2. MiniBit motors

Pins for the motors are below.

Pin	Purpose
pin12	Left Motor
pin8	Left Motor Backward
pin14	Right Motor
pin16	Right Motor Backward

From testing, analogue values for motor speeds below 100 don’t turn the wheels on most surfaces.

2.1. Motor pin constants

Set constants for the 4 motor pins.

e.g. left motor forwards LMF = pin12

Tasks

Set constants for the 4 motor pins.

2.2. Stop

Use write_digital(0) to stop the motors controlled by each pin.

Tasks

Write code to stop all motors in a def block: def stop().

2.3. Scaling speeds

The miniBit motors take an analogue value of 0 to 1023 for their speed.
Rather than specifying analogue speeds from 0 to 1023, it may be more convenient to use a speed scale from 0 to 10.
To do this, rearrange the equation: (to_value - to_min) / (to_max - to_min) = (from_value - from_min) / (from_max - from_min)).
This gives: to_value = int(((from_value - from_min) / (from_max - from_min)) * (to_max - to_min) + to_min).

scale(from_value, from_min, from_max, to_min, to_max): Returns a value, from_value, from a range of (from_min, from_max), to an equivalent value in a range of (to_min, to_max).

speed_scaled(speed): Converts a value from a range of (0, 10) to an equivalent value in the range (0, 1023).

The code below converts a speed from a value in the range of (0, 10) to an equivalent value in the range (0, 1023).

from microbit import *

def scale(from_value, from_min, from_max, to_min, to_max):
    return int(((from_value - from_min) / (from_max - from_min)) * (to_max - to_min) + to_min)

def speed_scaled(speed):
    return scale(speed, 0, 10, 0, 1023)

2.4. Drive forwards

Drive the buggy forwards.
Use a default speed as in def forwards(speed=2, duration=None).
If a duration, in milliseconds, is passed, stop() is used after that duration.
Use speed_scaled(speed) to convert from a speed in the 0-10 range to an analog_speed.
Use write_analog(analog_speed) to drive the motor where analog_speed is from 0 to 1023.
Use write_digital(0) to stop the other motors.
If the motor drives forwards, the backwards pin should be sent write_digital(0) to turn it off.
Use positive values for speed, 0 <= speed <= 10.

Tasks

Write code to drive forwards at speed 4 for 2 seconds.

2.5. Drive backwards

Drive the buggy backwards.
Use a default speed as in def backwards(speed=2, duration=None).
If a duration, in milliseconds, is passed, stop() is used after that duration.
Use positive values for speed, 0 <= speed <= 10.

Tasks

Write code to drive backwards at speed 3 for 4 seconds.

2.6. Turning calculation for differential motor speeds

Define inner_turn_speed(speed, tightness=2) that takes the motor speed of the outside wheel and calculates the speed of the inner wheel using a tightness factor.

Use a tightness of 0 to return a speed of 0, so that the inner wheel doesn’t move forward.

from microbit import *

def inner_turn_speed(speed, tightness=4):
    if tightness == 0:
        return 0
    else:
        return int(speed / tightness)

2.7. Turn left

To turn left, drive the right motors faster than the left.
Use a default speed, and tightness, as in def left(speed=2, tightness=2, duration=None).
If a duration, in milliseconds, is passed, stop() is used after that duration.
Allow positive values for speed, 0 <= speed <= 10.

Tasks

Write code to turn left using a speed of 3, tightness of 2, for a duration of 3000ms.

2.8. Turn left forwards or backwards

Modify the code to turn left to allow negative speeds as well as positive, so that it turns left backwards as well as forwards.

Use positive and negative values for speed, -10 <= speed <= 10.

Tasks

Write code to turn forwards and backwards to the left using: speed=3, tightness=4, duration=2000.

2.9. Turn right forwards or backwards

To turn right, drive the left motors faster than the right.
Use a default speed, and tightness, as in def right(speed=2, tightness=2, duration=None).
If a duration, in milliseconds, is passed, stop() is used after that duration.
Allow positive and negative values for speed, -10 <= speed <= 10.

Tasks

Write code to turn forwards and backwards to the right using: speed=4, tightness=3, duration=2000.

2.10. Spin left

To spin left, drive the right motor forwards and the left motor backwards.
Use a default speed, as in def spin_left(speed=, duration=None).
Allow positive values for speed, 0 <= speed <= 10.

Tasks

Write code to turn spin left using: speed=4, duration=2000.

2.11. Spin right

To spin right, drive the left motor forwards and the right motor backwards.
Use a default speed, as in def spin_right(speed=2, duration=None).
Allow positive values for speed, 0 <= speed <= 10.

Tasks

Write code to turn spin right using: speed=3, duration=3000.