👁️ → 🧠 → 💪 → 🔁

Three circles drawn in the sand joined by arrows into a ring, with a stick balanced on a fingertip beside them.

🎒 What you need

a long stick or broom handle
sand, dust or chalk to draw on
a friend and something to time with

✋ Do this

Balance the stick upright on your open palm. Keep it up for thirty seconds. You will be moving constantly.
Now freeze your hand completely and try again. It falls almost immediately. Say why: with no correcting, there is no control.
Draw the loop in the sand: SENSE (eyes see it tilting), DECIDE (which way and how much), ACT (move hand), then an arrow back to SENSE.
Balance it again but blink hard and often. Note how much worse it gets. You have just reduced your sensor's update rate.
Now try with your arm moving in slow motion on purpose. It falls. That is actuator lag, and it kills control loops.
Time three runs: normal, blinking, slow-motion. Write the three numbers down — that table is a real experiment about loop rate and lag.

💡 Why it works

A drone holding position, a self-balancing scooter and a line-following robot all run this loop hundreds or thousands of times a second. Your experiments showed the two things that break it: sensing too rarely, and acting too slowly. Every serious control engineering decision comes back to those two numbers.

🔥 Challenge

Balance the stick while a friend gently nudges it at random. Then describe, in three sentences, how your loop changed to cope with a disturbance.

📖 New words

control loopthe repeating cycle of sensing, deciding and acting

feedbackusing the result of your last action to choose the next one

latencythe delay between sensing something and acting on it

🔁

Loop Walker

Tap when you have finished this module.