I realise this is an old video (!) but I heard you talking about pressurised gas cylinders for automatic opening of greenhouse windows and vents. I think you may be referring to what's known as a "wax motor", a particular blend of waxes which expands from solid to liquid at a particular temperature, and grows in volume as that happens. (Hopefully useful to viewers at least!)
I realise this is an old video (!) but I heard you talking about pressurised gas cylinders for automatic opening of greenhouse windows and vents. I think you may be referring to what's known as a "wax motor", a particular blend of waxes which expands from solid to liquid at a particular temperature, and grows in volume as that happens.
(Hopefully useful to viewers at least!)
I'm not sure why but the link for the raspiviv won't take me to the correct page.