A trackball is a ball sitting in a socket, resting on rollers, which the player spins with the palm of the hand. It reports movement in two directions at once and at any speed: nudge it and the cursor creeps, spin it and the cursor flies. When Atari put one on the arcade game Football in October 1978, Video Games later wrote, players “experienced the most physically involving video game ever created”. Games such as Missile Command, Centipede and Marble Madness were then designed around it, and home trackballs followed so that the conversions could be played the same way.
Fast facts
- Mechanism: a ball on two rollers, one for each axis, each turning a slotted disc read by light sensors.
- Output: movement in two directions, not position.
- In the arcade: Atari’s Football (1978) and Soccer, then Missile Command (1980), Centipede (1981), Crystal Castles (1983) and Marble Madness (1984).
- At home: Atari’s Trak-Ball (CX22 for the VCS, CX80 for the computers, CX53 for the 5200), WICO’s Command Control trackball, Coleco’s Roller Controller and Commodore’s CD 1200 for the CDTV.
- Spelling: Electronic Games noted in 1983 that “no two manufacturers seem to spell the word ‘tracball’ the same way”. Atari wrote Trak-Ball.
How it works
Atari’s service manual for its 5200 trackball takes the mechanism apart. The case holds “the roller shaft assemblies, an idler shaft assembly and a cue ball”. “When the cue ball is spun, the two roller shafts rotate. Each shaft has a slotted encoding wheel at one end which interrupts the two light sources in the optocoupler for that channel.” Each wheel produces two square waves “approximately 90° out of phase”, and the circuit tells the direction from “which clock leads the other”. The pulse rate gives the speed. It is the same principle as a spinner, used twice, one encoder for each axis.
What happens next depends on the machine it is plugged into. An arcade board can count the pulses directly. A home console has to accept them through whatever port it already has, and that took some ingenuity:
- The 5200’s joystick ports expect potentiometers, so the CX53 is, in Atari’s words, “a 2-channel D to A converter which translates optically coupled clocks into analog currents”, fed into “the two paddle line inputs used for X-Y control”. Spinning the ball speeds up or slows down the charging ramp the console measures.
- The VCS and home-computer joystick ports only understand switches. WICO’s trackball carried “its own custom microprocessor built in. So it can talk to your system in a language all its own”, and its advert promised that spinning the ball “2 revolutions per second” gave “that exact same speed on the screen”.
Arcade trackball games
Missile Command’s designers never considered anything else. “My recollection is that it was going to be a trackball from the start and it never deviated from that,” programmer Rich Adam told The Atari Book. “From the moment we implemented it, it was pretty obvious that the trackball was optimum.” Dave Theurer added that Atari was already using trackballs “in a lot of our other games at the time such as Soccer and Football”.
Centipede used a smaller one. In March 1982 Electronic Games, describing how an arcade game was made, mentioned “the mini-trackball recently introduced on Centipede”. Crystal Castles, Video Games explained in 1983, “features a trackball with a jump button on either side” to move Bentley Bear around its maze.
Marble Madness made the match literal: the player rolls a ball to roll a marble. That did not win everyone over at first. Looking back in 1995, Edge said the game “initially had a mixed reaction, primarily because of its unusual controls — like other Atari titles, Marble Madness used a trackball”.
Home trackballs
Home trackballs appeared in 1983, sold on the promise of arcade feel. A mail-order listing in Video Games in February 1983 priced the WICO Trackball Controller at $69.95. WICO’s advertising that spring called it “The Authentic Arcade Trackball” and named the arcade games it was meant for: Missile Command, Centipede and Space Invaders. It worked “with Atari, Commodore VIC-20 and 8 other popular video game and home computer systems”.
Atari’s own came in three versions. The 5200 trackball, announced for early 1983, was in Electronic Games’ words “a nifty looking piece of work that actually fits over the face of the system”, with buttons on either side of the ball. The CX22 Trak-Ball was the VCS version, and ANALOG Computing reported the CX80 in July 1983 as “a TRACKBALL controller replicating those in the arcades” for the Atari computers. Coleco’s Roller Controller for the ColecoVision was to be packaged with a version of the arcade game Slither, and TG Products sold the TB-600 for the Apple II. By June 1983 Electronic Games reckoned that trackballs had “become so ubiquitous, in fact, that even the Apple’s getting at least one.”
The idea outlived the joystick port. Commodore’s CD 1200 of 1991 was a trackball for the CDTV that doubled as the remote control: “Use the ball in the center of the controller as you would normally use the arrow keys on the CDTV remote controller.” It ran on two C batteries, or on power from the player when plugged in with its cable.
Sources
- Video Games, March 1984, p. 24: Atari’s Football and its trackball, October 1978.
- The Atari Book (Retro Gamer, 2012), p. 141: Rich Adam and Dave Theurer on choosing the trackball for Missile Command.
- Atari, CX5200 Field Service Manual, rev. 4 (1983), section 7, “CX53 Trakball”: overview (p. 7-1) and theory of operation (pp. 7-4 to 7-5).
- Electronic Games, March 1982, p. 33: the “mini-trackball” on Centipede.
- Electronic Games, April 1983, p. 73, and May 1983, p. 17: WICO trackball advertisement.
- Electronic Games, June 1983, p. 25: controller survey, including the spellings, the 5200 trackball, Coleco’s trackball with Slither and TG Products’ TB-600.
- Videogaming Illustrated, December 1982: the 5200 Trak-Ball announced for early 1983.
- Video Games, February 1983, p. 95: mail-order price of the WICO Trackball Controller.
- ANALOG Computing issue 12, July 1983: Atari’s new controllers, including the CX80.
- Antic, October 1985: price list naming the CX22 and CX80 Trak-Balls.
- Video Games, November 1983, p. 66: Crystal Castles.
- Edge issue 18, March 1995, p. 69: Marble Madness retrospective.
- Commodore, CD 1200 Trackball Controller manual (1991), English section.