# Muscle Wire



## rhyman (Apr 19, 2009)

As winter slows our outdoor garden railroad activities, here is an idea for a way to spend those cold days doing something to enhance your layout. Has anyone thought about incorporating muscle wire to animate figures or accessories? One of my sons was explaining to me how muscle wire works when he was home from college over Thanksgiving. He is using the material to build miniature robots in one of his engineering classes. I didn’t know it, but muscle wire has been around since the 1930’s.

Muscle wires are thin strands of a special nickel-titanium alloy that actually shorten in length when electrically powered. They are easy to use, and they can lift thousands of times their own weight. They provide a source of motion that is very similar to that of a human muscle, providing possibilities that are not available with motors or solenoids. They are a lightweight, solid-state alternative to conventional actuators such as hydraulic, pneumatic, and motor-based systems.

I can see almost endless possibilities: engineers in the cab that wave to train watchers … conductors that swing their lanterns …people that turn their head to watch you as you walk by … operating coal chutes and water spouts … slow motion turnout operation … workers pounding nails or turning wrenches … just add your own vision here!

You can find a lot of information by searching on things like “muscle wire”, “shape memory alloy”, or “smart wire.” If you are as intrigued with this idea as I am, here is a link to an experimenter’s kit to play with:
link to kit
By the way, if anyone comes up with a new product using this concept, just send me a free sample!


----------



## rkapuaala (Jan 3, 2008)

Been thinking and tinkering for years now  So far nothing real convincing. Can't wait to see what you come up with.


----------



## Torby (Jan 2, 2008)

Never tried them. 

Of late, tiny airplane servos are real cheap. I thought I was getting 4 for $3 each, but I got 4 packs of 2 for $3 a pair.


----------



## Paulus (May 31, 2008)

Great idea, I saw H0 scalers use it to switch turnouts. Never thought of it using for figures but you are right; there are lots of options.


----------



## Semper Vaporo (Jan 2, 2008)

If I understand these things right... (I wish they had listed the specs in something more akin to what I am familiar with... what weighs a "gram"?)...

Anyway... As I figure it, you take a length of this wire and stretch it a wee bit, less than (at most) 8 percent (because if you stretch it longer than that it ruins it), but best to only stretch it 3 or 4 percent. So a 1 inch piece of this wire should be stretched until it is between 1.03 and 1.04 inches long! Then you apply a voltage to produce a current that heats the wire a small amount and it then will shrink back to the original 1-inch length, exerting a pull on whatever the ends are attached to at some "strength" of pull.

Unfortunately, they do not list the properties in terms I can understand beyond that once power is applied it takes 1 second to contract and anywhere from 0.35 to 13 seconds (depending on the thickness of the wire) to relax and re-stretch as it cools. The cycle rates can be from 55 to 4 times per minute depending on the wire size and type.

The "Max Recovery Weight" at "690 MPa" (whatever that is! or why?) ranges (depending on the wire thickness) from 29 to 6,630 grams or at 190 MPa from 7 to 2,000 grams for the "Rec Recovery Weight" (whick I assume is the "Recommended" value. But the "Rec deformation weight" (again I assume "Rec" means "Recommended") at 35 MPa is 2 to 393 grams. The best I can figure is that MPa stands for Mega Pascals... which tells me absolutely NOTHING! But I guess that if I hang a weight from a piece of this wire it cannot exceed 2 to 393 grams (depending on the wire size).

Now according to Stans "Handy Converter" that 2 grams is 0.07 ounce, which according to my handy-dandy portable digital scale from Harbor Freight is about the same as a U.S. Dime coin.

So, in the kit advertised, you get One 20cm (that is about 7 & 7/8 inches) piece of 075 diameter "LT" wire and 15.75 inches each of 100 and 125 "LT" wire. The "LT" stands for "Low Temperature" (as opposed to the "HT" wire which is "Hight Temperature") which activates at 68-deg. C (or 155 deg. F) (The "HT" activates at 88-deg.C or 190-deg.F)

That 7 inch piece of 075 wire can pull or lift 128 grams (a U.S. Quarter, a Nickle and a Dime), a distance of about 1/4 inch in one second if you apply 100 mAmps to it (about 2 Watts). Or a 1-inch length of it could move the same weight 0.04-inches in the same time for the same power consumption. And it can do it 33 times per minute.

Can anybody verify my cockeyed cogitations?


----------



## Torby (Jan 2, 2008)

Since 1000 grams is 2.2 pounds, a gram is a hair more than 1/500th of a pound. 

A zinc penny (since 1982) weighs 2.5 grams. An older copper penny, 3.5 grams. 

And now, you know, the Happy Hollisters' 100 pounds of pennies was $129.87.


----------



## Trains West (Oct 4, 2008)

have you seen this ?

http://www.rr-cirkits.com/actuator.html


----------

