# Analysis and Design of a Minimalist Step Climbing Robot
## 1 Introduction  
In the past few decades, enormous development in the field of robotics has resulted in replacing human tasks with robots. Similar advancement of technologies has also been observed in the development of delivery robots, such as packaging robots, autonomous driving robots, etc. One of the major aspects of today's delivery system comprises door-to-door delivery. In order to achieve complete autonomy in such delivery systems, a robot must be capable of climbing the stairs (up and down) of a building. Extensive research has been undertaken by many researchers to develop robots with climbing capabilities. These robots are broadly categorized into three groups: tracked, articulated leg and hybrid system. In a track based stair climbing system [1], track belts are used to drive the robot. [PERSON] et al. proposed to replace single track belt system with a set of two track-belt system to improve the stability of a step climbing wheelchair [2]. Research was conducted to develop a novel variable geometry tracked mechanism [3]. Such systems are highly controllable and can successfully maneuver on rough terrains and stairs. However, these systems are slower as compared to the wheel based systems. On the other hand, systems based on articulate legs [4] are highly effective in climbing stairs, although they are quite complex to control. Hence, many researchers tend to work towards the development of hybrid systems, which can be further classified into two categories: wheels with track [5] and wheels with articulated legs [6]. A hybrid shrimp mechanism consisting a front fork, a body and a parallel bogies was developed to maneuver in an unstructured environment for rescue operations [7]. [PERSON] et al. proposed a step climbing robot based on passive four bar linkage type locomotive motion [8]. In an another hybrid mechanism, the use of two legs with seven degrees of freedom is discussed [9]. In an interestingresearch study, a eight legged (four pair) hybrid step climbing robot was proposed. The step climbing is achieved by controlling the height of each pair of the legs [10]. [PERSON] et al. illustrated a novel step climbing robot consisting a pair of rotating links at the front and back of the robot [11]. A hybrid leg-wheel robot termed as the Mantis robot was developed and the front links were used as clamps and pulled the main body of robot to overcome any obstacle [12]. A novel step climbing robot consisting two pairs of half circled legs is proposed by [PERSON] et al. [13]. In yet another case, a separate attachable stair climbing module has been developed, which can be attached or detached based on the requirement [14]. The attached module consists of linear actuators that pushes the robot in an upward direction. Although this system is lightweight, it requires human assistance. In [15], powered linkage-based mechanisms along with clustered wheels for the purpose of achieving high step climbing capabilities have been proposed. While powered links help in pushing the robot, clustered wheels take care of obstacle avoidance. In another research study, a swing arm based linkage mechanism was proposed [16]. Another interesting group of hybrid systems are available in the open literature [17; 18; 19; 20; 21; 22], presented by [PERSON] et al. The authors explain the usage of sliders to overcome obstacles. Clamps are fixed on a subsequent step and then sliders are used to lift the robot. This mechanism is stable and it keeps the robot vertical during ascending or descending motions. Furthermore, advanced robots have also been developed which are not only able to climb the stairs but are also capable of balancing on two wheels. [PERSON] et al. [23] also proposed the use of two wheel clusters. In [24] [PERSON] et al. proposed to use sliding chair along with two wheel cluster. Research was conducted to develop stair climbing robots by using rotating multi-limb structure [25]. Moreover, a mechanism based on four bar parallel links was developed [26].