Article 1 of 8 in our new Motion Series will help you make an informed decision: Cruden’s Dennis Marcus introduces a series of blog articles on motion systems for real-time driving simulators.
In our recent Content Series of articles, we explored why the visual system is such an important element of a driving simulator and in some cases, more important than a motion system. After all, you can drive in a simulator without motion, but not without visuals to guide you! Nevertheless, motion is important too and for most people the most compelling component of a driving simulator. It’s often the aspect that gets considered first.
We get it. Motion systems are intriguing, especially to mechanical engineers who are contemplating the use of an engineering-grade driving simulator. But there’s a risk that this fascination can lead to a costly focus on the wrong things. With so many complex factors to consider, we’ll walk through them one by one. In this new series of articles on motion systems, we’ll give you the tools to make the most informed decision.
With many different motion concepts to choose from these days, it’s important to think carefully up front about what you want your simulator to achieve. There are many different motion system types out there and it’s good to remember that not every driving simulator needs a motion system.
If your goal is to add immersion to an HMI simulation, then 3-DOF motion as used in high end gaming simulators can be a very cost-effective solution. If you’re focused on high-end motorsport applications, you’ll primarily need short, sharp acceleration onsets around the center of the workspace. A 6-DOF hexapod setup works well in this scenario. Meanwhile lane changes, or other maneuvers that yield longer lasting, yet time limited, acceleration profiles, might require a workspace as wide as a two or three-lane highway. This is where huge simulators with 6-DOF motion on a large X-Y table, like those Bosch Rexroth is building for BMW and Renault, come into play. However, if your budget is limited, a simulator without motion that is set up so that motion may be added in future could also be a consideration.
With so many options on the table, it can be hard to perform a proper analysis of different systems and to meaningfully compare specifications. Often all we see is a series of numbers; if the number is bigger, then surely it must be better, right? Not always.
The maximum acceleration of the motion system, and its relationship to its maximum velocity and spatial workspace, is a good example. Higher accelerations may lead in a very short period of time to maximum velocity and as a result, the platform will race at constant speed towards the end of stroke without any noticeable cues. Increasing the maximum velocity will allow for longer lasting high acceleration levels but as a consequence, demand for more workspace becomes critical. As the end of stroke comes in sight a lot sooner in this scenario, the platform needs a lot more room in which to washout the motion to avoid end of stroke collisions.
Cruden manufacturers and integrates a range of motion and static simulators for different applications
You must also consider the level of acceleration that you’ll experience in the simulated vehicle. It’s common for buyers to specify acceleration for their motion system that’s far above 10m/s2 – more than 1g. For handling dynamics, that might be appropriate for a downforce-assisted race car, but tire performance makes that level of acceleration beyond the scope of most road cars. It’s important to always translate real-life performance into your expectations for a motion system and appreciate that high accelerations have limited value unless being used for vibration channels.
Payload is another factor to keep in mind. Put simply, the more weight you put on top of a motion base, the more difficult it becomes to move it around. Again, it comes back to what you want to achieve. If the goal is the highest possible level of immersion for people in the simulator, then you’ll need sufficient payload to handle a fully fitted-out vehicle body. But if you’re building a simulator to focus on vehicle dynamics, then you want the highest possible levels of acceleration and frequency responses so that the driver immediately feels any loss of grip, for example. The most accurate motion may go hand-in-hand with limited payload. For a Formula 1 car that’s not an issue, but a high performance luxury sedan maker researching vehicle dynamics might have to settle for a top frame that’s just a seat and a steering wheel, rather than a full car.
In this series of articles, we’ll address all of these topics, as well as exploring the roles of workspace (doubling stroke doesn't double the experience, it might even reduce it!) and frequency response, which is especially relevant to NVH research. In all cases, we’ll help you to understand the numbers on the spec sheets so that you can properly evaluate any type of motion system. We’ll also discuss the crucial integration between the motion and visual systems and a peek behind the scenes at motion cueing and auxiliary motion systems such as helmet loaders. We look forward to having you along for the ride!
For more information, please contact Dennis Marcus via d.marcus@cruden.com or on +31 20 707 4646.
Links to subsequent articles will be added below as they are published.
View all articles in our Motion Series of articles: here.
Article 4: Motion for immersion VS motion for vehicle dynamics and motorsport
Article 5: Good Vibrations: Using a Driving Simulator for NVH development
Article 6: Acceleration is not enough: there’s more to accurate motion cueing than meets the eye
Article 7: A real car in a virtual world: the pros and cons of chassis mockups in driving simulators
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