switch) and light. You could buy
additional sensors such as the motor
rotation types mentioned above, and
the simplicity of the RCX allowed you
to readily make your own. The NXT's
sensors include the touch and light
switches as with the RCX, but also have
a microphone for detecting sound and
ultrasonic, for measurement, and
determining nearby movement.
Various third parties sell enhanced
sensors for the NXT. For example,
Hi Technic Products (www.hitechnic.
com) offers an electro optical proximity
detector similar in function to the
popular Sharp IR units commonly
used in homebrew robotics. They also
provide color sensors, compasses,
accelerometer and tilt sensors,
gyroscopes, and a multiplexer that lets
you connect up to four NXT touch
sensor switches to one input port.
Construction Parts
Both the RCX- and NXT-based
robotics kits come with hundreds of LEGO
Technic parts. The exact assortment
varies between the two packages and,
of course, you are free to combine
parts from other standard LEGO and
LEGO Technic kits, such as the
low-cost Bionicle line. You can also
purchase specific parts sets from
retailers, including LEGO's own online
store. The basic building block is the
LEGO brick. Bricks are composed of
one or more raised "studs" or "nubs"
on the top and corresponding sockets
on the bottom. The studs and sockets
mate, allowing you to stack bricks one
on top of another. Plates are like
bricks, but are a third the height. Like
bricks, plates have one or more studs
on the top and corresponding sockets
on the bottom, and are made to be
stacked together. And finally, beams
are specific to the Technic brand of
LEGO parts, included with the
Mindstorms sets. Beams are bricks
with one row of studs and have holes
down their sides. Beam variations
include L- and hooked-shaped versions
which can be used for things such as
building robotic grippers.
Assembly parts hold things
together such as attaching one beam
to another or a wheel to a beam.
Connector pegs are typically used with
the LEGO Technic line to attach beams
together. Connectors pegs are either
1/2, 3/4, or full -- the difference lies
in the length of the connector on
one side of its middle collar. Some
connector pegs are half connector
and half axle (see below for more
information on axles). Available in a
wide variety of sizes and shapes,
friction connectors are used with both
LEGO Technic and standard parts for
such things as connecting beams
and wheels.
Other assembly parts include the
bushing and the cross axle. For turning
parts, there are wheel hubs provided
in a number of different sizes; pulleys
which are used with string, rubber bands,
or O-rings to create a kind of belt; and
gears which are used to construct more
sophisticated motion transfer mechanisms.
Rounding out the parts list are toggle
joints, sloped beams, catches, cross
blocks, axle connectors, cams, and a
raft of others. Check out the LEGO
website for more information on
LEGO parts. For some good books on
LEGO, go to the SERVO webstore at
( http://store.servomagazine.com).
All these parts are made to snap
together. When properly constructed,
the snap-together system provides for
relatively strong joints. In fact, most
"purists" frown on building LEGO
mechanisms in any other way, including
using fasteners or glues. Still, depending
on the type and size of robot you're
constructing, you might consider
cementing non-movable pieces using
ordinary household cement (such
as Duco), epoxy, contact, or CA
(cyanoacrylate) glues. If you want a
very permanent bond, use clear ABS
plastic solvent (LEGO parts are made
of ABS plastic). ABS solvent cement is
available at most home improvement
stores, as well as many hobby stores.
Another approach is to use hot melt
glue. You can use either the standard
or low-temperature variety.
Temporary constructions can be
taped together using black electrical
tape or even strapping tape used for
box packaging. Do note that most
tapes leave a sticky residue. Acetone
can be used to remove this.
Tie wraps are used to bundle
wires and other loose items. They
consist of a single piece of plastic with
Battlebricks extends the sport of combat robotics to LEGO Mindstorms creations.
SERVO 02.2009
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