creations together. There are three methods I can offer.
They each have their own advantages and disadvantages.
Jigsaw Cut and Glue
Figure 2 shows a method to attach two motors
together into an assembly which will then be attached to
the robot base. Notice the series of mortise holes and
aligning tenon extensions to the parts I plan on joining.
This technique resembles a jigsaw puzzle and at the end,
that’s pretty much what it is. Make sure the mortise holes
are the same width as the wood the tenon will be made of.
I have made the classical mistake where the mortise is too
small, and then the tenon will not go in.
The easiest thing to do with all of these parts is to glue
them. This technique is easy and cheap. The bond is
amazingly strong and the resulting contraption will
practically last forever! However, I do not recommend this
system for assembling robot platforms or components since
once you have glued the parts together, disassembly is no
longer feasible. The detail in Figure 2 was not glued.
Standoffs and Screws
You could use metal standoffs if you happen to find
the length you need. If you cannot find the right length,
allow me to offer an alternative.
For standoffs, I am using wood dowels. The first step
was to develop a quick jig such as the one you see in
Figure 3. It allows the positioning of the large wood dowel
and the cut of segments of different lengths. Because the
large dowel sits at the same starting point at all times, we
can direct the laser to the coordinate which defines the
desired dowel length and make the cut.
Drill a hole through the dowel center with either a
lathe or a bench drill. The resulting dowel can then be
either tapped or you can add a threaded insert. I actually
recommend the latter one. Figure 4 shows the base
assembled with wood dowels and screws.
Jigsaw and Screw
A hybrid between the two previous techniques would
be the jigsaw and screw. In this method, the jigsaw portion
is made such that it allows for a perpendicular screw and
hex nut to be housed. This is trickier to draw, but it solves
two problems at once. The box in Figure 5 shows the
technique in question. Notice the perpendicular surface has
an opening to hold the hex nut while the first surface is
made to hold the screw head.
How Much Will All of
This Cost Me?
Let’s face it. There is no way I am going to exhort
SERVO readers to go out and purchase a laser engraver.
Although it is an awesome tool and you will have a blast
with it, the cost of maintaining this piece of equipment is
not a trivial endeavor. Luckily, you can easily rent laser
engraving services and there are more than enough people
out there waiting to laser your job out.
A good place to check out is Pololu.com. As you may
know by now, Pololu is a great center to purchase your
robotic parts, as well as kits, but as it turns out they also
offer laser cutting services. They charge about $2.50 per
minute. The question may then arise as how do I know
how many minutes will my job take?
SERVO 02.2010 61