**7. Discussion**

This paper has explored the viability of numerous simultaneously functioning hormone inspired systems. To address this, a speed controller for a foraging swarm was designed using a hormone inspired system and proven to be effective for energy efficient item collection at a number of different item targets. This system was then combined with a previously developed sleep system. The combination of these two systems addressed issues found amongst each of the individual systems, creating large increases to performance with minimal drawbacks. Based on this success a third hormone system was introduced, allowing members of a heterogeneous swarm to form a preference for environment, based on how successful individual robots assessed themselves to be in a given terrain. This new system tested with the speed adapting virtual hormone, identified as the system that would cause the most issue when attempting to categorise robots, was still able to effectively categorise robots, with limited change as demand increased.

Finally, the combination of all of the hormone systems was tested. While not producing the best energy efficiency of the tested systems, the amalgamated hormone system produced the best combination of collection rate and energy efficiency for the environment the system was tested in. Considering the total performance of the system should definitely take into account both energy efficiency and item collection, as the values they represent show task effectiveness and task completion respectively.

The results from the work in this paper have shown that a complex system controlled almost entirely by virtual hormones can be an effective adaptation system within a swarm robotic context.

Future work will involve robustness analysis of the systems, ensuring that performance is not drastically reduced by problems to be expected in real world scenarios such as motor wear or actuator failure. Along side this, additional testing can further close the reality gap, introducing gaussian noise to both the power model and wheel speeds. This will introduce an element of variability to both, as it is expected that a group of robots in reality would experience non-perfect

energy consumption and navigational abilities. In addition to this tests using the PSI swarm robots (the robots approximated in simulation within this papers presented experiments) should take place to demonstrate the capabilities of a physically implemented system. These capabilities will provide evidence to suggest that swarms, equipped with complex hormone systems, would be capable of functioning well in real world applications that require on-line adaptation. These applications could involve disaster relief work, with systems investigating vast areas of volatile and changing environments associated with disaster aftermath, securing survivors or sustaining resources. Equally, hormone systems could be implemented to enable searching for valuable minerals or suitable areas for habitation on foreign planets with hostile and erratic weather.

**Author Contributions:** Conceptualization, J.W.; methodology, J.W.; software, J.W.; validation, J.W.; formal analysis, J.W.; investigation, J.W.; data curation, J.W.; Writing—Original draft preparation, J.W.; Writing—Review and editing, J.T. and A.T.; visualization, J.W.; supervision, J.T. and A.T.

**Funding:** This research received no external funding

**Conflicts of Interest:** The authors declare no conflict of interest.
