Introduction: Soft Robotic Insole
Soft robotics is an emerging technology that can have many real-world applications due to it being great for human-physical interaction. The goal of this project was to create a pneumatically conformable shoe insole that is versatile and comfortable. In other words, inflatable shoe insoles.
- A shoe (or pair of shoes) that you'd like to install the insole in
- Ecoflex 00-30 Silicone
- Check valve or manual valve (Check valve is recommended)
- 1/8" tubing
- Something to supply air that can connect to the 1/8" tubing (Squeeze bulb, syringe, etc)
- Drill with 5/16" drill bit
- Small flathead screwdriver
- Scissors or flush snips
- 3D printer
Also, I am entering this project in the Epilog Contest VII. It would really mean a lot to me if you voted, because a laser cutter would allow me to accelerate my development of soft robots and create new casting methods and new types of actuators.
Step 1: Molds
First you'll need to modify the 3D designs so the finished insole will be for your foot. Measure your existing shoe insole's length and width from the center. Record those measurements, and add 11 millimeters to each. Open up the design file in 123D Design. Use the Non-uniform Scaling tool to change the X and Y values until the lengths and widths of designs match up with your numbers. Then, print which pair of molds you want (right, left, both). I recommend standard layer height, 3 shells, and 5% infill. If the molds are too big for your printer, you can cut them up using Netfabb.
Step 2: Pour the Molds
Mix up a large amount of Ecoflex 00-30 by scooping equal amounts (by volume) into the cup and mixing it thoroughly. Pour the mold that has the air channels (the one with the funky shapes) all the way to the brim, and fill the other mold only halfway. If you didn't mix enough silicone, mix up some more. Let it cure for four hours.
Step 3: Complete the Cast
Carefully pull the cast with air chambers out of the mold by pinching one end and pulling away. Then, mix up a very small amount of silicone, and spread a very fine layer over the cast that is still in the other mold. This layer should only be about a millimeter high. Then, take the cast that you just demolded and gently place it on the uncured silicone in the other mold. Do not apply any pressure. Let this cure for another four hours.
Step 4: Demold and Connect Tubing
Pinch one end of the full cast and pull it out of the mold. Trim any flash if necessary. If any of the air channels or pockets on the inside are blocked, you will need to restart. Once it is out, use the flathead to open the opening of the air chambers at the back of the insole. Take the flathead and punch two slits on either side, about five millimeters from the central air channel that’s in the insole. Insert the 1/8” tubing into opening and make sure that about and inch of the tubing is inside. Push the tail of the zip-tie through each slit and tighten. Tuck the lock of the tie inside one of the slits.
Step 5: Testing
Connect your air source to the other side of the tubing and inflate. The pockets should bulge. If there are leaks, you can mix up some silicone and attempt to repair it. Take whichever valve you got and connect it in between the insole's tubing and the air source. If you are using a check valve, you can just inflate and the air will stay in. If you are using a manual valve, you need to inflate the insole then shut the valve. Keep it inflated for the next step.
Step 6: Plasti-Dipping
Note: I suggest doing this in a well-ventilated area. Take the inflated insole and spray it with a thick coat of the Plasti-Dip. This is a trick I invented to help protect soft robots. Let it cure for about half an hour.
Step 7: Prepping the Shoe and Installation
Take the drill with the 5/16” bit and drill a hole in the back of the shoe. Take off the valve and push the other end of the 1/8” tubing through the hole in the shoe from the inside. Tuck the whole insole into the shoe. This may take some wiggling around to get this right. Trim off any unnecessary tubing and reconnect the valve.
Step 8: Operation
Now your done! To use the insole, I recommend putting on the shoe with it deflated, then inflating it while the shoe is on. Happy walking!
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