Metallic bridges, nuclear plant ducts, telecom and electric power masts, truss shaped structures planted on gyms and showrooms ceilings, astronomy and military facilities are egregious infrastructures in modern age for which locomotion on them is inevitable in order to perform specific tasks including maintenance, constructions (welding and riveting) and periodic inspections (scavenging, searching for impairments) and etc. Therefore, climbing robots are designed to cover the mentioned duties. Since stability and precision of a climbing robot is inevitable, parallel mechanism is proposed. Considering the fact that maneuvering ability is an important factor for climbing robot in a complicated environment (truss shaped environment, scaffolds), the mobility of the robot is increased by a serial linkage added to the parallel portion of the robot to overtake obstacles and cross branches. Hence, a stiff and precise hybrid (parallel / serial) robot is proposed here by composing serial and parallel modules for climbing scaffolds. In this paper design and modeling of the mentioned hybrid climbing robot, consisting kinematics and kinetics is studied. The robot is a 3limbed gripping mechanism with one base (main body) to which the limbs are attached to. A closed kinematic chain is made by 2 limbs, grasping the support terrain firmly. The mechanism is a non-fully parallel mechanism which needs special calculations for modeling. Robot's movement is classified into two phases: 1 manipulation, 2-locomotion. In this manipulation phase is discussed as the primary design and all of the modeling is verified by conducting some comparative and analytic simulation in MATLAB. It is shown that the designed robot can successfully perform operational tasks after its climbing through the trusses
