alt Hacker NewsThere needs to be a gradient or the wax won't move due to temperature. The motion is the change in state, as you say, but it won't change state if you don't heat or cool it.
That's why it's a motor, like in dishwashers, not a thermostat like in e.g. greenhouse windows or radiators.
It doesn't need to be persistent, but without some way to create a state that is different than ambient, it's not a motor.
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Apples and apple seeds to me. The way I see it, the thermostat contains the motor (EDIT deleted the rest of explanation).
EDIT: the way I see it, talking about gradients here is nonsense. The wax motor works by expansion/contraction due to point temperature. No gradient is involved. Gradients are thermostat-level thinking, and even then, in the greenhouse scenario, there is no gradient to talk about, because the whole point is just to vent the heat from inside to outside when inside crosses certain absolute value of T, and the only "gradient" that matters is the assumption that outside side is less than T at all times.
I disagree, I think motor in this case only means “creating movement”. The motor is the thing creating movement depending on the ambient temperature.
Also you seem to have a miscommunication with the person replying to where they are talking about a special thermal gradient and you mean it in a temporal sense.
The wax expands due to ambient (even uniform) temperature. It's a linear actuator, so warm -> expanded and cool -> retracted.
no the material inflates proportionate to absolute temperature, causing motion, iiuc
things lietrally change its volume maintaining mass when its temperature changes, due to atoms moving more energetically, like something be 4x4x4 inches at 40F, but 4 1/16 x 4 1/16 x 4 1/16" at 200F
this isn't a Stirling engine with a displacer, just a sealed off piston