IEEE Int. Workshop Safety, Security Rescue Robotics, 2008, pp. 35-40.

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - December 2013