ably rigid. Therefore, hold off on
andwiching layers of the material
together until you’ve cut it to the size
you want. If the small pieces still seem
too thin and lightweight for the job,
cut an extra layer and use glue to hold
the layers together.
Attaching Parts to
Your Prototype Bases
Most of us use traditional
fastening techniques when building
permanent designs, such as metal or
plastic nuts and screws. You can use
these fasteners in a rapid prototype
base, of course, but there’s no reason
to always fall back on this design
pattern. There are other methods that
are faster, and yet allow re-use of
motors and other components.
First, let’s discuss what not to use.
Avoid gluing things like motors and
other parts to the base. This makes it
much harder to reposition things if
you need to make adjustments. Plus
gluing restricts you from easily reusing
items. For similar reasons, I don’t
recommend using double-sided tape.
It’s fine for bonding sheets of
cardboard together, but not so good
for motors and other parts because it
can leave an unsightly residue when
you take things apart. It also tends to
be rather sensitive to oil, moisture,
and dirt, giving a poor bond unless
everything is sparkling clean. I’m also
not keen on duct tape, though it
certainly has its uses.
It’s best to keep away from
motors and other parts that are too
big and heavy for the design. If your
robot needs a standard size servo
motor, avoid using a larger motor just
because you have it on hand. Same
with batteries. Leave the lead-acid
battery from your car in your car.
The lightweight nature of the
typical fast prototyping material
prevents you from mismatching parts.
If you don’t have exactly what you
need to experiment, either wait until
you can get the right part or use more
sturdy construction methods.
On my list of “okay to use with
caution” is Velcro. It’s a nifty product,
but not always ideal for robot
projects. Using Velcro to attach a
servo motor to a base is a quick and
easy construction technique, but bear
in mind that the Velcro interface isn’t
dimensionally stable. The motor will
likely twist and move — and even
come off — during use. You can get
heavy-duty Velcro where the bond is
much tighter, but these also tend to
use a more permanent adhesive to
stick the hook and loop fabrics to
their respective parts. You may have a
hard time peeling the Velcro off the
motor (or other component) when
you’re done with your prototype.
Among the cheapest and easiest
fastening methods I’ve found is the
cable tie, also known as a tie-wrap
(after the original name Ty-Rap) or zip
strip. These come in many different
widths and lengths, and are under 10
cents each even if you don’t buy them
in bulk. The typical cable tie is a “use
once” fastener: Slip the end of the
wrap through its ratchet gear rack and
cinch up. The ratchet holds the plastic
of the tie in place. You cannot remove
the tie other than cutting it off.
There are other ties that use a
two-way ratchet, so you can remove
the tie and re-use it. These cost most,
but are very handy in robot prototypes
because they allow you to reposition
and move parts on your bases without
cutting off the tie and using a new
one. A typical use of a cable tie is
mounting a motor to the base. After
marking the location for the motor,
cut or drill two holes on either side of
the motor casing for the tie to thread
through. Hold the motor in place,
insert the tie into the holes and
around the motor, and pull tight.
Make sure you use a tie that’s long
This method works with flat-case
motors like R/C servo motors and
round case motors (metal or round).
Use enough of ties to keep the motor
securely in position.
To work effectively, the case of
the motor should not be asymmetrical. Otherwise, the shaft of the motor
may not protrude at a perpendicular
angle from the base. If this happens,
use shims to level the motor. You can
make the shims using small pieces of
cardboard or even stiff paperboard
(from index cards, for example). Also
handy is compressible foam used to
pack static-sensitive integrated circuits,
or even florists foam (get it at a craft
store) or modeling clay.
Additional fastening techniques
Look to Hobby Engineering’s selection of construction toys for bits and
pieces to complete your next robo proto.