Design and development of a carbon dioxide based propulsion system for firefighting robot

Abstract

Firefighters typically fight the fire from a safe distance for their protection, which contributes to inefficient firefighting operations. As a result, firefighting robots (FFRs) are integrated into firefighting tasks to increase firefighters’ work performance. The power supply issue is one of the significant challenges when developing an FFR that operates in the real-life fire scenario. Electrically powered-dc motors (DCPM) are the most common power sources utilized for the mobility of the FFRs. However, the DCPM performance is unreliable in a high-temperature environment that characterizes a real-life indoor fire emergency. Therefore, this study aims to develop a carbon dioxide (CO2) gas based propulsion system for FFR application. The CO2 gas based propulsion system (CO2_PROS) is composed of a pneumatic (air) motor and a CO2 gas-power source. The pneumatic motor is used as the actuator for the FFR system, while the CO2 gas (instead of the conventional ‘air’) generated in-situ from dry ice within the robotic system is used as the power source. The mass of dry ice (MDi), is computed analytically using a governing equation that was based on the ideal gas equation. With an air motor consumption requirement of 33 lpm, an operating time of five minutes, and supply pressure to the air motor ranging from 14 psi to 22 psi, a volume of 165 liters was computed as the required volume to efficiently power the proposed carbon dioxide gas propulsion system for a selected FFR operating time. Previous studies that used the phase change of carbon dioxide are limited to generating a high volume of CO2 gas from dry ice without reference to the production rate of the gas. Thus such consideration remains a design requirement for the efficient driving of a FFR. Based on the limited data on the sublimation rate (SR) of dry ice, hot water is used as a catalyst in this research. An experimental approach was employed to examine the design parameters to investigate their effects on the system responses. Using a design of experiment technique, a full-factorial design along with response surface methodology approaches, MDi and water temperature (TW) were identified as the two influencing variables on the SR of dry ice. The results obtained showed that higher TW and MDi leads to increased SR, with MDi having a higher effect on the SR. An optimal SR of 0.1025 g/s was obtained at a temperature of 80 °C, mass of 16.1683 g, and sublimation time of 159.375 s. A prototype of the CO2_PROS power source, which is known as the dry ice power chamber (DiPC), was designed and prototyped in this study. An experimental test rig that integrates TONSON air motor with a prony brake arrangement was utilized to examine the functionality of the prototyped DiPC. The air motor was powered with the generated in-situ CO2 gas and air at different periods. The performance of the air motor, using air and CO2 as fluid media, was analyzed using the mechanical power output (Pout) and efficiency produced by the air motor. The results showed that the Pout of the air motor demonstrates the same trend when using air or CO2 gas as its power source. In both cases, Pout rises as the pressure increases when the torque is kept constant. The result obtained is significantly lower than the estimated result of 110 W, because the air motor did not perform as per the specification on its nameplate. This study, however, established the use of CO2 gas power source in firefighting robots. An air motor with less internal losses could be used to achieve the expected power.