This paper describes the design and modeling of a robot that swings on the end of a tether. Its height above the ground is controlled by the length of the tether. Its location on a spherical shell at the end of the tether is controlled by a pair of ducted fans. The vertical orientation of its body is determined by the point at which the horizontal thrust force acts relative to the centre of gravity (cog). The system acts like a double pendulum with two modes of natural movement. It is modeled with coordinate frames at the ends of the tether and at the cog. Due to the second mode of motion it may oscillate around its centre of gravity while it swings or flies in a circle. From the dynamic model we develop a model for simulating the motion of the tethered robot.