Bug Sport Redux
Despite the enduring popularity of the line following
task, many of our other kits were chiefly interested in tasks
like obstacle avoidance and did not have the means to face
off against the Scribbler and the Mark III. Our field was
filled, however, when we recalled the kits that one would
expect to be most at home in a more pastoral kind of field:
the OLLO Bugs from Robotis. We first encountered the
OLLO Bugs in the April ‘09 issue, where we were
introduced to the system’s unique connectors and colorful
personality. While the OLLO Bugs are simple kits meant to
be accessible to a younger audience, the bots do have
splashes of sophistication like a line following sensor.
The OLLO Bug line following sensor is actually built into
the control module, but a visual inspection reveals it to be
comprised of the classic combination of IR emitter and
detector in the same round packaging as the Scribbler
sensors. Also like the Scribbler, the OLLO Bug relies on two
sets of the emitter/detector pairs. Unlike the Scribbler,
however, the IR sensors are somewhat exposed and far
away from the surface they are sensing. The sensors peer
out from the control panel like recessed lighting in a
remodeled kitchen, but they are not as deeply ensconced as
the Scribbler’s sensors. Also, the OLLO Bug’s sensors hover
above the ground by about two inches — far higher than
the low riding sensors on the Scribbler and the Mark III. We
do think that the placement was determined more out of
aesthetics than of unbridled confidence in the
incorruptibility of the sensors. The control module happens
to serve as the OLLO Bug’s head, and so it is positioned
about halfway up its body.
The OLLO Bug actually has a line following program
preloaded into the robot. Interestingly enough, even though
the OLLO Bug uses two sensors like the Scribbler, the logic
of the program is different from both of its competitors.
The sensors are meant to straddle the line and keep an eye
on the white background. When one sensor sees the black
line, the bug makes a course correction. The six-legged
ambling provides a whimsical contrast to the smooth rolling
of the Scribbler and Mark III, and with a field of three we
were ready to put the line following sensors to the test.
Now that we’ve been reintroduced to our line following
kits, we can finally detect a problem that seems to be
common to every line follower: the problem of contrast. In
our experience, we’ve come under the impression that
many line followers will become less and less cooperative
when the contrast between the (usually black) line and the
(usually white) background decreases. This intuitively makes
sense because as the color of the surface changes, so does
its reflectivity. But alas, none of the datasheets seemed to
immediately suggest any such problem.
In many line following competitions, this is not a
problem. The tracks are ensured to be a pitch black line on
The Sensor Olympics
THE OLLO BUG'S INFRARED SENSOR.
THE SCRIBBLER FOLLOWS A LINE INSTEAD OF DRAWING ONE.
THE MARK III MAKES ITS MARK.
SERVO 03.2012 73