The paper is devoted to modeling the Stewart-platform based simulator for training of freight vehicle Kam AZ drivers that is currently under construction by the Transas Co. The car cabin is mounted on the platform for reproducing the desired motions of the cabin. The pneumatic servos are used as the actuators for the Transas simulator. An essential peculiarity of the described Transas simulator is usage of the on-off air valves rather than sliding piston-type selector valves for motion control, which imposes serious restrictions on the control law design. The mathematical model, including motion dynamics and pneumatic actuators is presented. The simulation results for quantized PD control are given.