HS Robot Controller - Part 1

I’ve been working on a controller for a robot I’m developing with other students at HackerSchool. HackerSchool is a non-profit academic association where you can find other people with similar interests to yours and develop projects in many areas. The goal of the project I’m working on is to build a 6-wheeled robot with a robotic arm from the ground up.

The robot can be controlled from an Android application. In the app you can change the mode of the robot to:

• manual control, where you can control the robot through a virtual joystick shown in the application.
• line following, where the robot follows a black line on the floor using its camera.
• maze solving, where the robot has to enter a maze, find a target, grab the target using its arm, and bring the target outside the maze.

I’ve been tasked with developing the robot controller code which will run in a Raspberry PI. You can check the controller repository here.

Structure

When I was structuring the controller, I had to guarantee that the robot hardware and the application would be easily plugged in later in development, since they were being developed by other teams. I needed to be able to test my work independently of the progress already made in the other areas, so I abstracted away the hardware and application, and implemented their interfaces with ‘simulated’ versions.

Simulation

So, how could I test the robot controller when there was no robot to test it with? I did some searching and found Webots, which is an open source robotics simulator. My colleague built a very simplified version of the real robot in Webots, and I have been using it to test the controller since then.

I implemented the robot hardware wrapper using Webots, and this enabled me to develop behaviour such as the line follower before we have a physical robot.

Application

At first, I implemented a simple WebotsApp which just read keyboard input from Webots. Then, I implemented the HSApp which implements a simple bluetooth communication protocol I designed with the app team. I was able to test this bluetooth connection without the app and robot by using Webots and an Android app which allows me to send arbitrary data by bluetooth.

This way I was able to control the simulated Webots robot using my phone, through bluetooth.

Behaviour

The robot behaviour is implemented through an abstract Behaviour class. I defined a Manager class which is responsible for registering behaviours and setting and updating the current behaviour. The behaviours are set by the current App implementation, and those in turn also use the App.

For example, the Manual behaviour is used to control the robot manually. It gets the current joystick value from the abstract App object and moves the robot accordingly.

There’s also a LineFollower behaviour which implements a line following algorithm by processing the camera image using OpenCV. You can see the line follower behaviour in action in this video:

Future plans

What comes next is adding the robotic arm model to the Webots simulation, implementing the maze solver behaviour, and finally making the robot able to grab objects with its arm. The robot still hasn’t been built in real life, but when it’s finished I will need to fine tune the controller to the real thing, which shouldn’t be difficult.