Marvin

After a few tests with walking, I decided to not give it a huge head after all. I tried a number of different heads (including several acrylic globes from a crafts store, a doll's head and a lightbulb) and finally settled on a cardboard outline. This is something that an 11-years old can see and say "I could do that!"

For now I used the same code for walking as the #Micro:Bob (I just had to swap some pins and adjust trims), but I want to make it controlled from a second Micro:bit.

import microbit


class Servo:
    def __init__(self, pin, trim=0):
        self.pin = pin
        self.trim = trim
        self.position = 90
        self.set_period()

    def set_period(self):
        self.pin.set_analog_period(20)
        self.write(self.position)
        microbit.sleep(80)
        self.pin.set_analog_period(20)
        self.write(self.position)
        microbit.sleep(80)
        self.pin.write_analog(0)

    def write(self, degrees):
        self.pin.write_analog(int(25 + 100 * degrees / 180 + self.trim))
        self.position = degrees

    def move(self, degrees, delay=5):
        if degrees > self.position:
            step = 1
        else:
            step = -1
        for position in range(self.position, degrees, step):
            self.write(position)
            microbit.sleep(delay)


class Robot:
    NORMAL_FACE = microbit.Image(
        "42024\n"
        "90009\n"
        "00000\n"
        "61016\n"
        "27972\n"
    )
    RIGHT_FACE = microbit.Image(
        "24024\n"
        "09009\n"
        "00000\n"
        "81001\n"
        "28952\n"
    )
    LEFT_FACE = microbit.Image(
        "42042\n"
        "90090\n"
        "00000\n"
        "10018\n"
        "25983\n"
    )

    def __init__(self):
        self.feet_servo = Servo(microbit.pin2, -2)
        self.left_servo = Servo(microbit.pin1, 4)
        self.right_servo = Servo(microbit.pin0, 4)
        microbit.display.show(self.NORMAL_FACE)

    def right_step(self):
        microbit.display.show(self.RIGHT_FACE)
        self.feet_servo.move(120)
        self.left_servo.move(60)
        self.right_servo.move(60)
        self.feet_servo.move(90)

    def left_step(self):
        microbit.display.show(self.LEFT_FACE)
        self.feet_servo.move(60)
        self.right_servo.move(120)
        self.left_servo.move(120)
        self.feet_servo.move(90)

    def right_half_step(self):
        microbit.display.show(self.NOLRMAL_FACE)
        self.feet_servo.move(120)
        self.left_servo.move(90)
        self.right_servo.move(90)
        self.feet_servo.move(90)

    def left_half_step(self):
        microbit.display.show(self.NORMAL_FACE)
        self.feet_servo.move(60)
        self.right_servo.move(90)
        self.left_servo.move(90)
        self.feet_servo.move(90)


    def walk(self, steps=1):
        step = 0
        for step in range(steps - 1):
            if step % 2:
                self.left_step()
            else:
                self.right_step()
        if step % 2:
            self.right_half_step()
        else:
            self.left_half_step()


robot = Robot()
robot.walk(8)

So this is a successor of the #Micro:Bob robot, that would be a little less "gangsta". I designed a PCB for attaching everything together -- the micro:bit, the servos and the battery -- so that you don't have an ungodly mess of wires held together with two-sided tape. I also left some extra holes in the PCB to which you can solder paperclips, to build on top of it and make it a little more interesting.

I found a nice method of mounting the micro:bit to the PCB without using the bulky edge connection -- just use loops of wire made out of paperclips, and plastic bolts (to not damage the micro:bit). The servos fit right into the slots -- I just made the screw holes a bit too tight, had to enlarge them a bit later. The battery holder is still attached to the backs of the servos with a two-sided tape -- there is no room on the board for a different way of attaching it, unfortunately.

In hindsight, I should have made more sockets for the servos -- letting you to plug several servos to the same pin, so they move together, so that you can make hands that move together with the legs, etc. -- maybe in the next version.