accommodate the servo. Without the axe fastened to the
arm, the assembly stood upright proudly like a victorious
We realized it would be best to do our initial testing
of the servo without a very sharp axe attached to it. We
debated trying to control the servo with a programmed
Arduino or Adafruit board, but we opted for something
that would give us a bit more manual control.
We selected our trusty VEX Robotics control system,
which would give us safe remote control over the spinning
axe of death.
The VEX controller is a little strange in that the PWM
connections are all female, while most standard PWM
leads on servos are also female.
Fortunately, we’ve wanted to connect standard non-VEX servos to the controller many times before, so we had
Frankensteined a male/male PWM cable for exactly this
sort of situation.
We wired up the servo, stood a safe distance away,
and let it rip. The ServoBlock-equipped servo spun the
plate with ease, but that was expected — the plate alone
was not very heavy. Even a servo without a ServoBlock
could have handled it.
So, our initial test confirmed that the ServoBlock
did not adversely affect the performance of the
servo. But could it handle the axe?
We zip tied the axe to the aluminum plate. The
plate was thin, but the haft of the axe lent some
rigidity to the unit. Even so, we could tell the
aluminum plate was going to give before the
ServoBlock. We added another zip tie to the very
back of the haft to ensure that there was added
rigidity throughout the length of the plate.
When we weighted down the base of our blade-swinging robot and let the axe go, the arm tilted
downwards slightly — but the ServoBlock held fast.
However, merely holding an axe is a far cry from
chopping something up with it.
So, chop up what? After considering everything
from a Batman action figure to a big stuffed bear,
We wanted to behead our cucumber with a horizontal
blow — more like what might happen in the heat of battle
rather than the vertical strike of an execution. A horizontal
strike would also provide the best test of the ServoBlock
by maximizing the lateral load on the servo.
We fashioned a support for our condemned cucumber
by using a few blocks of wood that we could lash the
prisoner to upright.
To achieve the correct head chopping height for the
axe, we put our servo assembly on top of a large 4 x 6
chunk of wood that we actually screwed the robotic axe
directly to. We weighted down the 4 x 6 with a few 14 lb
plates. The stage was set for our vegetable execution.
We painted a face on the cucumber and lashed it to
the wooden upright. We positioned the axe near the
doomed vegetable to ensure that the axe has
the maximum arc for its swing. We wired up
the axe to our VEX control system and stood far
back as we powered up the robot and the
Without even waiting for a final plea for
mercy from the plant, we jammed upwards on
the joystick and the axe made its deadly arc
with surprising speed. The cucumber lost its
painted head in one smooth blow.
The weight of the axe was deforming the
aluminum plate slightly, and with a few further
swings of the axe we were able to take a few
more slices off the cucumber. The ServoBlock
had worked like a charm.
58 SERVO 01.2018
THEVIKINGS WOULD BE PROUD.
READY FOR LATERAL LOADING.