## 1 Introduction  
Drains are an integral part of every modern city, where drainage systems are entirely subsurface in most countries. Statistics from Asia, Europe, United States show that major cities contain 4000 to 7000 km of drainage lines. The primary purpose of these surface and subsurface sewage systems is to remove excess water in a safe and timely manner, which plays a vital role in controlling water-related diseases or water-borne diseases. Drainage systems have its disadvantages, where these systems give problems to mosquito-borne diseases, clogging, internal damages due to ageing, excessive traffic which causes contamination of groundwater or overflow. To control these problems, serious inspection, monitoring and maintenance of drainage systems is required. At present, this task is labor-intensive as shown in Figure 1a that adds more difficulties in subsurface sewer lines like inaccessible areas with poor lighting, ventilation and safety concerns associated with insect bites. The cross-section of the drainage system with the approximate symmetric design shown in Figure 1b are widely found in Singapore [1]. The width, \(W\), of these drainages typically range from 1.1 to 1.8 m, \(w\) from 0.2-0.8 m and the height \(h\) between 0.3-1.1 m. Thus, there is a requirement to design the robot to traverse inside this type of drainage systems. The specially designed mechanism with suited locomotion as per the internal geometry of the drainage system is essential. Classification of the inspection robots can be done on the basis of locomotion as tracked, wheeled and legged. PIRAT [2] is a tracked small robot designed for the quantitative assessment of sewer systems surveyed in real time. The development of autonomous body for inspection of liquid filled pipes \"pipe rover/pearl rover\" has six-legged propulsion [3]. In another work, an autonomous sewer cleaning robot was published that cleans underwater sewers [4]. KARO is a wheeled tethered robot for smart sensor-based sewer inspection equipped with intelligent multi-sensors [5]. KANTARO is a wheeled platform and uses a special mechanism called \"naSIR Mechanism\" to access straight and even bends pipelines without intelligence of sensors or controllers [6]. KURT is a six-wheeled vehicle that can fit in 600 mm diameter pipelines [7] and MAKRO a worm-shaped wheel, multi-segmented and autonomous bodies for navigation in drain systems [8]. The wheeled robot with fixed morphology finds application in climbing of ropes for inspection task as in [9,10]. Even though a bunch of studies in the literature validates for monitoring or inspection of sewer systems, they mostly suffer from performance issues like modularity and adapting its height as per the geometry of drains that diminish their full potential. One major factor that results in the performance degradation associated with inspection robots design is their fixed morphology. We have proposed the model of quadruped robot for drainage systems that are mainly constructed to carry excess water to reservoirs, unlike the sewage pipes that are used to dispose of solid wastes and water. Tarantula has four-wheel drive and steering locomotion. The drain inspection task can include the identification of the potential mosquito inhabitants and locations that are prone to mosquito-borne diseases as presented in [11] using the images grabbed from the camera mounted on Tarantula in the near future. Quadruped robots are gaining increased attention among robotics researchers across a wide range of applications with its unique morphology to carry out various kinds of field work. These quadruped robots bring with them the unique advantage of efficiency. Several developments have been made after pioneering research on quadruped robot from MIT [12] and Tokyo University. Since then, a large number of quadruped robots have been developed, such as BISAAM [13], which has reptile-like walking and stabilizes itself using a flexible spine.