Simulators provide physical link to virtual analysis

Design engineers face constant pressure to develop better products in less time with less cost. In general, the challenge has been well met, particularly within big industry sectors such as automotive, where development time for a new car can be as short as 12 to 18 months. But it is a trend seen throughout most industries as firms look to increasingly satisfy customer needs, meet new market demands and diversify product portfolios. The trend has, in the main, been the increasing use and capability of CAD software, FEA and CFD analysis, and the exploitation of the virtual and digital world where any scenario can be played out and simulated reliably. Digital prototyping, photorealistic 3D design and even the design of virtual factories are all carried out before anything physical to make sure the design looks right, works well and is made in the most effective way. But, taking this a stage further, the virtual environment is now being linked to the physical. Simulators have been around for many years and are commonly used by pilots, motorsport drivers and even for some theme park rides. However, they are increasingly being used as development tools. "When simulating a car, one thing that we can simulate very well is the steering," says Frank Kalff, commercial director at simulator technologist Cruden. "That comes from a motor attached to the steering wheel that we can control and make it feel near 100% realistic. "When you steer and you increase the steering wheel angle, the slip angle increases. With a real tyre, if you steer too far and exceed a given slip angle, grip diminishes. This is where the car begins to skid which causes the steering to get lighter." However, the lateral and longitudinal forces that drivers experience in a corner is something different. That is unlikely to be mimicked by a simulator unless it could be set up to run on long rails. But that would be prohibitively expensive. "But what we can do is give certain representations," says Kalff. "They give people like racing drivers, pilots – even engineers – certain cues that can translate over to the real world." The secret ingredient of the Cruden package is its highly developed motion cueing algorithms – the complex and critical mathematics translate driver input into motion responses via the simulator's interactive motion platform base. Amongst the features are movement through six degrees of freedom, realistic g-force simulation, seat belt tensioning and 100% realistic steering feedback. State of the art graphics bring a race track to life and images are displayed on 42in monitors or projected on to a curved screen that wraps around the driver's line of vision. Simulators, particularly in automotive applications, are being increasingly used to evaluate components virtually and to set up the dynamic performance of a car long before anything is actually made. The ability to literally feel the ride quality and handling of a car before anything is actually made has helped designers immensely as it fills in valuable blanks that just can't be calculated from models, graphs or equations. Mercedes use simulators to evaluate ride quality and handling as they allow engineers to physically sit in a car and feel the difference that adjustments to ride height, suspension stiffness, shock absorbers, spring settings and even overall weight distribution make to ride comfort and road handling. Kalff notes: "Simulators were made that had Mercedes seats, belts and foot rests, to allow Mercedes' engineers to evaluate differences in ride by using different components and different seats. They would also compare these to the ride qualities of competitive cars. "But when you go down to more detail, you can feel the difference between shock absorbers. That is what they are used for; to decide which parts and component will be used when the car is built." Cruden has also worked with a well known Formula One team, which uses the simulator to prepare drivers for certain tracks. It allows the driver to gauge the braking and turn in points of various corners. But its engineers have also been able to exploit benefits and are using simulators to develop its car. Vehicle dynamic data from wind tunnel tests, CFD and FEA simulations are fed into the simulator to allow drivers to 'feel' how a new front will perform on the track, how it will change the handling and grip levels and, critically, how fast it will allow them to go. An engineer at the Formula One facility said: "Brake and tyre degradation affect the performance of a car, as do the numerous other variables that are encountered when the car runs for real. "Unravelling all these variables and assessing the true performance of an upgrade is difficult and very complex. The upgrade may give a performance gain, but graining tyres and brake wear may actually show an overall slower lap time. "Using the simulator allows us to control those variables more tightly. We can give the drivers optimal tyres and brakes so we can accurately assess the true effect of a new front wing for example. "Although there may be a theoretical optimum for a front wing, we often find this puts the car on too much of a knife edge and drivers actually prefer to come away from this limit slightly to get the most out of a car. These are the kind of tests we can do in the simulator and, with testing bans at various times during the year, we are finding we can do an increasing amount of virtual simulation with the drivers." Simulator set up The simulator uses a closed off driving cell that has steering wheel, pedals and seat, all facing three screens that cover forward vision, but which also gives some peripheral vision to add a sense of what is going on around the cockpit. That cell is mounted on six actuators that allow six degrees of freedom, providing around ±25° of movement and roll, pitch and yaw acceleration of 400, 500, and 900°/s2 respectively. The steering wheel is also connected to a motor which gives force feedback to the driver. Driving experience is largely about external factors and grip is often felt through the body and seat. But the simulator shows that drivers can recognise when the back of the car steps out and when the brakes lock up. It can also give the driver a jolt when grip returns after a skid or wheel spin. The movement is provided by six electrically driven proprietary ball screws that are connected to off the shelf motors. These are folded over on the actuators and drive the ball screws via a belt. This is a fairly unusual set up. Simulators are more traditionally associated with hydraulics and pneumatics. "Most people see it as an industry animal that uses a lot of energy," says Kalff. "But, in fact, it doesn't. That is because of the efficient power electronics that we have used on it. We also use regenerative energy, so when the system goes down, that energy is stored in capacitors and when the system moves back up it is reused. It is like regenerative braking on a car; it's basically a KERS system." But setting up a simulator to get these results can be a daunting task, which is why professional race and development driver Darren Turner set up Base Performance. With extensive simulator experience as a driver, Turner is using that knowledge to help others turn simulator platforms in to development tools. He is currently working with various top level motorsport teams and vehicle manufacturers to optimise simulators so they can be used in the design and development process, and not just for driver training. "Testing and cost restrictions are pushing engineers to increasingly rely on simulators to develop and improve both vehicles and drivers," he says. "What we offer is a blueprint to quickly develop and optimise simulators into workable tools that can achieve better results."