A Small-Sized Robot Prototype Development Using 3D Printing

In modern conditions of destructive man-made disasters and military events that can cover various regions of the world, issues of safety and efficiency of restoration are becoming increasingly relevant. One of the important accents when studying damaged buildings built on the principle of reinforced concrete panel structures is its fragility, unpredictability of behavior, as well as minimal working spaces inside or between the slabs. This complicates search and rescue operations and structural analysis of the strength of damaged buildings. An example of such destroyed buildings in the city of Kharkov, Ukraine, as a result of the military aggression of the Russian Federation is shown in Fig. 1.

Fig. 1.

Example of destroyed panel houses in Kharkov due to the war

Taking into account the peculiarities of structural damage to reinforced concrete panel buildings when hit by a shell or missile, they can be as follows: −

punching and penetration. A projectile or missile can cause penetration through the surface layers of reinforced concrete. This can create holes, cause panel deformation and lead to structural collapse in the form of panels collapsing or partial destruction;

It can be seen that the use of classical mobile robots for conducting research in damaged buildings is not advisable due to the minimally limited working space. Such conditions arise when building panel structures are assembled. Due to the large dimensions of such robots, the likelihood of a mobile robot falling into rubble increases. It becomes possible to lose it completely. This can lead to high costs due to the high cost of the robot itself, which can reach ~$5,000–15,000 or more. Examples of such mobile robots are shown in Fig. 2.

Fig. 2.

Classic mobile robots for conducting research in damaged buildings

Therefore, the development of small-sized robots is relevant. Of particular interest is the use of additive 3D printing technologies to produce most of the parts of these robots. Plenty of authors use such a technology for soft robotics [4]–[6], but we propose to use it for our small robots. They will be able to quickly and effectively interact inside destroyed reinforced concrete panel structures in a limited working space. This represents an important step in ensuring safety and rapid investigation of damage sites to make appropriate decisions regarding the condition of the building. It should be noted separately here that such a solution is cheap.

Robots for working in man-made disaster zones, especially in areas with limited work space, must be designed taking into account the specifics of their operation. As part of these studies, we will introduce the following requirements for the mobile robot design being developed: −

compact size and maneuverability: the robot must be compact in order to easily penetrate limited and hard-to-reach places, such as between reinforced concrete structures;

Based on the requirements stated above, there was developed a design concept for a small-sized mobile robot, a sketch of which is presented in Fig. 3.

Fig. 3.

A small-sized mobile robot design sketch

Let us describe the designation of the main elements that are indicated on a small-sized mobile robot design sketch (Fig. 3). 1,5 – caterpillars; 2 – ultrasonic sensor HC-SR04; 3 – camera OV2640; 4 – a mobile robot housing obtained using 3D printing; 6 – hardware for fastening housing elements.

The next stage is the development of a small-sized mobile robot detailed 3D model. The choice of the SolidWorks CAD system for developing a mobile robot 3D model was justified by its wide capabilities in the field of mechanical design and many years of success in the engineering field. SolidWorks provides an intuitive interface and powerful tools, allowing you to create complex mechanical designs with high precision. Its integration with CAM systems provides efficient preparation for 3D printing, making SolidWorks the optimal choice for developing innovative and technically complex projects, such as mobile robots. Based on the SolidWorks CAD system, a detailed assembly of a small-sized mobile robot was designed; the “explosive” model is shown in Figure 4.

Fig. 4.

Classic mobile robots for conducting research in damaged buildings

To print the designed parts, we will use an Anet 8a Plus 3D printer with the following printing parameters: plastic – PLA; printing characteristics: extruder temperature 200°C, table 56°C; extruder diameter – 0.2 mm; layer height – 0.2 mm; line width – 0.3 mm. To prepare stl files for printing, the Ultimaker Cura 5.2.2 slicer was used. The obtained 3D printing results are presented in Table 1.

To print the designed parts, we will use an Anet 8a Plus 3D printer with the following printing parameters: plastic – PLA; printing characteristics: extruder temperature 200°C, table 56°C; extruder diameter – 0.2 mm; layer height – 0.2 mm; line width – 0.3 mm. To prepare stl files for printing, the Ultimaker Cura 5.2.2 slicer was used. The obtained 3D printing results are presented in Table 1.

The assembled housing design of a small-sized mobile robot for research in the zone of man-made disasters, obtained on the basis of 3D printing, is shown in Fig. 5.

Fig. 5.

Assembled housing design of a small-sized mobile robot a) side view; b) front view

Considering the small overall dimensions of a compact mobile robot, to develop a control system it is necessary to select micro-controller modules that provide the following requirements: small overall dimensions, support for wireless information networks (Wi-Fi), the ability to create an access point with support for the HTTP protocol (HTTPS) and connection support cameras for computer vision system. Based on these requirements, the following micro-controller modules were analyzed, which are presented in Fig. 6.

Fig. 6.

Microcontroller modules a) ESP32-CAM [7], b) OpenMV Cam H7 R2 [8], c) Raspberry Pi Zero W [9]

Each analyzed module supports hardware connections of different video cameras models with the ability to support transmitted image quality UXGA 1600x1200 (15 fps) / SVGA 800x600 (30 fps). But at the same time they have fundamental differences, for example, Raspberry Pi Zero W+Cam allows you to deploy Raspberry OS/OS Android on it with support for C++ and Python languages, OpenMV Cam H7 R2 is designed for programming in the MicroPython language. At the same time, the basic operating principle is similar to the ESP32-CAM, which is programmed through the Arduino IDE (in a C-like language). Considering that the main task assigned to the mobile robot control system is to control movement and transmit the video stream to the operator, the main selection criteria will be the following parameters: power supply features, overall dimensions of the hardware module, weight and price.

Based on own experience [7, 10, 11] with these hardware modules, the authors consider it inappropriate to use the Raspberry Pi Zero W, since for its stable operation it is necessary to provide it with 5V 2.5A power. If these recommendations are not followed, the Raspberry Pi Zero W may freeze and reboot. This module also has large overall dimensions. The ESP32-CAM module and OpenMV Cam H7 R2 operate stably with a power supply of 5V 1A. At the same time, they have approximately the same overall dimensions. They also have different price criteria, ESP32-CAM is about 6 times cheaper than OpenMV Cam H7 R2. As a result, to develop an experimental mobile robot prototype on omnidirectional wheels, ESP32-CAM will be used for a control system. Based on the selected microcontroller module, we will develop a control block diagram (Fig. 7).

Fig. 7.

A small-sized mobile robot control block diagram

A general algorithm for controlling a small-sized mobile robot using wireless data transmission technologies is presented in Fig. 8.

Fig. 8.

Generalized control algorithm for a small-sized mobile robot

To conduct research, an experimental small-sized mobile robot prototype was assembled to work in areas of man-made disasters such as destruction or partial destruction of reinforced concrete panel houses and buildings. A general view of the assembled prototype during field testing is shown in Fig. 9.

Fig. 9.

Assembled small-sized mobile robot prototype general view

The purpose of the first experiment was to test the operating time of a mobile robot and find the distance of a stable control signal with the streaming video transmission. To conduct the experiment, a location was chosen that contained small fragments of concrete and graphite, as well as complex terrain. The results obtained are presented in Table 2.

As can be seen from the obtained experimental values, the developed mobile robot for working in areas of man-made disasters makes it possible to confidently receive a video stream about the surrounding space, as a result of which to conduct research and analysis of the degree of damage to reinforced concrete structures at distances of 100–150 meters using an additional antenna that is installed to the ESP32-Cam module. The cost of the developed mobile robot housing was less than $10 At the same time, the total price of the developed mobile robot does not exceed $300–350, taking into account the cost of PLA plastic, and the printing time with the above slicer parameters was ~ 72 hours.

The article proposes the development of a small-sized mobile robot, the body of which is created using 3D printing technology. Currently, in conditions of war, destruction of panel buildings has become extremely common. It is advisable to use mobile robots to study them. Moreover, such robots had to be small to provide access to the cracks formed by the folded panels. Moreover, the risk of loss or destruction of such robots is high, so the cost should be as low as possible.

The development of just such a robot is proposed in this article. Studies have shown that the developed robot can work without recharging the batteries for up to 15 hours. Without an antenna, Video stream transmission (open area) ranged from 50 to 70 meters depending on the direction of signal transmission, Video stream transmission (reinforced concrete structure) ranged from 35 to 55 meters depending on the thickness and number of reinforced concrete structures. With an antenna, ideo stream transmission (open area) was from 170 to 200 meters, and Video stream transmission (reinforced concrete structure) was from 100 to 150 meters. Remote control will be possible from any mobile device: phone, tablet, etc. This robot is under development. In the future, it is planned to improve the model for greater impact resistance.