Soft Robots: Making Robot Air Muscles

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: https://www.instructables.com/id/Soft-Robots-Make-An-Artificial-Muscle-Arm-And-Gri/

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: https://www.instructables.com/id/How-To-Make-Your-Own-Sugru-Substitute/

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: http://www.sparkfun.com/search/results?term=vacuum+pump&what=products

12 volt solenoid air valves from: http://www.allelectronics.com/make-a-store/item/SOL-132/SOLENOID-VALVE/1.html

Aquarium air hose from: Amazon.com

Raintree drip irrigation fittings from Amazon.com

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.

Comments

[paulie_g]

You are an absolute legend. I was looking at soft robotics enviously but didn't want to shell out for the massive amounts of Ecoflex silicone required.

[PascalJ]

Love your work, and thanks for sharing. Have you been able to test a pressure at which the oogoo bursts?

Is the key to inflation, the inner plastic liner? Could an oogoo baloon (likely very low corn starch) be made, and how much would it expand by?

[GordieGii]

Actually, these would be a lot more like a real muscle:

http://www.shadowrobot.com/products/air-muscles/

http://en.wikipedia.org/wiki/Pneumatic_artificial_muscles

...and wouldn't be restricted to 15 PSI which is the maximum you can get from a vacuum.

[Starsword7]

There's an instructable for something like that:

https://www.instructables.com/id/How-to-make-air-mu...

[ScottMurchison]

Hi. Thanks for sharing your project. I am inspired to use some of your ideas in a project I'm currently working on. I was hoping you can offer me some advice. What I want to do is have a small platform about 12" in diameter held up by three small air pillows (at 120 degrees from each other). The weight of my platform and payload will be approximately 3 lbs. I guess the best way to picture it is how a server in a restaurant holds a round tray with a drink on it. The tray will wiggle randomly because the server cannot hold it perfectly still. This hand motion is what I'm trying to simulate. The little purple pillow in your photo above looks like something that might work. What I want to be able to do is partially inflate/deflate each pillow independently using an Arduino at a rate up to 10 times per second. I could use an air pump and three air valves to inflate the pillows. Would I simply use a second 12V valve on each pillow to let air out; i.e. each pillow would have one 12V valve to inflate the pillow and a second to deflate it. I think this might work, unless you have a better idea. Do you know where I could find inflatable rubber balloons with the two connections I need? I've never heard of oogoo until I read this article today and would prefer something already available. Thanks.

[GordieGii]

Would something like this work?:

http://www.leevalley.com/en/wood/page.aspx?p=70432&cat=1,43456

[chubby8]

hello, love the instructable. !! :)

do you think you could come up with a simple and effective way to also make the hoses from oogoo?.

I know they are a more tricky shape to form. though it would save money on buying a silicone hose, plus the satisfaction of making more of the robot and extra customisability are advantages.

[mikey77]

Yes, you can fairly easily make square hoses with Oogoo.

Make a form using 1/8" acrylic or other plastic sheet. On top of a base sheet, glue two strips side by side with a gap between them. Make it 1/8" wide by 1/8" deep and as long as is reasonable.

Tape a piece of wire suspended down the middle, centered in the form. Hardened wire like piano wire works best, but copper wire will work if you can get it very straight.

Fill it with Oogoo and after it has set up, pull it out of the form and pull out the wire. Test it under water under pressure and fix any leaks you find with a patch of Oogoo.

I prefer the hoses because the vinyl hoses are inexpensive and allow you to use fittings that make the muscles and valves plug and play.

[jlyvers743]

A very clear instructable and an awesome idea! My mind is in overdrive thinking of the many possible applications of your muscles!

[vatosupreme]

Awesome, I love this! On step 3 you could use a 2" hole saw and cut all six segments in the plastic so you could screed an entire muscle in one shot.

[danzo321]

This is wonderful. Would it help if each muscle segment was more the shape of an orange segment? I think I could rotocast silicone rubber.

[mikey77]

I have only tried a dozen different shapes for Oogoo air muscles. I have by no means found the optimum configuration. I suspect there could be several hundred useful forms of silicone air muscles. Lots of room for experimentation.

Roto-casting the Oogoo is a good Idea. It could make for some unique hollow shapes. I think some commercial silicone bellows are made that way.

Have you roto-casted before? I would be interested in trying it.

[roliop]

Another neat Oogoo app !

You mention glueing the air-hose to the muscle: does Oogoo stick to the hose, or did you find another glue ?

Thanks,
rp

[mikey77]

Oogoo glues extremely well to set up Oogoo and to some kinds of silicone hose. The 1/8" hose I used that worked best is very supple and almost sticky to the touch.

Unfortunately, the less expensive, smooth and stiffer, silicone hose that they sell for aquariums does not glue well enough to easily hold air pressure.

[old.bodger]

Could you give any details of the air valves - manufacturer - source etc? I've been trying to find some with no success. Thanks

[old.bodger]

Now I read it carefully and see that you have! Thanks Sorry!

[vroom...vroom...]

I will try to mow an raise version. Don't ask me how.

[WWC]

Very cleaver. If you said what the green " hinged " pieces were i could not find. What are those?

[mikey77]

I have updated the step 1 pic and added to the step 4 explanation.
I hope that helps.

[WWC]

It does. Thank You very much!