
\section{Summary of the project}

This PhD project answers the question ``How can the aerodynamic drag-inducing tails and mechanical advantage-varying knee joints of mammals inspire improvement in the agility and precision of jumping robots?" by designing a bioinspire agile jumper robot that features a C-SEA leg and an AeroTail balancer. In order to design such robot, extensive literature review is conducted on topics including bioinspired legged robots, jumping robots and robotic balancing to fully explore the ideas and to gain insights. Then, the theoretical AeroTail and C-SEA leg are conceptualised based on the inspirations from natural organisms as well as research gaps in related areas of study. The contributions and results of this project are summarised in this section.

\subsection*{Key Validated Outcomes}

The main quantitative outcomes validated through modelling, simulation, and
experimental studies in this thesis are summarised as follows:

\begin{itemize}
    \item The proposed aerodynamic drag-based balancing mechanism (AeroTail) achieves stabilisation performance comparable to reaction-wheel-based approaches while reducing the peak required balancing torque by approximately 33.2\%.

    \item Optimisation of the drag-inducing components demonstrates that the
    aerodynamic torque generated by the AeroTail can be increased by up to
    approximately 20.8\% through appropriate geometric configuration and connection
    design.

    \item The continuously variable transmission enhanced series elastic actuator
    (C-SEA) enables substantial reduction in peak ground reaction force during
    jumping compared to a conventional series elastic actuator, while maintaining
    comparable jump height and overall jumping performance.

    \item When the jumping and balancing mechanisms are integrated, the resulting
    robotic system achieves stable jumping behaviour with an overall reduction in
    system energy consumption of approximately 6.2\%, without compromising
    stability or jumping height.
\end{itemize}

\subsubsection{AeroTail balancer}
We formulated a simplistic mathematical model based on the inverted pendulum and control methods suitable for the AeroTail and did computational simulations and comparative studies to quantify and visualise the advantages of the AeroTail mechanism over traditional RW based tails. The lightweight nature of the AeroTail allows it to maintain a low increase in peak motor torque output as the robot body mass increases, achieving a $33.2\%$ reduction compared to RW. Additionally, AeroTail does not even require mass and inertia to function, whereas RW tail experiences dramatically high energy consumption with a low tail-to-body mass ratio. 

\subsubsection{Drag-inducer optimization study}
To design the drag-inducing devices on the AeroTail, we conducted a specialised CFD simulation study on a selection of shapes to explore how specific geometric features influence aerodynamic drag. This study reveals that among the evaluated shapes, DIs with slender frontal surfaces, arch-like profiles and closed ends generally yield higher drag coefficients. Moreover, with the current frame structure, maximising frontal area is the most reliable approach to optimise drag force. The findings from this study lead to an optimisation framework to identify the optimal frame design that maximises aerodynamic drag while adhering to predefined constraints such as weight and dimensional limits. The findings are then validated by experiments, and the DI prototypes are tested in practical scenarios. The experimental results confirms that most torque is generated by DI with a semi-cylindrical film with the optimised orientation outperforming the original by $20.8\%$.

\subsubsection{C-SEA leg mechanism}
A CVT enhanced SEA leg is designed and manufactured to be jumping mechanism of the robot. The theoretical innovation in this study consists of mathematical models for the hopping robot powertrain, including the CVT gearbox and a simplified model for an electric motor powered prismatic actuator suitable for iterative simulation. Comparative studies are done to examine the performances of both C-SEA and SEA in various scenarios. The results indicate that the C-SEA manages to reduce the peak ground reaction force by approximately $50\%$ compared to the regular SEA. Moreover, C-SEA demonstrates superior performance in most cases with higher $m_{2}$ and $k_{m}$ when actuated by a motor with linear behaviour. The leg mechanism prototype utilises a rack-and-pinion transmission to transfer rotation to linear motion, a torsion spring enabled elastic element, and a non-circular gear based CVT element. 

\subsubsection{Integrated planar jumping robot}
The integrated robot featuring a C-SEA jumping mechanism and an AeroTail balancing mechanism is put to test in the form a simulation study using the software PyBullet. A SLIP based dynamics model is used to describe the jumping locomotion of this robot and appropriate control strategy is implemented so the simulated robot can achieve constant speed jumping locomotion. The simulation results verifies that the AeroTail and C-SEA performances largely coincide with the observations and conclusion from previous chapters in which they are studies individually. At the same time, new findings have been made proving when the C-SEA and AeroTail are used in combination, they manage to overcome each other's limitations. For example, the overall robot energy consumption for Robot-B in \chapref{chap_robot} is cut down by $6.2\%$ even though the AeroTail itself consumes more energy. 




\section{Further works}

There are several future research works planned that are not within the scope of this PhD project but are the logical next steps to advance the research. 

\subsubsection{Jumping mechanism experiment}

Even though the jumper prototype has been constructed, experiments are yet to be done to verify the findings in the simulation. The main obstacle at the moment is the motor control system not being able to deliver the required behaviour. When this obstacle is lifted, various tasks can be done on the experiment platform to not only validate the simulation studies but also to demonstrate the functionality of the C-SEA jumping mechanism. 

\subsubsection{Fully functional AeroTail balancer}

The experiment results regarding the AeroTail ID design are obtained from a very controlled laboratory environment that does not entirely reflect the working condition of a jumping robot. Various modifications are still available to be made for the balancer, such as material and motor choice. Furthermore, bi-directional torque-generating capability is required for the AeroTail to be actually used on a jumping robot. Therefore, research works are planned to advance the AeroTail into a fully functional balancer that are able to achieve robot body re-orientation in a jumping locomotion scenario.

\subsubsection{Full robot experiment}

\chapref{chap_robot} introduced a strategy of integrating the C-SEA and the AeroTail into a jumping robot as well as simulation study to show functionality and its advantages over more conventional designs. In order to validate the simulated results, designing and building a real-life integrated jumping robot and putting it to the test is inevitable. In this case, a more advanced control strategy is needed for the task. This robot could be planar at the early stages but expending it into a 3D jumper that is capable of controlled locomotion and obstacle bypassing is also a possibility. 

%All the future works mentioned are research topics whose results can be arranged into future publications. For each one of them, some groundwork has been done and later expanded. 


%\subsubsection{Gliding}

%As mentioned before, the lightweight robot can be incorporated into a jump-gliding robot. The fundamental work for this plan has already been published. Because of the aerodynamic nature of the AeroTail, it can be re-purposed onto the potential glider without major changes to overall structure. It would be tremendously beneficial if a mechanism can be functional in both the jumping and glide mode. Furthermore, there are plans to design a height booster for the glider since it needs to gain initial elevation and thus initiate the gliding process. Some initial work has been put into using combustion mechanism to rocket the device, as well as simply lifting the robot with a quadcopter drone. The work done on the gliding mechanism is included in Appendix \ref{app_glide}.






