Dec 18, 2014 | By Alec

Instructables user Mikey77 – who has been sharing several very interesting and innovative 3D printing tips, like a flexible circuit board – has developed a way to 3D print cheap and easy muscles that could potentially replace servos and gear-motors in robots in the future.

To illustrate his latest technique, he has created a beautiful and very impressive flower with six petals that can open and close. And, It could, for instance be used in soft robotic creations and prosthetics. At an even smaller level, a number of biomedical applications can be imagined. As Mikey said himself, 'This is still at the early stage of experimentation, but it shows great promise.'

The secret behind this technique? Air pressure. Using a standard filament 3D printer, Mikey has developed a method for creation air-powered muscles that can be filled with, and emptied of, air, forcing them to take up certain shapes. A simple robot could be developed that indicates air pressure, that opens and closes the flower.

An individual petal, relaxed (top) and pressurized (bottom).

And the technique behind it is remarkably simple; Mikey relied on his trusty Makerbot Replicator 2 to print a series of hollow muscles in the flexible Ninjaflex filament. As this filament – and other, less flexible ones – leaves many microscopic holes in its surface, preventing it from holding air pressure, the 'muscles' are dipped in a flexible, elastomeric glue after printing. 'This allows them to hold air pressure of 22 PSI or higher.'

While the flower petals are the smallest possible muscles to create with this setup, as you simply need walls of a certain thickness, he Mikey envisions using a stereolithography printer like the Form 1+ printer 'to produce smaller and more precise types of muscles and robot skin that a filament printer cannot. More intricate air channels and unusual shapes that do not need supports could also be printed. A flower robot like this could be printed assembled in one piece.'

His flower experiment, however, is very impressive as it is. He developed all individual muscles in 123D Design software, which was drawn and extruded as a solid shape. To do so, he relied on an infill of 100%, a layer height of 2 mm and worked without any support structures.

The finished print was then hollowed out to create walls that are .026" thick, leaving an internal air channel of about 002" thick. Mikey then inserted a nozzle, and sealed the connection and the petal itself in his glue solution (two dips). 'The sealant is composed of Loctite Fabric Glue that is thinned with 10 to 20 per cent MEK solvent by volume. The MEK slightly dissolves the Ninjaflex resulting in an extremely good fusion of glue and Ninjaflex.'

Once done for six separate petals that are assembled together, you have yourself a 3D printed flower that can open and shut its petals by relying on air pressure. What's more, you can easily recreate it yourself using Mikey's STL files (see his Instructables page here), provided your FDM printer is capable of working with Ninjaflex filament.

Mikey, meanwhile, has already moved on with his muscle experiments, having constructed a zig-zag pull muscle using the exact same manufacturing technique. This setup already proved to be capable of lifting more than 4 pounds. He believes that this technique could be crucial in the development of affordable soft robotics; 'I believe that the future of robotics, if it is to become more affordable and useful, will involve the 3d printing of soft robot muscles and skin teamed up with 3d printed stiff bones and shells. This will minimize the number of expensive servos and gear-motors that will necessary.'

Posted in 3D Printing Applications


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