CHAPTER 25 ■ LAUNCHING THE LINE-FOLLOWERSolving Steering Problems
If the robot is struggling to complete certain turns, there are three simple changes that you can make to
significantly improve performance.
Reducing Battery Voltage
A fresh alkaline battery produces around 9.5 V. In comparison, after a couple of runs around the track, a low-
end NiMH battery produces a nominal voltage of around 7.2 V. The fresh alkaline battery causes the robot to
drive 32% faster.
As the battery voltage drops, so does the robot’s speed. This gives the sensors more time to adjust to the
changing surface brightness and prevents overshoot due to motors engaging and disengaging. Ultimately,
the slower the robot proceeds, the better it turns.
This causes an interesting phenomenon. Upon discovering that the robot can’t complete a certain turn,
the builder makes adjustments to the robot and the course. After a number of attempts, the robot starts to
consistently make the turn. The builder congratulates himself or herself on the alterations, only to discover
the robot can’t make the turn the next morning. The actual source of improvement was likely the decline in
battery voltage.
At first, you may be offended at the thought of intentionally slowing down the robot. After all, doesn’t
greater speed imply greater capability? Well, if you find yourself disappointed with the robot’s line-following
aptitude, then perhaps the ability to follow a line is in fact a greater indicator of capability than is pure speed.
Potential solution: Replace those old 9 V batteries in your smoke detectors with fresh ones and use the
depleted batteries to follow lines. Alternatively, switch the robot to a 6 V battery pack consisting of 4 AA or 4
AAA cells. With such a pack, the robot runs more accurately and lasts longer.
Reducing Wheel Size
This is an easy one. If your robot is popping wheelies (the front end is lifting up temporarily at the start of the
course), the wheel diameter is too large.
Wheel size makes a tremendous difference in speed, which makes all the difference in the ability
to turn. The most successful change I made in Sandwich during development was to switch to smaller-
diameter wheels.
Modifying the Course
Let’s face it; you’re a cruel course designer.
At first you may not think that you’re being unfair or unkind to the little robot. But, consider this: How
well could you make a turn in your automobile if all you were allowed to look through were a slit in the
floorboard? You’d sure miss a lot of those 90° turns! Especially if you were driving fast.
Review the course requirements presented toward the beginning of the book. Keep the course turns
gradual and with high contrast.