Introduction: Fabricating Fishing Line Artificial Muscle at Home

About: I am a learn it all, nothing-is-impossible-er, mad scientist bent on inspiring the world using technology and science.

Welcome to my first instructable where I will explain my methodologies for creating nylon liner material actuators (NLMAs), also referred to as nylon artificial muscle. I will be brief in my explanations of the ‘rigs’ that I have built to create the muscle, as they are fairly simple in concept and will instead focus more on the steps to fabricate the NLMAs.

By the end of this Instructable you will be able to turn simple strands of fishing line into material that can contract under heat. Thus the material cost will be fairly small and I will give multiple suggestions on tools and their alternatives while we work through this project.

What is Nylon Artificial Muscle? Roughly, it’s tightly wound nylon strands. A recently utilized discover about hyper-wound nylon is that under heat it contracts along it's length and expands around it's width. Mimicing the contractions of muscle fibers.

Why would someone want that? It could have applications in DIY passive-cooling as some researchers make auto-venting windows, smart-materials that can alter shape under heat and varied forms of robotics.

Articles about NLMA:

Step 1: Tools and Supplies

Nylon fishing line: This is pretty simple and should not cost you more than $10, be sure that the fishing line is nylon and mono-filament. When it comes to making NLMAs you just need to know that thicker strands of nylon yield stronger NLMA that contract slower while thinner strands are weaker but contract rapidly. It is usually true that the thickness of strands scales up in proportion to the ‘test’ or rated weight limit of the fishing line.

An example: My 50lb test line can lift a bowling ball, and my 8lb test line can only lift about a pound. Keep in mind that the 8lb contracts instantly where the 50lb takes about three seconds.

*An alternative to fishing line is to buy Nylon yarn, peel it apart and make micro strands but I’ve had limited success.

Spinning Tool: When I first started I used an electric dewalt drill and stood on a ladder to spin material. Now I use a small DC motor recycled from a broken printer. You could order a cheap drill or a DC motor from Amazon. I’ve also included a link to another instructable that will explain how you can power the DC motor with a battery but the same principle applies if you have a variable voltage power supply.

Heating Element: The nylon contracts under heat so you will need a controllable heat source. In Pure Carbon’s instructable he uses a lighter. I suggest buying a heat gun which is what I use or if you are feeling particularly ambitious you could try using a conductive wire and joule heating it in proximity to the NLMA. (Joule heating is basically electrical friction, running high voltage through thin wires.)

Weights and a Stopper: You will need something to place strain on the strand and to stop it from unwinding until you are done. I have modified a metal coat hanger illustrated in the pictures above. I simply clipped it in the middle with pliers (Watch out, it can be sharp after being cut!), I bent one arm into a hook and unfolded the other to act as a catch arm. For weights I purchased some washers from a hardware store. But you would be better off with scientific weighs, I am just cheap.

You’ll see more about how they are used in the next steps. What is important it obtaining something that will give a good deal of control on the level of strain.

Misc and Fasteners: If you plan on building a rig for spinning muscle you will likely need a handful of screws and some zip ties. Additional work shop tools like a drill, screw drivers, a saw, hammer, pliers, electrical wire (20g is fine), alligator clips and a motor power supply are assumed.

*Without a rig you may still need a ladder and a drill.

Step 2: I Don't Want to Build a Rig

Get a ladder, unfold it, plug-in your screw gun and stand on the ladder. You may skip to step #4 and continue. But know this is tiring and stressful when for $30 you can make a frame and use a hobby 12v DC motor.

*Please forgive my crude diagram, I just don't have any pictures from my old project.

Step 3: Cut Boards and Construct Frame

First grab some lumber to make the frame, 2X4 or even 1X2 14ft, culled pine board is fine. Cut a 70in main board, two 16in boards and one 32in back board. See picture above. Firstly I attached the a 16in board to either end of the 70in main-board with screws. Both 16in boards point the same direction off the main board. See the following pictures. Next I attached the 32in back board to one end of the main-board perpendicular to the 16in board with screws. The rig should be able to stand on it’s own no problem.

After That I drilled out four holes in the end of the top 16in board, zip tied my DC motor to it and trimmed the tails of the zip ties. Again, see pictures above. Then I ran 20 gauge wires from the motor, down the side of the rig to the variable voltage power supply. Your rig it now complete and you should be able to spin the motor in either direction by inverting the ends of the power supply.

Step 4: Tying Off and Straining

Now lets spin our first muscle. Start by cutting out a strand of nylon fishing line(See About Length below for how much) tying nylon to your spinner(DC Motor or drill) and then the other end to your stopper. Next place the spinning weights on your stopper(See About Weight below for how much), check that the line is taut and that the stopper will stop the strand from unwinding. With my stopper the arm of the metal clothes hanger collides with the Main-board as winds and stops unwinding.

*About length: Know that the length of the NLMA will be under half the length of the beginning nylon. If you want a certain length of NLMA then you can refer to this formula.

ℓ = π(drod + dnylon)Ncoils

*About weight: If you are not sure how much weight to use to place strain on your line you can use the following formula. If you place too much the line will snap and too little will result in a bundled mess known as 'whiskering'.

m = (π(rnylon)2T)/g

*I did not come up with these formula, usually I will just use trial and error. Credit goes to: Go visit his site and see his awesome work with nylon muscle and robotics!

Step 5: Spinning and Unwinding

Next you will begin spinning by turning on your drill or motor. (Note: A slow and steady spinning speed will save you many snapped lines.) The nylon will start to wind and you will start to see the nylon getting shorter and your stopper rising. If you look carefully you will see the nylon is starting to curl up like a spring. Continue winding until the entire body of the strand is wound like a spring.

Next I usually add a little more weight, no more than thirty percent more. Once that is complete the line should be very taut and not very springy. You can run the motor in reverse a small amount, not enough to unwind the nylon, but enough to make the nylon springy. This relaxing and addition of weight is the give the muscle will use to contract with.

Step 6: Annealing

Now you may use your heat source to on the NLMA and you should see it contract around 12-20%. You will need to heat it and cool it in intervals for about twelve to fifteen minutes. This is called Annealing and will alter the structure of the nylon to keep it’s spring like shape after you remove the strain from the stopper.

The heat temperature varies a lot based on thickness of the material. I try to use around 250-280 degrees(Imperial Fahrenheit) to activate the muscle with my heat-gun. If the heat becomes too much, around 400 degrees, you will most likely just melt or denature the muscle.

Step 7: What's Next?

Now that you can produce NLMAs strands, go wild. Build some animatronics or soft robots! Design some passively cooled vents and make your own instructable!

If you complete the instructable please let me know how it went or if you have any clarity based questions please feel free to leave them below!

I'll keep my eyes peeled for what uses people find and you look for my follow up instructable where I guide you through some applications in robotics/animatronics with our little NLMAs! Thanks for reading!