Soft robotics is a new and young field of robots that uses (mostly) soft and compliant materials as opposed to rigid and hard materials. Most soft robots are composed of multiple soft robotic actuator, most of which are actuated by air. This project is an actuator that extends when inflated.

Materials:

Smooth-On Ecoflex 00-30
GE Silicone
A large zip-tie
Small piece of 1/8" tubing

Tools:

3D printer
A large vice
Spoon
Cup
Small scoop
Small flathead screwdriver
Large flathead screwdriver
Syringes or electric pump that can connect to the 1/8" tubing (this is for using the actuator)

Step 1: 3D Printing the Mold

Here are the amounts of the different parts:

2x Outer.stl
1x Core.stl
1x Adapter.stl

I would recommend printing all parts in PLA or ABS at .2mm layer height with 3 shells.

Step 2: Preparing the Mold

Start by taking the two outer and core pieces of the mold and assemble it as shown in the pictures. The two outer pieces fit together to make a cylinder and the core fits in between them. Take the assembled mold and secure it in the vice, making sure that nothing gets misaligned. Then, take the GE Silicone, and spread it in/on the seams of the mold. Making sure every crack is sealed as shown in the picture. Let the GE Silicone cure for about 30 minutes.

Step 3: Pouring the Molds

Take the Smooth-On Ecoflex 00-30, and use the scoop to scoop equal amounts of each part of the silicone mix into the cup. Start with ~3 scoops of each part of the mix; you can always add more later. Use the spoon to mix it thoroughly. Then, pour the mixed silicone into the main mold we assembled in the last step and the circular adapter mold. Fill the adapter mold to the brim, but do not fill the main mold to the brim. You may want to tilt both molds around a bit to release air. If the molds needs more silicone to be full, repeat this step. Let the silicone cure for about 4 hours.

Step 4: Demolding

Take the mold out of the vice. With your fingers and the small flathead screwdriver, scrape and peel away the GE Silicone around the seams of the mold. Once most of it is cleared away, use the large flathead screwdriver to pry open the mold. Go slow and work your way around the mold's seams. After one side can be pulled off, use your fingers to pull the silicone cast out of the the other side of the mold. Now, all that's left to do in this step is to take out the core mold. To do this, try and turn the silicone inside out in order to push the core out. It may also be helpful to break off chunks of the core and pull them out of the silicone.

Step 5: Attaching the Adapter

Mix up a small amount of silicone. Take the adapter mold that has cured silicone in it and spread the mixed silicone on it. After that, take the silicone cast from the last step and place the open end on it. Let it cure for 3 hours.

Step 6: Finishing Touches

Pull the now fully-molded piece of silicone out of the adapter mold. Take the large flathead screwdriver and push it through the opening in order to clear the inside for the tubing. Insert the tubing into the actuator and secure it with the zip-tie. Now you can connect your new extending actuator to your air source and try it out!