Next, we’ll cut out the hand and drill holes into it for
the fingers. Figure 4 shows how I’ve marked on the plastic
washer where I want to make my cuts. This plastic is very
hard, and cutting is very difficult. I have a band saw that I
use to cut small things like this. A scroll saw will also work.
The plastic tends to melt and harden quickly, so use a
slower speed to cut it. If you don’t have these particular
tools and don’t have friends or neighbors who have them
either, you could use a sander or a hand file. Or, you could
just leave the plastic the way it is (giving it a cute, little
round hand). Now we need to drill the holes into the plastic
to put the fingers into. Make sure that the drill bit you are
using is the diameter of the tubing (or a little smaller), so
40 SERVO 06.2010
you get a snug fit (Figure 5a). It’s a good idea not to glue
it in permanently. I’ll explain why in a bit. Drill only the
depth of the first joint of the finger. Look at your hand; the
first joint is at the palm of your hand. Test the depth of the
finger as you drill (unless you have one of those fancy
depth stops for your drill bit).
Once you get the holes for the fingers drilled, you need
to drill a 1/16” hole towards the middle hole, through the
finger holes you just made (see Figure 5b and Figure 5c).
Next, drill a 1/8” hole in the bottom of the hand towards
the middle hole (Figure 5d). All the fishing lines will come
out of the 1/8” hole. The middle hole (that I talked about
earlier) ended up being perfect for “fishing” the line in
through the hand. If you use something other than the
plastic washer I used, you might consider drilling a hole in
the middle so you can see what you’re doing.
Putting It All Together
Our next step is to take the fishing line and cut about a
foot for each finger. Then, we take a pair of needlenose
pliers and bend an inch of it on one end and crimp it, so
that it keeps a hook-like shape. Feed the fishing line in
through all of the fingers, letting the hook of the fishing
line rest on the tip of the finger (Figure 6).
If you couldn’t find the bolt end covers, you can hot
glue the inside of the tip of the finger. This should hold the
fishing line in place. I know that hot glue gets a little
messy, but you can trim any excess after it cools. If you do
have the bolt end covers, then cut them so they are about
10 mm long from the tip. Put a drop of super glue (Figure
7) on the tip of the robot finger (not your finger!) and the
hook of the fishing line, and then slip on the rubber tip.
Make sure the hook of the fishing line is on the bending
side of the finger as shown.
After the glue sets, you should be able to hold the
finger in one hand, pull the fishing line with the other, and
make the finger bend (Figure 8). Now, feed the fishing line
all the way in through the hand. Put the fingers into the
holes you drilled for them; they should fit snuggly. I did not
glue the fingers into the hand because if the fishing line
should break, it’s going to be difficult to feed a new line
into both the finger and the hand at the same time.
Figure 9 shows a completed hand. You must lay out
the aluminum with the hand and the servo where you want
them. Trace the hand and the servo so you can cut the
excess aluminum. Use a pair of tin snips. Gluing the hand
to the aluminum didn’t seem like a strong enough idea, so I
screwed the hand to the aluminum. Make sure you don’t
drill into your fishing line, however! On the other hand (pun
intended), I attached the servo with hot glue. If you would
rather mount the servo to the aluminum, then you will