The joy of sticks

Legislation and cost are the only obstacles to the car of the future

When it comes to electronic innovation in cars there are two arguments. Either smart technology is divorcing us from reality, cocooning us in our vehicles and deadening our instincts, or, it is enabling us to react more quickly to unforeseen situations, and thereby actually enhancing our interaction with the surface of the road.

Whatever side of the fence you reside on, progress is inevitable, and the recent findings of researchers at Daimler Chrysler illustrate how compelling the arguments are for this next generation of vehicles.

The idea of replacing car steering wheel and pedals with a joystick is not new – Jaguar’s PROMETHEUS project looked into exactly the same thing. However, Daimler-Chrysler’s engineers have taken this notion one step further, and demonstrated its feasibility by building dual `force-feedback’ sidesticks into a simulator.

The `joystick’ is the tip of the iceberg – the front end of this `drive-by-wire’ technology with control of acceleration, braking and steering by computer logic. Engineers have so far invested around 10 years in developing the technology in a simulator based on the Mercedes-Benz SL roadster.

The simulator is equipped with two sidesticks coupled by logic. One is in the central console, the other in the armrest of the driver’s door and the driver can use them together or independently.

Built by Fokker Control Systems, the sidesticks are active in the transverse axis and isometric in the longitudinal axis. This means that they can only be deflected left and right for steering, while acceleration and braking is proportional to the force exerted in either pressing forward or pulling back on the stick. The absence of forward-backward motion of the stick allows the clear separation of steering, acceleration and braking, resulting in increased steering accuracy.

If the driver doesn’t push or pull on the sidestick, the car maintains a constant speed. Cruise control is automatic, and when the vehicle is at rest the brakes are automatically applied until the next acceleration. Features like the indicator and horn are activated by push buttons and triggers mounted on the sidestick.

The sidestick differs from a steering wheel mainly in terms of rotation. When a steering wheel is turned, the rotation is reduced by a ratio of 1:20, allowing precise movement. However, sidesticks can only deflect around 20 degrees to the left and right, and transmitting this motion directly to the wheels would make the vehicle undrivable at speed.

Thus, it is the force exerted on the stick, and not the deflection of the stick, that is measured.

Like many of the force feedback devices currently under development around the world the sidestick provides sensory feedback. For example, the force required to move the steering wheel when a car is standing on ice is minimal whilst significant resistance is encountered if the wheel is against a curb.

The control electronics evaluate the steering command and determine the desired steering angle dependent on the current driving situation.

The actual steering movement of the wheels is measured by sensors and signalled to the driver as a displacement of the sidesticks. This steering angle is translated into the actual steering angle by another electronic control unit. The sidestick mechatronics translates the signal into a proportional deflection of the stick-grip, meaning that the driver `feels’ the resistance.

The elimination of the steering wheel and pedal cluster and the resultant freedom of positioning for the driver open up a range of possibilities in cockpit design.

Drivers only have to reach the sticks, allowing greater freedom of positioning making it unnecessary, for example, for short-legged people to sit close to the steering wheel and and providing a greater safety buffer.

The lack of steering wheel also improves access to the vehicle and allows more space for controls and displays. It’s also thought that the use of drive-by-wire technology could dispense with the major structural differences between right-hand and left-hand drive vehicles.

Other benefits of the technology relate to `Active safety’. Conventional cars respond to commands given via the steering wheel and pedals, but in critical situations new technology offers enhanced safety through intelligent support systems like ABS.

To illustrate, in crosswind tests. a conventional car hit by a gust of crosswind often deviates considerably – it takes time for the driver to respond. However, with drive-by-wire, wheel sensors sense the deviation, compare it to the position of the sidesticks, and adjust the steering to compensate: all this in a split-second.

Studies also show that drivers take around 0.2 seconds to move their foot from the accelerator to the brake. At 30mph, this adds 3m to the braking distance, and it’s thought that by speeding braking reaction the number of rear-end collisions could be reduced.

We all behave uncharacteristically behind the wheel from time to time, and the company has also developed a filter function that instantaneously evaluates all commands given by the driver. Inappropriate commands, like excessive steering, are corrected by the control logic.

Clearly, drive-by-wire systems must be fail-safe. This requires redundancy of systems, and making this affordable is a major challenge. The Fokker sidestick has 3-fold redundancy of force sensors and dual redundancy of displacement sensors, but redundancy is also required in the data bus, control logic, sensors and actuators. As drive-by-wire requires power to operate, clearly the vehicle power system must also be fail-safe, generating power whenever the vehicle is in motion.

Tests carried out in DaimlerChrysler’s simulator to gather data on the learnability and safety of sidesticks yielded interesting results.

The tests were conducted with two groups of 17-year-olds, none of whom had significant driving experience. One group learned to drive with sidesticks, and the other with conventional controls. The two groups were set identical tasks including driving on an open road, stopping at lights and reacting to critical situations.

There was no significant difference in the speed with which students learned to drive using either method, but subjects using conventional controls demonstrated a tendency toward sequential control of steering and braking whilst sidestick users tended to control things simultaneously. To illustrate: 8 of the 32 test drivers using conventional controls would – in the real world – have been involved in accidents resulting from slow control response. Under the same conditions, not one sidestick driver had a problem.

Daimler-Chrysler’s engineers are confident that the concept will take off. The main obstacles are, they say, cost and acceptance, although, unsurprisingly, the notion of driving with sidesticks has proved exceptionally popular amongst youngsters.

However, before they hit the streets, the sidesticks are most likely to appear on specialist vehicles such as those used by road sweepers or foresters.

Daimler Chrysler Tel: +49 711 17 93271

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