MOTION-BASED SIMULATION
Force Dynamics 401CR simulator can revolve continuously in either direction
limits; gains; slew rates; rate limiters; band widths; filters. But you have to start with an understanding of how the brain works and what information it needs.’ Kalff points out that such
complexity is not cheap. ‘We don’t make games. The equipment we make is what they need to do what they want to do, and that costs money.’ A Cruden motion platform as used for entertainment, for example, starts at around 100,000 euros (£87,750 / $141,450), and the image projection required by some motorsport teams costs at least another 100,000 euros.
professional motorsport, rather than just a game platform, things become much more complex. ‘Racing drivers don’t like large amounts of pitch or roll,’ reveals Kalff. ‘They are very susceptible to any change of acceleration and all have a very low threshold for influences on their body. For instance, if you consider a chicane. Using g-tilt, he does not feel the g force on his body, he feels the platform tilting sideways, backwards or forwards. They pick that up very quickly and say, “I don’t want this. You are tilting my head all over the place.” So we cannot use that to the degree we would use it in entertainment, or at shows where the non-professionals that sample our technology don’t have that threshold. ‘So you need the yaw. You need a slight amount of roll – just two or three degrees. I know that sounds like very little, but to these drivers it’s everything. It’s often small movements, but if you don’t have them they don’t have enough cues to judge what they’re doing. It’s the change in the direction and, if you don’t have all the six inputs, you cannot fool the brain well enough to make the drivers feel it’s realistic.’
The Hexatech platform’s
flight simulator heritage has led some to question whether it can handle the high-frequency inputs generated by a racecar model. But Kalff is adamant that it can. ‘The output of vehicle models from automotive and motorsport teams is around the 17-18Hz mark. Our standard system can handle that as it goes up to 20Hz, but our bespoke professional systems can go up to 40-60Hz.
‘The visual input is always going to be your limiting cue. We
FORCE DYNAMICS ‘What is the difficulty of driving a racecar?’ asks David Wiernicki of Force Dynamics. ‘The thing is to get it to point in the right direction. Everything you feel about what the car is doing is around that. The rotation of the car is going to tell you more than anything else.’ This is the philosophy that underpins the company’s motion-based simulator design. It puts rotation at the top of the functionality hierarchy. The company was established in the 1970s to build bespoke automated systems, mostly for manufacturing. ‘That gave us lots of experience with motion control,’ says Wiernicki. But when that type of work started to drift away from the company’s US home territory, its directors started to diversify. Its founders
Regardless of how
mathematically correct a system seems, unless it engages the driver, it’s not going to work
still have TVs that run at 60Hz, so it takes 1/60th of a second to draw a new image. If you don’t change the image, but you do change your motion base you get motion sickness.’ Kalff notes that this is a fast developing science. ‘There is a vast amount of parameters you can change:
34
www.racecar-engineering.com • September 2011
were enthusiastic racers, so the link with racecar simulation came naturally. The first simulator, the 301,
was a three-degrees-of-motion platform. Mounted on three legs it could rotate around longitudinal and lateral axis and heave. Trying to come up with a fourth
degree of freedom, the company mounted this on a turntable that could give +/-90 degrees, much more than the 20 degrees or so found on other motion- based simulators. ‘We got in and thought, holy shit,’ says Wiernicki, ‘it was absolutely amazing. You could learn to correlate side forces. It made the car live.’ Impressed with the success
of this, they have now made the 401CR (CR for continuous rotation), which can revolve continuously in either direction. ‘With a small yaw angle, by definition the simulator has to keep returning to its centre position,’ explains Wiernicki. ‘With a small excursion angle – say, +/- 20 degrees – this has to happen quite rapidly. So what happens is that by definition the simulator is turning the wrong way half the time. No matter how subtle your washout is, you either have to ‘crush’ the motion output so much that you’re getting only a small percentage of the real movements, or turn up the speed of the washout so much that you can feel the deltas as the machine changes direction. ‘People will swear you don’t
need a large excursion angle, but our experience is different. Where you would expect it to work or not work is oval racing and we got some good feedback from Stock Car drivers. Also from World Rally level drivers who drove it with yaw. As soon as I turned it off they went off the road instantly.’ Originally, the target
market was entertainment, but the company has found a growing demand for simulation applications. Force Dynamics does not write its own simulation, so the machine is designed to work with other company’s products. By keeping it simple, they have produced a device that is both very responsive and cost effective. According to Wiernicki, response times are down to 10ms and prices start at $85,000 (£52,700) for the continuous rotation machine or $65,000 (£40,300) for the 90-degree yaw version.
The simplicity also makes
it compact so it can be moved around on a standard fork lift
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