## 5 Discussion and Future Work  
In Figures 11, 14 and 15, examples of characters and sentences written with the [PERSON]'s Dynamixels are presented. While for most of the alphabet characters, accurate straight and curved lines were achieved, for some others, oscillations were observed in the drawing trajectories. These oscillations were more evident in smaller alphabet characters (\(r<0.5\) cm). However, the transcribed sentences could be read and understood properly by the human user, and overall, they were well defined. A quantitative metric, termed as the percentage of similarity, was proposed to evaluate the accuracy of the robot-assisted handwritten characters, and an average of 73.44% was obtained for characters with \(r=0.5\) cm. Particularly, for drawing of small characters, as those presented in this  
Figure 14: Transcription of a short sentence with the Bioloid’s right arm and the kinematics models (\(r=0.3\) cm). Figure 15: Transcription of a long sentence with the Bioloid’s left and right arm and the kinematic models (\(r=0.3\) cm)  
work, no other similar drawing application with the standard humanoid Bioloid has been found in the literature. In this work, several practical factors were identified that affect the smoothness and accuracy of the drawing trajectories:  
1. Stability of the robot's pose: Several poses were considered for the robot in order to have proper stability for the writing task. Initially, the kneeling position was considered; however, significant instability was observed. Then, the standing position was considered with more stability. In this work, however, the kneeling position was considered for the task, because it is a more identifiable pose for the writing task. More stability was achieved by disabling the knee Dynamixels (dyn13, dyn14) to allow the whole body to \"rest\" on the \"back-feet\" Dynamixels (dyn17, dyn18). Then, by enabling the thigh Dynamixels (dyn11, dyn12), a straight pose of the upper body was achieved. This was also helpful to produce a \"reaction force\" in case of a significant friction between the pen and the writing plane (e.g., paper or transparency sheet). Nevertheless, due to the nature and characteristics of the Bioloid's different elements and moving parts, the robot's structure is not rigid, and it is susceptible to vibrations and instability. 2. Trajectory accuracy and feedback frequency: The Dynamixels have a relatively low trajectory accuracy and low feedback frequency [25], which reduces the precision of the required movements. As such, there are disparities between the straight and curved lines that were planned and the actual trajectory executed by the robotic arm [25]. 3. Friction: During the writing task, there is a friction force caused by the texture of the pen and the writing plane, which restricts the smooth movements of the Dynamixels. This may also depend on the type of ink and pen. As a consequence of this situation, the tip of the pen may get stuck in a trajectory point. This leads to the following events: (1) the arm's Dynamixels continue the movement required to complete the trajectory, which increases the force on the pen; (2) when this force is more significant, the tip of the pen is released abruptly, leading to an alteration in the drawing pattern. 4. Axis deviation of the writing line: As presented in Figures 14 and 15, a small deviation on the \(y\)-axis was observed in both arms while writing the short and long sentences. This may be caused by the approximate conversion from radians to 0-1024 values and the reference values considered for the coordinate axes on the 0-1024 range (see Figure 9). However, the experiments presented in this work demonstrated the suitability of the Bioloid system for the complex task of handwriting and speech transcription. More work is required to overcome the practical factors identified in the experiments and to extend this application. Thus, future work is focused on the following points:  
1. Develop the dynamic models required for the handwriting task [11]. 2.