> For the complete documentation index, see [llms.txt](https://delta-robotics.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://delta-robotics.gitbook.io/docs/hardware/nitinol/spring.md).

# Spring

Delta Robotics Nitinol tension springs, per-size force, resistance, current, and cooling data, cycle life, and how to drive and mount them without cooking them

We sell more than wire. We also sell wire coiled into little powerhouses. Our Nitinol tension springs are precision-formed from shape memory alloy to yank, lift, and contract with muscle-like motion: more compact than straight wire, and every bit as strong. This page covers what they are, how they perform, and how to keep them springing instead of snapping.

{% hint style="warning" %}
Springs reach an activation temperature of about 90 C and can draw tens of amps at larger sizes. Keep hands clear while powered and use adequately rated wiring. See [Safety essentials](/docs/get-started/safety.md) for the full hazards.
{% endhint %}

## What is in the coil

Here is what you are getting:

* **Material:** Shape memory alloy (Nitinol)
* **Form:** Precision tension spring, trained to contract when heated
* **Actuation method:** Joule heating (run current through it)
* **Length:** 50 mm
* **Spring ODs:** 5 mm, 10 mm, 20 mm
* **Wire diameters:** 0.5 mm, 1.0 mm, 2.0 mm
* **Activation temp:** about 90 C
* **Mounting:** pre-mounted with 5052 aluminum fixtures on both ends, conductive and ready to plug into your project

These are not passive mechanical springs. They are active, electrically actuated devices.

## Spring specifications

We are still validating these values, so treat them as provisional. If something looks off, tell us.

| **Spec**              | **0.5 mm Spring** | **1.0 mm Spring** | **2.0 mm Spring** |
| --------------------- | ----------------- | ----------------- | ----------------- |
| Wire Diameter         | 0.5 mm            | 1.0 mm            | 2.0 mm            |
| Outer Diameter        | 5 mm              | 10 mm             | 20 mm             |
| Max Force (Estimated) | 2–3 N             | 8–10 N            | 25–30 N           |
| Stroke Length (Est.)  | 15–20 mm          | 30–40 mm          | 40–50 mm          |
| Resistance (Ω)        | 0.79 Ω            | 0.41 Ω            | 0.17 Ω            |
| Contraction Current   | 4 A               | 16 A              | 60 A              |
| Actuation Power       | 12 W              | 105 W             | 600 W             |
| Cooling Time (Air)    | 5–15 s            | 20–30 s           | 60 s              |
| Cooling Time (Fan)    | 2–6 s             | 8–15 s            | 20–30 s           |
| Cooling Time (Water)  | 1 s               | 2–3 s             | 5–7 s             |
| Efficiency            | 2–5%              | 2–5%              | 2–5%              |
| Cycle Life (at 3–5%)  | 100,000–1,000,000 | 100,000–1,000,000 | 100,000–1,000,000 |
| Operating Temp Range  | 0 °C – 120 °C     | 0 °C – 120 °C     | 0 °C – 120 °C     |

## Cycle life

Spring fatigue is real but manageable. Stay within the strain limits and these springs run for months.

| **Strain** | **Cycle Life**       |
| ---------- | -------------------- |
| 2%         | 1,000,000+ cycles    |
| 4%         | 100,000+ cycles      |
| 6%         | 10,000–20,000 cycles |
| 8%         | 2,000–5,000 cycles   |
| >8%        | Not recommended      |

Springs settle in over their first runs. Cycle them a few times to stabilize force output.

## Control it

Like the wire, these springs run on the TF Node Controller:

* 60 A output, enough to drive 2 mm springs
* USB and CAN control for scripting and sync
* Built-in current sensing for over-temperature protection
* Custom ramp profiles for smooth motion

See the [TF Node Controller](/docs/hardware/thermoflex/tf-node-controller.md) page for details.

## Cooling

A spring cycles only as fast as it cools:

* **Air:** 5 to 60 s depending on size
* **Fan:** 2 to 5 times faster
* **Water:** 1 to 7 s depending on size

An integrated cooling system is in development.

## Mounting and wiring

These springs ship pre-mounted with 5052 aluminum fixtures on both ends, so most builds bolt straight in. For mounting methods, electrical connection, pre-tension, and the soldering caveats, see [Mounting and wiring](/docs/hardware/nitinol/mounting-and-wiring.md).

## Best practices

* Pre-tension the spring slightly for faster response
* Use mechanical mounting over adhesives
* Stay under 5% strain for high cycle life
* Target about 90 C; do not overheat
* Do not cut a spring unless you know what you are doing (ask us first)

Questions or bugs? Email Kevin: <kevin@deltaroboticsinc.com>

## Related pages

* [Wire](/docs/hardware/nitinol/wire.md): The straight version of the same alloy.
* [Mounting and wiring](/docs/hardware/nitinol/mounting-and-wiring.md): Anchor and connect the springs correctly.
* [TF Node Controller](/docs/hardware/thermoflex/tf-node-controller.md): Drive the springs with precise current.
* [How to Train Nitinol](/docs/learn/how-to-train-nitinol.md): The materials science behind the coil.