EcoBot I: Sugar powered autonomous robot




EcoBot I is a proof-of-concept study in our work. It is a 960g robot, powered by microbial fuel cells (MFCs) and performs a photo-tactic (light seeking) behaviour. This robot does not use any other form of power source such as batteries or solar panels. It is 22cm in diameter and 7.5cm high.

The biocatalyst in the MFCs’ anode was a freshly grown culture of E. coli fed with refined sugar whereas the catholyte was ferricyanide. Methylene blue (MB) was used as the redox mediator to extract a portion of the electrons produced from breaking down the sugar in the metabolic pathways of E. coli. Electrons are then transferred to the anode electrode and flow through the external electrical circuit to the cathode, thus producing electrical current. (For more details on the operation of this type of MFCs please click here).

Energy produced by the MFCs is stored by an onboard 'accumulator' consisting of a bank of capacitors. Two photo-diodes provide the input to the "tracking system" of the robot and are indirectly connected to two high efficiency, high torque motors. Once the energy is accumulated up to a specific threshold, it is then released to either or both of the motors according to the indication from the photo-diodes. The system does not employ any other form of power supply such as batteries or solar panels.

The robot is moving towards the light in burst motions which are governed by the threshold voltages of the onboard accumulator. The open circuit voltage of the MFC stack was measured to be 5.4 V with a short circuit current of 15mA and the operating range was between 1.93-2.83 V. Overall, EcoBot I travelled a distance of 80cm in 20mins at the speed of 2.4 meters/hour, whereas the speed whilst in motion was 1.7cm/sec.


Our study builds on the foundation work of Stuart Wilkinson (Gastronome, 2000) at the University of South Florida. EcoBot however, differs in several significant aspects than Wilkinson's Gastronome. It is smaller (~ 1/8th the weight of Gastronome), performing a behaviour-based task (photo-taxis) whereas Gastronome moved unidirectionally on fixed 'tram lines'. The charge/discharge cycle of EcoBot (30sec/2sec) was shorter than that of Gastronome (18hrs/15min). EcoBot’s energy management was performed through capacitors, while Gastronome’s through batteries.


Figure 1. Snapshot of EcoBot I performing photo – taxis. Click on the image to watch a 2.01 MB video clip of the robot in action.


Figure 2. EcoBot I fully assembled


Figure 3. Schematic diagram of the robot


Figure 4. Distance travelled by EcoBot I


Questions on the IAS Laboratory to Chris Melhuish: