Muscle Wire FAQ


Questions and Answers to some commonly asked questions about Muscle Wires.

What are Muscle Wires?

Muscle Wires are thin, highly processed strands of a nickel-titanium alloy called Nitinol - a type of Shape Memory Alloy that can assume radically different forms or "phases" at distinct temperatures.

How do Muscle Wires work?

At room temperature Muscle Wires are easily stretched by a small force. However, when conducting an electric current, the wire heats and changes to a much harder form that returns to the "unstretched" shape - the wire shortens in length with a usable amount of force.

How much do Muscle Wires shorten?

Muscle Wires can be stretched by up to eight percent of their length and will recover fully, but only for a few cycles. However when used in the three to five percent range, Muscle Wires can run for millions of cycles with very consistent and reliable performance.

How strong are Muscle Wires?

Large wires are stronger than small ones, and strength varies with diameter. The strength to expect from a wire when heated is shown by the Recovery Weight in the table below.

The Deformation Weight indicates the amount needed to stretch a wire when cool - about one sixth the force exerted when the wire is heated. Our largest wire has over 110 times the strength of the smallest size, so you can easily match wire strength to your needs.

What if I need more strength?

For more strength, use two or more wires in parallel. This gives you as much strength as needed, and still keeps the fast cycle times of smaller wires.

How fast can Muscle Wires activate?

Muscle Wires contract as fast as they are heated - in one thousandth of a second or less. To relax, the wire must be cooled, which depends on the conditions surrounding the wire, and its size. Our new Flexinol HT series of wires has a higher transition temperature and cools up to 50% faster than the LT wires. The table below gives typical cycle rates for both LT and HT wires in still air. Moving air or immersing the wires in a fluid like a water/glycerine mixture can increase these by ten times or more.

How long do Muscle Wires last?

When used in the three to five percent range under proper conditions Muscle Wires can run for millions of cycles. Often, other parts of a device will fail or need adjusting long before the Muscle Wire does.

What are the advantages of Muscle Wires?

Compared to motors or solenoids, Muscle Wires have many advantages: small size, light weight, low power, a very high strength-to-weight ratio, precise control, AC or DC activation, low magnetism, long life, and direct linear action.

These features let you create whole categories of amazing new devices that would be difficult or impossible with anything other than Muscle Wires.

What are the keys to using Muscle Wires?

For longest lifetimes and best performance from your Muscle Wire devices, follow these key points:
  • Have good electrical and mechanical connections.
  • Protect the wire from overheating.
  • Protect the wire from overstraining.
Each of these can be accomplished in many different ways. These topics and more are covered in detail our 128 page Muscle Wires Project Book.

How much power do Muscle Wires use?

The power needed to activate a wire depends on its diameter, length and the surrounding conditions. The table below gives typical current levels for "room temperature" conditions. Power can be increased, but once the wire has fully shortened, power should be reduced to prevent overheating.

Wire Name
Wire
Diameter
(microns)
Linear
Resistance
(Ω/m)
Typical
Current
(mA)
Deform.
Weight**
(grams)
Recovery
Weight**
(grams)
Typical
Rate**
(LT/HT)
Flexinol 025
025
1770
20
2
7
55/na
Flexinol 037
037
860
30
4
17
52/68
Flexinol 050
050
510
50
8
35
46/67
Flexinol 075
075
200
100
16
80
Flexinol 100
100
150
180
28
150
33/50
Flexinol 125
125
70
250
45
230
Flexinol 150
150
50
400
62
330
20/30
Flexinol 200
200
32
610
116
590
Flexinol 250
250
20
1000
172
930
9/13
Flexinol 300
300
13
1750
245
1250
7/9
Flexinol 375
375
8
2750
393
2000
4/5

* Multiply by 0.0098 to get force in Newtons
** Cycles per minute, in still air, at 20 Centigrade
LT = low temp 70°C, HT high temp 90°C