Intro: Digital Sculpting, 3D Printing and Animatronics
This Instructable is going to show how to use digital sculpting software and a 3D printer to create a skin for an animatronic puppet. I am currently an art student studying entertainment/industrial design and have access quite a bit of high tech equipment, such as digital sculpting software, laser engravers and 3D printers. I was brainstorming ideas for my thesis project when I realized that there can be many advantages to using these tools to create animatronic characters. Digital sculptures are much easier to transport and use far less materials than traditional methods. Plus, it is very difficult to carry a sculpture and molds back and forth to school when riding a bicycle! They are also more accurate and (in my opinion) easier to change and refine. When paired with a 3D printer, one can be holding just about any model in a day or two. This process just one way to integrate digital and rapid prototyping tools into the design process and to eliminate some of the waste involved in bringing an animatronic creature to life, without limiting creative possibilities.
Step 1: The Traditional Method
I am using photos of an animatronic eel that I recently created to help illustrate how the traditional process works. The sculpture was first sculpted and detailed. It was then molded in Ultracal 30, which is a type of plaster that can withstand the heat necessary to bake the foam latex skin. A layer of clay that is the desired thickness of the final skin is placed inside along the inner wall of the mold and more plaster is then layered inside to fill the remaining space, creating the core. After the mold and core are finished, foam latex is mixed up and poured into the mold. The core is placed inside and the mold is closed. It is then baked and the foam skin is ready. I'm not going to go into too much detail as to how this process works since there is quite a bit of info on creating molds and foam latex pieces to be found in books and on the internet. But it is important to keep in mind these basic steps though, since the digital workflow differs in a few key ways.
Step 2: Designing the Digital Sculpture
I designed the digital sculpture for this project using Zbrush 3.1. I have also used Silo, which is much more affordable (under $200 for the professional version) and offers a displacement painting feature that is similar to sculpting in Zbrush, but most 3D modeling software will work fine to create most models. I drew up several pages of sketches using Sketchbook Pro before committing to a design. I had to be sure that the printer could produce the level of detail I desired and that the creature would not be too difficult to mold. I chose a simple design since I only had a couple of weeks to get everything done and to eliminate as many potential problems as I could. I decided to produce a creature called Three-Armed Ground Leech that is was based on one of my concept sketches. The design appeared to be rather easy to mold and did not require an extremely high level of final detail, which I was sure the printer could accommodate. A small scale test print of an early sketch helped me to refine the design.
Step 3: Creating the Digital Sculpt
Zbrush has many features that make it easy to produce really great sculptures without having to invest a lot of time. Again, I'm not going to get into too much detail on how to use Zbrush, since the concepts can translate to many 3D modeling/sculpting programs. Since I knew what I wanted the creature to look like, I began by creating the core of the sculpture first. This differs from the traditional method because you must have the sculpture fully molded before you can make the core. The digital core was duplicated and was used as the starting point for my sculpture. I made sure to thoroughly check the sculpture as I was developing it to make sure there was adequate space between it and the surface of the core. Knowing that this space would eventually become the final skin, I made the sculpt thicker in areas where I did not want as much movement and thinner in areas that move more. Some of the details seen in the final rendering were left out of the final model because they could have been problematic to the molding process.
Step 4: Preparation of the Digital Files
The final sculpture and core were exported from Zbrush and imported into Rhino 3D. This was done to make it easier for me to scale the models and add registration points that would be necessary to make sure everything was where it needed to be during the molding and casting process. Both the sculpture and core shared the same origin when imported, which made it easy to check that everything was properly aligned. Identical registration columns were set the same distance apart so both pieces would fit in the appropriate place in the final mold. After the registration was added, the core and the sculpture were exported in the proper file format to be sent to the 3D printer.
Step 5: Rapid Prototyping
The finished files were sent to a Dimension SST 1200 ABS printer. It prints by layering heated ABS plastic and a support material in .010" layers. The support material dissolves away when placed in a special bath after the model has finished printing. The ABS models are durable and can be molded several times as opposed to a clay model that is usually destroyed in the molding process. This reduces material waste and can allow for several molds to be made if many castings will be necessary. If further detail is desired, you could sculpt on the surface with clay or if you would like a permanent solution, Apoxie Sculpt from Aves is great. It is a non-flammable, non-hazardous synthetic clay that sets a 2-3 hours without shrinkage. In this case, I like the fingerprint-like texture the printer left behind, so I decided to leave the model how it was. Before committing to the full size sculpture, I printed a quarter scale version of each to make sure they were what I wanted. You can see how the core and sculpture register into a test mold box.
Step 6: Molding the Sculpture
I designed the mold box in Rhino around the models and fabricated if from laser cut acrylic. This allowed me to accurately place registration points in the mold box that matched core and sculpture. I attached the sculpture to the mold box, sealed it and measured the interior volume with water so I knew how much silicone to mix up for the mold. After thoroughly drying the box and sculpture, I poured the silicone. While double checking for leaks, I noticed that the sculpture was floating in the silicone. I had to pour the silicone back out and re-mount the sculpture using a couple of screws. I poured the silicone back in and let it set for 18 hours.
Step 7: Casting the Skin
After the mold had set, I removed it from the mold box and cut the sculpture free using a razor blade. The shape of the sculpture allowed me to create a one piece mold, making the process rather simple. Next, I lubricated the interior of the mold with petroleum jelly to act as a release agent for the silicone skin, since silicone will bond to silicone. I placed the core inside the mold and put both in the mold box, being sure to securely mount the core in the registration holes. I mixed up the appropriate amount of silicone and poured it into the mold and let it set. When I removed the core and skin from the mold the next morning, I noticed that I had a hole and thin spots on one side. The hole was caused by the hasty re-mounting of the sculpture in the mold box when I noticed it was floating. I decided to modify the core sculpture and to reprint a new one instead of modifying the existing core. The castings that used the new core were much better. I tinted the rest of the castings by mixing a small amount of oil paint into the silicone before pouring them into the mold.
Step 8: Designing and Building the Mechanism
I decided to use tentacle mechanisms to give the creature movement because they are simple to build and seemed to fit the creatures personality the best. I first built a few test mechanisms out of whatever was available to make sure they would give me the movement I wanted. I designed the final mechanisms in Rhino by taking cross sections of the core mesh and laser cutting them out of some scrap acrylic. The center piece was 3D printed from a section of the same core mesh. Since all of the final pieces were extracted from the core, I knew that they would fit precisely into the skin, allowing for better movement and greater accuracy. I was able to build the entire mechanism (with the exception of the center piece and a few small sections of thin steel wire) from scrap materials that I have saved from other projects or taken out of scrap bins. This helped save some money on the project and reduced waste.
Step 9: Installing Servos and Final Assembly
Since I was building the leech for my graduation project, I mounted the mechanism to a box with an open back to show how the servos were connected. I made the servo brackets from scrap aluminum and the box from some poplar I had from another project. The cables run down the center umbilical and connect to the servo horns. Here is a video of the movement: http://www.youtube.com/watch?v=pY9mn1jmH3s
Feel free to ask any questions or for more information about the process. This is my first Instructable and any feedback is appreciated!