Printed Circuits as Part of a 3-D Printed Object (Video)

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Affordable 3-D printing is still young; just a few years ago, it would have been nearly impossible to have an arbitrary three-dimensional piece of plastic (or resin, or sometimes metal) created from a software description in a box that fits on your desk. But in the several years the printing of *things* has moved fromquaint, quixotic, futzing-about hobby into something that works (fairly) reliably in ever more garages, schools, and hackerspaces, it's gotten good enough that you can now download and print quite a few objects that are available for download, or scan small items to replicate, or scan your friends to print out as statuettes. However, for the most part, these printed pieces are static, and finished. With care, you can print things like a chain, or even a ball joint, but you're still limited mostly to one basic material at a time. (Printing with multiple colors is getting easier, though.) If you want to print a flashlight or a robot, you'll need to add wires and other circuitry as a separate step. That's what the folks at Rabbit Proto (get it?) are trying to change. With the system they're working on, a filament printer is used to fabricate the object itself, but at the same time, both capacitive and conductive features can be baked -- or rather printed -- right in, with a separate print head. We talked with Alexandre Jais and Manal Dia of Rabbit Proto about how the system works, and why you might want to use it. (Alternate video link.)

Tim: Manal and Alex, I want you to talk to me about Rabbit Proto, and what it is.Why do you call it that?

Manal: Great question.So initially Rabbit Proto came from ‘rapid prototyping’, and it is sort of a word play on that. We started thinking about Rabbit Proto as a prototyping platform.The project came out of a class of a year-long design class here at Stanford that Alex took last year.Maybe you want to talk about the origins of that?

Alex: Yeah.Absolutely. It was a class where we were basically trying to design a platform for innovation where we would use electronic inks, conductive inks or functional inks.We came up with this idea of having a physical prototyping platform. 3D printers came naturally after that. We noticed that people had sort of an urge to get this kind of device. Because consumer devices and the prototyping of those consumer devices integrating printed electronics seemed to be something that was more and more and more important for a bunch of people. At the end of the year, the project was presented.And I decided to take it on as more of a personal project after that.That’s where Rabbit Proto comes from.And there is another fun story, that originally when I presented the project, I wanted to print a rabbit with glowing eyes with a printed circuit inside and small LEDs bringing the current or bringing light to get the eyes glowing.That’s where the rabbit comes from as well.

Manal: Because the rabbit is a very traditional object to be printed to calibrate a 3D printer.

Tim: So with the Rabbit Proto system, what you are doing is you are adding both capacitive and conductive abilities to existing 3D printers.So that means essentially an object can do if this is correct sort of as its own batteries as well, by adding both of those things in there.

Alex: So let me just clarify this in that case.So what we are doing is that we have a 3D printer add-on that can be adapted on an open source machine that allows you to deposit both a plastic filament, but most importantly a conductive paste in our case, and that conductive paste is great at doing at what you call capacitive touch sensing.So it is not exactly having a capacitor inside your object, but when you link it to a micro controller or some sort of measuring device you can actually form a virtual component by touching the trace—you can do capacitive touch sensing; however, there is research at Stanford’s lab and other places that is looking at printed batteries or printed capacitors other kinds of functional materials that could do that.So that might be a vision in three, five, or ten years.

Tim: Your vision does include printing nearly everything though.I notice that you have one demo of using peanut butter, so anything that has the right consistency?

Alex: Yeah.

Manal: For us, Rabbit Proto is not only printing circuits inside of plastic but really kind of opening up 3D printing to printing other kinds of material, and printing materials that don’t only come in the form of a filament but materials that come in viscous or liquid form.And that’s why the extruder and the add-on that we have designed have this capability of depositing not only the plastic filament that traditionally gets 3D printed, but also liquid electric ink, peanut butter and exploring the range of these different materials.Thinking about applications that we could print with Rabbit Proto is really the next step for us.The powerful applications that we have come up with which include a remote controller, we have made styluses and we are also now thinking of more interesting artistic interfaces.So all of this is really the tip of the iceberg in terms of what becomes available. Again the power of Rabbit Proto is that not only these new materials but also thinking of going from the pads of one design on a computer to the actual printed thing.Right now, this is a first generation product and what it enables is to prototype, and prototype faster.And making the iterative process of prototyping and going through multiple iterations of the product that you are prototyping just much faster, much more integrated asa process.So you can design your object, print it out, realize that maybe the buttons need to be bigger or maybe the shape needs to be different, and rather than going through again the painful steps of making the plastic, making the circuits—and that usually takes many days and involves multiples parties, you can just print that with one button, one printing button basically.

Alex: Yeah.

Tim: What sort of printers does your add-on work it? Since you have got both as an add-on and as a complete printer, as possibilities,I noticed some pictures of some Delta Box and some RepRap looking ones.Talk about how flexible that is.

Alex: Absolutely.So the good thing with RepRap is that most of the parts are available open source, and if you want to modify your carriage that has the print head moving on it—it is possible, and the only requirement right now is that your electronic board that controls the stepper motors for the extrusion is available to welcome a print head for a plastic object anda stepper motor for the conductive paste extrusion.After that, right now, we have noticed that on all the RepRaps that we have seen here, and I think that the variety of RepRaps as well, there is a hole on the carriage that what decides pretty standard to adapt extruders, so right now we have designed it for this.

Tim: What about the actual conductive material?Is that a mix that you have come up with to have the right consistency? Or is that an off-the-shelf product?

Manal: So we have started with two different materials.The product that we are using right now is graphite ink, and the reason we are testing with that, is that it is cheap enough to be used in our prototyping process, but also conductive so it works well with our sensing applications.And it is nontoxic and sort of easy and fun to play with.

Tim: Now, you are raising a question for me about the interface between an object that you create that has these internally printed conductive parts—when you want to connect that to an USB port or an Arduino board or anything else that you might have as an adjunct to the actual object—what is the actual interface there between your printed object and external devices, external things?

Manal: This is something that has a little logo that we made to showcase our logo mostly.The process right now is this is connected to an Arduino Yun.

Alex: And this was for the game controller, the IC circuits that you would then you can connect the computer on two.

Manal: And then this plugs into the USB of a computer.

Tim: How does the speed compare of printing an object with the embedded conductive circuitry—is it much slower? Is it the same speed as if you were printing it full stop on the same kind of filament based printer?

Alex: The speed of printing the conductive trace versus the speed of printing the plastic trace?

Tim: Yeah, since you are embedding the conductive traces, is it a very much slower process than if you weren’t—if you were just printing the object without those traces?

Alex: Not really, in fact, it is right now, to be perfectly honest, inside the software, both speeds are set up at the same rate, in our plastic objects the way that we accelerate it is by saying: I want my object to be 20% emptier or something like that.In our case, that would be the difference in terms of speed between the conductive material and the plastic object.

Tim: Let me ask you a little bit about licensing too, because you’ve made a point that this is an open source project. Can you talk about in what way people can either take advantage of some of the ideas that you have come up with, or possibly contribute to making things better? Do you have a Git repository? Or are your objects on Thingiverse? Is there anything that people can do to take part and sort of experience this?

Manal: Yes, so we do have a GitHub repository. This project started on open source 3D printers and so a lot of our development has been about benefiting from 3D printers that are open source, and we want to give back to the community and we also want to build a community around our product.