Modelling power flow in a hoist motor of a Rubber Tyred Gantry crane

A method for calculating the power demand of the hoist motor in Rubber-Tyred Gantry (RTG) cranes has been developed in order to measure the energy consumption in a typical lift cycle. From measurements taken at the Port of Felixstowe it has been observed that the peculiar geometrical characteristics of the hoisting mechanism causes the power demand to increase with the container height in constant speed conditions. By using information extracted from the crane´s schematics and trigonometry it has been possible to calculate the potential energy increase given the weight and vertical position of the container. In addition, the torque load on the hoist motor and the vertical speed of the mass have been calculated, allowing for the modelling of the hoist motor power consumption when lifting containers with constant rotational speed.