instructables

Remote Controlled Microbit Robot

by huffee

I use Microbits in tech clubs and wanted a simple remote controlled robot that was easy enough for children to
build and code. This project uses two Microbits, one as the controller and one to drive the motors. The robot is
controlled by tilting the Microbit controller, it broadcasts the value of the x and y orientation using the
accelerometer. They communicate over the onboard Bluetooth ('Radio' in the PXT editor) To keep things simple it
uses the Kitronik motor driver board and their own block to drive the motors. It also uses two micro metal gear
motors, 3d printed wheels and an old CD as a chassis.

Both hex files needed are included in the discussion about the code. Alternatively you can see both scripts at the
following links;

Controller - https://pxt.microbit.org/45274-63007-00432-610197

Robot - https://pxt.microbit.org/50000-70822-21817-78361

(Robot requires Kitronik block - See https://www.kitronik.co.uk/blog/using-pwm-kitronik...)

Parts needed

2 x Microbits
Kitronik Microbit motor driver board
2 x micro metal gear motors with connector shim
Battery box 4 x AA and connector
Battery box 2 x AAA with JST connector
An old CD (ask your parents!)
4 x Nylon Nuts and Bolts M3x20
4 x Metal M2x30 nuts and bolts
2 x 3d printed wheels and mounts**
2 x o rings / elastic bands for tyres
4 x M-F jumper leads to connect the motors
Some sticky pads

** These links are to designs by bellbm on Thingiverse. If you haven't got access to a 3d printer round plastic lids
work as wheels, use a bit of cork glued to the lid to mount them to the motor shafts.

Tools needed

Remote Controlled Microbit Robot: Page 1

A drill to make holes in the CD
A 3d printer, or a friendly makerspace that has one.

https://youtu.be/UezvuJPL-Uc

Step 1: Build the Robot

To build the robot you need to drill some holes into
your CD chassis so that you can fix the board and
motor mounts in place.

Put the pieces on the CD as shown above and mark
where you need to drill the holes. There are two for
each motor mount and four for the motor controller
board. It's important the motors are opposite each
other, draw a line right across the CD going through
the middle to help with this.

Now

carefully drill the holes in the CD.

Use the four nylon bolts to fix the motor controller
board in place.

Fix the wheels to the motor shafts and add the tyres,
then use the four metal bolts to fix the motors to the
CD using the motor mounts. (NB I didn't have the
correct bolts when I took the photos so I used

threaded bar)

Use the jumper wires to connect the motors to the
terminal blocks on the motor controller. Use the
'Motor 1' and 'Motor 2' blocks. Then connect the other
ends to the motors. At this stage it doesn't matter
which wire connects to the + and - pins. If your robot
doesn't behave as it should swap them round.

Connect the 4AA battery box connector to the power
terminal block. Make sure the + and - are the right
way round!

Use the sticky foam pads to fix the 4AA battery box to
the other side of the CD to the motor controller. Leave
the battery unconnected for now.

Your robot is built, now to write the code.

Remote Controlled Microbit Robot: Page 2

Remote Controlled Microbit Robot: Page 3

Step 2: Program the Controller

The code for the controller is fairly straightforward.

Start loop

In the 'On start' loop you need to set the radio
channel with a 'Radio set group' block. I'm using '1' in
the attached code but as long as you use the same
for both Microbits it will work. I also use a 'Show icon'
block to display a heart image on the LEDs, this is
just an extra clue to show the code is successfully
deployed, it's not needed for the robot to work. (But

So that the receiving Microbit knows if the controller
is sending an X or a Y value we use 'Radio send
value' blocks. This lets us transmit the value from the
accelerometer and a name that tells us which
direction of tilt the number relates to. So 'x' for the X
value and 'y' for the Y value.

Before we send the value of the acceleromoter we
divide it by ten. This is because the accelerometer
gives us values between -1024 and +1024, but the
motor block wants values between 0 and 100. So if
we divide these numbers by ten we save ourselves
some work later.

who doesn't like a bit of extra love?)

Forever loop

The only other code needed is in the 'Forever' loop.
We are going to broadcast the values of the X and Y
readings from the accelerometer over and over. X is
the value that tells us if the Microbit is tilted left or
right, sometimes called the roll. Y tells us if it's angled
forward or backwards, know as the pitch.

Then all we need to do is send the numbers. This
code sends the x value, pauses for 100ms and then
sends the y value. After another quick pause it
returns to the top of the loop and starts again. The
pause is there to give the receiving Microbit time to
receive and store the numbers. Try experimenting
with different pause times, or miss them out
altogether and see what happens.

That's it. Download the code and send it to one of
the Microbits.

Download (https://cdn.instructables.com/ORIG/FA5/WCNF/J2UPHJGK/FA5WCNFJ2UPHJGK.hex)

http://www.instructables.com/ORIG/FA5/WCNF/J2UPHJGK/FA5WCNFJ2UPHJGK.hex

…

(https://cdn.instructables.com/ORIG/FA5/WCNF/J2UPHJGK/FA5WCNFJ2UPHJGK.hex)

Remote Controlled Microbit Robot: Page 4

Step 3: Program the Robot Microbit - Part One

This code is a bit more tricky, so it gets two steps! But
don't worry we'll go slowly. (and you can download
and deploy the hex file and then upload it to the PXT
editor to play with if you like.)

Start loop

The 'Start loop' code is very similar to the controller.
We need to set the radio group so that the Microbit
knows what it's listening for. I've also added a 'Show
icon' block with a different image so that it's easy to
work out which Microbit is which. In this code I've
also set up two variables called xValue and yValue to
store the numbers we receive from the controller.
They are both set to 0 to start with.

On radio received loop

We also need to write the code that catches the
numbers broadcast by the controller Microbit. The on
radio received loop is triggered every time a message
is sent from the other controller. Each time it receives
the name and value we sent from the controller. So
that we can store them in the correct variable we use
an 'If' block and some logic to check the name. Then
we can store the value in either xValue and yValue
depending on which name, x or y, we received. We
will use these values in the next step to control the
motors.

Download (https://cdn.instructables.com/ORIG/FU0/Z8HL/J2UPHKQU/FU0Z8HLJ2UPHKQU.hex)

http://www.instructables.com/ORIG/FU0/Z8HL/J2UPHKQU/FU0Z8HLJ2UPHKQU.hex

…

(https://cdn.instructables.com/ORIG/FU0/Z8HL/J2UPHKQU/FU0Z8HLJ2UPHKQU.hex)

Remote Controlled Microbit Robot: Page 5

Step 4: Program the Robot Microbit - Part Two

Now the code that makes the wheels turn. I'm using
the Kitronik motor driver and they have provided
some helpful code that goes with it that makes it
easier to control motors. To get their code click 'Add
package' in the PXT editor and then paste this
address into the box. (Clicking the link here will take
you to the code page on Github if you want to see
what they have done.)

https://github.com/KitronikLtd/pxt-kitronik-motor-...

More details of this code can be found on the Kitronik
blog post about the motor controller board.

Forever loop

There are two parts to the forever loop, doing the
maths to work out the speed and direction of the
motors and then sending this information to the motor

Putting this together we can add the xValue and
yValue together to come up with a value for each
wheel called 'leftWheel' and 'rightWheel'

leftWheel = yValue + xValue

rightWheel = yValue - xValue

Actually making the wheels move

Now we have our leftWheel and rightWheel values
we can send them to the motors. There is an 'If' block
for each motor, this is to check if the leftWheel (or
rightWheel) value is positive or negative. To do this
we check if the number is greater than 0 (leftWheel >

driver board. This is the hardest bit of the project so
you might need to read it a few times!

Deciding on speed and direction for each wheel

To make the robot move we are going to use the Y
value, tilting the board forward and backwards, to
move the robot forwards and backwards. To make
this happen we need to turn both wheels at the same
speed in the same direction. If the yValue is a
positive number we'll go forward, if it's negative we'll
go backwards.

For turning we'll use the xValue number as the speed,
but turn the wheels in opposite directions. This will
make the robot spin. A positive X value will mean the
wheel turns forwards, and a negative value
backwards. So for the left wheel we will use +xValue,
for the right wheel we will use -xValue.

0, rightWheel > 0). If it's a positive number we use the
'forward' option in the motor block, if it's negative we
use 'reverse'. Notice in the reverse blocks there is
also an 'Absolute of' block before the wheel variable.
This is because the motor block needs a positive
number for the speed, 'absolute of' tells the Microbit
to ignore the minus sign if a number is negative and
use it as a positive number.

That's all we need! Download this code to the other
Microbit and you are ready to go.

Remote Controlled Microbit Robot: Page 6

Step 5: Using Your Robot

Plug the controller Microbit into the motor driver board and connect the 4AA battery box. The motor board powers
the Microbit and the motors, so you should see your icon on the LEDs.

Plug in the two AAA battery box into the remote Microbit.

Now if you tilt the remote board your robot should move!

If you want to extend this project you can;

Think about how we calculate the leftWheel and rightWheel variables. As the code stands these
variables can be greater than the 100 maximum the motor block expects. This isn't a problem, it
works, but can you think of a way to change the calculations so that the variables are always less
than 100?
Add lights, a buzzer or a micro servo to the breakout pins on the motor driver board so your robot
can do more. You can use the buttons on the Microbit to control these extras.
Design a new chassis to replace the CD

Remote Controlled Microbit Robot: Page 7