## 2 Related Work  
In this section, we present an overview of the existing mobile rescue robots designed for casualty extraction. The summary of major contributions to the field of casualty extraction is depicted in Figure 1[23; 24; 25; 26; 27; 28; 29; 30; 31]. One of the very first casualty extraction proposal incorporating a mobile robot is the iRobot Valkyrie project, as presented in [26; 32]. In this proposal, the idea is implementing a flexible stretcher that is tethered to a multi-purpose mobile robot (see Figure 1, iRobot Valkyrie [24]). First, an operator or medic is remotely operating the robot to find the casualty. Then, the casualty needs to roll with its own strength onto the stretcher. After the casualty rolls safely on the stretcher, the robot then pulls away the stretcher to the safe place for further treatment [26]. The US Department of Defence then introduced the robotic extraction (REX) and robotic evacuation (REV) rescue robot system for casualty extraction missions as presented in [25]. This system combines several differently-sized, unmanned ground vehicles (UGV) to perform a rescue mission. A small, mobile manipulator (REX) is used for short-range extraction from the site of injury to a larger and faster vehicle (REV), which transports the casualty to a medical facility (see Figure 1, REX and REV). The system is part of a more extensive tactical amphibious ground support system (TAGS). This project was proposed to extract battlefield casualties from hostile environments and from under fire, designed mainly for outdoor battlefield terrain [6]. One of the most sophisticated robot platforms designed and developed specifically for casualty extraction procedures is a robot with a semi-humanoid design. The humanoid robot is roughly the size of a human male. Its upper torso is equipped with a heavy-duty dual-arm manipulator built on top of a mobile base with tank tracks on its thighs and calves. The battlefield extraction assist robot (BEAR) developed by Vecna Technologies [6; 7], the combat robotic nursing assistant (cRoNA) [8] from Hstar Technologies [33], and the humanoid rescue robot for calamity response (HURCULES) robot [29] developed by the Agency for Defense Development, South Korea [34; 35] are examples of a semi-humanoid form mobile robot platform, designed and developed specifically for casualty-extraction procedures (see Figure 1, BEAR, cRoNA, HURCULES). Compared to all previous designs, these robots are designed to be highly agile while performing casualty extraction using their arms by scooping, lifting up, and carrying the casualty (see Figure 2a). While this casualty extraction procedure seems to be flexible, feasible, and mimics how a normal person handles a casualty, medical safety remains an unsolved issue as this design does not stabilise the sensitive areas, including the casualty's spine, neck, and head. Figure 1: Timeline of the major contributions to the field of casualty extraction (photos on the diagram are adapted from [23; 24; 25; 26; 27; 28; 29; 30; 31]). In [29], the authors highlight that one of the noticeable features in the mechanical design of the HURCULES robot is to use the worm gear in the joint to maintain the safety of the casualty even with the power off and to reduce the energy through a selected operating mode. Moreover, unlike the upper body of a conventional humanoid robot, a chest plate is installed and used to properly distribute the casualty's weight to the dual-arm manipulator and the chest plate when carrying the casualty. Nevertheless, the lack of body support (especially spine, neck, and head) during the procedure, in comparison to the conventional stretcher, remains a critical concern. In addition, in terms of operating the robots, controlling such complex robots performing intricate and sensitive tasks is a significant challenge. Teleoperating such a complex system most likely requires more than one highly skilled and experienced operator with complex teleoperation devices.