Via Paolo’s Blog.
During the last 9 months I have been busy working on my latest robotic project: a two wheeled self-balancing robot. I previously wrote about the reasons; in essence I think it is a great way to better understand the technologies that surround us and also a good personal development to derive some teachings about management and leadership on which I will soon write.
In the beginning I thought it would have been a few week-ends project; now almost one year in the process I just started scratching the surface of it. I thought that I had most of the necessary knowledge, instead I had to learn new tools, new programming languages and new engineering concepts.
The purpose of this article is to outline particular aspects of the design of the robot with special regards to some tricky issues I solved long the way, not to be a step-by-step guide. In case you are interested in missing details just drop me a line and I will do my best to provide you the information.
Knowledge needed
The project is multidisciplinary and you will need to have a good grasp of many elements of engineering, software development and physics.
- Inverted pendulum physics – this is the fundamental model of the system. The robot senses the tilting angle and corrects it by applying momentum to the wheels. It is very much like balancing a broom upside down on the palm of your hands: you see the broom moving away from its equilibrium and you move your hands to compensate.
- Control theory – from the engineering perspective it is a non-linear, unstable mechanical control problem, so the control strategy is the one thing that must be mastered. I suggest to start with the Proportional Derivative Integral (PID) as it is simple to understand and implement.
- Signal acquisition and filtering – the world is a messy place and sensors rarely output stable measures that can be used to take decisions. So this part really makes a difference. Luckily there are plenty of libraries to choose from as some of the concepts like Kalman filters might me mathematically daunting.
- Electronics – you will need basic knowledge of which component to choose and how to integrate them into the system. This seems simple for a robot using a relatively limited number of components but I made every possible mistake. For example I got the wrong motor driver, the very expensive one I bought in first instance was not suited for the application and had to replace it with a simple, few dollars one that worked very well (will write about this lesson in my other article).
- Programming – I have a Raspberry Pi connected with an Arduino Mega via USB and I use a tablet to remote control the robot. This implies that you need to be able to use some advanced features (e.g.: multitasking, events, non-blocking code, etc) of at least 3 platforms. Also here I was stuck several time and had to learn new languages and re-write entire programs just because the platform I choose in first instance was not really a good fit for the application. Frustration? No! Learning opportunity!
- Design – I made the 3D printed parts from the scratch and had to learn how to use a CAD modelling system.
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