Line Following Common Questions

Keep answers short and friendly. Add detail only if students ask for more.

“What does reflection() actually measure?”

How much light bounces back to the sensor, as a number from 0 to 100. Black tape soaks up light, so it reads low; the white floor bounces a lot back, so it reads high. That gap is what lets the robot tell the line from the floor.

“What number do I put for BLACK and WHITE?”

Whatever your tape and your floor read — there’s no universal answer. Hold the sensor over the tape, read the reflection, write it down; do the same over the floor. The threshold is the midpoint between them.

“Why does the robot wobble instead of going straight?”

Because it’s following the edge of the line, not the center — it’s always correcting a little. A small, steady wobble is normal. A big wobble means GAIN is too high; lower it.

“My robot drifts straight off the line. What’s wrong?”

Usually GAIN is too low (it’s not steering hard enough) or the threshold is off. Re-measure BLACK and WHITE, recompute the threshold, then bump GAIN up a little.

“It steers the wrong way and runs away from the line.”

It’s following the other edge. Start the robot on the other side of the line so the edge is on the side the code expects. (In the two-sensor stretch, swap the sensors.)

“How do I stop it? It won’t quit.”

while True: runs forever on purpose — that’s how it keeps following. Press the editor’s Stop button to end it.

“What’s GAIN, really?”

It’s how hard the robot steers for each unit of deviation. Small deviation × big GAIN = hard steer. Tuning it is the whole point today: too low = sloppy, too high = wobbly. Change only GAIN between runs so you can tell what it did.

“Do I have to use Python? I want to use blocks.”

Blocks are totally fine — you’ll learn the same things. Use the Block Coding Guide. Younger students can start with a simple if/else “turn one way on white, the other on black” version and upgrade to proportional later.

Teaching Notes for Instructors

Test the line surface before students arrive — black electrical tape on white poster board or a light floor; without contrast nothing works. Resist handing out “correct” BLACK/WHITE/GAIN numbers; measuring and tuning is the entire lesson, and GAIN is where the real learning happens, so protect time for experimenting. Say out loud that the robot follows the edge, or the wobble will read as a malfunction. Finally, leave a hard stop for the showcase — it’s the payoff for the whole week, so don’t let gain-tuning eat into it.