# Remote Control Device to Drive the Arm Gestures of an Assistant Humanoid Robot
## 5 Experimental Evaluation
### Measurement of the Telecontrol Delay  
In networked communication, the communication delay or latency is the time delay between sending a control command and obtaining an output response [2]. The communication delay depends on the time required to pass via the communication channel established between the remote control device and the mobile robot [72]. The total telecontrol delay during a robot telecontrol is twofold, caused by the communication delay (time required to send target information from the remote control device to the robot) and the structural delay (time required by the robot to imitate the joint positions received). Figure 11: Evolution of the joint angles when the arms of the remote control device perform three lateral trajectories in the air: starting from a neutral position, moving upwards-left, and then horizontally to the right, returning to the left and repeating to the right: (**a**) right arm; (**b**) left arm. Solid lines depict the joint position received by the mobile robot, and dotted lines depict the real evolution of the joints of the robot. In a previous study, the average latency measured in the WiFi network available in the experimentation area was 266 ms [73], showing low variability. Therefore, the combination of this communication latency (266 ms) and structural delay (274 ms) makes that an average telecontrol delay of 540 ms must be expected during mobile robot telecontrol. In general, it is assumed that a teleoperator remotely tracking a trajectory with a robotic manipulator will show compromised performances if the cumulated latency exceeds 300 ms [74], a threshold that decreases task efficiency when grasping objects [20]. However, this is not the application case because the telecontrol of the humanoid robot is designed for arm gesture imitation and pointing during human interaction instead of object tracking and grasping. In such applications, latency variability can be more problematic than average latency when using gestures for non-verbal communication [75]. The total average telecontrol delay has been measured by comparing the motion of an operator moving the arms of the remote control device and the motion of the arms of the humanoid robot. Some of the gestures assessed include upwards, downwards, lateral and circular movements, waves and claps. In all experiments, the starting position of the arms is the neutral position. Table 2 shows a sequence of frames extracted from a video recording of an upwards movement. The relative time-lapse between the frames displayed is approximately 0.42 s. In each picture, a circle has been manually used to mark the position of the arms of the human operator and the robot, and the trajectory between frames has been depicted with a spline line. Blue color has been used to identify the right arms of the robot and the user, while green color has been used for the left arms. The lines help to appreciate the time delay between the remote control device commands and the robot's accomplishment. Although this gesture requires rapid joint acceleration and deceleration, the robot was able to replicate this upwards gesture without any noticeable problem or difficulty, showing an average telecontrol delay of 680 ms. Similarly, Table 3 shows a sequence of frames extracted from a video recording of an upwards and lateral movement, in which the arms start at the neutral position, move diagonally slightly upwards and to the left, and then move to the right horizontally. The relative time-lapse between frames is 0.42 s, circles are also superposed to the arms of both devices and curved lines join the positions in each frame. Again, although this gesture requires rapid joint acceleration and deceleration, the mobile robot was able to replicate this gesture without any noticeable problem or difficulty, showing an average telecontrol delay of 445 ms.  
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Finally, Table 4 summarizes the structural delay of the robot and the total telecontrol delay measured while performing nine arm gestures.