Ratae Robot Blog

1. Finding help, applying and finally getting into Pi Wars 2019

Because our secondary school doesn’t have a Robot Club my Mum (Miriam) and I (James (14)) found out about Leicester Hackspace (http://leicesterhackspace.org.uk/) and went along with my sister (Mary (12)) to see if they could give me some useful advice about robot building.

We became Members of Leicester Hackspace in January 2018 and my Mum and I started to attend regularly because there are lots of really supportive people with lots of experience to help. Plus lots of different resources (i.e. 3D printers, soldering station, electronic equipment to hack and borrow, etc.)

Steve has been the main helper at Leicester Hackspace. Lots of other people at Leicester Hackspace have also offered help and encouragement including: Divya, Bill, Matt, David and John.

We decided to name the robot ‘Ratae Robot’ because of all the help from Leicester Hackspace and because in Roman times, the town of Leicester was called Ratae Corieltauvorum or Ratae for short.

Steve told me (James) about Raspberry Fields and suggested we go on 30 June 2018.

At Raspberry Fields my Mum and I spoke to the organisers of Pi Wars at Raspberry Fields and I experienced one of the Pi Wars challenges. We also looked at and talked to people on the different stalls selling different robot components and with advice from them and Steve purchased some components.

We submitted an application for Pi Wars in September 2018 and were placed on the reserve list. We decided to carry on working on the robot and to keep the organisers up to date with our progress.

When we were invited to Cambridge Makespace Robot Club (http://makespace.org/) on 12 January 2019 I decided to go along with Ratae Robot and my Mum because the Pi Wars organisers were there, along with other people who were entering Pi Wars. Brian C and Brian S both gave lots of help and advice and we found out more about the competition.

We were given a Pi Wars place in February 2019.

2. Researching how to build a robot and what components to use

I looked at the requirements of Pi Wars and thought about possible approaches to build the chassis (see Table 1).

I then prototyped with a simple LEGO and Meccano chassis, to get it moving and to try out different codes with lots of help from Steve.

Table 1: Chassis Material and Design Options

Possible
approach
Pros Cons Select y/n Why
Meccano (see Photos)Easy to adapt
and relatively
robust
Heavy, after
awhile can fall
apart when the
screws come
lose
Yes Can keep
tightening
screws to keep it together.
Coretec ‘Tiny
4WD’ Robot
Rover
All of the robot
design is done
for you and all
the code for it is
available
on-line
No flexibility
Very little
learning and
design required
No I like the
designing part of the process
Laser cut
chassis
Accurate, fast Design
limitations, has
got to screw or
slot together,
hard to adapt
No Can’t be very
creative with
designs
3D printed Can get almost
any shape you
want
Open source
designs available from
Thingiverse
Slow, can deform when printing,
hard to adapt
Yes, for
Raspberry Pi
holder (white
plastic – see
Photo 1)
Very time
consuming
LEGO Technic
(see Photos 1 and 2)  
Easy to change design Falls apart and not very robust Initially I started with
this, but it kept
falling apart.

Photo 1: Earlier LEGO and Meccano prototype – too top heavy

Photo 2: Another prototype, as you can see the wheels are off centre, the power wire is too long, and the majority of the weight is outside the wheelbase.

Table 2: Other Material Resources Used

Resource Use
Raspberry pi zero w
(pre-soldered 40-pin GPIO)  
A really small computer – with mini-HDMI, micro-B OTG USB, and 40-pin GPIO
Explorer phat   To control the components
Pimoroni moon buggy wheels x4 Grippy wheels so the robot can move
Micro metal gear motors 50:1 and shim, plus bracket and washer   To move the wheels
NOOBS 16GB microSD card   To store the code used by the Raspberry Pi
2000mAh – LiPo Battery Pack
Adafruit Lithium battery charger
To supply power to the robot  
Battery charger
LiPo SHIM To connect the Lithium battery to the
Raspberry Pi
Raspberry Pi Compatible Wireless Gamepad / Controller with dongle and 3AAA 800 mAh rechargeable batteries and charger Controls the robot for the remote control
challenges
Breadboards and Male to Female and Male
to Male – Jumper strips
To wire the components together
Ultrasonic sensor Reads the distance to obstacles – for
autonomous challenges
Line follower Allows the robot to follow a line on the
ground – for autonomous challenges
Various cables with appropriate connectors (mini HDMI to HDMI adaptor and micro-B
USB shown)
Transport power, and sometimes also data
Wireless RouterTo connect the Raspberry Pi with the laptop

Table 3: Critique of Different Batteries for the Raspberry Pi

Possible
approach
Pros Cons Select y/n Why
AA battery
holder
Can get them
quite cheap,
has a switch
on them
Doesn’t come
with batteries
(would have to
buy some
separately),
Different voltage if using
rechargeable
batteries
No Couldn’t get the
right voltage
with these (The
closest would
be 4.8v with
rechargeable and 4.5v with
alkaline)
Pound land
power banks
Very cheap, light, small Short life, not
very reliable, can catch fire
Yes – initially
(see Photo 1)
Started with
these, but found
they didn’t last
for long enough
Power Bank
Anker Astro 6700mAh
Long lasting,
lights to show
roughly what
percentage of
charge
Heavy and big Yes – tried these second (see
Photo 3 under
Explorer)
Used this type of battery
because it was
recommended by Brian C a
previous winner of Pi Wars
2000mAh –
LiPo Battery
Pack
Light, long
lasting, small
Can catch fire.
Have to buy a
special battery
charger for
charging it.
Need to solder a
shim onto the
Raspberry Pi.
Yes – used in
final robot
(Photo 4)
Used this in the
final design
because we had
to replace James’ Pi with Steves’
because the
James’ Pi was only
working
intermittently.
Steves’ Pi has got the
shim for this
battery soldered on so now only works for this
battery.

Photo 3: An earlier version of Ratae Robot with chassis for the Power Bank Anker Astro 6700mAh battery

We tested to check that rechargeable batteries can also be used for the robot controller, which reduces electronic waste which is especially harmful to the environment because of the chemicals and heavy metals used.

Table 4: Software resources

Resource Use
Etcher To burn images to the SD card to save what is needed for the Raspberry Pi to work
OpenSCAD 3D printing software
VNC Viewer and PuTTY To remotely control the Raspberry Pi from a laptop for coding purposes
Python 3 (IDLE) Code to control robot often available as open source code which I modified and improved
for the challenges with lots of help from
Steve at Leicester Hackspace
Angry IP Scanner To find the IP address of everything on a network to find the Raspberry Pi IP address

Table 5: Risk assessment

Risk How I could resolve it
Short circuiting Check circuits before plugging in the power.
Burns (soldering iron) Make sure where soldering is not messy or
cramped, access to cold water and a first aid
kit in case of burns.
Components getting hot If anything is getting too hot – fit a
heatsink
lithium-ion and lithium-polymer batteries
catching fire.
Keep them in a metal tin whilst charging and don’t leave them unattended or on charge for
too long
Burning out motors If the robot isn’t moving, make sure nothing is stuck in the gear box.

Table 6: Problems identified and how I overcame them

Problem Overcame by
2 LEGO wheels and caster used to start with – slow moving and not very stable Replacing with 4 grippy wheels (see Table 2)
Chassis too long Re-designing and test driving
Robot top heavy Re-designing and test driving
Breadboard only stuck on with double-sided sticking tape so loose Use thick elastic band to hold in place
(see Photo 4)
Bolt head of the motor mounts too small to be compatible with Meccano Reusing a plastic lid to make washers
Wi-Fi crashing Using a spare router from Leicester
Hackspace to create a separate network for the Raspberry Pi and laptop.
Insufficient battery life for the Raspberry Pi Changing the batteries used (see Table 3)
Problems charging the AAA rechargeable
batteries for the controller
Using a better battery charger (on loan from
Divya) which charges each individual battery
and has an indicator to show when each
battery is charged.
Problems with Raspberry Pi working
intermittently
Replacing with a different Raspberry Pi and
Explorer pHat

3. Finalising Ratae Robot

Photo 4: Final Robot with Attachment for Pi Noon and Spirit of Curiosity Remote Control Challenges

Photo 5: Attachment for Space Invaders Remote Control Challenge

Photo 6: Attachment for Line Following Autonomous Challenge – still working on this!

4. Test Driving

As well as my sister and I test driving each version of Ratae Robot at home and at Leicester Hackspace. I also went to the Cambridge Makespace Robot Club on 12 January and 9 February 2019 to test drive Ratae Robot with my Mum. Steve came with us in February.

My sister and I really enjoyed Leicester Hackspace Raspberry Pi Birthday Party on 2 March 2019 where the Pi Noon challenge was replicated and guests drove Ratae Robot in competition with another robot. Ratae Robot performed well as it was very quick and more manoeuvrable than the other robot.

5. Useful tip

LEGO Technic, Meccano and Breadboards are compatible and can be attached together for robot prototyping and building

6. How I would change the project if I did it again

Spend more time thinking about how to make a lighter, more robust chassis.

Have better weight distribution.

Use strip board and solder instead of bread board because this would give a better connection and would be less likely to come loose.

Try out different turning methods, such as Ackermann steering geometry and/or omni-directional steering.

Develop the autonomy further.

7. Thank yous

Leicester Hackspace and Cambridge Makespace are really supportive and inspiring, Ratae Robot would not have been built without them. They have taught me lots and really helped me. I really enjoy the collaborative atmosphere and I will keep going regularly to Leicester Hackspace to work on other projects. Leicester Hackspace members also really helped me find lots of open source code and information that helped me with my research of the components and coding I needed. Thank you!

Table 7: Information Sources

Resource Reference
The Unofficial LEGO Technic Builder’s Guide (book) By Pawel “Sariel” Kmiec, 2017, No Starch
Press, San Francisco
Robot Wars – Build Your Own Robot (book) By James and Grant Cooper, 2017, Haynes,
Somerset.
Know Your Tractor (book) The Shell Petroleum Company Limited,
1955, London.
Pi Wars 2019 website https://piwars.org/2019-competition/
Pi Wars competition information and advice
GPIO Zero https://gpiozero.readthedocs.io/en/stable/ and https://pinout.xyz/ Example open
source codes and information
Pimoroni https://shop.pimoroni.com/ Shop selling
robot components
Pi Hut https://thepihut.com/?gclid=EAIaIQobChMI5eDIqf304AIVyrztCh2y Yw8QEAAYASAAEgJpkPD_BwE Shop selling robot components
MagPi magazine https://www.raspberrypi.org/magpi/
Magazines including advice on how to build
robots for Pi Wars in Issue 68
Git Hub (coding) https://github.com/ApproxEng/approxeng.input/tree/master/src/docs/examples