define what the mechanical properties are -- such as vibration absorption, stiffness, damping -- and directly realize those using 3D printing."
The previous work on printed hydraulics was the first example of using a non-solidifying liquid as a building material in a 3D printing context, said MacCurdy. The new PVM approach also uses this, but it mixes liquid and solidifying material more finely, creating what's in effect a new material.
The ability to print two kinds of materials at the same time "makes it possible to algorithmically predict the mechanical properties of a 3D-printed part, and then fabricate that part," said MacCurdy. "Because multimaterial additive manufacturing allows continuous control over material deposition, the mechanical properties that we're controlling can vary throughout the printed part, in the same way that color can vary throughout an image. We're giving designers a 'mechanical properties' design palette."
MIT researchers outfitted their cube robot with shock-absorbing skins (left) that transfer less than half of the energy normally transferred to the ground. This allows the robot to land more precisely and therefore more safely. (Source: Jason Dorfman/MIT CSAIL)
In a comparison of two robotic cubes that move around by bouncing, one made with traditional viscoelastics and one made with a skin of 3D-printed PVM, the PVM-covered cube land nearly four times more precisely. You can watch a video of that comparison here. More precise landing is also safer, making it less likely to be damaged by a sensor cracking when it hits the floor, or by a rotor breaking off, said Rus. The material's motion-damping ability also makes the robots easier to control.
The team was able to change the elasticity of collisions by varying the concentration of liquid in each cube: more liquid produces more bounce. Each cube robot includes a rigid body, two motors, a microcontroller, a battery, and inertial measurement unit sensors. Four layers of looped metal strip are the springs that propel the cube.
The method, and the materials, could also be used to protect, and improve the durability, of other things like phones, as well as shock-absorbing running shoes and headgear. "We are very excited about the possibility of making exoskeletons with different patches of hard and of flexible materials," said Rus. "For example, a long glove that gives the arm support, with flexible parts around the joints, could remove tremors from the hand."
"Being able to program different regions of an object has important implications for things like helmets," says MacCurdy. "You could have certain parts made of materials that are comfortable for your head to rest on, and other shock-absorbing materials for the sections that are most likely to be impacted in a collision."
Another example would be the socket of a prosthesis, where designers have to map the stiffness level of the bone protrusions on one side to the stiffness level of the prosthesis on the other side, said postdoc Lipton. "Our new platform will make it more likely to succeed. It would also be much more cost-effective for making a