Six foundational questions exploring acoustic thermodynamics, sensor blind zones, power degradation, and multi-sensor interference.
Nearer. Sound travels faster in hot air, so the echo returns sooner. The code assumes a fixed speed of sound, so it calculates a shorter distance. The error is small (a cm or two), but it is always in the “too close” direction.
The sensor faces forward, so the car backs up blind. It can hit a wall, a person’s foot or another robot behind it. The fix is a rear sensor, or only reversing for a short, safe distance.
Time isn’t angle. As the battery drains, the motors slow down and the car turns less. Floor grip, wheel slip and uneven motors also change the result. Encoders on the wheels or a gyroscope measure the actual turn instead of guessing it.
They interfere, because each sensor hears the others’ pings and echoes. This is the same “phantom obstacle” problem as Quiz Q2. The fix is to fire them one at a time, with a short pause between, so each one only listens for its own echo.
When no echo comes back (nothing in range, or the echo is lost), the timing function typically returns 0, which turns into a distance of 0 cm. Without > 0, the car would treat that as an obstacle right in front of it and stop for nothing.
The HC-SR04 has a blind zone: it can’t measure very short distances (its minimum is around 2 cm). The echo returns while the sensor is still finishing its own ping, so it can’t tell them apart. Objects that close are effectively invisible to it.