The Mantis roller coaster jerks you up a steep hill, grinding and creaking toward an even steeper plunge. At the crest, you rush down the incline, 60 miles an hour, and screams blast through the air. You swing around a curve, around another, up, down, then upside down. You are dizzy, you swing around and around again -- and then, slowly, you creak to a halting stop and take a deep breath.

All from an unassuming warehouse in Sterling.

There, Ron Borta and his wife, Leslie Davis, are building a company that is building a roller coaster simulator -- soon to be a $3 arcade ride that one reporter can attest will leave you with a good two hours of slight queasiness.

"Kids love it. I knew we'd done it right when I let two 17-year-old boys test it," Borta said. "They said it was `awesome.' "

Borta is like a kid himself, immersed in this project and obviously loving it. An engineer who has made millions of dollars several times over on software inventions -- mostly home video games -- he delights in making things smaller, faster, cheaper.

This time, he has set his sights on motion platforms, the mechanical bases that make flight simulators soar and arcade rides gyrate. He started the business, Ronbotics, when he figured out a way to mass-produce motion platforms for far less money than anything on the market. He thought he would sell them to arcade game manufacturers and the military, but he ended up making his own arcade game, too.

"Mechanical stuff always came easily to me," he said.

It seems like no big deal, really, walking around the plant with Borta and his wife. They explain things with a cool reserve. It all seems organized and fairly simple. They're not beating the drums and calling the crowds.

But the math behind Ronbotics suggests a potential for pay dirt. Borta willingly shares the numbers, obviously confident that what he has created could not be duplicated by anyone else. The brains of it are in his head and encrypted in software.

The cheapest full-motion arcade game costs about $80,000, a price most of the 300,000 arcades in the country can't afford. Ronbotics sells its Coaster Rider -- a stationary gondola that sends people up and down and around six of the nation's best roller coasters -- for $17,000.

The company already has orders for 1,200 of them, before the first one has even been delivered. He's expecting to sell 13,000 of them a year by 2002.

That alone would be $221 million in sales, but what's really striking is the margins: It costs just $3,500 to make each one. So for 13,000 sold, that's roughly $175 million gross profit. And the gondola can easily be adapted to other motion games with other software, Borta said. New video, a new soundtrack, new motion -- and a lot more profit.

The motion platforms also are a moneymaker. Ronbotics will sell them for $3,500 apiece, but they only cost about $800 to make. Borta figures within two years, he'll be selling about 100,000 each year. That would be another $350 million in sales.

The demand for Ronbotics' products is, indeed, huge. Motion rides are the rage right now, which is why the company has been featured prominently in several of the industry's biggest trade journals, touting the revolution Ronbotics has brought to motion games.

Soon, the company hopes to move from its 30,000-square-foot space to a 100,000-square-foot factory near Leesburg that is better suited to mass production. Ronbotics employs 26 people now, and eventually expects to employ 40.

On the subject of money and the potential behind his invention, Borta reveals his scorn for the way most people seem to be making money these days -- not by making things.

"We're going to do something different here," he says, referring to the many dot-coms with millions from the stock market but huge losses. "We're going to be the first company in Northern Virginia to go public based on profitability."

How did Borta, 46, get here? It took a circuitous route through many other companies, a considerable talent for electronics and mechanics, and, perhaps most importantly, his eventual union with a woman who channels his work into something marketable and organized.

Davis, 36, is president and chief operating officer. Borta is chief technical officer. Outwardly, they share a friendly, if quiet, disposition. But the differences between them are fundamental.

They had known each other for six years, first as colleagues at the same company, before they decided to get married seven years ago. "I had to decide if I could live with him," she says. (They both laugh.)

Borta started his first company when he was 21, writing software for companies like IBM and Microsoft. Of 18 employees, he was the oldest, and they made a lot of money very quickly.

"We were just kids, and we argued about money all the time," he said. So everyone went off to start their own companies.

Borta's next project was a company called Roklan, also a software developer. His first project was creating a version of Pac Man for the home video market. He was paid $25,000. It sold more than $1 billion dollars worth.

So for his second big project, Donkey Kong (remember that?), he asked for 10 percent of sales. That's how he made his first million.

He tried to retire, but even after building a 35-foot wood bridge on his property, he got bored. So he went to work at an interactive television company in Chicago, where he met Davis, who worked in customer service. They eventually started dating and moved together to the Washington area, settling in different suburbs.

Soon they were working together again for a government contractor and then for TVAnswer, an interactive television company that later became Eon.

"They had more vice presidents than any place I'd ever worked in my entire life," Borta said.

Finally, Borta and Davis got married, left Eon and started their own software company, Borta Inc., in their Sterling dining room in 1993. Davis ran the business, Borta did the programming, and soon they had six employees, some of whom lived in.

They moved to nearby offices and had, at one point, 40 employees. But still, they often worked 24 hours, and it drove Davis crazy. The last straw was coming home one day when it was still light and seeing the overgrown grass.

"We'd been leaving before dawn and coming home after dark, and we hadn't noticed it," she said. "You lose perspective, you lose track of time and your priorities get all screwed up."

So they decided to sell. In 1995, Aristo International Corp. of New York bought Borta Inc. for $10 million in stock and an undisclosed amount of cash. Borta and Davis stayed on, for one year.

"They bought the company, and they wanted to run it their way," he said. "I was president of the company, and I wanted to run it my way."

After a year of vacation, lawn mowing and a little consulting work on the side, they had a daughter, now 18 months old. But try as she might, Davis couldn't keep Borta from tinkering, and soon, life was all about motion platforms.

It was last summer that "all hell broke loose," Borta said. They took his concept to a trade show -- although at the time it was nothing more than a couple of office chairs in front of a big-screen television blaring roller coaster video. They got 1,200 orders. Then they had to build it.

"It exploded literally overnight," he said. "Basically, we had to go into overdrive."

Now, Ronbotics is days away from shipping its first Coaster Express games, and Borta and Davis are ready to hit the Northern Virginia technology scene with something other than a software product or Internet company.

"It's kind of nice to be different," Davis said. "It's nice to actually see what you're building."