Using the standard overhead controller, that is distributed by K-Team, the communication range between the Kilobots and the overhead controller (OHC) is limited only to an area of 1m diameter from 1m height.
However, research projects may study large-scale swarms (composed of hundreds of Kilobots) which operate in a much larger area. Additionally, it may be necessary to place the OHC higher than 1m to avoid the interference with overhead cameras that might be used to record the experiment or track the robots. In the experimental setup of Sheffield Robotics, they use a grid of 4 cameras mounted on a frame at 1.6m above the table. Also, it was observed that under different lighting conditions the connection was lost (shadows of people around the table contributed to that issue too).
How we got to the solution:
After performing a set of tests and studying the ambient light of the lab, we have identified the reasons that were limiting the communication between the Kilobots and the overhead controller (OHC) and provided solutions.
After testing different light sources and walking surfaces (for the Kilobots) we have concluded that by increasing the amount of infrared (IR) light on the table and by changing its surface from glass to whiteboard material, we were able to not only increase the area of coverage by a couple of centimeteres regardless the distance of the board from the table, but also to solve the problem with the shadows and the limited lighting. Now we have connection even in the absense of light!
To provide full coverage of the 4m x 4m table, we designed our own board (PCB) that you could connect up to 6 OHCs! This allowed us to increase the area of coverage by 2 more meters (4m x 6m).
The cost for one OHC was around €590 and our version with 6 boards costed €80-€100!