Porsche 944

Shrikumar, Michael Kehr, Bob Joyce, George Beuselinck, Albert Broadfoot, Leonard Zech, Walter Spector, Pete Dillon, Marc Belanger, Ryoji Sumida, and many others have contributed to the care and feeding of the FAQ and to the authorship of the information contained within it. Some remotely-controlled devices are loosely called robots, but are more properly categorized as teleoperators since they do not operate autonomously, but only under control of a human operator. Dennis Mitsch, Jim Pasha, Michael Bremer, Clint Cummings, H. Radio-controlled teleoperators are used for such purposes as inspections, and special vehicles for disarming of bombs. Version 1.8.2
17 January 2006
The current FAQ maintainer is Kevin Gross, who can be reached at kgross@connact.com . Today radio control is used in industry for such devices as overhead cranes and switchyard locomotives. The 944 was on Car and Driver's Ten Best list from 1983 through 1985, and the Turbo made the list for 1986. The most outstanding example of remote radio control of a vehicle are the Mars Exploration Rovers such as Sojourner.

The 944 S2 is the best choice among the 944's because its gas mileage is better than the Turbo's and has considerable horsepower for a normally-aspirated engine (208hp for the US model). Instead of a "turn left" signal that is applied until the aircraft is flying in the right direction, the system sends a single instruction that says "fly to this point". During its time, the 944 S2 had the largest 4-cylinder petrol engine in the world (3.0L). Remote control military applications are typically not radio control in the direct sense, directly operating flight control surfaces and propulsion power settings, but instead take the form of instructions sent to a completely autonomous, computerized automatic pilot. Today it is actually necessary to equip the S2 with the 951 (944 Turbo) gearbox because this one is the only one with an oil cooler that is necessary through the immense torque. Advantages include bit error checking capabilities of the data stream (good for signal integrity checking) and fail-safe options including motor (if the model has a motor) throttle down and similar automatic actions based on signal loss. An additional 5640 944S2 cabriolets were produced in these years, with 2,402 being exported to the United States. More recently, high-end hobby systems using "Digital Proportional" features have come on the market that provide a computerized digital bit-stream signal to the receiving device, instead of analog type pulse modulation.

A total of at least 6,439 944S2 were made between 1989-1991, with 1,929 being exported to the United States. The relative simplicity of this system allows receivers to be small and light, and has been widely used since the early 1970s. Torque was a problem at low RPM, power curve started at 5,000 RPM to 6,800 RPM. The pulse trains representing the whole set of channels is easily decoded into separate channels at the receiver using very simple circuits such as a Johnson counter. A total of 12,936 944S were made between 1987-1988, with 8,688 being exported to the United States. The latter produces a voltage proportional to the output position which is then compared with the position commanded by the input pulse and the motor is driven until a match is obtained. "SP" designates a sport package option.. An electric motor and reduction gearbox is used to drive the output arm and a variable resistor or "potentiometer".

A different source, Jerry Sloniger's article in the October 1991 issue of Excellence indicates that the factory built 525, of which 255 were exported to markets outside Germany. Off-the-shelf servos respond directly to pulse trains of this type using integrated decoder circuits, and in response they actuate a rotating arm or lever on the top of the servo. * - Includes 1000 Turbo S
† - Includes 625 Turbo Cabriolet. The pulse is repeated in a frame of between 14 and 20 milliseconds in length. A total of 25,107 944 Turbos were made, with 14,235 being exported to the United States. In the type of system most commonly used today PWM is used, where transmitter controls change the width (duration) of the pulse for that channel between 920 µs and 2120 µs, 1520 µs being the center (neutral) position. A total of 113,070 944s were made between 1982 and 1989, with 56,921 being exported to the United States. These R/C systems made 'proportional control' possible, where the position of the control surface in the model is proportional to the position of the control stick on the transmitter.

The 968 debuted in 1992 and was sold alongside the 928 through 1995, when both models were discontinued. Typical radio control systems for radio-controlled models employ pulse width modulation (PWM) or pulse position modulation (PPM), and actuate the various control surfaces using servomechanisms. Porsche quickly rethought their plans, and shifted development from a 944 S3 to a car that would replace the 944 entirely, dubbed 968. While early control systems might have two or three channels using amplitude modulation, modern systems include 20 or more using frequency modulation. Once invested into the development process, they realized that so many parts were being changed that their "evolution" had really amassed to an almost entirely new vehicle. The mechanical resonant systems using reed relays were replaced by similar electronic ones, and the continual miniaturization of electronics allowed more signals, referred to as control channels, to be packed into the same package. In early 1990, Porsche engineers began working on what they had intended to be the third evolution of the 944, the S3. These systems were widely used until the 1960s, when the increasing use of solid state systems greatly simplified radio control.

The S2 was also available as a cabriolet, a first for the 944 line. These were typical on/off signals. The 944S2 had the same rounded nose and valence body of the Turbo model. The controller's radiotransmitter would play the different frequencies in response to the movements of a control stick. This was the only year for the 2.7 L, as this year saw the introduction of the 944S2 with a 3.0 L engine displacement which saw sales through 1991. The vibration would push on electrical contacts connected to the actuators of the control surfaces of the missile. The regular 944 displacement was increased to a 2.7 L engine. In front of the speaker were a number of small metal "fingers" with different resonant frequencies, each one tuned to vibrate when a particular tone was played in the speaker (a so called reed relay).

In 1989 the 'S' was dropped from the 944 Turbo S, and all 944 Turbos featured the 'S' package as standard. A small radio receiver was placed in the missile, the signal from the controller (transmitter) was "played" into a small speaker. Starting with the 88 model year, dual air bags became standard equipment on all 944 series. Radio control systems of this era were generally mechanical in nature. For the 87 model year, ABS anti-lock brakes became an available option. However none of these systems proved usable in practice, and the one major US effort, Project Aphrodite, proved to be far more dangerous to its users than to the target. 1988 saw the introduction of the 944 Turbo S, with 250 bhp (186 kW) and a standard limited slip differential. Both the British and US also developed radio control systems for similar tasks, in order to avoid the huge anti-aircraft batteries set up around German targets.

The 944S had a little more power thanks in part to the series' first sixteen valve engine, as well as other slight improvements. The German development teams then turned to wire guidance once they realized what was going on, but these systems were not ready for deployment until the war had already moved to France. In 1987 a "Super" version, the 944S (naturally-aspirated), was introduced while dual air-bags and an anti-lock braking system were introduced as options on the base model. Jammers were then installed on British ships, and the weapons basically "stopped working". Major engine component revisions, more than 30 in all, were made to the 951 to compensate for increased internal loads and heat. After initial overwhelming successes, the British launched a number of commando raids to collect the missile radio sets. The Turbo also featured several other revisions, such as improved aerodynamics, a strengthened gearbox, wider wheels and uprated suspension. The effectiveness of the Luftwaffe systems was greatly reduced by British efforts to jam their radio signals.

This had a turbocharged and intercooled version of the standard car's engine that produced 220 bhp (164 kW) at 6000 rpm. However by the end of the war the Luftwaffe was having similar problems attacking allied bombers, and developed a number of radio-controlled anti-aircraft missiles, none of which saw service. In 1985 Porsche introduced the 944 Turbo, a higher-performance variant, known internally as the 951. Their main effort was the development of radio-controlled missiles and glide bombs for use against shipping, a target that is otherwise both difficult and dangerous to attack. The "cookie cutter" style wheels used in the early 944s were upgraded to the new "phone dial" style wheels. Radio control was further developed during World War II, primarily by the Germans who used it in a number of missile projects. Other changes included a change in oil sump capacity, new front and rear cast aluminum control arms and semi-trailing arms, a larger fuel tank, optional heated and powered seats, revised starter, and revisions in the mounting of the transaxle to reduce noise and vibration. Nikola Tesla patented a radio-control scheme as early as 1899, and various radio-controlled ships were used for naval artillery target practice by the 1920s.

The alternator was upgraded from a 90 amp alternator to a 115 amp alternator. The possibility of radio remote control was appreciated almost as soon as the first demonstrations of radio itself; the credit for the first to suggest radio control of aircraft may belong to Patrick Young Alexander as early as 1888. The interior's ergonomics and air conditioning system was improved and the radio antenna also moved from a standard vertical position to being embedded in the windshield. . In mid-1985 the 944's underwent its first significant changes. The term is used frequently to refer to the control of model cars, boats, airplanes, and helicopters from a user-held control box (radio.) Industrial, military and scientific research all make use of radio-controlled vehicles as well. Porsche had to pay Mitsubishi a fee of $8 for every engine using this system. Radio control is the use of radio signals to remotely control another device.

The 944's engine used the patented balance shaft technology developed by Mitsubishi (as used in the 2.6 L Astron engine) to minimise vibration. Compared to the 924, the 944 had updated bodywork and many improved parts such as its engine, brakes etc. The 944 was introduced in 1982 with a 2.5 L straight-4 engine whose design was based on one half of the Porsche 928's V8 engine. .

The 944 was a huge success for Porsche throughout the 1980s, and was available in several forms throughout its evolution: 944, 944S, 944 Turbo, and the 944S2. Production ended in 1991 when it was replaced by the Porsche 968. It was introduced in 1982 to replace the Porsche 924 as their entry level model, although the two cars were sold in parallel for a number of years. The Porsche 944 was a high performance sports car produced by German auto manufacturer Porsche.

The 924/944/968 FAQ
. ISBN 0-75252-072-5. Parragon. Porsche: The Legend.

Wood, J (1997).