 
 The final conclusions of this dissertation are detailed on this chapter, evaluating the success of the initially proposed objectives and paths that this work took. For future works, some proposals are made, suggesting some approaches considering the present work results.
 
\section{Conclusion and Considerations}



The main objective of this dissertation work was to implement and test a balance disrupting system. This objective was accomplished, an balanced inverted pendulum was built and stimuli were applied to it and studied giving valuable information about the concept of disturbing balance using pull forces. On a first step some background information was gathered that influenced some decisions throughout this project. Then the hardware and software needed was acquired, designed and built. And finally the concept was test, evaluated and discussed.

As for the hardware needed: a protective case for the DETI Dynamixel Interface was designed, printed and implemented; a small circuit board was designed and built to supply the DETI Dynamixel Interface with 5 V; a mechanism to use load cells as tensile force sensors was successfully designed and implement. Regarding the software: a ROS infrastructure was created to control the servos, read the load cells and process images all in real time and while storing important information. A Solidworks assembly of the pendulum and SimMechanics tutorial was created.

The PID controller obtained by trial and error allowed the identification of problems, such as: its speed which can be good for a fast responding system but can also be bad because it can easily produce instability; the rope's non linearity makes the stabilization harder, when the intended tensile force is reached the ropes begin to settle and thus making the tension drop, to avoid this problem a rope with a higher spring stiffness should be used; and finally the fact that the system is coupled makes it very hard to lower the difference between the ropes tensile force after they are tensioned.

The dynamixel servos are very easy to communicate with and control, yet the fact that the servo don't control torque, as it was thought, is a considerable disadvantage. By torque control it was thought that the servo would maintain an intended torque value in the commanded direction, as an example: if the servo is commanded to produce 1 \si{N.m} in the CW direction and it is pulled in the CCW direction with a greater torque it locks; and what was expected was that it should adapt it's rotation to maintain 1 \si{N.m} in the CW direction.

Finally, some stimuli were tested which allowed the conclusion that not all types of stimuli are repeatable, meaning that it is necessary to test every new type of stimulus to assess it's repeatability. As for the initial conditions that are required for the reliability of the stimuli application, they  still need to be studied better because the trials that were done seem to indicate that an error up to $\approx 10 \%$ doesn’t influence the trials repeatability. By error it is meant the difference between the initial tensile force measured on the ropes for the repeated tests.




% % %The main objective of this dissertation work was to implement a reliable disrupting system for PHUA. This objective was not accomplished because the problem was underestimated. As it was previously decided the first steps into the exploration of the system's control a simple pendulum connected to two servos was used to simplify the problem. Initially it was thought that controlling such a system would be simple and with a trial and error method a PID controller could be designed. This was not true as the method used consumed a lot of time and could only produce a controller that wasn't good and suffered from positive feedback.
% % 
% % %After this the next step was to try and find the system mathematical equations which also was not achieved possibly to a lack of experience, little time spent trying to obtain the equations or simply because they are to hard to obtain considering that the only inputs are the ropes tensile force.
% % 
% % %Continuing to try to find a suitable controller it was decided to create a virtual model of a simple pendulum, on SimMechanics. This procedure also failed because the mechanism could not be exactly replicated, mainly the sensor reading could not be done in the virtual model. This was possibly due to a lack of experience with the software or limitations in the program since rope's physical properties are very hard to model. Also the fact that this is a coupled system only makes it even more complicated.
% % 
% % %Disregarding these bad results this work produced significant mechanisms, software and knowledge. A protective case for the DETI Dyamixel Interface was designed, printed and implemented. A mechanism to use load cells as tension sensors was successfully designed and implemented. A ROS infrastructure was created to control the servos, read the load cells and process images. A Solidworks assembly and SimMechanics multybody of the pendulum was created. Some stimuli were applied to the pendulum and data was collected to confirm the system's repeatability and give general information about the system.
% % 
% % %Looking back at what went wrong it is clear that a more deep search for information should have been done but at the beginning of this work there was not a fully awareness of all the problems this project would have.
% % 
% % %These articles \cite{Zhang2008}, \cite{Yu2009} ,\cite{Zhang2009} ,\cite{Sinica2010} and \cite{Zhang2011} were found too late. Unfortunately all the of the present work was done when these papers were found unintentionally. They describe a similar system to the one that this dissertation aimed to build. The problems faced building the Cable-driven Auto-levelling Parallel Robot are the same as the stimuli application servo-system encountered. 
% % 


\section{Future Work and Recommendations}

For future work it is recommended an extensive search on different types of controllers and controllers for rope coupled system's. Also it is recommend to read all the articles about the Cable-driven Auto-levelling Parallel Robot (\cite{Zhang2008}, \cite{Yu2009} ,\cite{Zhang2009} ,\cite{Sinica2010} and \cite{Zhang2011}) and to search more about that project. The Cable-driven Auto-levelling Parallel Robot project managed to built a control for a system with four cables with tensile force sensors and faced the problem of it being a coupled system. They used a fuzzy controller and also did the stabilization of their system in two steps, their robot would stabilize a pair of ropes and then the other pair. Yet, their system had more than the tensile force inputs, so all their strategies might not help this project.

The future steps should be as follows:
\begin{itemize}
%  \item The load cells need to be better calibrated;
 % \item Obtain two more 40N load cells;
  \item The influence of the initial conditions need to better understood.
  \item Try to do a simulation of the system using the tutorial or something else, and try to obtain the system's equations of motion.
  \item Test more stimuli, possibly with longer duration, such as a sinusoidal wave.
  \item Find the best way to control the dynamixel servos or find another type of servos that produce the intended torque control.
  \item Consider the concept requirements, maybe make the initial tensioning of the ropes slower.
  \item Create a graphical user interface that allows the user to create and apply stimuli as intended.
  \item Acquire more or other tensile force sensors.
  \item A structure needs to be designed and built to accommodate four servos and have PHUA in the middle to apply stimuli to the humanoid robot;
  

\end{itemize}


