Electronics-Free Robots Straight from the 3D Printer

Andrew Corselli

This robot can walk, without electronics, and only with the addition of a cartridge of compressed gas, right off the 3D-printer. (Image: UCSD)

Imagine a robot that can walk, without electronics, and only with the addition of a cartridge of compressed gas, right off the 3D-printer. It can also be printed in one go, from one material.

That is exactly what engineers have achieved in robots developed by the Bioinspired Robotics Laboratory at the University of California San Diego. They describe their work in an advanced online publication in the journal Advanced Intelligent Systems.

To achieve this feat, researchers aimed to use the simplest technology available: a desktop 3D printer and an off-the-shelf printing material. This design approach is not only robust, it is also cheap — each robot costs about $20 to manufacture.

“This is a completely different way of looking at building machines,” said Senior Author Michael Tolley, Professor, UC San Diego Department of Mechanical and Aerospace Engineering.

Here is an exclusive Tech Briefs interview, edited for length and clarity, with First Author Yichen Zhai, Postdoctoral Research, UC San Diego Department of Mechanical and Aerospace Engineering.

Tech Briefs: What was the biggest technical challenge you faced while developing this robot?

Zhai: To me, the design of the robot wasn't a challenge at all. First, when I was in this lab, Professor Tolley asked me to write the proposal for our sponsor. I had no knowledge of robotics at that time because my Ph.D. was in electrical engineering and our lab is in the mechanical engineering department. I talked to my colleagues and heard that there are some things we might be able to do. So, I wrote in the proposal that we want to design a monolithically 3D-printed walking robot that is powered by air and doesn't need any post assembly.

For the traditional pneumatically powered walking robots, they used an oscillator to power the motion of the legs, but that oscillator isn't suitable for printing. So, I needed to design something else to power this robot. We came up with a solution so that the pneumatic oscillator could be 3D printed in one piece and can output four different phases to power the motion of the robotic legs.

That process took us half a year to do. Then, from the oscillator to the walking robot, we just designed all of the things together on the computer and made the first walking robot. But after making the first one, there were some more challenges.

After making the first one, in the next three months, we could not repeat the results. We printed 30 to 50 robots, and each of these takes two and a half days to print. But almost all of them were not working. They were leaking because there were some defects during printing. Once the robot is leaked, it is depressurized, then we cannot make it work. It must be airtight. So, it took us a lot of time to deal with these defects during the process. But, for the design itself, I don't think that was challenging. The most challenging part is still in the manufacturing processes.

We need to find some way to improve the processes, like modify the 3D printer to increase the yield and also we can modify our designs to make it stronger so that it can still be processed by the normal 3D printing systems that might cause defects.

Tech Briefs: Can you please explain in simple terms how it works?

Zhai: We have a robot with legs. Each leg has a pair of a horizontal pneumatic actuators and a pair of vertical actuators. By the coordination of the four bending actuators in two pairs, the whole leg or the tip toe can swing in a loop. However, we need to pressurize these actuators one by one in a loop. So, we need to design the key thing: the pneumatic oscillator or we also call it the pneumatic oscillating wall. The function of the wall is that it takes one constant pressure as the power source in, and it has four output ports. It can output pressure through each of the ports, one by one, to inflate the actuators and also depressurize the actuators one by one.

Inside the pneumatic oscillator there are some different chambers and there are membranes separating the chambers. When some chambers are inflated, then the membrane between them will be inflated and cause it to bend one way. When the membrane is bent, it can push a pneumatic channel to be kinked. The pneumatic channel is just a horizontal piece of thin tube. When the channel is kinked, air cannot flow through it. Then, by a complex motion between these different membranes and the channels, we can open and close some channels inside and redirect the air flow through the whole system.

So, we can control the air, control which part to output air or take air in. Then the air flow is controlled in the loop. Also, we designed the system to measure the threshold of the pressure between the chambers. That is when the pressure between two chambers reaches some level, when one is being inflated, the other is being deflated. Then, the mechanism can measure this difference and it suddenly shifts the states. It causes the one chamber to be inflated suddenly, the other to be deflated suddenly, and it can shift the state to the other one. So, the leg changes from its horizontal motion to a vertical motion or from one direction to the other direction. Basically, it's controlled by mechanical valves, which are soft material and redirect the airflow through the actuators so the leg can bend in two different directions, and if it bends in these directions the whole robot can move forward.

Tech Briefs: Do you have any set plans for further research, work, etc.?

Zhai: The robot is a demonstration that a 3D-printing machine or an automated system can make another automatic system that can do something. I think the best usage for the robot is a toy. It can be used as a toy for recreation and also as an educational tool to educate the young generation about how these robots work or how 3D printing works.

In our current project, we are trying to make the robot move faster. Now, the robot only moves four centimeters or one and a half inches per second. It takes five seconds to move for its own body length. That is way too slow. Even if we use it as a toy, it's too slow.

Tech Briefs: Is there anything else you'd like to add that I didn't touch upon?

Zhai: Similar designs published by other researchers are not able to do [what our robot can] because we have more legs and high clearance. Also, for this pneumatic robot, it is suitable for underwater walking in an aquarium environment.