# Improvement of the Sensor Capability of the NAO Robot by the Integration of a Laser Rangefinder
## 2 Materials and Methods
### Design and Manufacturing of the Helmet  
The helmet must present a structural support function for the rangefinder sensor, whose weight is about 140 g (plus the LiPo battery required for its power supply and the respective charging circuit board). Therefore, the piece must have adequate strength to hold the payload weight; consequently, it must be manufactured with a high-density material. In addition, the fixing of the different parts requires the use of self-tapping screws. After several tests were performed with other materials, a PLA (polylactic acid) filament was chosen, since it was a reasonable compromise between density, dimensional accuracy, and sustainability features. The designed structure Is composed of the following three different pieces:  
* The _rear hooking bracket_ (Figure 4a). This part is hooked, by two M2 screws (not visible) placed into two holes, onto the bottom of the back of the robot's head. * The _payload support base_ (Figure 4b). This part must hold the payload and can be placed laterally on the robot's \"ears\". * The _payload protection enclosure_ (Figure 5a). This part must host the rangefinder laser device and the LiPo battery. In addition, it hosts the relative electronic board used for its recharging. Figure 5b depicts the protection enclosure with the rangefinder laser sensor. Figure 4: (**a**) Rear hooking bracket; (**b**) payload support base. Figure 3: Front (**a**) and back (**b**) view of the PCB design for the recharge and voltage regulation board. The particular shape of the helmet employed in this design is dictated by the almost complete absence of flat surfaces and any attachment points on the robot's head. Indeed, the robot skull is essentially a solid of rotation generated by the rotation of a low arch profile around a horizontal axis. Consequently, an object resting on the head tends to rotate and fall at the slightest movement. Therefore, the _near hooking bracket_ was designed to make use of the holes for two M2 screws located at the base of the occupt, near the robot's neck, and was hooked onto this part, avoiding any unwanted rotation. In addition, this part was designed to join the _payload support base_ where the rangefinder laser was placed. The dimensions of the _near hooking bracket_ are 120 \(\times\) 100 \(\times\) 100 mm, and the weight is 49 g.  
The _payload support base_ is composed of two parts connected through a flange and three screws. This feature allows for easier mounting of the piece on the robot's head because of the low elasticity degree of the PLA material that does not tolerate extensive bending. Moreover, the helmet has been designed to finely adjust this piece's position to fine-tune the rangefinder beam's orientation (not only horizontally, but with a downward inclination to detect obstacles on the ground or upwards). For this purpose, this part presents two lateral grooves in the shape of an arc of a circle, where two screws that are placed in two holes have been arranged on both top sides of the _near hooking bracket_. In this way, the _payload support base_ is free to rotate around an axis, passing through the center of the robot's \"ears\", and it can be held in place by these screws once tightened. In particular, it can be tilted at an angle of \(\pm\) 10\({}^{\circ}\) toward the horizontal plane. Its inclination does not vary during the robot's motion since it has been fixed in advance, based on the conformation of the environment or measurement requirements. Finally, the _payload support base_ was prepared with different holes to allow the part to house various size enclosures or to allow a small digital camera to pass through a hole tailored to host a 1/4\" screw. The piece's dimensions are 75 \(\times\) 142 \(\times\) 100 mm, and the weight is 132 g.  
Figure 5 depicts the _payload protection enclosure_ that was customized to host the rangefinder laser sensor. This enclosure was designed to host the base of the sensor.