Introduction: Soft Robots: Making Robot Air Muscles

About: I believe that the purpose of life is to learn how to do our best and not give in to the weaker way.
Pneumatic robot air muscles can be easily made using Oogoo. These flexible, silicone artificial muscles have the advantage that they are inexpensive and can be easily molded to fit almost any robot body.

The intro pic shows a six segment elbow muscle, a three segment actuator muscle, and a single segment muscle under low air pressure. The thumb pic shows the artificial muscles with no pressure.

You can see a robot arm and gripper that was made using this type of artificial muscle, here:

Step 1: How Artificial Robot Muscles Work

These artificial robot muscles are made by laminating thin layers of Oogoo which is a silicone rubber that can be cast in any thickness. For info on Oogoo see here:

An artificial muscle segment is cast in two layers with a thin piece of plastic between the layers to allow for air expansion. This creates a simple air bladder that can glued together in many segments with spacers to create curving or straight robot muscles.

The step one pic shows a 3d illustration of a six segment silicone robot muscle. Ideally, an artificial robot muscle like this could be directly printed in one piece. I have not found a 3d printer service that can print silicone or rubber at an affordable price. So, for now, I can only do the illustration and must use hand techniques to create the muscles. I am looking into the 3d printing of plastic molds that could be used to cast the Oogoo robot muscles in one step.

123D was used to create the illustration.

Step 2: Materials

The step 2 pic shows the pieces that were cast to make the six segment robot muscle.

Corn starch
100% silicone caulk
plastic cups
plastic bag

1/16" thick plastic sheet. I used phenolic sheet that I had, but polycarbonate, acrylic or any other plastic sheet material could be used.

6"x6" plywood

Spray Lacquer from hardware store.

12 volt air/vacuum pump from:

12 volt solenoid air valves from:

Aquarium air hose from:

Raintree drip irrigation fittings from

Step 3: Molding Muscle Segments

Cut Plastic Sheet
Two six inch squares of plastic 1/16" thick are bolted together with three small bolts and a 2" circle is cut on a scroll saw to make a mold.

Make Mold
One of the sheets is mounted on a piece of wood that has been sprayed with Lacquer to prevent sticking.

Mix Oogoo
A small batch of Oogoo is mixed by volume in a plastic cup. I used 1/2 tablespoon corn starch to 1 tablespoon 100% silicone caulk. If you want, you can add a small dab of artists oil paint to color it.

Screed The Oogoo
Rub an angled straight piece of plastic across the mold that is over filled with Oogoo, to create a 1/16" thick layer of Oogoo.

Add Polyethylene Air Spacer
A plastic circle is cut out of a plastic bag and placed on the smoothed first layer. It is cut at 1-3/4" to leave a gap around the edges of about 1/8"

Screed The Second Layer
The second sheet of the form is put in place and the second layer of Oogoo is screed-ed to seal in the plastic bag circle between the two layers. Once set up, the Oogoo will not stick to the bag creating a space for air to fill. A hole is later drilled through the plastic bag circle to introduce air to the finished segment.

Step 4: Gluing Robot Muscle Segments

The step 4 pic shows the assembled six segment robot air muscle under pressure.

The first thumb pic shows the pieces that will be glued together with thin layers of Oogoo. The green pieces are 1/16" pieces that were cast in the full circle mold and then cut to 3/4" wide semi-circles. These create the spacers that are glued between the inflatable circle segments.

Oogoo will glue pieces of Oogoo that are set up, extremely well. It actually fuses it together.

The next thumb pic shows the assembled muscle.

A hole is drilled through all the layers and then one end is sealed with Oogoo and on the other end of the hole a silicone tube is glued to introduce air.

Step 5: Smaller Robot Air Muscles

The step 5 pic shows the small 3-segment 1" diameter air muscle under pressure.

The thumb pics show the pieces used to make the muscle and then the pieces glued together.

Step 6: Robot Muscle Air Valves

Step 6 pic shows the setup I am using to test robot air muscles.

A twelve volt air pump is adjusted with a relief valve to provide air pressure of around 7 lbs/sq-in.

12 volt air valves are controlled by a Picaxe micro-controller that also uses PWM to control the speed of the air pump.

If I have time, details of this muscle controller may be included in a future instructable.

Step 7: Other Possibilities

The step 7 pic shows one way of using the six segment robot air muscle for a robot arm or finger.

The thumb pic shows the muscle relaxed.

Vacuum Muscles
The muscles I have made so far are pressure muscles. I made them this way because they are the simplest type of actuator. Vacuum muscles that have larger volume cavities that collapse under a vacuum can also be made. This makes them closer to animal muscles that can be used with "tendons" to mimic natural motions.

3d Printing
It should eventually be possible to print the skeleton, muscles, and skin for a robot. This would make for more economic and efficient robots.

Extremely Small Robots
My main interest is in building small robots one foot long or less. These low pressure muscles are ideal for that. It may even be possible to make extremely small microscopic muscles by painting or spraying them on.

Smaller Pumps
Smaller and quieter pumps will be needed to make extremely small robots. There are several robot researchers working on small chemical generators that create gas to provide the pressure.
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