There are several papers describing control systems for hexapods available on the web, including some open source software. However these articles are more interested in positioning than motion simulation. A system with an off-platform projection display needs to compensate for the viewer's positioning and so requires feedback from the platform giving the actual position and rotations. The most common types of actuators are pneumatic, electrical, and hydraulic. Hydraulic systems are more powerful and accurate but also more costly.
Hydraulic fluids are also a hazardous material, especially under pressure.
An alternative actuator, the PemRAM, was a very promising device that combined pneumatic and electrical techniques to produce a responsive, quiet actuator that could also be used as a force input device. It is currently the largest simulator facility in the world. It will be used to simulate sustained acceleration cues. The many commercial motion platforms are often used for multi-person motion theatre rides. These systems sometimes have the screen mounted off-platform, although many have been built as enclosed pods.