It was supposed to be one of the greatest days of their lives.

Buckfield-based duo Fritz Grobe and Stephen Voltz were scheduled to shut down a major New York City street Tuesday for an appearance on “The Late Show with David Letterman” to demonstrate their latest strange invention: a soda-and-candy-powered rocket car.

The guys known as Eepybird found out just minutes before the cameras and the car were set to roll that their day was about to go from great to downright awesome. Out the door from the Ed Sullivan Theater walked Letterman himself, ready for the ride of his life in their contraption powered solely by Coke Zero and Mentos.

“It was way too exciting. It was awesome,” Grobe said of seeing the late-night master of comedy coming out onto West 53rd Street Tuesday afternoon. “It literally was a decision he made at the desk. He made the choice to come out and pilot the rocket car.”

Grobe, Voltz and a crew of four friends made the trip south with the rocket car and a 17-foot-long U-Haul filled with assorted gear, including 108 custom-built pistons, Mentos candies and 120 cement blocks.

The car — a combination girl’s bicycle and utility trailer — is powered by the duos’ specially designed piston drive, which harnesses the geysers of gas and soda and propels the car from a cement-block blast wall.

Grobe said Letterman’s fast, fizz-powered journey took him 364 feet down the Manhattan street and lasted less than a minute. Of course, he also admitted that Letterman had a little “gravity assist” since West 53rd has a downhill slope.

Eepybird’s rocket car Internet video has been watched more than 4 million times since its debut at the beginning of this month. And while it may be considered viral in its first month, it still has a long way to go to reach the 50 million who watched the guys’ first experiments, creating fizzy, Vegas-style fountains by dropping Mentos into 2-liter bottles of Diet Coke.

That original video sent the guys on their first round of national TV appearances, and led to international appearances as far away as Japan and Turkey. It even led to a new category of world records, measuring the number of Diet Coke and Mentos geysers released at one place and time.

Next week, the guys plan to travel to Germany to reclaim the record, firing off 2,400 geysers.

In addition to Letterman, the pair from Buckfield will be appearing on “The Early Show” on CBS. Eventually, they plan to bring the rocket car back to Maine for a performance.

Only subscribers are eligible to post comments. Please subscribe or to participate in the conversation. Here’s why.

Use the form below to reset your password. When you've submitted your account email, we will send an email with a reset code.