32 SERVO 08.2015
single eyelet loop into the hole. I repeated this on the palm,
but had to align these final guides with the servo
placement on the forearm (Figure 11).
An eyelet was added at the thumb segment closest to
the palm. This would provide the anchor point to swivel the
thumb assembly up and down. Another eyelet was added
to the end of the forearm where it met the palm, right
beneath the point where the thumb assembly was
attached. This second eyelet would guide the thumb swivel
tendon directly back to the servo.
A third eyelet was added further down the side of the
forearm to keep the thumb swivel tendon from getting
caught on the other servos.
One of the most important steps
was mounting and aligning the servos.
Each servo horn had to line up with the
final tendon guides. So, I placed each
servo and eyeballed the position, then
made basic mounts using right angle
plastic brackets, and drilled and screwed
them into place.
You’ll note the staggered
arrangement in the picture — this is
because they couldn’t all be lined up
next to one another or they just wouldn’t
fit (Figure 12).
Once the servos were locked down, I
tied the string to the fingertip eyelet of
each digit, then fed the string down through
all the eyelets until it reached its respective
servo horn (Figure 13). With all hand parts
now assembled, I moved to soldering all the
components to the control board PCB.
The control board PCB is quite easy, as all
you need to do is solder six sets of three
header pins (break-away header pins) to plug
the servos into, four momentary pushbuttons,
four 10K ohm pull-up resistors for the buttons,
and wiring to go to the Arduino (Figure 14).
Finally, pick a DC jack that fits a 5V power
supply. In my case, I had an old Canon camera
USB battery charger sitting in a box. I won’t go
into the detail of soldering the control board,
but the supplied Fritzing diagram will guide you
on the layout (Figure 15).
With assembly and soldering complete, I
sat back and thought, cool! Now, let’s get this
Arduino and Testing
Once I built the mechanics and soldered
the control board PCB, it was time to do the
coding. I used four pushbuttons on the control board so I
could activate the functions I wanted. Each button required
a 10K ohm pull-up resistor between the button legs (both
positive and ground connections) and jumper wires going
from each button to four available digital pins on the
I had thought about using flex sensors in a separate
glove arrangement instead of buttons to control the
functions, but that would have required more code and
putting together a suitable glove. I still liked this idea,
though. So, the four pushbuttons would trigger four basic
functions, each containing a set of actions:
Figure 14. Testing the control board PCB connected to an Arduino Uno,
with all six servos.