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Comment by geokon | Hacker News Reader

Seems this would make it possible to make a relatively cheap waterproof actuator if you made it out of something corrosion resistant?

I've been looking for actuators to use in damp/wet environments and sealed actuators are rather expensive and supposedly don't last too long

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Some hot water radiator systems use wax actuated valves made from brass (Taco brand is common). They are extremely simple and robust.

thank you for the pointer!

I've struggled to protect eletronics. Waterproof enclosures all fail over time. Though I have some ideas for immersion in mineral oil. But finding actuators that could work has been a bit of a struggle. These look cool, though maybe not something one could run off 5V :) Ill keep looking around

This is why wax motors are used for washing machine door locks.

how does it work for a door lock?it seem it works pretty slowly.

Mayne you know, are the internal components already designed with corrosion in mind?

In washing machine application the locking action is quite fast as the heating element is PTC connected more or less directly to mains, pretty substantial amount of energy gets dumped into the wax over few AC line cycles. In that application (and also in most industrial automation situations) ~100ms is more than fast enough because when most of the effector components are AC powered you end up with ~40ms worst case actuation delay just from the physics of AC electricity. On my washing machine it is quite noticeable that when you press "start" the door gets positively locked well before the capacitive sensing "button" finishes playing its haptic feedback non-sense. (the fact that front panel of cheap-ish toploading washing machine is actually a huge touchpad with haptic feedback that is designed to look and behave like five physical buttons says many things about economics of manufacturing stuff for that somewhat hostile environment at these scales)

oh interesting - I didn't realize PTCs can be used that way safely. I thought it hits a target temperature and then will continue heating at that temperature (which in your scenario would be unsafe). Maybe for my usecase it'll be hard to find a suitable actuator b/c I have a 5V system running of battery (looks like 12V ones do exist though)

From the linked page:

> When a cycle is started, a wax motor is actuated pushing a pin outward and locking the door. This design has cost, reliability and safety advantages. In moist conditions a wax motor costs less for equivalent reliability than an electromagnetic solenoid or motor latch. It has a predictable passive release delay. If power is lost the door remains briefly locked, designed to be longer than the high speed spin cycle coast-down time, then reliably unlocks as the wax cools.

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