Update: Oh, by the way, I didn’t mention in my last update but I cleaned the cylinder again and it’s been running fine ever since. I’m sorry for anyone that was emotionally committed to this experiment and was disappointed it was over. We’re at 2 years 9 months more-or-less constant use. I put a strobotach on it a long time ago and if i recall correctly at that time it was running about 300-400 rpm, but looking at it right now I bet it’s more in the 100-200 rpm range. I didn’t do the math how many revolutions this is total but I probably will someday.————Update: tonight I came home and the engine was oscillating back and forth, but not rotating. As others have mentioned, because of its magnetic coupling to the displacer, this engine can rotate in either direction. So if the engine loses enough energy (for whatever reason) the flywheel will stop rotating and begin to oscillate. If it can regain enough momentum it will restart in one direction or the other but if not it will eventually stop. Such drama as I was watching this! With each oscillation I’m wondering, “Will it get over the top??” Sadly it did not, and it eventually stopped.I have to admit, after 2-1/2 years it’s getting increasingly difficult to keep this running continuously. I think there are several factors, the first being that it’s been running continuously for about 2-1/2 years. Second, I cracked the power piston cylinder when I sprayed compressed air on it (inverted). Finally, in the past few months I put an UV LED over it so my painted-on glow-in-the-dark dots are glowy all the time. For some reason this has motivated gnats to think the power piston is a super place to call home even though the engine is under a glass globe. I don’t think the mass of the gnats on the piston is a problem but I could believe some gnat guts on the cylinder walls could be. Anyway, she’s all cleaned up and running again.———Update: it’s been a long time and I’m starting to lose track, but IIRC I’m at about 2yr 2mo of running this engine constantly on a 6w heater. I’m not going to do the math to see what that cost me on the electric bill. Ok, I probably will eventually. Anyway, it’s still going. There was a little while when it slowed down and even stopped but I cleaned up the power piston and now it’s going again full speed 24x7x365-1/4.——Update: Coming up on a year of constant operation. At some point I painted glow-in-the-dark spots on it. That’s fun.—-Update: I’ve had this running 24/7 on the aforementioned warming plate I made for it for about 6 months now. There’s no indication that it’s going to quit. I would have thought that the arm would have sawed off the pin by now, but nope. As for the squeaking, contrary to the directions I put a small drop of light oil on the pin and that fixed it right up. Now for another PSA, if you get the urge to use an inverted can of compressed air to supercool the top plate, be careful not to get it on the glass cylinder because it *will* crack (I was able to fix mine). But, man, that engine will book when you spray it!________________Update: Just so you know, the DWCL-01 will not run if it’s set on a magnetic surface because of the magnet in the displacer, unless that metallic surface happens to be extremely warm. That means if you buy or build a warming plate it has to be non magnetic. I built a warming plate out of some spare power resistors I had laying around (we all have a collection of spare power resistors, right?) using a pickle jar lid as the surface. The engine would not spin! Unless I picked it up then it would run like crazy but if I set it down it would stop again! Turns out the magnet in the displacer was sticking to the jar lid. So I got rid of the lid and set it down with a thin piece of cardboard between the engine and the resistors and it ran ok. Turns out the resistors are also slightly magnetic. Anyway, not a knock on the product, just a PSA. Your physics may vary.————I got the DWCL-01 because some other people said it was a little better construction and had real bearings. When mine came today I opened it right off the UPS truck so the machine was pretty cold. I held it in my hand and it started right up. I heated up a couple mugs of water at work and it ran for just about an hour on each one. It’s neither noisy nor silent; sometimes it makes kind of a sqeaking sound, but overall I find the repetitive sound soothing! This one will be my home engine but I might get another for my office just for the sound! Tonight I put it in the fridge then took it out, held it in my hand, and it ran like gangbusters. I have many experiments planned for it.As for the construction, it’s smaller than expected but fit perfectly over the mug I had for it. The screws around the circumference actually held it in place nicely on the mug. The fit and finish is maybe not quite as nice as the photos but it’s fine.While I had it in my office every engineer that came in wanted to talk about it. (One non-engineer came in and was like, “What’s that?” and I said, “A Stirling Engine,” and she rolled her eyes and goes, “Ok, whatever.”) So, in summary, it’s cool and fun. Is it $40+ of fun? I don’t know. Between the price and fit and finish I’m torn between four and five stars. For the fun factor I’m going to give it the benefit of the doubt and go with five.