Watch this video. If you’re confused about how it works, check the diagram above.

If you’re still confused, don’t worry–you’re in good company.

Nederlander Jan Ridders, who is something of a legend in the model engineering world, built what he calls his Thermo Pulse Mobile without really understanding how it works, basing his model solely on a YouTube video demonstrating another one in operation. At first it didn’t work. Then…

After a lot of random experiments, which I shall not enumerate here because of their irrelevance, I almost gave up until I took a closer look at the video. I noticed a kind of restriction at the place were the brass cylinder was fixed in the glass tube… Because I hadn’t the slightest idea how the restriction should look, I used numerous small brass cylindrical plugs from my scrap box, including those with and without all kinds of bores in them and other deformities. I started random experiments, putting all kinds of plugs in the glass tube at the place where it is fixed in the stand…

By far, most of the plugs didn’t bring any positive effect, but with some of them the engine started to show some sign of life. I was pleasantly surprised and at the same time extremely astonished when I found one plug that caused the engine to keep running, although yet not fully reliable. Using the typical characteristics of this “reference plug” I made a new plug, adding step by step changes to the geometries of the reference plug. This was still a random way of working, but at least somewhat more systematic. Finally I succeed in making a restriction that allowed the engine to run reliably.

Even though they’ve now got a working model, Ridders and his fellow model engineers have been unable to come to a consensus explaining the thermodynamics.

If you’re interested in this or any of Jan Ridders’ engines, he will e-mail you high-resolution technical drawings for free upon request. Apart from this remarkable curiosity, Ridders’ more traditional model engine work is not to be missed.