Tech Briefs
Stick or non-stick?

DaimlerChrysler's sidestick employs an integrated dc motor to provide a realistic feel of steering resistance. The drive-by-wire system consists of sensors and control elements connected by a redundant databus (yellow). Steering with sidesticks.

DaimlerChrysler calls it "The new Cockpit Controls Project" and the use of the word "cockpit" in a vehicle sense is, for once, entirely appropriate. For this is all about sidestick controllers, something the aerospace industry has had for many years. DaimlerChrysler initially built a Mercedes-Benz SL-based sidestick demonstrator to test the technology and the feasibility of abandoning the steering wheel. The company says the technology is now doable, with multiple benefits.

"The two key inhibitors are cost and acceptance," said Ulrich Hipp, a senior member of DaimlerChrysler's Automobile Vehicle Concepts unit. "As one might expect, the acceptance of sidesticks is greater among young people and high-tech fans. The initial use of sidesticks in production is most likely to be in special applications, such as forestry and road sweeping vehicles, and in small-volume, high-prestige niche markets. There are no current plans for broad application of the technology to large series. Current regulations require steering to be mechanical; for this reason, drive-by-wire vehicles are not 'roadworthy.' So, in addition to the development work required to make the systems totally reliable and affordable, action will be required to amend legislation."

Sidesticks, he explained, represent an element of drive-by-wire — the control of acceleration, braking, and steering by computer logic — and DaimlerChrysler teams have spent about 10 years working on the concept. Sidestick control dispenses not only with the steering wheel but also with the pedals. Fokker Controls built the first generation of sidesticks and was also responsible for the Mercedes demonstrator. The sticks have right and left deflection for steering but are isometric in longitudinal axis. The system contains a 2-D force sensor that reacts to forward or backward hand pressure, registering commands to accelerate or brake. Indicator and horn operations are also on the sidestick. Automatic transmission selection is via dashboard-mounted buttons. The demonstrator has a sidestick in the central console and another in the armrest of the driver's door, coupled by logic.

As speed rises, the sensitivity of the stick decreases to avoid over-control inputs. The Fokker Control Systems sidestick has a three-fold redundancy of force sensors and dual redundancy of replacement sensors. "Redundancy is also required in the databus, control logic, sensors, and actuators," said Hipp.

Essential to such a system for production cars is ease of human adaptability. So the DaimlerChrysler simulator in Berlin was used in trials. The tests were conducted with two groups of 17-year-olds. Although some of the participants had experience with joysticks (for example, from computer games) none had significant driving experience. One group learned to drive with sidesticks, another group with conventional controls. Two hours into the trial, each group was given identical driving tasks that involved driving on the road, stopping and starting at traffic lights, freeway driving with lane changes, overtaking, driving in crosswinds, maintaining a set distance from a leading car, and reaction to critical situations. Participants had no problem driving with sidesticks and there was "no significant difference" in the speed at which students learned to drive using sidesticks or conventional controls.

According to DaimlerChrysler, the people who used conventional controls demonstrated a tendency toward sequential control of steering and braking. Sidestick users, on the other hand, tended to control steering and braking simultaneously. This was reflected in responses to critical situations: eight of the 32 test drivers using conventional controls would — in the real world — have been involved in accidents resulting from slow control response, for example braking and/or swerving to avoid a collision. Under the same conditions not one sidestick driver had a problem. These initial simulation tests suggest that control via sidesticks is not inferior to conventional control with regard to functional capability, handling, safety, and driving comfort. In fact, the company says the opposite is true: because the steering ratio and steering forces are variable and can be adapted to the driving situation, the wheels can be turned faster and easier using sidesticks than with a steering wheel, such as when parking or maneuvering.

Stuart Birch