## 2 Materials and Methods
### FireBot System Overview
#### 2.1.2 Hardware Specifications of an Experimental Platform  
In this subsection, a brief overview of FireBot's hardware components will be presented. At the starting point of developing our complex system, the commercially available robotic platform TurtleBot2 (Willow Garage, Menlo Park, CA, USA) was used for the implementation of the SLAM algorithm and for the first tests. TurtleBot2 is a low-cost robot platform with open-source software, and it is a platform based on a differential drive, equipped with a gyroscope, three front bumper sensors, and three cliff sensors. Additionally, RPLidar A2 was added along with the Orbbec Astra RGB-D camera (Orbbec 3D Technology International, Inc., Troy, MI, USA). Since TurtleBot2 does not have a central processing unit, a portable computer (Intel i7-10610U, 32 GB DDR4, Ubuntu 18.04) was used on top of a robot. After an initial custom robot specification was defined, a custom robotic platform was built that is presented in Figure 3. Hardware specifications of the first custom prototype are presented in Table 1 along with the approximate prices of publicly available components. Labor hours for software development, hardware assembly, and indoor-developed components are not included in the final price.  
Figure 2: The proposed FireBot system-architecture diagram.  
After the initial tests in different environments, several problems appeared. First of all, a skid-steering drivetrain with rubber wheels was inefficient, as it was very dependent on the surface type. Slight changes in ground textures resulted in different behaviors of the robot. That problem was partially solved by switching to mecanum wheels, but at the same time, it introduced another problem. Due to the nature of mecanum wheels, a lot of vibrations were introduced, which significantly reduced video quality from the visual camera. For that reason, the final version of FireBot will be equipped with a differential drivetrain with two stronger motors with rubber wheels and two cater wheels for stability. In addition, full suspension will be added to the chassis to further improve stability. A second problem was that the Raspberry Pi 4 did not have enough processing power for both navigation and image processing. That problem will be solved by using an industrial PC (i7-10750H, 32 GB DDR4, 512 GB SSD, Ubuntu 20.04) for navigation and an NVidia Jetson Xavier AGX 64 GB for image processing. In addition, sensor-data management will be upgraded from Arduino Mega to dedicated custom electronics with a CAN Bus interface. The lead batteries that were used are very heavy, and their capacity proved to be insufficient for the required autonomy. Therefore, the battery capacity will be increased, the battery technology will change to LiFePO4, and the total weight of the battery pack will decrease. The hardware specifications of the final version of FireBot along with the  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Component Type** & **Component** & **Approximate Price** \\ \hline \multirow{3}{*}{Drivetrain} & Skid steering, 4 rubber wheels and & USD 150 \\  & motors with encoders (40 W) & \\ CPU (navigation) & RaspberryPI 4 8 GB & USD 120 \\ CPU & RaspberryPI 4 8 GB & USD 120 \\ (image processing) & & \\ Battery & 2 \(\times\) Lead 12 Ah, 5 h autonomy & USD 80 \\  & Gyroscope, accelerometer, & \\ Sensors & temperature, 5 \(\times\) ultrasonic sensors & \\  & in front + 2 on the sides, 3 \(\times\) IR & \\ Sensor-data management & Arduino Mega & USD 45 \\ LiDAR & RPLidar A2 (2D, 12 m range) & USD 320 \\ RGB-D camera & Orbbec Astra (640 \(\times\) 480 @ 30 fps, & \\  & RGB and depth) & USD 150 \\ Weight & 15 kg & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Hardware specifications of the first prototype.  
Figure 3: The first prototype of FireBot.  
approximate prices of publicly available components are presented in Table 2. Labor hours for software development, hardware assembly, and indoor-developed components are not included in the final price.