Brief Design Overview for Capstone 1

The team has finalized the 3D model design concept for the autonomous firefighting device. The following figures show the design idea from different perspectives in SolidWorks.  

 

 

Figure 1: 3D model of the Autonomous Firefighting Device 

The autonomous firefighting device is designed to be mounted on a wall behind a kitchen stove. The device will be equipped with infrared (IR) flame sensors and a light detection resistor (LDR) to be able to detect a fire within the stove perimeter. Upon detection of fire, the device will expel extinguishing powder from an internal chamber through a nozzle. For the device’s powder delivery system, it was decided to use an air blower that could blow the powder out through the network of plastic tubing to the nozzle. As seen in the figure above, the nozzle will be connected to 2 servo motors that will move the nozzle as the IR flame sensors and LDR detect the flame. Once the presence of a flame is detected, the device will be coded to open a gate to drop the powder down from the compartment into the tubing. After the powder is dropped, the 16 CFM (cubic feet per minute) air blower will start, and the powder will be blown out through the nozzle directly onto the fire. If the fire were to persist even after the initial nozzle spray, the relay switch module will cut power to the air blower, allowing more powder to drop from the compartment into the plastic tubing track. The blower will start again to expel the powder out until the fire is extinguished and no longer detected.

For the device’s technical analysis, a heat analysis on the outer shell using COMSOL was performed. This outer shell will protect the Arduino related electrical components from the high temperatures produced from the kitchen stoves. Through preliminary research, it was decided that Nylon would be the best material to build the outer shell since it could withstand the high temperatures of a possible kitchen fire. The following figure demonstrates how nylon dissipates the heat when exposed to a maximum temperature of 400K in COMSOL: 

 

Figure 2: COMSOL Heat Analysis on the outer shell of the device 

As seen in figure 2, the base of the device was exposed to a maximum temperature of 400K. As the heat rises on the device; the heat dissipates. It is important that the heat dissipates as it reaches the top of the device because most of the electrical components will be located there within the nylon shell. Very little heat will be absorbed into the nylon shell because of the emissivity of nylon, which is 0.7, thus protecting the powder and electrical components.

Air pressure analysis was also conducted on the powder delivery system’s air blower. Initially, it was found that the air blower had some leaks, which caused the air pressure and speed in the system to not be constant. It was decided to seal the blower from its sides and another air pressure analysis was conducted using ANSYS. The following figure demonstrates the static pressure of the air blower when functioning at 3500 rpm in ANSYS: 

 

Figure 3: Static Pressure analysis of air blower in ANSYS

In figure 3, the static pressure measured within the air blower can be determined with the green contour lines indicating that the blower experiences a low pressure of 1.72*10^3 pascals at the top of its fan blades and high pressure of 3.94*10^2 pascals at the outlet of the blower shown with the red contour lines. It is important that the blower maintains this high pressure at its outlet as it will provide the pressure required for the powder to travel through the plastic tubing.

To prepare for the project execution in Spring 2021, the team will be collaborating during Winter 2020 to buy the nylon material for the outer device shell. A work order will be placed to the UH 3D printing lab so that they can begin the 3D printing of the outer nylon shell of the device. During the winter break, the team will also start ordering some of the physical components such as the plastic tubing, nozzle, and hanging brackets. Once the semester begins, the team intends to begin the building phase of the internal powder compartment, the tubing network, and further development of the code. The challenges we anticipate are delays from the 3D printing lab due to the nylon material availability and the possibility of having to reprint the shell due to some unforeseen error. A second challenge we foresee is the delay of shipment for some of the materials the team may order due to COVID-19. Therefore, we intend on beginning such tasks within the winter 2020 break to mitigate the impact of these issues.