In the process, Ryan Kung and David Shulman, two Silicon Valley engineers behind "Eclectical Engineering" -- a YouTube channel dedicated to bringing imaginative contraptions to life -- knew they'd be embarking on their most dangerous project to date, a reality that did little to deter the duo.
Previous projects include a massive Nerf gun capable of exploding watermelons and turning their faces into 3-D selfies made of chocolate.
"In a lot of ways the way we pick these projects is by finding engineering we really want to improve our skill set in," Shulman, 28, said. "We hadn't done any projects involving water and wanted to get better with motors."
Combining battery-powered motors and water is, of course, is a recipe for electrocution. That explains why the two men spent the bulk of their time figuring out how to create a watertight seal for the jetpack's battery compartment, which contained powerful lithium batteries.
The sealed battery pack was initially tested in three feet of water. That meant the men couldn't be certain the pack would remain water-resistant if the depth, and pressure on the pack, increased.
How did Shulman feel jumping into the water for the first time?
As their finished YouTube video attests, Shulman survived, and the project was a complete success. At top speed, the underwater jetpack clocked in at 6.25 mph, breaking Phelps' record of 6 mph. The propellers were more powerful than expected, Shulman said, noting that at times it felt as if they were "going to pull my arms off."
The pair, who do most of their DIY engineering on the weekends, estimate they spent 60 hours and $1,000 to make the jetpack a reality.
They hope to refine the contraption, but they already have another project occupying their imaginations.
"We want to create a launcher that helps you skip rocks easily and a lot further than anyone can by hand," Shulman said. "We have a backlog of 80 projects, so our problem is not coming up with fun things to do, but finding the time to do them."
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
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