3D-Printed Pneumatic Quadruped Robot Adapts to Rough Terrain

Soft legged robot
Photo: UCSD
This little legged robot may one day walk straight out of a 3D printer.

At IROS in Chicago a few years back, then Harvard grad student Michael Tolley introduced us to a robot that used explosions to jump. It was soft, it was pink, it had three wiggly legs that it used to position itself, and it was kinda freaky looking. As it turns out, Tolley now has his own robotics lab at UC San Diego, and they’ve been working on ways of efficiently fabricating useful soft robots. Their latest paper, which will be presented at ICRA in Singapore next week, throws a fourth wiggly leg into the mix to make a soft quadruped robot that can walk.

Soft robots (with soft actuators) have the potential to be easy and cheap to construct in lots of very different, very adaptable, and intrinsically safe configurations. The problem, at the moment, is that they tend to be really difficult to construct, since you have to mold and cast all of the complicated bits by hand. Dylan Drotman, along with other students in Tolley’s UCSD lab, have come up with a leg design that can be 3D-printed all in one go, and in fact, nearly an entire quadruped can "easily" be printed as a single part:

Predictably, you can’t just whip up these legs with any 3D printer: You need something that can print a custom mix of soft rubbery material and rigid material, resulting in an end product with adjustable firmness. The researchers used an Objet350 Connex3 from Stratasys, which costs “get a quote,” meaning that you almost certainly can’t afford it. 

The legs themselves consist of three flexible, inflatable rubber tubes stuck together to make a sort of tube-y triangle in cross section. By inflating two of the tubes but not the third, the leg will bend in the direction of the uninflated tube, giving you a leg that can be controlled in two axes.

I’m a little curious whether you could get another axis of control by inflating all three tubes simultaneously to get the leg to elongate, or alternatively, using a vacuum pump to get the leg to shrink, but maybe that’s either past or future research. Anyway, four of these legs mounted in an “X” configuration gives you a quadruped, with the ability to actually walk (as opposed to crawl), so it can lift each leg, move it, and put it down somewhere else. 

With all of this flexibility, the researchers were able to successfully test out different gaits, optimizing for movement on rocks, sand, and for squeezing into tight spaces. It’s a reasonably powerful little thing, too: You can load it up with up to 0.62-kilogram when it’s all splayed out on the ground and it can stand up, or significantly more if you let it stand up first.

Payload is important, not just to carry useful things like sensors, but because the robot will need some significant modifications to be functional: As with (almost) every pneumatic robot, we have to point out that this little guy is very significantly tethered to some mostly off-camera system that has a big pile of actuators hooked up to those tubes with a pressurized air supply behind it and a bunch of batteries and electronics.

Solving this challenge was not the point of this research, of course, and this is not a criticism, we just want to make sure that it’s clear what it’s going to take to get robots like this out of a lab. Having said that, the researchers will be developing “an untethered quadruped” that could be used for “surveillance or capturing sensor readings in environments that may be harmful to humans.”

“3D Printed Soft Actuators for a Legged Robot Capable of Navigating Unstructured Terrain,” by Dylan Drotman, Saurabh Jadhav, Mahmood Karimi, Philip deZonia, and Michael T. Tolley, from the University of California San Diego, will be presented at ICRA 2017 in Singapore.

[ UCSD ]

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