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Trivially you can prevent rocking with many vehicle by eliminating the suspension. But is it possible to allow a floaty suspension that glides over potholes, without also having to rock back and forth, with some kind of stabilization? I know that it's possible in buildings, but having a fixed platform really helps.

I ask because the rocking motion is one of the primary sources of carsickness, and a bus trip this evening left me feeling rather queasy. This seems like something that could be improved, especially in such expensive vehicles.

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There are in fact cars available with this type of feature. For example, the Mercedes S class is scanning the road ahead to counter imperfections in the road with its active suspension: https://en.wikipedia.org/wiki/Active_Body_Control#Magic_Body_Control

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  • $\begingroup$ This probably more for comfort than safety. A passenger car will generally spin out of control before it rolls over. The problem with buses and HGVs is their high centre of gravity, making them more prone to rolling over. $\endgroup$ – am304 Jun 18 '15 at 14:39
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    $\begingroup$ @am304: Yes, that's for comfort. As I understood the OPs question, he was asking about comfort, not about safety. :) $\endgroup$ – Daniel Hilgarth Jun 18 '15 at 14:45
  • $\begingroup$ That's pretty cool, I wonder if they'll ever use it on their buses or other large vehicles. We'll just have to see! $\endgroup$ – SilverbackNet Jun 22 '15 at 21:47
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You could have active suspensions, which could keep the vehicle level or even roll it into the corner (see for example this PhD thesis), but they are typically prohibitively expensive and not feasible in practice.

Semi-active suspensions, which can lock the anti-roll bar solid just ahead of a turn, are sometimes a good compromise between performance and feasibility.

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The Citroën Xantia Activa was one of the earliest mass production active suspension vehicles I know of.

Activa active anti-roll bars

In 1994, the Activa technology was introduced, which is an extension to the Hydractive II suspension, where two additional spheres and two hydraulic cylinders are used together with computer control to eliminate body roll completely. This technology is more broadly known as active suspension, and the Xantia Activa has exceptional road holding comparable to true sports cars. It employs active anti-roll bars.

In the Swedish magazine Teknikens Värld's moose test the 1999 model of Xantia V6 Activa still holds the record speed through the manoeuvre - faster than the Porsche 996 GT2.

UK Models of the Activa came fitted with a XU10 2 litre turbocharged engine also fitted to the Citroën XM 2.0CT and Peugeot 605 SRi. It produced 150 bhp and 171 lb ft of torque and was a 'low-blow' type for smooth power delivery rather than outright bhp.

So it's very possible to create a flat platform.

Anecdotally, friends as kids used to get car sick more often in Citroën cars with hydraulic suspension than normally sprung cars, my guess is that the ride makes you feel sea sick.

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Active suspensions have been around for 15-20 years in motorsport, so F1 and other regulated events have strict rules on what is and isn't allowed. It's fairly well understood. That said, it's understood well enough that the cost/benefit hasn't really worked out for production vehicles.

The problem isn't just the initial cost, it's also maintenance and robustness. Whatever actuators you use, they need to be in the wheel well, and that's a hellish tough environment. You also need sensors to check distance from the road (typically on the four corners of the vehicle), and again the underside of the vehicle is a tough place to live. It's OK on the track, but when you add all the mud, stones, water and small furry animals that appear on the road, vulnerable things show that they're vulnerable. If your kit isn't 99% sure to survive past the manufacturer's warranty, the manufacturer isn't going to go for it.

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