Design and Application of a Motion Platform for a High-Speed Craft Simulator

Aalesund University College has built the first full-size high-speed craft simulator in Norway. An important part of this work has been to design the motion platform which supports the bridge and imitates the motion of the ship. This construction is based on a Stewart platform in three degrees of freedom (roll, pitch and heave). The platform deck is moved by three frequency controlled servo drives. The servo motors are placed at the corners of an equilateral triangle with its centre aligned with the mass centre of the deck. The motion of each motor shaft is transferred to the deck through a lever arm connected to a rod. The ship movements are generated by a ship motion simulator running on a PC, giving corresponding values for roll, pitch and heave at each instant. These values undergo linear transformations to derive the equivalent values for the positions of the three servo motors, and the resulting values are given as reference signals to the servo drives over a RS422 communication bus. The motor positions are updated 40 times each second. The motion simulator is synchronized with a visual simulator through a NMEA-protocol over a serial communication. The NMEA protocol provides the necessary information to synchronize the ship movements with the visual presentation. This information is fed into a simple hydrodynamic ship model to derive the position coordinates of the ship, which is used to manipulate the motion platform. Test results show that the motion platform is capable of imitating the movements of a ship in a satisfactory way