Making A Wax Motor For Micrometer-Level Control

November 4, 2026 by Maya Posch 13 Comments

Although not very glamorous, wax motors are a fairly common type of linear actuator. They use the thermal response of waxes and the resulting volumetric expansion or reduction to create a relatively fast, smooth, and highly predictable actuator that can work for decades. They can often be found operating valves and things like the door mechanisms of washing machines. As [BubsBuilds] demonstrates in a recent video, you can even build your own wax motor for very precise control.

Here simple paraffin wax is used, which changes in volume by 1.15 times when it goes from solid to its molten state. Calling it a ‘waxtuator’, [BubsBuilds] characterized this expansion rate over the temperature range between solid and fully molten to make it a controllable actuator. In his experiments, a gap of less than 5 µm was maintained over twelve hours, showing how precise this device can be if you can control the temperature that the wax is kept at.

One major issue is the low conductivity of paraffin wax, which as some commentators remark can be solved by mixing something like fine copper particles into the wax to increase the thermal conductivity. In the shown implementation instead multiple channels in the aluminium block are used, which are melted by a TEC element.

The wax exerts pressure on a working fluid, which then pushes on a hydraulic cylinder that can be used for whatever precise linear actuating task has to be performed. Although initially water was used as a working fluid, this posed many issues with wax-water interface compatibility and vacuum degassing.

Although ethylene glycol makes for a better working fluid, this proved to be its own hassle. With the water-wax version a displacement sensor was thus used to measure and calibrate the whole setup. The electronics used to control the TEC in combination with the current temperature and displacement are a story in itself, but essential for making this device work.

While not something we often see tackled in the DIY space, we’ve covered a few teardowns of commercial units over the years.

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Dissecting The Elusive Wax Motor

June 18, 2018 by Tom Nardi 34 Comments

We’d wager most readers aren’t intimately acquainted with wax motors. In fact, a good deal of you have probably never heard of them, let alone used one in a project. Which isn’t exactly surprising, as they’re very niche and rarely used outside of HVAC systems and some appliances. But they’re fascinating devices, and once you’ve seen how they work, you might just figure out an application for one.

[AvE] recently did a complete teardown on a typical wax motor, going as far as cutting the thing in half to show the inner workings. Now we’ve seen some readers commenting that everyone’s favorite foul-mouthed destroyer of consumer goods has lost his edge, that his newer videos are more about goofing off than anything. Well we can’t necessarily defend his signature linguistic repertoire, but we can confidently say this video does an excellent job of explaining these little-known gadgets.

The short version is that a wax motor, which is really a linear actuator, operates on the principle that wax expands when it melts. If a solid block of wax is placed in a cylinder, it can push on a piston during the phase change from solid to liquid. As the liquid wax resists compression, the wax motor has an exceptionally high output force for such a small device. The downside is, the stroke length is usually rather short: for the one [AvE] demonstrates, it’s on the order of 2 mm.

By turning heat directly into mechanical energy, wax motors are often used to open valves and vents when they’ve reached a specific temperature. The common automotive engine thermostat is a classic example of a wax motor, and they’re commonly found inside of dishwashers as a way to open the soap dispenser at the proper time during the cycle.

This actually isn’t the first time we’ve featured an in-depth look at wax motors, but [AvE] actually cutting this one in half combined with the fact that the video doesn’t look like it was filmed on a 1980’s camera makes it worth revisiting the subject. Who is going to build a wax motor power device for the Power Harvesting Challenge in the 2018 Hackaday Prize?

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Wax Motors Add Motion To Your Projects

November 10, 2014 by Adam Fabio 19 Comments

[electronicsNmore] has uploaded a great teardown and tutorial video about wax motors. Electric wax motors aren’t common in hobby electronics, but they are common in the appliance industry, which means the motors can be often be obtained cheaply or for free from discarded appliances.

As explained in the video below, wax motors are rather simple devices. A small block of wax is sealed in a metal container with a movable piston. When heated, the wax expands and pushes the piston out. Once the wax cools, a spring helps to pull the piston back in.

The real trick is creating a motor which will heat up without cooking itself. This is done with a Positive Temperature Coefficient (PTC) thermistor. As the name implies, a PTC thermistor’s resistance increases as it heats up. This is the exact opposite of the Negative Temperature Coefficient (NTC) thermistors we often use as temperature sensors. PTC’s are often found in places like power supplies to limit in rush current, or small heating systems, as we have in our wax motor.

As the PTC heats up, its resistance increases until it stops heating. At the same time, the wax is being warmed, which drives out the piston. As you might expect, wax motors aren’t exactly efficient devices. The motor in [electronicsNmore]’s video runs on 120 VAC. They do have some advantages over solenoid, though. Wax motors provide smooth, slow operation. Since they are resistive devices, they also don’t require flyback diodes, or create the RF noise that a solenoid would.

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