Obstacle Avoidance Common Questions

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

“My robot never stops! Is it broken?”

No — it’s a while True: loop, which runs forever on purpose. Click the editor’s Stop button to end the program. A sensor robot keeps checking and reacting until you tell it to quit.

If they want more: That’s exactly what you want for a robot that reacts to the world — it has to keep looking. “Forever until I press Stop” is the design.

“distance() shows 2000. Why is it stuck?”

That’s not stuck — 2000 mm is the “nothing detected” reading. With nothing in front of the sensor, it reports 2000. Put your hand or an obstacle in front of it and watch the number drop.

“Which port is the sensor in?”

Check where the ultrasonic (distance) sensor is actually plugged into the hub, and use that port in your code. The starter uses Port.C, but yours may be different. eyes = UltrasonicSensor(Port.C) has to match reality.

“What number should the trigger be?”

There’s no universal answer — you measure it on your course. Start near 200 mm and adjust: if the robot stops too far from the wall, lower the number; if it bumps the wall before reacting, raise it.

“What’s the difference between if and else?”

if runs its code only when the condition is true (“if something’s close…”). else runs when the condition is false (“…otherwise, drive forward”). Exactly one of the two runs each time through the loop.

“Why do we need wait(10)?”

It’s a tiny pause so the loop doesn’t race ahead faster than the robot can react. It also keeps the hub from getting overwhelmed. Ten milliseconds is plenty.

“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. You can peek at the live Python preview whenever you’re curious.

Teaching Notes for Instructors

Confirm the distance sensor’s actual port on every robot before students start coding — a wrong port is the most common early snag. Teach the Stop button before the first while True: run so nobody panics when the robot won’t quit. Resist giving students a “correct” trigger distance; measuring and adjusting it on the real course is the lesson. The big “aha” today is the shift from a fixed script to sensor-driven behavior — name it out loud the first time a robot backs away from a hand on its own.