Propelling Into the Silent World

BlueRobotics is about to make waves with its inventive underwater thruster.

“We thought it’d be cool to take a surfboard and put solar panels, propellers, a small computer and GPS on it and send it from Los Angeles to Hawaii.”

We live on a planet that is more than two-thirds covered in water yet only a drop of it has been explored. Much of the underwater world is simply very difficult to reach due to physical or financial limitations. With the Thruster-100 marine propulsion system, the two-man team at BlueRobotics is hoping their idea will provide the accessibility needed to advance aquatic exploration to new levels.

Rustom Jehangir and Joe Spadola are mechanical engineers who both work full-time day jobs, but since 2013, they’ve been moonlighting as co-founders of California-based BlueRobotics. Over the past six months, the company has developed a design for an affordable and reliable thruster that affixes to marine vehicles used in many applications. From collecting ocean temperatures and monitoring current readings to filming exotic sea creatures and searching for lost shipwrecks, the adventurous spirit of a certain red-capped explorer named Cousteau is evident in the ambition of BlueRobotics.

Early prototype models contained an excess of parts that needed to be reduced before a low-cost thruster could realistically be launched.

The idea for the thruster began when Jehangir and Spadola were looking for an interesting engineering project to work on. “We thought it’d be cool to take a surfboard and put solar panels, propellers, a small computer and GPS on it and send it from Los Angeles to Hawaii,” explains Jehangir. The path of the autonomous solar boat involves a two-and-a-half-month trek across the Pacific — one that requires a motor and propeller unit that can power it throughout the lengthy duration while surviving the corrosive nature of saltwater.

They started researching the hardware needed but every existing propulsion system was priced way beyond their budget with an average motor and propeller cost that exceeded the rest of the components combined. As they dug deeper, a trend emerged. “There’s a developing online community of people who are doing marine robotics projects for fun and ecological reasons. And they’re all having the same problem,” explains Jehangir. “They don’t have an affordable underwater thruster.”

And there are not just affordability roadblocks, there are reliability issues. Sure, you can rig a cheap thruster out of a bilge pump or use a remote-controlled airplane motor, but it’s a temporary solution. Even the more expensive traditional units need oil and grease replaced after about 50 hours of operation, something that’s not feasible during a 75-day trip across the ocean.

With that in mind, Jehangir and Spadola created BlueRobotics to develop and launch the Thruster-100.Their initial two prototypes resembled existing thrusters. They purchased a brushless motor, enclosed it in a sealed tube and built a magnetic coupling to drive the propeller. The coupling allowed the motor to be completely sealed from the surrounding seawater. The first iteration used an axial magnetic couple, which was replaced in the second prototype iteration with a radial magnetic couple that didn’t require a steel thrust bearing that would corrode and require lubrication. Parts were manually lathed out of ABS plastic and more complex parts were 3D printed. Early prototype models contained an excess of parts that needed to be reduced before a low-cost thruster could realistically be launched.

“Our prototypes worked, but our part count was high with all of the extra pieces and magnetic couplings. The thruster was big and long because it had to fit all of the components in it and we realized that it was still going to have the same issues that other thrusters have like depth limitations and oil that could spill and leak,” says Spadola. “The best step was to simplify things a lot; we ended up cutting the part count in half. What we came up with is a much more robust, much more capable design.”

BlueRobotics prototyped its revamped design with parts made from stereolithography (SL), then rigorously tested them in saltwater, followed by additional stress testing, all with successful results. Jehangir and Spadola then used Proto Labs’ CNC machining service to thoroughly vet the functionality of the thruster’s plastic parts before shifting to Protomold for low-volume production tooling.

"We were pretty blown away by the quality of the Firstcut parts and they made quite a difference versus our old 3D-printed parts," says Jehangir. "We've been making small changes to different parts of the design, mostly aimed toward improving performance ... the Thruster-100 is now more efficient than nearly every thruster for which we have data."

The final thruster assembly will have injection-molded parts from Protomold that include a plastic nose cone, motor base, propeller, and nozzle and tail cone as well as a mounting bracket. The design’s electrical components, produced outside of Proto Labs, are composed of a steel rotor with high-performance Rulon plastic (in place of steel ball bearings), an iron stator and copper windings, and a sealed electronic speed controller. The motor is then tightly integrated into the propeller and all of the parts are sealed using a protective coating; it’s one of the differentiating characteristics that gives the thruster its unique ability to resist saltwater corrosion as well as pressure at very deep ocean depths.

The exploded view illustrates the thruster's injected-molded mounting bracket, nose cone, motor base, propeller, and nozzle and tail cone.

The final Thruster-100 assembly is a compact unit about the size of a grapefruit.

The Thruster-100 is designed for a broad user base that includes hobbyists, students, researchers, filmmakers and photographers along with various commercial uses. Operators can mount multiple thrusters to a marine vehicle that not only power it through the water with forward and rear propulsion, but also control the roll and pitch for directional navigation. The thruster itself can be controlled remotely with a unit much like that of an RC aircraft, or even plugged in to a mobile device or operated online.

Whether vehicles take the shape of handheld units for divers, surface vessels like canoes, or something yet to be invented, Jehangir sums up an important reason why they wanted to develop an affordable thruster: “It creates this enabling technology that allows others to build what they want with it.”

BlueRobotics is moving towards a summer 2014 release with an initial consumer cost of approximately $100 (compared to a current market price that ranges from $550 to nearly $4,000). As a Proto Labs Cool Idea! Award winner, an initial run of plastic injection-molded parts were granted to them by Proto Labs and electric components will be funded by a potential Kickstarter campaign and/or capital provided by Jehangir and Spadola themselves.

Having designed a low-cost, highly durable underwater propulsion system that can run longer than any of its predecessors, the guys at BlueRobotics also hope to now take that surfboard from L.A. to Hawaii. It’s a challenge that has been attempted by others but has yet to be completed. With a board powered by Thruster-100s, we like their chances.