Virtual horse gives riding a kick

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High-tech horse
The movement of the horse simulator at the French National Equestrian School is derived from the action of six SKF linear actuators with roller screws. The actuators link a triangular plate on the floor to another triangle offset by 60 degrees that is fixed under the horse’s body. Each “leg”‘ is propelled by an SKF linear actuator driven by planetary roller screws via an electric motor. A linear potentiometer regulates the precision of the movements.
Controlled by a computer, the arrangement can accurately recreate any movement a horse can make. “It’s a classic arrangement for simulators, only miniaturised. For us, the problem was how to make it small enough to fit under something the size of an actual horse,” comments Jean-Louis Jouffroy, who headed the project to build the horse simulator.
With up to 90 kg on its back, the simulator’s six roller screws are subjected to considerable mechanical strain. But the system has proved itself to require very little maintenance. In eight years of operation at the National Equestrian School, only one electric motor has had to be changed. “We tighten the nuts and bolts at the start of the year, and that’s it,” says Patrick Galloux, head of the research department at the school. The SKF roller screws have proved to be 100 percent reliable and have never required any maintenance despite the heavy demands placed on them.

With Persival II in the stable, riding practice will never be the same again. Persival is a sophisticated horse simulator.The French National Equestrian School, home to the celebrated Cadre Noire display team, is an impressive institution. Set in the countryside near Saumur in the Loire valley, the school provides top-class training facilities for France’s national jumping and eventing teams. It offers four-star accommodation to some 400 horses, which are kept in state-of-the-art stables with automatic feeding systems, mechanical manure extraction and even sun lamps to dry them off after their showers.
But the school is also home to a stranger beast. Behind a door marked “virtual obstacle jump” stands Persival II, a sophisticated horse simulator. The size and shape of a real horse and clad with a conventional saddle, Persival II can accurately imitate the entire range of a horse’s movements, including jumps.
The name “Persival” is an abbreviation of “Programme de Recherche de Simulation du Cheval,” which translates to Research Programme on Horse Simulation.
The development of the horse is a tale of enthusiasm and technical perseverance. The idea was hatched by Jean-Louis Jouffroy, a former French air force pilot with a passion for riding horses. In the mid-1980s, he suggested to Col. Pierre Durand, then head of the Cadre Noire, that a simulator might offer new possibilities for rider training.
Jouffroy says reaction to the idea among the very traditional equestrian community was at first sceptical. “People said it was technically and economically impossible, and also psychologically unacceptable for riders,” he recalls. ” `We’ve learnt with real horses for 2,000 years,’ they said, `so why change?’”

Electric propulsion
Undeterred, Jouffroy created the Persival Association and set about seeking funding for the project and finding technical solutions to meet the challenge of creating the world’s first mechanical horse.
A competition was organised by the National Robotics Committee and development was started in 1986. The technical development was done in conjunction with the National Civil Aviation School in Toulouse. The school was an obvious choice, since the horse uses technology that is very similar to flight simulators, although on a much-reduced scale. “If we hadn’t had the aeronautic school’s involvement, we could never have done what we did,” Jouffroy acknowledges.
Jouffroy’s team was faced with a choice between hydraulic or electric propulsion for the horse’s “legs.” “We decided that electric propulsion offered better precision of movement and could better withstand the permanent acceleration and deceleration of the repetitive up and down movements,” says Jouffroy. The team chose a system using SKF linear actuators with roller screws, driven by electric motors.
Finding a system to reproduce animal locomotion was only part of the challenge; the designers also had to know precisely which movements had to be recreated. To calibrate this, accelerometric receptors were attached to the saddle of a real horse. Measurements were taken, and the results were fed into a computer. “At the time, there were no data available on what either the horse or the rider does when riding. We put captors on the reins, stirrups and saddle and analysed the movements. Surprisingly, it gave extremely useful readings,” Jouffroy recounts.
A prototype was produced a following year. The results were better than expected, and Persival I was presented at the Paris horse fair in 1987. Two more examples were developed over the next few years, and in 1993 the simulator was linked to a visual simulation to provide a virtual image of a jumping or racing course.

Persival II
The Persival II version stands in front of a screen, and the computer-generated image is provided by an overhead projector. Alternatively, the rider can wear a visor on which the image is projected. The sound of hooves completes the realistic effect.
Persival II can walk, trot or gallop and can be programmed to imitate difficult characteristics such as a trot with a lateral gait. For the jump course, the simulator “canters” up to the fences before lurching upward to take the fence and then dipping forward exactly as a real horse does on landing. It can be programmed to simulate a sequence of up to three consecutive fences, which requires great precision on the part of the rider.
The simulator can run in two modes: automatic or interactive. In the automatic mode it negotiates the course automatically and the rider must learn the correct movements to follow it. In the interactive mode the simulator takes instructions from the rider via the horse sensors in the reins, on the horse’s flank and under the saddle.
Today, Persival II has become a valuable asset for the National Equestrian School. The school uses the simulator as part of its selection process for riders, since it gives an objective view of a rider’s ability without a particular horse’s character playing a part. It is also used for warm-up and rectification of specific problems. For example, Persival II can be programmed to simulate a horse refusing a jump. “Learning to ride horses is about repetition, but it’s difficult to make a horse repeat exactly the same action,” says Patrick Galloux, head of the research department at the school and a former member of the French national three-day eventing squad. “Horseback riding is a sport in which a badly executed move can result in damage to the `equipment.’ If a javelin thrower makes a poor throw, he just goes and picks up the javelin again. A bad manoeuvre with a horse can be serious. The simulator allows us to practise repetitive actions with no risk of fatigue or injury.”
The sessions are very intense: 10 minutes on the simulator is equivalent to about an hour on a horse. Galloux says the simulator also allows better communication between pupil and instructor, since the instructor can stand right alongside. “Mentalities are changing, and there is an increasing demand for simulators,” he says. “At first people found it strange, but now they’re getting used to it. For example, it helps children gain confidence as they move up to a gallop.” The school also has a simulator adapted for vaulting, which can “canter” at various speeds while the pupil masters the acrobatic moves.
So far, only about a dozen simulators are in use, including one in the horse-racing school at Chantilly and one in the French officers’ academy of St. Cyr. A range of more basic models offering a limited range of movements has been developed at prices accessible to equestrian schools. However, the very limited production means the simulators remain expensive. The most basic model costs about 60,000 francs (about US$10,000).
“We’re working on a new generation,” says Jouffroy. “We want to produce a range of products for specific disciplines. For instance, we’d like to develop a model for polo riders for the Middle East market.” The Persival Association is planning to develop a simulator at about 30,000 francs (US$5,000), and production could then run to about 100 units a year. “The challenge now is how can we transform this technical success into a commercial success.”

Charles Masters
a business journalist based in Paris
photos Alastair Miller




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