don't always hold still long enough for the sensor to see
them. Plus, a lot of folks walking and moving in the
background confused the calibration mode. It's also not a
good idea to cram servos into a tight cloth body filled with
insulation that causes them to overheat and die.
Building Cal Averas
Calaveras is the Spanish word for skull. I split the word
in half to give my other new friend a name.
I decided to build a new puppet. I wanted it to have
eight joints, so I ordered some more servos from ServoCity
and found a 16 inch skeleton in a local costume shop. This
pile of parts would soon become Cal Averas.
Building Cal was pretty easy since I wasn't worried
about aesthetics (as usual). The hardware used consists of
four Futaba S3004 servos for his shoulder and hip joint,
and I recently upgraded his knee and elbow joints to four
Hitec HS322HD servos since the original mini Futaba S3114
stripped their gears in testing.
The shoulder servos are separated and mounted using
four 3” long #8 machine screws and nuts, and the hips are
mounted with four 2-1/2” #8 screws and nuts, with no
spacing between the bottom of the servos. I had to do
this to make sure the arms clear the legs during movement.
I also added a wood dowel to make the shoulders even
It was sort of weird when I used a Dremel tool with a
cut-off disc to remove Cal’s ribcage so I could mount the
servos for the shoulders. I felt a bit like Dr Frankenstein and
told Cal he might feel a little pressure. (I don't think he was
amused by my little joke.) Actually, he didn't say much and
took it like a trooper.
It was a bit tedious trying to attach all of his bones to
the servo horns using a 1/16” drill bit while holding a bone
for alignment. I did drill a couple of holes in my own fingers
when the drill bit slipped. For some unknown reason, most
of my robot builds seem to always require some of my own
flesh and blood during their creation.
Eventually, all of the bones were attached to the servo
horns with the small #2 screws that come with the servos. I
had to extend all of the servo wires about three feet using
three-conductor servo wire. I also made an interconnect
board using header strips and a project board I bought at
RadioShack. This allowed me to provide the 5 VDC power
and ground from a PC power supply to the servos and the
signal, and the always important common ground VSS from
an Arduino MEGA 2560 board. I also added a 7809 voltage
+ 9 VDC regulator so I could power the Arduino from the
12 VDC from the computer power supply.
I like to run the Arduinos at no more than 9 VDC input
to their internal voltage regulator so they stay nice and
cool. I also added two three-color LEDs to Cal’s skull so he
has multi-colored eyes.
SERVO 08.2014 55
Cal’s shoulder servos are bolted together with four 3” long #8
machine screws. I also had to add some wood dowels to
provide additional spacing to keep his arms from colliding with
his legs. Cal is a bit narrow in the hips and broad in the
shoulders. This was done for purely mechanical needs and not
for aesthetics. If I was to build him again, I'd probably just buy
a couple of feet of all threaded rod so I wouldn't need the