C onventional motion platforms are installed below the cabin. Therefore, the center of rotation is below the driver. This causes undesirable reverse forces during sudden maneuvers. For example, in the figure below which depicts the forces on a driver during a sudden left hand turn, the driver is expected to experience a pulling force toward the right due to centrifugal forces.
To reproduce this force, the motion platform is tilted as in the figure so that gravitational forces simulate the pull due to centrifugal forces. However, with conventional platforms, at the start of the tilting motion, the driver experiences a force in the opposite direction for a short period of time due to inertial accelerations.
This ' opposite' force (herein referred to as 'parasitic' forces) is undesirable and is amplified when the motion becomes more abrupt or sharp. With the inverted motion platform, the initial force at the start of the tilt and the resulting force due to gravitational pull after the motion platform is tilted are in the same direction.
Therefore, with proper motion modulation, the driver can be made to feel the desired force in the correct direction right away from the beginning of motion. Fig. 2 shows a typical diagram of forces felt by the driver of a simulator during braking. As shown, conventional motion platforms cause parasitic forces during the beginning of braking whereas inverted platforms can follow the desired forces from the beginning of the braking maneuver.
With conventional motion platforms, the 'parasitic' forces exist for all maneuvers including braking, accelerating and turning.
They can be reduced to some degree when using higher degree of freedom motion platforms (such as a 6DOF motion platform) and is less noticeable during slow maneuvers. However, when high bandwidth vehicles are being simulated, such as automobiles and racing vehicles, the 'parasitic' forces become significant and are the main reason for unrealistic motion cues.
The inverted motion platform concept applied to motion simulators is a patent pending concept only found in Simuline products. It is applied to the VR-Racer product, making VR-Racer the most realistically reacting driving simulator in the market today.
