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Robotics with Python · Module 8 of 8
🤖 Salvage kit

Capstone: The Sorting Arm

Build a machine that sees a decision, acts on it and repeats — and prove it with numbers and a photograph.

🌽 → 🦾 ↙️✅ ↘️❌ 📸
A servo arm on a cardboard base flicking grains into one of two tins, with a phone propped up filming it.

🎒 What you need

✋ Do this

  1. Draw the state machine FIRST, on paper, the way you learned in module 2: WAITING, DECIDING, SORTING LEFT, SORTING RIGHT, back to WAITING.
  2. Build the physical path: a chute that delivers one item at a time to the arm's reach. Getting one item at a time is harder than the code and you should expect to redesign it twice.
  3. Write the control code as one loop with a function per state. Keep each function short enough to read on a phone screen without scrolling.
  4. For version one, you are the sensor: press a key for good or bad and let the arm act. Separating deciding from acting is a design choice, not a shortcut.
  5. Run 30 items. Record: how many were correctly placed, how many jammed, and the total time. Three honest numbers.
  6. Fix the single biggest failure, run 30 again, and put the two result sets side by side. Then photograph the rig with your state diagram and code beside it, and explain the whole thing to someone in under two minutes.

💡 Why it works

You have now built a complete cyber-physical system: a state machine, a control loop, an actuator, a mechanical feed and a measured evaluation. Industrial grain and coffee sorters differ from yours in speed and in having a camera where you stood, but the architecture on the whiteboard is the same one you drew on paper. Jams, incidentally, are where real sorting machines actually spend their engineering budget.

🔥 Challenge

Replace yourself as the sensor. Use the phone camera and your classifier work, or a simple light sensor, so the machine decides for itself. Then measure how much worse it is than you — and be honest about the number.

📖 New words

cyber-physical systema system where software and moving hardware control each other
throughputhow many items a machine can handle per minute
iterationone round of build, measure, improve
🎖️
System Builder

Tap when you have finished this module.