Rapid Radio-Receive Tilt Plus Forward/Backward Control

The radio_tilt_bot_fb_only receiver script has statements added that will make the cyber:bot roll forward and backward based on the y-axis tilt measurement from the transmitter.  
For best results, the receiver script should repeat at top speed, so all print and sleep statements have been removed.  

Example script: Rapid Radio-Receive Tilt Plus Forward/Backward Control

• Make sure you are working in the browser with the micro:bit Python Editor that is connected to the radio tilt controlled cyber:bot.
• Set the project name to radio_tilt_bot_fb_only. 
• Enter the script into the editor.
• If you are in a classroom, adjust the channel= in the script to your assigned channel.
• Click Save, and then click Send to micro:bit.  

# radio_tilt_bot_fb_only

from cyberbot import *
import radio

radio.on()
radio.config(channel=7, queue=1, length=64)

sleep(1000)

while True:

    packet = radio.receive()

    if packet:

        dictionary = eval(packet)

        x = dictionary.get('x')
        y = dictionary.get('y')
        needle = dictionary.get('needle')
        
        display.show(Image.ALL_CLOCKS[needle])

        fb = y / 10

        vL = fb
        vR = -fb

        bot(18).servo_speed(vL)
        bot(19).servo_speed(vR)

• Tilt the micro:bit transmitter and verify that the receiver cyber:bot displays a copy of the needle in its 5×5 LED matrix display.  This “micro:bit transmitter” will also be called the “tilt micro:bit”.
• Hold the micro:bit tilt transmitter level, with the 5×5 LED matrix display facing upward and the USB connector pointing toward you.  (At this point, there is nothing to tell you that you are holding it level, the needle will still point in some direction.  The holding level feature is coming soon.)
• Set the cyber:bot board PWR switch to 2.
• Tilt the micro:bit transmitter slightly away from you (like maybe 30 to 40°), and verify that the cyber:bot rolls forward.
• Tilt the micro:bit transmitter slightly toward you (like maybe −30 to −40°), and verify that the cyber:bot rolls backward.
• Set the PWR switch back to 0.

How It Works

The radio_tilt_bot_fb_only script is also almost identical to radio_tilt_receive_test from the previous activity.  One difference is that the sleep(500) was not reduced to 50; it was completely removed.  Without the sleep, the receiver script will recheck for radio data at top speed.  The only thing limiting the responsiveness is that the transmitter has 50 ms sleep calls, so it’s only transmitting every 20 ms or so.

Some statements were also added to the if… block after the x, y, and needle variables are unpacked.  

First fb = y / 10 takes the y tilt value that could hold a value in the -1024 to 1024 range and scales it down to -102 to 102, which is a perfect range for servo control.  The fb variable name is shorthand for forward/backward.  

        fb = y / 10

Next variables for velocity-left (vL) and velocity-right (vR) are set with the value stored in fb.  Let’s say you tilt the micro:bit away from you and that the fb value might be around 50.   To make the cyber:bot roll forward, vL can be 50, but vR has to be -50 to make the right wheel turn the opposite direction.  That’s why vR = -fb.

        vL = fb
        vR = -fb

Now that the vL and vR variables store equal and opposite values based on your y-axis tilt, they can be used to set the left (P18) and right (P19) servo speeds.

        bot(18).servo_speed(vL)
        bot(19).servo_speed(vR)