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pu-robot-kit-js-15

#Robot PU Autopilot

Lesson: Autopilot Navigation with Sonar (Explore)​

Robot PU can navigate using an ultrasonic sonar distance sensor. The extension provides an explore() action that implements a simple sonar-based "autopilot".

This lesson explains:

  • what sonar data Robot PU uses
  • how robotPu.explore() works internally
  • how to use it safely in your own programs

1. Sonar distance sensor​

Robot PU uses an HCSR04-style ultrasonic sensor.

In this extension:

  • Read distance (cm): robotPu.sonarDistanceCm()
  • Default wiring pins used by the extension:
    • Trigger: P2
    • Echo: P8

2. The simplest autopilot: call explore() repeatedly​

robotPu.explore() is an action (it advances when called repeatedly). The simplest "autopilot" loop is:

basic.forever(function () {
    robotPu.explore()
})

Notes:

  • explore() reads sonar, updates its internal navigation state, then calls walk(speed, turn).
  • turn is a bias in the range -1.0 .. 1.0.

3. How explore() works (high-level)​

Internally (in robotpu.ts), explore() does these steps:

A. Build a small "point cloud" of distances​

Robot PU maintains an internal distance array:

pr.exploreDistance (length 4)

Think of it as 4 directional "bins" from left to right.

Each time explore() runs:

  • it decides which bin index d_i to update (0..3)
  • it reads current sonar distance
  • it updates only that bin using a rolling average:
exploreDistance[d_i] = (exploreDistance[d_i] + sonarCm) * 0.5

This acts like a simple low-pass filter to reduce noise.

B. Convert the point cloud into steering​

The helper getTurnFromSonar(distances, turnGain) computes a weighted "center of mass" of the distance readings:

  • if open space is more on the right, turn right
  • if open space is more on the left, turn left

It returns a turn value in [-1, 1].

C. Convert obstacle distance into speed​

setExploreParam() looks at the minimum distance and computes a target speed:

  • if there is room, it approaches a forward speed
  • if too close, it slows down or backs up

It also smooths both speed and direction with low-pass filters so motion is less jittery.

D. Execute the motion​

Finally:

  • explore() calls walk(exploreSpeed, exploreDirection)

So you can think of explore() as:

sonar perception → steering decision → walking output

4. Example: start/stop autopilot with buttons​

let enabled = false

input.onButtonPressed(Button.A, function () {
    enabled = !enabled
})

basic.forever(function () {
    if (enabled) {
        robotPu.explore()
    } else {
        robotPu.stand()
    }
})

5. Example: safety stop if sonar is too close​

Even when using autopilot, it can be helpful to add your own "emergency stop":

basic.forever(function () {
    const cm = robotPu.sonarDistanceCm()

    if (cm > 0 && cm < 8) {
        // Too close: stop and stand for a moment
        for (let i = 0; i < 200; i++) {
            robotPu.stand()
        }
    } else {
        robotPu.explore()
    }
})

6. Summary​

  • robotPu.sonarDistanceCm() gives distance in cm.
  • robotPu.explore() implements a sonar-based autopilot:
    • builds a 4-bin distance "point cloud"
    • computes steering using a weighted center-of-mass
    • computes speed from obstacle distance
    • drives motion via walk(speed, turn)