(CNN) It may be the droid that launched a thousand merchandising opportunities, but BB-8 started life humbly: on a napkin.

In 2013, long before shooting the film and even before the cast had been announced, the plucky robot was born.

Out of the mind of director J.J Abrams came a rudimentary sketch, a ball on top of a ball; clearly an astromech akin to the beloved R2-D2, but different. Simple, spherical -- even revolutionary.

The crude napkin doodle was enough to pique the interest of Lucasfilm concept designer Christian Alzmann, who -- along with Neal Scanlan, head of creatures and robots on the film -- got the ball rolling on what became BB-8, the tiny star of "Star Wars Episode VII: The Force Awakens."

It was a project shrouded in secrecy, misdirection and non-disclosure agreements, but after a long enforced silence the men who made BB-8 have finally spoken about their mission to bring the Resistance droid to the silver screen.

"We had to keep it secret for a year and a half"

Just your average day sitting at the holochess table on the millennium falcon :D #bb8 #StarWars pic.twitter.com/5JB31RRwb5 — Matt denton (@mantisrobot) December 6, 2015

BB-8 has many fathers, but if J.J. Abrams was responsible for the spark of life, Matt Denton and Joshua Lee nurtured the droid to adulthood.

They were the animatronics experts who crafted BB-8's brain and body, and traveled with it around the world, guiding it through the shoot.

"We had to keep it secret for a year and a half," says Lee. Even when his ten year old son began to come home with BB-8 merchandise, neither his nor Denton's family or friends could know about their involvement.

"I never read the script," Lee says. "I don't really know what happens in the film. I was there on set, from the first week to the last, but there are massive plot points that I don't know about."

"Every day we'd turn up on set it would be a surprise... It was a bit strange to start off with, but it was good fun."

Until something happened.

The day it all went wrong for BB-8

During the Abu Dhabi shoot, BB-8 was traveling at high speed across the desert on a tow cable when it flipped over. Lee was at the controls but was unaware of the crash, and carried on winching the cable before eventually, agonizingly, the droid ground to a halt.

"There was shocked silence on the set," he says. "BB-8's head was totally smashed up... It was as if someone had been hurt. The crew didn't know where to look."

Luckily there was a selection of fresh heads waiting in the wings, but the tale shows just how much the droid meant to everyone involved.

"This is the first project we've done where the character's been appreciated this deeply and at this level by the cast and crew," explains Denton. "When we did our last shot on the last day BB-8 was wrapped like an actor and got a round of applause. It was amazing."

Building 8 BB-8s

BB-8 going at full tilt across the desert on Jakku, filmed in Abu Dhabi.

Their journey with "The Force Awakens" started in England in August 2013, with a basic concept to test their software. "You could instantly tell it was going to work," says Lee. The duo then set about creating what Denton calls "the five main versions."

Yes, BB-8 has siblings. In fact, it's an octuplet.

Each of the eight droids had specific characteristics: Two were on trikes, one with a stabilizer on the left, the other the right (later CGI-ed out); another rod-puppet version was put into the capable hands of Brian Herring and Dave Chapman. Then there was the "wiggler," great for close-ups with a super-articulated head, and the "bowling ball": motorless, but a BB-8 that would right itself no matter what was thrown at it -- or indeed if it was throw itself.

The "red carpet version" was the final creative flourish and the fullest expression of Abrams vision. As seen at the Star Wars Celebration in Anaheim in April, it is entirely self-contained and reflects the BB-8 seen on screen -- except with no digital tinkering required.

BB-8 alongside R2-D2 and director J.J. Abrams at Star Wars Celebration.

All bar the red carpet version were created within the space of five months, and "literally finished with moments to go before they were put on a flight to Abu Dhabi," says Denton.

In the Emirate, BB-8 was met with 113-degree heat, "with salt and sand blowing into all the mechanism... it was the ultimate harsh start to a shoot," Denton explains.

"I was hosing out the bearings on a daily basis."

The conditions meant some of BB-8's capabilities had to be scrapped. "We had a sound system in their heads," says Lee, "but on day one we realized it wasn't going to work. There was too much interference."

Patented secrets

The red carpet version of BB-8 alongside actor Oscar Isaac at the Star Wars Celebration in Anaheim. Isaac plays pilot Poe Dameron, who the drone has an allegiance to -- one of the few plot points known about the film.

It's likely that the engineering keeping little BB-8 rolling is what's known as a "magnetic spherical balancing robot drive," an invention patented by Disney in 2010 -- a full three years before Abrams first took pen to napkin.

Denton and Lee can neither confirm nor deny what goes on inside BB-8, but it matters little to the audience. Fans worldwide have embraced their creation because it marks a return to the tactile, tangible special effects of the original Star Wars trilogy.

"People seem to adore BB-8," says Lee, "he's very huggable."

Denton and Lee are clearly fond of their creation, and continually have to correct themselves and remind each other that the droid is actually an "it."

Cast and crew are likely to be reunited with BB-8 on December 14 for "The Force Awakens" premiere in Los Angeles, although Denton and Lee demur as to whether we'll be seeing the plucky droid in Episode VIII.

"We're working on the film," says Denton, "but we can't say what we're involved with. We have to be careful -- we don't want to be the ones to ruin Star Wars."

Whatever they've got prepared for Episode VIII, set to hit screens in 2017, it'll be a long time before any of us will find out.