pin difficult to remove. To overcome that shear force, you
need a linear actuator with some real strength. Would the
mightyZAP be up to the task?
We crafted our mangonel from scrap wood, and used
some aluminum conduit tubing for the fulcrum shaft. For
the mangonel basket, we employed a short section of PVC
tube, and for our pumpkin stand-in we used a bright
orange inflatable rubber ball that became appropriately
festive with a drawn-on jack-o-lantern grin. We used a nail
for the pin, then mounted a bracket that the mightyZAP
could pull on with the aid of some zip ties.
We weren’t entirely sure that the trigger mechanism
would work. The torsion spring we used had been fairly
beefy, and it took a little effort to pull the boom arm back
all the way. Our simple trigger pin design was easy, but not
necessarily the most effective way of minimizing shear
stress on the pin.
Our initial tests showed that without being under
tension, the pin moved back and forth smoothly. So, under
tension would it work like a silver bullet on a werewolf, or
fail like a silver bullet in the torso on a zombie?
After the promising initial tests, we were ready to
chunk punkins (or at least our orange rubber punkin stand-in). We set up the mangonel and VEX robot in a favorite
backyard punkin chunkin spot, weighted down the catapult
with some steel plates, pulled back the boom of the
mangonel, and armed the trigger.
We found that the easiest way to arm the trigger was
actually to have it move under the power of the linear
servo. The movement was smooth and reliable, and the
boom was held fast by the pin.
The 100N mightyZAP — even at less than full voltage —
worked like a charm. It pulled the pin smoothly and easily,
and the mangonel sent our rubber impostor pumpkin
rocketing into the wild blue.
The mightyZAPs — like wooden stakes and garlic to a
vampire slayer — are sure to become essential tools in our
robot projects. The compact units truly deliver on their
promise of being an easy and efficient way to achieve
The servos are a little pricey (ranging from about $80
to just over $200), but the quality makes them a
worthwhile investment that we think is very competitive
with other high-end servos. Mighty indeed. SV
SERVO 10.2017 53
READY FOR CHUNKIN.
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