This method allows the team to print the robots in a single step, with no assembly required, using a commercially-available 3D printer.
“Our approach, which we call ‘printable hydraulics', is a step towards the rapid fabrication of functional machines,” said CSAIL director Daniela Rus, who oversaw the project. “All you have to do is stick in a battery and motor, and you have a robot that can practically walk right out of the printer.”
To demonstrate the concept, the researchers 3D printed a six-legged robot that can crawl via 12 hydraulic pumps embedded within its body. As an alternative to the bellows, the team also demonstrated they could 3D print a gear pump that can produce continuous fluid flow. They also printed robotic parts that can be used on existing platforms, such as a soft rubber hand for the Baxter research robot.
To move, a single DC motor spins a crankshaft that pumps fluid to the robot’s legs. Among the robot’s key parts are several set of ‘bellows’ that are 3D printed directly into its body. To propel the robot, the bellows uses fluid pressure that is then translated into a mechanical force.
For all of the progress in 3D printing, liquids continue to be a big hurdle, making it hard for liquid-based methods to be employed for factory-scale manufacturing.
With printable hydraulics, an inkjet printer deposits individual droplets of material that are each 20 to 30µm in diameter. For each layer being printed, different materials are deposited in different parts, high-intensity UV light is then used to solidify all of the materials except the liquids.
“Inkjet printing lets us have eight different print-heads deposit different materials adjacent to one another, all at the same time,” Robert MacCurdy, MIT researcher, explained. “It gives us very fine control of material placement, which is what allows us to print complex, pre-filled fluidic channels.”
Another challenge with 3D printing liquids is that they often interfere with the droplets that are supposed to solidify. To handle that issue, the team printed dozens of test geometries with different orientations to determine the proper resolutions for printing solids and liquids together.
While it’s a painstaking process, MacCurdy says that printing both liquids and solids is even more difficult with other 3D printing methods, such as fused-deposition modelling and laser-sintering.
“As far as I’m concerned,” he said, “inkjet-printing is currently the best way to print multiple materials.”
MacCurdy envisions many potential applications, including disaster relief in dangerous environments. Many nuclear sites, for example, need to be remediated to reduce their radiation levels. Unfortunately, the sites are not only lethal to humans, but radioactive enough to destroy conventional electronics.
