Yank and bank, turn and burn

DN Staff

February 3, 1997

12 Min Read
Yank and bank, turn and burn

There are places where a person with no previous experience can spend fifteen-hundred bucks, climb into a primary trainer, and engage another weekend warrior in air-to-air combat--with real pilots on hand in case something goes wrong. The planes fire lasers (like the U.S. Army uses in exercises), and hits are scored on photo-receptors. This sort of diversion is not for everybody. After all, gravity kills.

MaxFlight Corp., Bayville, NJ, is applying hydraulics, motors, linear actuators, and computers to the purpose of providing the G-pulling thrill of the dogfight without the attending risks of death and dismemberment. Not simply a video game, not quite a training simulator, the VR 2000 fuses elegant mechanical systems with state-of-the-art graphics.

The result: the first multi-axis full-motion flight simulator for non-military use.

Inside the fully enclosed cockpit shell, the participant is immersed in a world of texture-mapped graphics, stereo sound, and 360-degree physical motion in the roll and pitch axes. Bystanders are treated to a display of actuated acrobatics reminiscent of Shamu, the Killer Whale.

Inside his unassuming workshop, designer, former military pilot, and President of MaxFlight, Frank McClintic, watches a breaching VR 2000 reach the apex of a loop that arcs just shy of the ceiling. It is one of two units cavorting in the building, located between the edge of the Pine Barrens and the Jersey Shore. The "pilots" are members of the MaxFlight development team, and they are hunting each other through mountain valleys in the same database. McClintic is on the verge of seeing a decade-old dream come to fruition--if only Windows 95 would cooperate.

Once over the hump, the looping pilot executes a series of rolls, levels out--and just keeps on rolling. Another programming problem. Nursing a killer cold, McClintic hangs his head, trudges over to a PC, and dives deep into the flight program.

"We developed the system software under OS/2 but we are in the process of porting to Windows 95," McClintic explains, indicating that a greater variety of relevant applications are available for Microsoft's teething operating system. "It worked better before, but we'll get it."

The gremlins are banished in a week's time and McClintic soon expects to network up to ten units via dial-up connections. So, Bronx bombers and California angels may one day tangle over a virtual Great Divide. A number of units with the earlier, shaded-polygon graphics have been sold and shipped to a Saeyang entertainment center in South Korea. In the U.S., MaxFlight has deals in the works with several major theme parks and entertainment companies.

Hold on tight. Mechanically, the VR 2000 resembles a see-saw on a swing-set frame high enough to enable one to loop over the bar, or under it. The VR 2000 performs with primarily off-the-shelf components. Looping requires the unit to be precisely balanced to avoid strain and the heavy-blanket-in-the-
washing-machine-effect pulling the unit this way and that. Prospective players are required to weigh-in on electronic scales that mercifully do not display the results graphically. System software automatically adjusts the counter-weight with an EMAL40-500 linear actuator from Duff-Norton, Charlotte, NC.

According to Duff-Norton Design Engineer Jim
Costner, his greatest concern initially about the MaxFlight application was preventing side-loads that might cause buckling of the actuator screw, which has a total travel length of 54 3/4 inches. Total load on the central shaft exceeds 600 lbs, however this is evenly distributed. "The shaft itself provides sufficient guide to avoid buckling," Costner says.

After the counter-weight hums into place, the player steps up onto the access platform. The angular cab looks like the front third of an F-117 Stealth Fighter, an effect McClintic, who designed it, intended. Appropriately painted black, the fiberglass skin is molded by Edon Corp., Horsham, PA, from a plug produced by Burns & Wohlgemuth, Bensalem, PA. "After we positioned the seat, image projectors, display screen, and control hardware, we were faced with the problem of creating a cool-looking hull around them," McClintic says. "The Stealth Fighter has that boxy-yet-lethal look."

The simulator opens up on hinges, canopy-like. The participant sits and the operator secures him into place. The harness has two shoulder straps, which presages the experience to come. Right hand grasps the joystick: a heavy-duty surplus Army helicopter model. Left hand is on the throttle. The operator lowers and latches the door, leaving the player alone with his anticipation. Eventually, an intercom system will link the player with the operator and, more importantly, with opponents, enabling the trading of taunts and insults.

Pistons raise the assembly free of the platform and high enough to provide floor clearance in a nose-up or nose-down attitude. All simulated flight motion is hydraulic, and a Rexroth hydraulic power unit from the Industrial Hydraulics Division of Mannesmann Rextoth, Bethlehem, PA, is the muscle of the operation. Berendsen Fluid Power, Rahway, NJ, a value-added-reseller of valves from Vickers Inc., Troy, MI, and Ross hydraulic motors from Parker Hannifin Corp., Greenville, TN, perform much of the component integration.

Berendsen Application Specialist Michael Riccardi says getting the feel of moving the joystick tuned to the simulator's movements was a significant design challenge. "Proportioning valves, such as the Vickers valves we work with, provide a good trade-off between cost and performance," Riccardi says. "Servo valves provide better performance and repeatability, but cost more up front and require more calibration and maintenance. Low-end frequency response valves are cheapest of all, but are not responsive enough."

Berendsen has had plenty of experience with mechanical devices for the entertainment industry. The company's credits include a mock 18th-century frigate battle at the Treasure Island casino in Las Vegas, the Lion King ride at Disney World, and the elaborate "Sunset Blvd." set on Broadway.

McClintic says the Ross motors equipped with 5.2:1 reduction gearboxes from Heco Inc., Sacramento, CA, provide the performance he was looking for with a price tag the market would allow. Roll action, initiated by moving the joystick laterally, is provided by a seven-in3 Ross motor positioned in the rear of the cockpit cab. Pitch action, initiated by pulling the stick back or pushing it forward, is enabled by a 13-in3 motor located in an enclosure off to the side. Hydraulic and electric slip rings from Hydromotion Inc., Spring City, PA, permit data to pass between motors and the controller without inhibiting motion.

For reasons of safety, the player does not control the hydraulics directly with joystick motion. Instead, a custom-written application extracts aircraft position data from the flight software, which runs on a PC under the pilot seat, and relays them to the controller: a 2-axis version of the MC-3628 3-axis servo motion controller board from Omnitech Robotics Inc., Englewood, CO. The ISA Bus-compatible board is installed in a second PC located in an enclosure off to the side. Thus, the operator can intervene at any time to stop or adjust the simulation.

The Omnitech controller interfaces with Dynapar encoders from Danaher Controls, Gurnee, IL. Each motor has its own encoder providing 50,000 lines of resolution per axis. This resolution permits nearly instantaneous response time. "You can really yank and bank," McClintic grins.

A full-throttle zoom-climb has the pilot (player is no longer an adequate description) feeling pressed back into the seat. Pushing the stick diagonally left and forward has the pilot upside down and then hanging in his harness. All loose change falls from pockets at this time and rattles around for the duration, evoking Astronaut Gus Grissom's misadventure in "The Right Stuff."

Moving in all directions. Full-motion was McClintic's goal from the very beginning. His experience with virtual flight dates back to the rocking-platform helicopter simulators he trained on for the U.S. Army in the mid-'70s. These were simply hollowed-out flight decks with instrumentation and controls mounted on tables moved by hydraulic pistons. The latter's range of motion only permitted the rather shallow nose up, nose down, and banking attitudes expected of utility helicopters moving soldiers and supplies from point A to point B. "There were no visuals," McClintic recalls. "You couldn't fly the terrain." And you could not do much in the way of aerobatics, something the Army discourages anyway.

After his military service ended in 1981, McClintic started Gateway Helicopter, a charter air taxi and maintenance operation that generated revenue ferrying New Yorkers to and from Atlantic City casinos and servicing aircraft. All the while, McClintic was ruminating over how the experience of flight could be packaged and offered to a mass-market. Ever the entrepreneur, McClintic sold his interest in Gateway (now Gateway Pace) in 1986 and devoted his full attention to developing a marketable flight simulator for entertainment.

McClintic would not compromise on full motion or flight-real graphics. So when market research showed that such capabilities would require units costing over $1 million apiece, McClintic shelved the project. By 1994, McClintic concluded that his simulator design could sell for under $100,000 each, and MaxFlight was born.

'Check your six.' Design-wise, McClintic strives to balance the goal of a realistic experience with the requirement for a shallow learning curve. The "learn-while-you-burn" philosophy may be bracing for those with plenty of time, but kiosk pilots want to climb in and start flying. The intended market is location-based entertainment centers with quick customer turn-around.

For this reason, flight controls are kept to a minimum, and even these are quite forgiving. In basic mode, the VR 2000 flies like a car, albeit one that can roll and go grille over tailpipe. More advanced settings simulate speeds up to 1,200 knots and require a defter hand on the stick.

McClintic enhanced realism with the use of texture-mapped graphics, provided by a P10 image-generator board from Primary Image Ltd., Surbiton, England. Developed with the cooperation of the UK Defense Research Agency, the P10 is compatible with the Distributed Interactive Simulation (DIS) standard for networking multiple users in the same database. At the SIGGRAPH '96 trade show in New Orleans last summer, more than 20 vendors networked their games into the same scenario using DIS.

The simulation includes an effective heads-up display for monitoring flight conditions and tracking opponents. It also has a generic "missile system" that destroys air and ground targets with equal effectiveness: the latter's demise leave big, satisfying stains on the ground that remain when you victory roll over them later. Hits cause the simulator to buck uncontrolled for a moment, and it is possible to get on the tail of an opponent and continually kick the unfortunate in the...six o'clock position.

By altering software parameters, Max-Flight developers are able to simulate flight characteristics for a wide range of fixed-wing aircraft. McClintic says his team gets plane-specific information from detailed technical sources, such as Jane's. Currently, the VR 2000 can simulate a Cessna 150, the WW II-era P-38, and modern day F-16 and F-18 fighters. More aircraft can be added according to demand.

The mechanics of the VR 2000 permit flexible, software-based alterations using the same motion hardware. Science and science-fiction versions involving space flight and submarines are under development, as is a stock racing car driving simulator.

More immediately, MaxFlight is putting the finishing touches on a two-seater VR 2002 roller-coaster simulator model. Passengers will be able to select a sequence of nine track sections featuring impossible physics. Otherwise, the unit will permit 360-degree roll and pitch motion, like its cousin. Because of the heavier loads, this unit is powered by a 38-in3 Rineer motor and hydraulic system from Rineer Hydraulics Inc., San Antonio, TX. Virtual Concepts Corp., Orlando, FL, is developing the graphics.

"Passengers will have a virtual track as a visual frame of reference, as fantastic as it may be," McClintic assures, addressing concerns about motion-sickness. "No yanking and banking, so everybody should be OK."

Controller gives realistic flight simulation

Fargo, ND--Aircraft tend to decelerate going into a maneuver. To compensate, pilots generally have to power through the move. However, most controller cards have equal acceleration and deceleration rates on a particular move profile, according to Triple Quest Manager Tom Berglind. "That's good for robotic applications, but for a flight simulator it just doesn't provide realistic movement."

Triple Quest, a builder of motion simulator amusement rides, wants to accurately recreate aircraft motion on its next-generation flight simulator. "We need a controller that lets us change the s-curve profile on the fly," says Berglind. That's why Triple Quest chose Needham, MA-based nuLogic's FlexMotion controller for its new simulator.

Two dc amplifiers power two gear box-mounted dc servo motors. The ride has 360 degrees of rotation about the x-axis, and a cable lifts the capsule about 80 degrees from horizontal with about 20 degrees of down movement.

Encoders provide position feedback to the controller. FlexMotion offers up to 10 axes of servo and stepper control in a single computer bus slot (ISA or PCI). The dual-processor controller architecture employs a Motorola 68331 real-time 32-bit CPU combined with an Analog Devices AD2111 DSP and custom FPGAs.

Motion profiles include: point-to-point; vector motion; jogging; contouring; electronic gearing; master/slave, camming; and linear, circular, helical, and spherical interpolation.

nuLogic's FlexMotion uses Infinite Trajectory Control ProcessingTM that simplifies blending complex profiles for continuous motion and provides the user with powerful, C-programmable motion commands for coordination of multi-axis control. "Although FlexMotion offers complex control, it integrated readily into the design, and its Windows-based programming made it easy to use," says Berglind.

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