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Robotics Institute Seminar,
April 22
Time
and Place | Seminar Abstract | Speaker
Biography | Speaker Appointments
Scaling Issues in Robotics:
Strength, Range, and Communication Limits on Big and Small Robots
Mel Siegel
Associate Research Professor
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Time and Place |
Mauldin
Auditorium (NSH 1305)
Refreshments 3:15 pm
Talk 3:30 pm
Over
the last two or three years I have been developing this talk and presenting it
to a wide range of audiences. The first
time or two I worried that its content
and conclusions might be too trivial to be worth taking up even 20 minutes as a
contributed paper at a conference.
But to my growing amazement, every time I give it I get more invitations
– now at the
level of hour-long keynote addresses at
international conferences – and more requests from people who want to
draw on it in
upcoming courses and books. So I figured the
time has come to expose it to the light of day here at home, and to hear if my
colleagues think this topic and my
approach are actually worth the interest they are attracting far away.
I
will start by discussing the fundamental strength and consequent design issues
that arise as robotics moves in the
directions of machines and systems
that are much larger and much smaller than human scale, and to the inevitable
new issues
of energy storage capacity and
communication efficiency. Some of the most interesting systems we envision
manifest
simultaneously the difficulties of
being very large and very small, e.g., spatially and numerically large networks
of small
robotic sensor nodes. In these complex systems,
deployment is limited globally by the fundamental problems of transporting
and controlling large systems, and
locally because node function is hampered by the problems of small-scale
devices, i.e.,
operating time limited by the small size of
on-board energy reservoirs, and inter-node communication efficiency limited by
the small sizes of the antennas that
can be deployed whilst continuing to call the whole “small”.
Interesting possibilities arise
when we imagine individual devices that
have different scales in different dimensions, e.g., decameter-length filaments
of
micrometer-diameter.
Regarding
strength and energy, two generalities counterintuitive to the non-technical
population are well-known to
scientists and engineers: (1) big
is weak, small is strong, i.e., it is large structures that collapse under
their own weight and
large animals that break their legs when
they stumble, whereas small structures and small animals are practically
oblivious to
gravity, and (2) horses “eat like
birds” and birds “eat like horses”, i.e., a large animal or
machine stores relatively larger
quantities of energy and dissipates
relatively smaller quantities of energy than a small animal or machine. The
critical
consequence of (2) is that the
smaller the robot the smaller its range and its operating time between refuelings. Applying
simple scaling models to contemplated
small robots, the conclusion is quickly reached that robots at currently
contemplated
small scales will be never be able to
carry enough energy to complete any sensible mission. They will rather have to
forage
for fuel in the environment, just as
microorganisms have to forage for their nutrients in the energy-rich liquid
environments –
the soup! – to
which their lives are mostly constrained. I will show that in any model
scenario in which the lion’s share of
the onboard fuel is used to overcome
frictional drag a mobile robot’s range is a scale-independent constant
multiple of its
length, and its running time is the same
scale-independent constant multiple of the time it takes to traverse its own
length. I
will discuss the corresponding
relationships for several other energy consumption rate scenarios, e.g., where
the lion’s share
of the on-board energy is expended
climbing hills.
If
time permits I will outline how large and small scale issues come into play
simultaneously when considering systems
composed of large numbers of small devices
spread over large areas or dispersed through large volumes. The fundamental
issues hinge on the universal fact that
antennas are efficient only for wavelengths around their own size. Small
devices are
thus good antennas only for small
wavelengths, i.e., high frequencies, i.e. high energy per photon, making naive
approaches
to communication unacceptably high
energy-cost propositions for devices whose energy storage capacities are
limited by
their small scale.
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Speaker Biography |
Mel Siegel received a B.A. in Physics from
For appointments, please contact Mel Siegel (mws@cmu.edu).
The Robotics Institute is part of the School of Computer Science, Carnegie Mellon University.