Variable speed motors and radio control

This is a quick project I came up with to use the first DAVE robot I made, which was gathering dust and feeling a bit unloved. I wanted to demonstrate two things: variable speed motor control and radio communication between two micro:bits.

Remember, my first DAVE does not use the micro:bit motor controller board by Kitronik. This was not available back then, so I had to make my own much simpler one with transistors and stripboard. Pin 1 of the micro:bit controls the left motor, pin 2 controls the right motor. There is no option to reverse the motors. 

I used the Mu MicroPython editor to write some code that takes control inputs from a handheld micro:bit and transmits data to a receiver micro:bit on the robot.

This is the MicroPython code for the transmitter:

from microbit import *

import radio

radio.on()

speed_both = 0

speed_left = 0

speed_right= 0

wait_until_time=0

while True:

    

    #stop the robot if A+B are pressed, decrease speed with A and increase speed with B 

    #there is a slight delay in the increase/decrease to improve controller usability

    if button_a.is_pressed() and button_b.is_pressed():

        speed_both = 0

    elif button_a.is_pressed() and running_time() > wait_until_time:

        if speed_both > 0:

            speed_both = speed_both - 1

            wait_until_time=running_time() + 200           

    elif button_b.is_pressed() and running_time() > wait_until_time:

        if speed_both < 4:

            speed_both = speed_both + 1

            wait_until_time=running_time() + 200  

    

    #split speed into left and right motor values

    speed_left = speed_both

    speed_right = speed_left

    

    #tilting will steer the robot

    steering = accelerometer.get_x()

    

    #reduce left motor speed according to amount of left tilt 

    if steering < -200:

        speed_left = speed_left - 1

        if steering < -400:

            speed_left = speed_left - 1

            if steering < -600:

                speed_left = speed_left - 1

                if steering < -800:

                    speed_left = speed_left - 1 

                    

    #reduce right motor speed according to amount of right tilt

    if steering > 200:

        speed_right = speed_right - 1

        if steering > 400:

            speed_right = speed_right - 1        

            if steering > 600:

                speed_right = speed_right - 1

                if steering > 800:

                    speed_right = speed_right - 1

 

    #motor speeds are not allowed to be negative

    if speed_left < 0:

        speed_left = 0 

    if speed_right < 0:

        speed_right = 0

    #show motor speeds on LED display    

    display.clear()    

    display.set_pixel(0,4 - speed_left,9)

    display.set_pixel(4,4 - speed_right,9)

    

    #transmit a three char string where the second and third chars are left and right motor speeds  

    #the +100 fixes the string length at 3 and allows string indexing in the receiver to get the speed values

    speed_left = speed_left * 10

    radio.send(str(100 + speed_left + speed_right))

    

    #this pause helps reliability when using the radio

    sleep(50)

And this is the MicroPython code for the reciever:

from microbit import *

import radio

radio.on()

pin1.write_analog(0)

pin2.write_analog(0)

speeds = "100"

display.show(Image.NO)

while True:   

    

    #get a string from the radio message queue

    #if nothing is recieved, the robot continues as before

    #the sleep helps reliability when using the radio

    sleep(50)

    speeds=radio.receive()

    if speeds != None:   

        #speeds '100' is stop

        #speeds '144' is forward

        #speeds '104' is hard left turn

        #speeds '142' is wide right turn, etc

        speed_left = int(speeds[1])

        speed_right = int(speeds[2])   

    

        #analog output values can be 0 up to 1023  

        pin1.write_analog(speed_left * 255)

        pin2.write_analog(speed_right * 255)        

        

        #show motor speeds on led display

        display.clear()    

        display.set_pixel(0,4 - int(speed_left),9)

        display.set_pixel(4,4 - int(speed_right),9)