Twin Tweaks ...
TESTING WITH OUR STANDARD OBSTACLE.
FIXING THE COSMIC WEDGIE.
70 SERVO 05.2012
Up next was the Mark III. Even without LEDs, the
robot’s sudden backtracking made it easy to note when it
saw the obstacle. The Mark III also consistently spotted the
obstacle, and it did so at a far more consistent distance
than the Scribbler. Every trial resulted in the bot starting its
moonwalk at about 34 to 35 cm. A little variation is to be
expected. The motors aren’t perfectly calibrated, so the
slightly different angle of approach could mean slightly
different distances when the object is detected. This was a
very pleasing result, however, given that the obstacle
avoidance program we downloaded to the Mark III dictated
that the bot take evasive maneuvers once an obstacle was
36 cm away. The discrepancy between the program and
our measurements could be explained by the fact that our
measurements used the front wedge of the Mark III as a
guide while the rangefinders were set slightly back (about a
centimeter) into the bot.
After our first round, it looked like the Mark III was
ahead based on its excellent consistency. Now, we wanted
to devise a test that would really separate the winners from
Once Upon a Time in the West
Much like with our light box last time, we wanted to
test the sensor’s vulnerability to interference and non-ideal
conditions. With the infrared sensors, we wanted to do
something similar with our disappearing track but in a way
that seemed more practically relevant to obstacle avoiders.
Pondering what a problematic obstacle would look like
conjured memories regarding a certain race through the
desert in 2004.
It was a brisk March morning in Barstow, CA when a
lumbering mechanical beast struck out on its ill-fated
journey across the desert, doomed never to reach its
destination at the gateway to the hedonist’s paradise in
Primm, NV. The lumbering beast was TerraMax — the
impressive entry from Big Truck Robotics. TerraMax was
easily the biggest entry in the 2004 DARPA Grand
Challenge, as it was based on a tactical military vehicle.
The robot was outfitted with LIDAR and cameras for
navigation, and when we first watched TerraMax at the
qualifying races it exemplified the adage that slow and
steady wins the race.
On race day, however, TerraMax’s dreams of
greatness were stymied shortly into the race. After
lumbering along for a little while, the massive bot stopped
in its tracks. Had it gone off course and come face to
face with an impassable ravine or massive boulder? Had
some catastrophic mechanical failure crippled the
behemoth to stop its inevitable march to the finish line?
No, the reason for the robot’s stoppage was much smaller
than that – a bush was in the way. A small, unsuspecting,
prickly desert bush turned out to be the David that slayed
This was not because TerraMax was a die-hard
environmentalist, but rather because the bot’s sensors