An ordinary home-computer joystick knows only which way it is pushed. A flight stick knows how far. Pull it back gently and the aircraft on screen lifts its nose gently; haul it into your lap and the nose comes up hard. That difference is why people who flew simulators on home computers, and above all on the IBM PC, bought separate sticks shaped like the ones in real cockpits, and why a small industry grew up to sell them throttles, rudder pedals and, by the mid-1990s, sticks that fought back.
Fast facts
- What it measures: the stick’s position along two axes, often with a throttle as a third and a twist or rudder pedals as a fourth.
- On the PC: read through IBM’s game control adapter at I/O address hex 201, by timing how long a resistor takes to charge a circuit.
- Early dedicated stick: CH Products’ Flightstick, reported as new in November 1987, $79.95 for the IBM PC.
- Cockpit replicas: Thrustmaster’s Flight Control System (stick) and Weapons Control System (throttle), on sale by 1991.
- Optical sensing: the RC Simulations Free Flight (reviewed 1992) and Microsoft’s SideWinder 3D Pro (1996) measured position with light rather than potentiometers.
- Force feedback: CH Products’ Force FX, due to ship in late September 1996, and Microsoft’s SideWinder Force Feedback Pro in 1997.
How the PC reads a stick
A flight stick measures position with potentiometers, variable resistors like a volume knob, one for each axis. Edge explained the principle in 1996: the potentiometer “changes the amount of current running from the stick to the computer, enabling the computer to know exactly how far and in what direction the joystick has been moved.” The paddle controllers of the 1970s were the same idea with one axis.
IBM’s game control adapter, a plug-in card for the PC, turned those resistances into timings. IBM’s technical reference describes four resistive inputs, each expecting 0 to 100 kilohms, and four button inputs, all read with a single IN from address hex 201. A program starts a measurement by writing anything to that address. That fires four timing circuits at once, and the low four bits of the port go high together. Each bit then drops back to 0 after a time that depends on its resistance. The PCjr’s technical reference gives the formula as 24.2 microseconds plus 0.011 microseconds per ohm, so a stick at the far end of its 100-kilohm travel holds its bit high for about 1.1 milliseconds.
The adapter hands back a pulse, not a number. To find the stick’s position, a program has to sit in a loop reading port hex 201 and counting until each bit falls. Two things follow from that:
- It costs processor time. The loop runs for up to a millisecond or so on every reading, and a game has to read the stick again and again. Edge reported in 1996 that “up to 17% of the CPU’s processor power must be dedicated to continuously checking the state of the joystick.”
- The numbers are not fixed. The count depends on how fast the loop runs as well as on the resistor, and on the tolerance of the parts in each stick. PC games asked players to calibrate. PC Review’s 1992 guide to PC joysticks described the “joystick calibration screen, called up when you select joystick control for the game”, and explained that it, and the stick’s trim controls, stop “the joystick from favouring a certain direction when left in neutral”, something that “can cause all sorts of problems when your biplane suddenly starts diving for no apparent reason.”
Most PCs had no joystick port at all. The same PC Review guide opened with that fact and walked readers through opening the case to fit a “game card”. The adapter’s four axes and four buttons also set the limits of what a stick could offer: CH Products’ Flightstick for the IBM PC used its thumbwheel as a throttle on an extra axis, “eliminating the need for a second joystick”, in Computer Gaming World’s words.
Sticks for pilots
CH Products’ Flightstick appeared in Computer Gaming World in November 1987 as a “new” stick for players of Flight Simulator, Jet and Chuck Yeager’s Advanced Flight Trainer, at $74.95 for the Apple II and $79.95 for the IBM PC. By 1992 PC Review called it “possibly one of the most favoured flight simulator joysticks around”, with two buttons on the top of the shaft and its own throttle wheel.
Thrustmaster went further and copied the cockpit. Its Flight Control System was “shaped like a standard cockpit joystick, with buttons sticking out at every conceivable angle”, and its Weapons Control System was a throttle, “a replica of a full-size HOTAS (Hands On Throttle And Stick)”, that handled landing gear, chaff and flares as well as speed. The name describes the aim: functions a player would otherwise reach for on the keyboard sit under the fingers on the stick and throttle. By mid-1991 both units were advertised in Computer Gaming World at $89 each. PC Review’s Paul Presley liked the “in-cockpit feeling” but not the construction: the sticks were set up for particular games with ten dip switches, so “with only 10 switches, the sticks are only compatible with 10 games”, and their small bases went “skidding across the desk with the greatest of ease”.
Light instead of resistance
Some makers dropped potentiometers altogether. PC Review in 1992 described RC Simulations’ Free Flight, “an over-sized joystick without a base” that used “optical sensors to precisely measure the joystick’s angular movement”. Microsoft followed in 1996 with the SideWinder 3D Pro. Edge reported that Microsoft had “removed the gears, resistors, and potentiometers (think of them as volume knobs) used by ThrustMaster and CH Products, and replaced them with a light emitting diode (LED) optical system. Tiny photosensors, placed in the base of the SideWinder 3D Pro, track the position of an LED on the bottom of the joystick.” The stick also twisted, doing some of the work of rudder pedals, and had a throttle lever. According to Microsoft, the optical system was “both faster and more dependable than potentiometers”, and let the stick work in analogue or digital modes “without the processor overhead” of a true analogue stick.
Sticks that push back
In August 1996 Edge reported Immersion Corporation’s prototype force feedback joystick, whose motors let the computer “command forces to the joystick handle”, and said at least one major PC joystick maker planned to have one “on shelves by the end of 1996”. CH Products had one ready that autumn. Computer Gaming World flew Fighter Duel with a prototype of CH’s Force FX and reported in November 1996 that it was due to ship in late September, with gears and motors in place of the usual gimbal, “simulating bumps, jolts, vibration, and resistance.” Microsoft’s SideWinder Force Feedback Pro, reviewed by the same magazine in November 1997, was a second-generation design; the review named CH’s Force FX as its “first-generation predecessor”. The force feedback entry covers the technique across other controllers.
Consoles and later sticks
Console makers built analogue sticks too. Edge’s 1996 survey of controllers pictured Sega’s analogue flight stick for the Saturn, and Sony’s first PlayStation analogue pad, the Dual Analog, had a mode that imitated Sony’s earlier analogue joystick. On the PC, flight sticks and throttles kept developing: in 2004 Edge described Saitek’s X52 “flight control system” as the company’s “latest innovative PC peripheral”.
Sources
- IBM, Technical Reference: Personal Computer XT (IBM, part 1502234), “IBM Game Control Adapter”, pp. 1-211 to 1-216: the resistive and digital inputs, the
INandOUTat hex 201, the 0 to 100 kilohm range and the timed pulse. - IBM, PCjr Technical Reference, “Games Interface”, p. 2-119: the pulse formula, 24.2 µs plus 0.011 µs per ohm.
- Computer Gaming World issue 41, November 1987, “A Flightstick of Angles”: CH Products’ new Flightstick, prices and thumbwheel throttle.
- Computer Gaming World issue 44, February 1988: the Flightstick, “We like it.”
- Computer Gaming World issue 83, June 1991: advertisement listing Thrustmaster’s Weapons Control System and Flight Control System at $89 each.
- PC Review issue 10, August 1992, Paul Presley, “Joysticks and game ports”: game cards, calibration and trim, the Flightstick, Thrustmaster’s FCS and WCS, HOTAS and the Free Flight optical stick.
- Edge issue 35, August 1996, “Joypads” feature (from p. 50): potentiometers, the 17% processor figure, the SideWinder 3D Pro’s optical system, Immersion’s force feedback prototype, and Sega’s Saturn analogue stick.
- Computer Gaming World issue 148, November 1996, Denny Atkin: CH Products’ Force FX.
- Computer Gaming World issue 160, November 1997, Denny Atkin: review of the Microsoft SideWinder Force Feedback Pro.
- Edge issue 139, August 2004: the Saitek X52.
- psx-spx, “Controllers and Memory Cards” (web, secondary), and Wikipedia, “Dual Analog Controller” (web, secondary): the Dual Analog’s green-LED mode imitating Sony’s analogue joystick. https://psx-spx.consoledev.net/controllersandmemorycards/