■ FIGURE 2. Stiquito hexapod
with AAA battery pack.
memory alloy wire for propulsion.
The wire contracts when heated and
returns to its original length when
cooled — assuming an opposable
force is available to stretch the wire
back to its original size. This force is
supplied by the Stiquito’s music wire
legs, and the heat is generated by
current through the Nitinol wire.
In operation, the microcontroller actuates two wires on one side
and one on the other side creating a
tripod support. The pattern is then
reversed and the robot moves forward
and momentarily rests on the second
tripod support. The pattern and pace
can be modified by programming the
onboard microcontroller, as described
in STIQUITO Controlled!.
■ FIGURE 3.
applications in your robotics work.
Start the mod by coating the
Stiquito battery pack and leg ends with
a 1/4 inch layer of Floam. Wait a few
hours and apply another layer. You can
also use the Stiquito with a tethered
power supply to avoid having to coat
the battery pack with Floam. Make certain to angle the Floam feet parallel to
the bends in the wire so that the Stiquito
will move forward. Allow the Floam to
dry overnight and then coat with clear
nail polish or other lightweight sealant.
You’ll find Floam useful in
creating biomimetic robots because it
can be molded into organic shapes.
For structural components, consider
covering aluminum tubing or screen
with the compound for added support
with little weight penalty. It’s also
useful for cradling laser rangefinders
and other impact-sensitive sensors.
For your first test run, try the Water
Strider in a shallow pan with about 1
cm of water — without the batteries
installed. If your robot sinks to the bottom of the pan, you’ll need to add more
Floam. If you’ve opted to pull the two
AAA batteries behind the Water Strider,
then make certain you test the flotation
of the Floam-coated battery compartment, as well. On subsequent runs, try
reprogramming the microcontroller for
different stride sequences in an attempt
■  B. Bergeron. Physics-Based
Animation for Qualitative Assessment
of Biomimetic Subterranean Burrowing
Behaviors. 2007. IEEE CIRA 2007.
■ [ 2] www.bdi.com/content/sec.php?
WATER STRIDER MOD
■ [ 3] J. Conrad, STIQUITO Controlled!
2005: IEEE Press.
The bare-bones Stiquito is an
impressive learning environment and
— within the limits of its load bearing
carrying capacity — a good experimental platform, as well. Continuing
the theme of biomimetics, we can use
the Stiquito as the basis for a water
walker inspired by the Water Strider,
an insect that floats on water by virtue
of microscopic hairs or setae on its
legs that trap tiny air bubbles [ 4, 5].
For the air bubbles, we’ll substitute the microbeads within Floam — a
self-adhesive craft compound available
in toy stores and online (see Figure 3).
The compound, which has the consistency of fish eggs when wet, air-dries
to a rigid, extremely lightweight foam.
Granted, you could simply insert the
wire leg ends into precut cubes of
closed cell foam, but once you get the
hang of Floam, you’ll find numerous
■ [ 4] R. Britt. Walking on Water:
Insect’s Secret Revealed. Live
Science, 2004 [cited 2007 June 21];
Available from www.livescience.com/
■ [ 5] X. Gao and L. Jiang, Biophysics:
Water-repellent legs of water striders.
Nature, 2004. 432(7013): p. 36.
to maximize speed in the water.
You might ask yourself why go
through the trouble of creating a faux
Water Strider when a plastic boat with
an underwater screw is faster and simpler to construct. Granted, the standard
technology may be superior in some
cases, but the Water Strider generates a
smaller wake and audible signature than
a motor-powered boat screw. Both factors could be critical in a stealth military
application or for something as simple
as a platform for a fish sensor. NV
■ FIGURE 4. First layer of
Floam on the Stiquito.
■ Floam microbead crafting compound — www.buyfloam.com
■ CrustCrawler HexCrawler —
■ Lynxmotion BH3 hexapod —
■ FIGURE 5. Water Strider
with Floam flotation.
August 2007 79