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This Robotic Hand Can Shift Gears to Catch a Beer Can and Crush It

By creating a lightweight, 3D-printed “transmission,” engineers were able to build a hand that is strong when it needs to be and fast when it needs to be.
Robotic hand holding a crushed can

Engineers from Cornell University have built a robotic prosthetic hand that can alternate between strength and speed, so you can catch a brewski, chug it, then smash it, all with your robo-appendage.

For many engineers, the goal of building a robotic prosthetic hand is to make one capable of doing everything a biological hand can do. Typically, one problem they’ve faced is that a robotic hand can be either fast or strong, but not both. Now, thanks to a lightweight, 3D-printed “transmission,” that problem has been at least partially solved, according to a study published Wednesday in Science Robotics.


“You have to select a gearing ratio to make the hand really strong, but then it’s slower, or really fast, but then it’s a lot weaker,” Kevin O’ Brien, a PhD candidate at Cornell and lead author of the study, told me over the phone. “But in your car you have a transmission that allows you to change gears so the car can be strong when it needs to be strong and fast when it needs to be fast. So we made a little, simple, 3D-printed transmission that can sit inside the robotic prosthetic hand.”

O’Brien explained that the “transmission” works using a fairly simple mechanism. It’s essentially a cylindrical spool with a prosthetic tendon in the hand wrapped around it. The spool is made from a flexible, rubber-like material, so it can stretch and be fatter—allowing it to reel in the tendon quickly for speed—or shrink down to be narrower—allowing it to reel in the tendon with more force, for strength. The transmission itself is triggered by the tension in the tendon, as well as sensors on the hand’s fingertips that detect force and proximity of objects, so it automatically responds those stimuli in order to grip or catch an object.

“It does it without needing any extra input: all of the sensation and changing of the gears happens in the material,” O’Brien said. “That makes it really simple and low cost.”

We’re still far from a robotic prosthesis that’s as complex and advanced as a biological human hand, O’Brien said. He estimated that the most advanced robotic hands currently have about a third of the strength and one fifth of the speed of a biological hand. But by combining advancements like this with other progress that’s been made—such as embedding motors for robotic hands in the forearm, which is more similar to a biological arm—-we’re able to creep closer to a real analog.

“We’re getting closer, but it’s still going to take a long time and a lot more innovations to get us there,” he said.