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Robot PU State Machine

🤖 Robot PU Tutorial: Using a State Machine to Build a Dance Routine​

JavaScript Tutorial for MakeCode + Robot PU

Robots are great at repeating patterns, but if you try to write a dance routine using only basic.forever(), you quickly end up with a messy tangle of timers, pauses, and nested conditions.

A state machine gives you a clean, predictable way to organize complex robot behaviors — especially sequences like dancing.

This tutorial shows you how to:

  • Understand what a state machine is
  • Build a simple state machine in MakeCode
  • Use events and timers to transition between states
  • Implement a full Robot PU dance routine

🎯 What Is a State Machine?​

A state machine is a design pattern where your robot is always in exactly one state, such as:

  • IDLE
  • STEP_LEFT
  • STEP_RIGHT
  • SPIN
  • POSE

Each state defines:

  • What the robot does
  • When and how it transitions to the next state

Think of it like choreography: "Do move A for 1 second → then move B for 1 second → then move C…"

🧱 1. Defining States​

We'll define states using numbers or strings. Numbers are faster, but strings are easier to read.

enum DanceState {
    Idle,
    StepLeft,
    StepRight,
    Spin,
    Pose
}

let state = DanceState.Idle

🕹️ 2. State Machine Loop​

We use a forever() loop to run the current state.

basic.forever(function () {
    switch (state) {

        case DanceState.Idle:
            robotPu.walk(0, 0)
            break

        case DanceState.StepLeft:
            robotPu.walk(1.2, -1)
            break

        case DanceState.StepRight:
            robotPu.walk(1.2, 1)
            break

        case DanceState.Spin:
            robotPu.walk(1.5, 1)
            break

        case DanceState.Pose:
            robotPu.walk(0, 0)
            basic.showIcon(IconNames.Heart)
            break
    }

    basic.pause(20)
})

This loop does not decide when to change states — it only performs the current state's action.

Transitions come next.

⏱️ 3. Timed State Transitions​

We'll use control.setTimeout() to schedule transitions.

Helper function:

function nextState(s: DanceState, delay: number) {
    control.setTimeout(() => {
        state = s
    }, delay)
}

This lets us write choreography like:

StepLeft for 800 ms → StepRight for 800 ms → Spin for 1200 ms → Pose

💃 4. Starting the Dance Routine​

Let's trigger the dance when button A is pressed.

input.onButtonPressed(Button.A, function () {
    startDance()
})

The dance sequence:

function startDance() {

    // Start with left step
    state = DanceState.StepLeft
    nextState(DanceState.StepRight, 800)

    // Then right step
    nextState(DanceState.Spin, 1600)

    // Then spin
    nextState(DanceState.Pose, 2800)

    // End in pose
    nextState(DanceState.Idle, 4000)
}

Notice how each nextState() call is offset in time. This creates a timeline of moves.

🧠 5. Why This Works So Well​

  • ✔ Clean separation — The state machine loop handles movement; the transition scheduler handles timing
  • ✔ Easy to extend — Add new moves by adding new states
  • ✔ Easy to debug — You always know what state the robot is in
  • ✔ No tangled pauses — control.setTimeout() avoids blocking the main loop

🕺 6. Full Dance Routine Code (Complete Example)​

enum DanceState {
    Idle,
    StepLeft,
    StepRight,
    Spin,
    Pose
}

let state = DanceState.Idle

// State machine loop
basic.forever(function () {
    switch (state) {

        case DanceState.Idle:
            robotPu.walk(0, 0)
            break

        case DanceState.StepLeft:
            robotPu.walk(1.2, -1)
            break

        case DanceState.StepRight:
            robotPu.walk(1.2, 1)
            break

        case DanceState.Spin:
            robotPu.walk(1.5, 1)
            break

        case DanceState.Pose:
            robotPu.walk(0, 0)
            basic.showIcon(IconNames.Heart)
            break
    }

    basic.pause(20)
})

// Helper: schedule next state
function nextState(s: DanceState, delay: number) {
    control.setTimeout(() => {
        state = s
    }, delay)
}

// Dance routine
function startDance() {
    state = DanceState.StepLeft
    nextState(DanceState.StepRight, 800)
    nextState(DanceState.Spin, 1600)
    nextState(DanceState.Pose, 2800)
    nextState(DanceState.Idle, 4000)
}

// Start dance on button A
input.onButtonPressed(Button.A, function () {
    startDance()
})

🎉 You Now Know How to Use State Machines for Robot PU​

With this pattern, you can build:

  • Dance routines
  • Patrol loops
  • Maze‑solving sequences
  • Multi‑step animations
  • Game logic
  • Swarm behavior states

You can:

  • Add music to the dance
  • Add LED animations
  • Add random dance variations
  • Build a multi‑robot synchronized dance