The necessity of motion for immersive simulation

There are many challenges we face in the domain of automotive simulation. While it is of course important to recognize the clear and numerous benefits of simulation, it is also important to recognize the need to implement appropriate systems in a simulation environment. In other words, recognizing and adapting a simulation environment to its use-case is just as important as the making decision to use simulation itself.

We know there are many crucial elements to maximizing the realism and immersion of a simulator; screen size, resolution, type of display, size and shape of cockpit, components of the cockpit, the list goes on. All of these play a key role in immersion, but today I would like to focus on one of the most important elements of simulation, motion.

Motion in simulation can take many forms, as well as many different levels of fidelity, ranging from simple rotation on a yaw table to continuous exposure to g force emulated with large x-y rail systems.

First, let’s take a look at how the level of fidelity of motion in simulation is measured. Degrees of Freedom, commonly abbreviated as DoF, is a measure of the positional state of a system, which follows the predefined parameters listed below:

Roll – left and right tilt of the systems
Pitch – forward and backward tilt of the system
Yaw – the spin or rotation of the system
Heave – elevational movement of the system
Sway – left and right movement of the system
Surge – forward and backward movement of the system

The primary degrees of freedom used in simulation.

The actuators on each wheel of this cockpit provide motion for Roll, Pitch, and Heave

A 3DoF system provides adequate motion to achieve immersion, especially when coupled with a full cab as a cockpit, but depending on the use case, much more advanced systems may be necessary to provide higher DoF and therefore immersion. For example, a lab conducting simulation for Autonomous Driving, Advanced Driver Assistance Systems or Human Factors studies, a 6DoF system may be more appropriate. In general, 6DoF refers to taking roll, pitch and heave, and adding yaw, sway, and surge. This can usually be accomplished with a motion system that uses multiple diagonally aligned actuators.

The “hexapod” as seen here, is a common configuration of actuators used to achieve a 6DoF system.

While 6DoF systems can of course be expected to be a bit pricier than their 3DoF counterparts, they add the very important sensations of turning, acceleration and deceleration. This is particularly important for immersion, especially when it comes to accelerating and stopping in a simulation.

Even more advanced, we also have the 7DoF systems. These are very similar to the 6DoF systems, but with the added exception of a rotating table, commonly referred to as a Yaw table. While 6DoF hexapod systems are able to provide a degree of yaw, a dedicated table allows for continues yaw. Additionally, a dedicated table means yaw can be emulated without taking the resources of the other actuators; they can continue to provide movement for other degrees of freedom while the yaw table focuses on rotation.

The yaw table, as seen here, is often placed under the actuators, allowing the rotation of the entire system.

Finally, for only the most elite simulation, the upper echelons of simulation technology, there are the 7+DoF systems. The most common of these systems are called 9DoF, as they add x-y rails, large-scale mechanical rails on the floor that the entire cabin can move along freely, to the system. These rails increase the fidelity of sway and surge, allowing for continuous forward, backward, side to side and diagonal movement at forces of up to more than 1 G.

AVSimulation’s SimELITE shown with full 9DoF systems.

All of these intricate and fancy systems sound great, right? Well, the truth is they all amount to nothing if they aren’t properly configured. This brings us to the next step in ensuring immersion in a simulator: motion cueing. In short, motion cueing is defined as the process of translating movements of a real vehicle into movements to be interpreted and then output by the motion system. This means that all movements expected by the driver during a simulation should be felt, to the most realistic extent possible given the simulator’s capabilities, during a simulation. This can be done a few different ways upon setting up a simulator, whether it be manually, or using a given cueing strategy provided by the simulation software, or a combination of both. It is imperative that cueing be done by a seasoned expert in the field of motion, preferably with experience working with the same type of simulator to be integrated. It is a very precise process that requires the utmost knowhow the complete properly.

A diagram showing the limits of a motion system imposed by the cueing algorithm. 

Motion cueing settings as seen in SCANeR Studio. Note the options for preset strategies as well as custom values.

You may be thinking, “Well, what if I don’t have an expert configure the motion settings? It can’t be that important, right?” This brings us to our final topic: Simulator Sickness. Sometimes called SSS, or Simulator Sickness Syndrome, this is a feeling of sickness or nausea that can occur when the body’s physical sensations don’t match what the eyes are perceiving. In the real world, this is a common phenomenon when riding cars, boats or planes, and is referred to as motion sickness. In the simulation world, this sickness can happen quite easily if the driver expects a certain feeling based on what they see, but then fail to experience that feeling. A common trigger for simulator sickness is braking. It is only natural for any driver to expect to lurch forward when braking. When this sensation is not felt in a simulation, it can cause sickness quickly. Large turns without any feeling of yaw, or improper surge feelings during acceleration are also common triggers.

Written by Terry Vanbaalen.