Servo - March 2012

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.

Line Dancing

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.