The basic concept of PiWars as detailed on the [official website](http://piwars.org) is that competitors pit their robots against each other in a series of challenges to earn points. At the end of the day prizes are given out for various objective and fun categories such as *Robot with most LEDs* etc. > Update: 20th Feb, 2017 > Python code is now available at [alexellis/wild_robot](https://github.com/alexellis/wild_robot). If you've ever seen the TV classic of *Robot Wars* then think of this as a toned-down version of that where the **Raspberry Pi** is king and everyone gets to go home with their robots in one piece at the end. ### PiWars 1 vs 2.0 The first PiWars was held in part of the Cambridge Astronomy campus in 2014, I took along a [small yellow robot](http://blog.alexellis.io/raspberry-pi-collection/) which I had converted from an RC car and won the best non-competing robot category. It was a complete geek-fest with robots of all shapes and sizes entered by individuals, colleagues, parents with children and a couple of school classes. This year PiWars was rebooted at the Cambridge Computer Laboratory - a spacious hall with canteen, lecture halls and additional rooms for the competitors to go to and tweak their robots. The organisers had clearly spent a huge amount of time designing all the courses from the hardest obstacle course I've ever seen to *Pi Noon* (pop the balloon) to skittles to a printed rubber mat for line following. ![Wild Thumper Pi](/content/images/2015/12/12331626_1531721950485982_312920144_n.jpg) ### My Robot I had planned to enter a robot this year, but decided to go for a brand-new chassis and that presented some unexpected problems. My robot was only really ready for the *obstacle course* and would have needed much more work for the autonomous challenges. So I brought it along as a spectator and had some fun dragging chairs across the floor and playing with the cones. > I caught the eye of Linux User and Developer magazine using my robot's arm to take part in a skittles competition. This really caught the eye of Gavin Thomas from Linux Developer and User magazine who went on to take a quick interview about my robot and then published a full page photo of it in the middle of the obstacle course in [issue: 161](https://www.imagineshop.co.uk/index.php/catalog/product/view/id/4100/s/linux-user-and-developer-issue-161/?utm_source=LinuxUserAndDeveloper&utm_medium=cover&utm_campaign=Product-Widget). It was a nice surprise so I've bought a copy to put away. ![](/content/images/2016/02/lud_1.jpg) ##### The build Most of what you can see is from a kit called the *Wild Thumper* manufactured by Dagu in the far east. I bought mine from [Robosavvy](https://robosavvy.com/store/) but a few other places also stock the kit. The base kit includes: * 4x 75:1 geared brushed motors, which stall at 6A each * 4x all-terrain tyres and hubs to connect to the motors * Heavy duty metal chassis * Full suspension for each wheel * Robotic arm with 2 DOF driven by 2x metal-gear servos In addition to the base kit I had to do quite a bit of work to find an affordable motor controller, write code to connect the Arduino and a PS3 controller. It is primarily direct-drive from the controller. * Raspberry PI 2 * 1x Arduino Nano clone to generate servo and PWM pulses * [Edimax WiFi dongle](http://www.amazon.co.uk/Edimax-EW-7811UN-150Mbps-Wireless-Adapter/dp/B003MTTJOY/ref=sr_1_1?ie=UTF8&qid=1449350162&sr=8-1&keywords=edimax+wifi) * [Racksoy Bluetooth dongle](http://www.amazon.co.uk/dp/B00KNPTHS8/ref=sr_ph?ie=UTF8&qid=1449350182&sr=1&keywords=bluetooth+dongle) * PS3 Controller (must be genuine, not a copy) * 1x 5600mAh generic USB battery pack from eBay to power the RPi * Generic dual motor controller (digital) supporting 60A continuous draw * 2 cell 5000mAh LiPo battery (~7.2v) for the motors and servos * 2x UBEC - one for the servos and another for the PI. *Final checks in the workshop before the event* ![](/content/images/2017/02/robot_preview.jpg) ### How it works: In my PiWars 1.0 robot I used the [RPIO.PWM](https://pythonhosted.org/RPIO/pwm_py.html) library to generate PWM pulses through software and the PI's DMA interface. This library has sadly been abandoned by the author - from what I have seen on the Github issue tracker a lot of work would be required to support the Pi2. This made me look to the Arduino Nano - as a co-op board, they are effectively cheaper than £2.00 and very easy to program. #### Motors The Arduino is responsible for sending left/right, forward/back and servo positions through to the motor controller and servos. I needed something that could drive a motor controller reliably and I settled on an Arduino which excels at generating the required signals. I connected the Arduino (at 5v) to the Raspberry Pi (at 3.3v) through a short USB cable meaning I do not need to worry about any voltage differences. > An Arduino can be connected to an RPi through serial cable with a logic level converter or through a USB cable without extra electronics. **Writing a simple comms. protocol:** I then opted for a simple one-way message from the Pi to the Arduino of a fixed length: ``` 050:050:000:000:090:090 Forward left @ 50 Forward right @ 50 Reverse left/right @ 0 Servo 1 angle @ 90 degrees Servo 2 angle @ 90 degrees ``` While there are other ways of doing this, it appeared to have very little lag or jitter so I kept things simple. #### Controls & comms I paired the bluetooth controller to the PI with a program called *sixaxis*, then installed *bluez tools* packages and set the bluetooth service to start on boot-up. In my main program (written in Python) I make use of the pygame library for reading the buttons and stick positions and then feed that into the Arduino. I also set up a WiFi dongle to connect to a hotspot on my phone - this lets me upload/edit/debug code, upgrade the base system and start/stop the code. With the original robot and its single USB port - I had to reboot every time I wanted to use WiFi or Bluetooth, this is much more time-efficient. > If you want to use a PS3 dual-shock controller it has to be a genuine product or the Pi won't be able to pair wirelessly. #### Code > Update: 20th Feb, 2017 > Python code is now available at [alexellis/wild_robot](https://github.com/alexellis/wild_robot). The Arduino's code is written in C and involves some basic string parsing and then GPIO/servo messages. It's one-way communication meaning I can keep the code concise. **Control loop:** The Raspberry Pi code was written in Python with unit testing in mind, I have fake joystick and Ardiuno classes which let me code on my laptop instead of on the device directly. I also wrote unit tests against the string formatting I mentioned above for the motor/servo messages. #### Where next? This is still very much a work in progress, but I will release some of the code to Github and hope that will be useful to some people. I would like to add in a GPS receiver and digital compass, as long I can find a way to shield them from the motors and interference of the large metal chassis. ### See also: * My [PiWars 1.0 debrief](http://blog.alexellis.io/raspberry-pi-collection/) where I re-purposed an old RC car and won the best non-competing robot. * [Self-host a Ghost blog on a Pi](http://blog.alexellis.io/tag/blog/) * [Build a Raspberry Pi cluster with Docker Swarm](http://blog.alexellis.io/live-deep-dive-pi-swarm/) * Blog series on the [Raspberry Pi and Docker](http://blog.alexellis.io/tag/raspberry-pi/) ### Share & Follow on Twitter

12 months ago I built a @Raspberry_Pi #robot that could move furniture. Blog + Python code @ https://t.co/MbqHSE3Twh #learnpython pic.twitter.com/RB3qq79PqL
— Alex Ellis (@alexellisuk) February 20, 2017

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