## 1 Introduction  
Commercial liquid handling robots are often employed in biochemical laboratories in order to automate specific, repetitive tasks. Most commercial robots use the same technology as for manual liquid handling, air displacement pipettes or syringes, while a few others use positive displacement pipettes or non-contact dispensing methods; see [1] for a useful overview and [2; 3; 4] for recent applications of commercial robots in biochemical laboratories. For these robots, reliability, performance, and precision are of high priority, and typically, less priority is given to their flexibility and extendibility. As a consequence, commercial liquid handling robots are rarely appropriate when tasks change often. This is unfortunate as this is the case in the early stages of biochemical research, which then lacks automation support. As an answer to this problem, there is an emerging trend in research labs to build ad hoc robots for specific experiments based on open-source 3D printing technology (e.g., [5; 6; 7; 8; 9; 10]). Similarly the commercial ones, do it yourself (DIY) robots also use air displacement pipettes or syringes. However, the open-source basis reduces the cost and makes it possible to design a robot tailored to a specific experiment [11]. While the price for commercial robots starts at around $10,000, the open-source robots are at least one order of magnitude cheaper [12]. The EvoBot that we are developing (see Figure 1) is similar to these DIY liquid handling robots but with a unique focus on reusability and extendibility. Thus, EvoBot is, due to its modular design, unlikely to require a major redesign if it is to be reused for different types of experiments compared to those for which it was originally designed.  
The modular design allows a non-expert user to reconfigure the robot for specific experiments. A modular approach also increases the cost-effectiveness of liquid handling robots because with relative ease they can be reconfigured for many different types of experiments during their lifetime. Some commercial liquid handling robots also have a limited form of modularity because their work spaces can be reconfigured. Our approach extends the modularity to the moveable head itself allowing us to mount self-contained pipetting modules as well as sensor, grippers, etc., inheriting a significant number of advantages from modular robots [13]. To further increase the usefulness of EvoBot, we have made it open source, which allows researchers to build on our reliable platform and extend it with new modules for their specific experiment. In this paper, we expand the description and implementation of EvoBot, which has been previously introduced in [14]. In addition to previous results, new modules and a new standalone controller are shown, and the liquid handling performance is rigorously analysed. Finally, the paper shows how, by making few changes to EvoBot, we can apply it to new tasks such as nurturing microbial fuel cells, positioning an Optical Coherence Tomography (OCT) scanner precisely, and optimizing chemotaxis of droplets.  
We hypothesise that this robot will enable labs with limited resources to setup experiments that run for short periods of time, change frequently, or are interactive. Hopefully, EvoBot will accelerate exploratory research at the frontiers of chemistry and life sciences.