On June 24th, 2018 we learned about

3D-printed watercraft propel themselves without fuel, engines or sails

Swimming requires a lot of effort, easily consuming hundreds of calories in an hour’s worth of work. Muscles throughout your body have to contract and extend to push your body through dense water, easily leaving even the most seasoned swimmers hungry for more fuel. Even whales and submarines burn a lot of fuel to travel through the water, even with their hydrodynamic specializations. However, engineers may have figured out a way around all of this, creating small watercraft that can move themselves around without motors, sails or batteries. All that’s really needed are some very specially designed snap bracelets.

Snap bracelets never propelled anyone through the ocean, but the way they could release potential energy when their geometry changed is similar to what engineers are developing. When a snap bracelet is straightened, it holds some energy imparted from the fingers the pressed it into that rigid shape. Flexing the bracelet back into a curve then releases that energy, causing the bracelet to curl itself back up with a satisfying snap. So while a coiling fashion-accessory isn’t great for paddling through the water, collecting and releasing energy thanks to changes in geometry does allow for a paddle to function with requiring a motor to move it.

Pushing with paddles

Instead of a motor or set of fingers, these specialized paddles are 3D printed with multiple layers of material that expand and contract at different rates from each other. As one face of the paddle expands, it forces the paddle essentially stiffen up, like a rigid snap bracelet. At a certain threshold, that geometry pops into a more relaxed position, pushing the paddle back, propelling the small watercraft forward. By varying the materials in each paddle, researchers are able to build structures that allow for relatively complex movement. For example, one small, motorless drone could paddle forward, flex smaller “paddles” to release a coin it carried as a payload, then eventually flex its paddles in the opposite direction. It’s not a speedy way to get through the water, but it does allow for more autonomy than simply riding in the ocean’s currents.

At this point, these tiny robots aren’t about to replace the more robust robots that are exploring the oceans. However, because they can be 3d printed at small sizes, they could be a cost-effective way to send sensors or delivery devices into the ocean en masse. Alternatively, the basic paddle design could be used in conjunction with a more traditional motor as a low-power method of locomotion, allowing a craft to remain active for extremely long duration of time without needing to recharge or refuel.

Source: Swimming without an engine by ETH Zurich, Science Daily

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