Momentum - The Magazine for Virginia Tech Mechanical Engineering Vol. 3 No. 2 Summer 2018 | Page 21

Sena Hunde, a master's student, and Howard
Guo, a double major ME/EE, hold the
plaque for first prize at agBOT 2018.
above a particular threshold, what we call
the sub-band short-time energy ratio, then
the watermelon is ripe and harvested. If
not, it is left on the ground.”
As the vehicle rolls past melons, they are
channeled into a funnel where the slapper
hits the melons and the sound is analyzed;
melons that meet the frequency for ripe-
ness are scooped up into the machine’s
storage unit. A linear actuator relays how
much current is used to lift the scoop and
this provides a size and weight estimate for
the melon.
The entire process of collecting a melon
takes only a few seconds after the ripeness
of the melon has been determined. From
that point, the melon is harvested and the
scooper lowered to repeat the process in
about five seconds.
alone, we were able to really focus on the
requirements of the challenge.”
With the tow vehicle, Guo and his special
studies group used computer vision and
machine learning technologies that allowed
the vehicle to locate watermelons. When no
melon was in sight, the vehicle used way-
point navigation to find its way through the
fields. When a watermelon was spotted, the
machine’s cameras guided it toward the fruit.
Once there, it was up to the harvester to
determine whether or not the melon was ripe.
The process humans have used for centuries
to determine if a watermelon is ripe is to slap
it and listen for a deep, hollow sound. This
sound has a particular frequency range, which
the team made into a mathematical model to
develop their automated system.
“We placed a microphone under the unit
and angled it to the bottom of the melon
where it captures the reverberations from the
slapper,” said Guo, who will graduate in 2019.
“If the audio analysis indicates a sound ratio
The harvester won’t be making a return trip
to agBOT next year, according to Hunde. The
2019 event will feature weed and feed, and soil
testing and treatment as the two competition
categories. It’s a new challenge Hunde and
Guo are looking
forward to with a
hope of repeating
as champions.
The team
is advised by
Professor Alex-
ander Leonessa,
with additional
advising from
Associate Pro-
fessor Kevin
Kochersberger,
and Associate
Professor of
Practice Robin
Ott.
MOMENTUM
SUMMER 2018
PAGE 21