Everything was fine for about half a second.

But then the students heard a loud pop from the motor and watched a spark fly across the meeting room.

Anyone peeking through the glass walls of Rice University's Oshman Engineering Design Kitchen early in the second semester of 2018 would have seen six very concerned mechanical engineering students race to unplug their senior project, which had just blown a capacitor in a pretty dramatic fashion.

In an instant, the group's mood had switched from confident to "Oh God, what just happened?" team member James Phillips remembers.

Faculty adviser Marcia O'Malley just sat at a table and laughed.

Turns out, building a robotic horse simulator has its challenges.

It might seem like an unusual pursuit, but the students were creating a machine that could be used in hippotherapy. "Hippo" comes from the Greek for "horse." You already know what therapy means.

The notion is that a horse's movement affects a rider's core posture, balance, coordination, flexibility and strength, while also stimulating the neurosensory systems we need to function, says Ruth Dismuke-Blakely, faculty coordinator at the American Hippotherapy Association. That helps explain why physical, occupational, speech and language therapists use hippotherapy to help patients with a wide range of issues -- from Down syndrome and cerebral palsy to coordination disorders and traumatic brain injuries.

"Everything you do as a functioning human -- whether it's walking or handling a fork or talking or getting dressed -- all depends on your core postural mechanism," Dismuke-Blakely says.

Which means that robotic horse had to move like the real thing.

By the end of the school year, the students finally produced a mechanical horse called Stewie -- named for the Stewart Platform that provides freedom of movement along six axes: longitudinal, lateral, vertical, pitch, roll and yaw. Stewart Platforms are used extensively in flight simulation.

With Stewie's jaunty brown cowboy hat atop a black mane, the simulator provides the benefits of hippotherapy when there's nary a horse in sight. Plus, there's nothing to clean up, if you know what I mean.

Hippo what?

It's May in Louisville, Kentucky. The sun is up, the grass is shockingly green and the air is thick with pollen.

I've driven out to Green Hill Therapy, in the middle of horse country. Executive Director Lee Ann Weinberg shows me around the grounds and leads me to a large barn where an 18-year-old horse named Frejya is midsession with a 6-year-old girl named Reese.

Reese's grandmother, Candora McKinley, tells me her granddaughter was born with hypotonia, or low muscle tone.

"It has been tremendous for her. When Reese first came, it was really hard for her to sit up real straight," McKinley says as she watches Reese bump along on Frejya, flanked by a therapist and a volunteer. "It's really good for her core."

When horses walk, their hips and torso move side to side, front to back and rotationally. Each rhythmic movement can benefit a child's specific needs. The horse's gait moves riders' hips for them, stimulating a young paraplegic's muscles and nerves that are otherwise unused. It can also help build core strength, important for children like Reese.

Or take a kid whose brain has trouble processing information that comes through the senses. Every bump on the horse sends a message along the child's spinal column telling the brain where her body is in space and helping to regulate her system, says Julie Minnick, equine manager at Green Hill Therapy and certified occupational therapy assistant.

Taking the reins

So how do you build a robot that moves like a horse?

"Our first step was to ride horses," Matt O'Gorman tells me over Google Hangouts one morning. He's with classmates Phillips and Kelsi Wicker just hours after they've turned in their final report.

No, really -- they had to collect data on how horses move. But since you're a lot more likely to find information on how racehorses run than on how the average horse walks, the students had to use their phones' accelerometers to collect those stats. That helped them program the Stewart Platform to mimic horses' gaits.

And they prototyped the hell out of it.

"All of a sudden they had a horse," says Matt Elliott, a lecturer in Rice's Mechanical Engineering Department and co-adviser for the team.

Stewie can hold about 250 pounds and is programmed with the gaits of different horses.

Move it

Movement is a powerful thing.

A few studies have found there's not a whole lot of difference between simulators and horses when treating kids with cerebral palsy or those paralyzed on one side.

Weinberg and Minnick, though, would argue it's not just about movement.

Minnick describes the bonds kids forge with the horses, how the horses just seem to absorb emotion and respond to the children, and how even nonverbal kids scan the barn looking for the sweet creatures that don't expect anything from them.

So, why would you opt for a simulator over a real horse?

"[Horses] have to be fed, exercised; they need people to manage them," Phillips tells me over Google Hangouts. "A lot of people who live in the city can't sacrifice the time or the resources."

Even Weinberg agrees the simulators have value, although she'd recommend getting to a ranch so you can take in the fresh air, chirping birds and earthy smells.

A horse is a horse, of course. 

This story appears in the fall 2018 edition of CNET Magazine. Click here for more magazine stories.

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