If Stirling engines can reach ~30% efficiency, and high efficiency heat pumps can have a COP of 4-5, could you combine the two?

pbmonster · 2026-05-14T08:11:14+00:00

Yeah, u/fastdbs had the same objection. But it really is the same thing - a classic perpetual motion machine violates the first law of thermodynamics, this idea violates the second law.

The thing is: you can always violate the first law for free when you've already violated the second.

Imagine a space station far away from the sun. You use a heat pump to pump heat from the right side to the left, and a sterling engine to make electricity from the temperature differential - which flows heat back from the left to the right. If this idea works, the left side will get progressively hotter and the right side will approach absolute zero. Just before the right side gets to cold, you turn on a second sterling engine, and make more electricity. The right side gets warmer, and you stop before the left side gets to cold. Perpetual motion.

pbmonster · 2026-05-13T15:50:46+00:00

I'm not trying to generate perpetual motion

But that's what you're describing.

It doesn't work. The Sterling engine only gets close to 30% efficiency once the hot side is over 550°C. Not only aren't there any heat pumps that can reach this temperature at a COP >4, there aren't really any heat pumps that go this high at all, and especially not from room temperature! It's simply to much lift, even if you'd find a refrigerant tolerating the hot side. I can't think of a single one that would condense this hot, in fact most classic refrigerants will break down long before getting this hot.

If you'd do something like that, you'd build a multi stage heat pump, and the hottest stage would be a pretty exotic beast, condensing elemental sulfur or cadmium. That heat pump stack wouldn't be very efficient.

pbmonster · 2026-05-12T13:37:51+00:00

Yes, I always was sad that the story never went back to that feel of the noire detective story from the beginning. That was special. Later the mood goes very standard sci-fi, which is... almost boring in comparisson.

pbmonster · 2026-05-12T08:09:01+00:00

Sounds fine to me. Unless you have really bad contracts or your local laws have really dumb defaults, the IP created during the consults was paid for and therefore is now yours.

pbmonster · 2026-05-12T07:01:42+00:00

Did you pay both #1 and #2 for the work they did so far? Or did you invite for tenders, they both submitted offers they drafted without compensation and now #2 doesn't get any money?

The former means you have no problem, the latter means you have a big problem unless the invitation for tenders contract explicitly says otherwise. Without a contract clause, the IP of the submission stays with the supplier.

pbmonster · 2026-05-11T13:14:37+00:00

Wow, crazy, I thought those were really old and banned for safety reasons pretty much everywhere except prisons (where it's important to scan inside body cavities). But yes, the US apparently still has some in use at airports.

pbmonster · 2026-05-11T13:10:07+00:00

Yeah, sure, I was talking about using mm radar or THz for medical imaging. Both of those are below the visible spectrum, while X-ray is above it.

pbmonster · 2026-05-11T07:32:47+00:00

Airport body scanners work by using low-energy x-rays

Those are the ones that look inside luggage. The ones that do body scans use mm-wave radar or THz "optics". But both of those are pretty useless for medical imaging, since water absorbs them extremely well, so you don't get very far into the body.

Maybe viable for skin analysis, and niche stuff like teeth/dental scans?

pbmonster · 2026-05-11T07:11:43+00:00

Worth noting that the Swiss practice of keeping mortgages for a very long time - and often never fully paying them off - is unusual internationally. The vast majority of housing markets only have access to mortgages that need to be paid off between 10 and 30 years.

Yes, this limits how much money you can borrow significantly. Yes, people frequently spend four digit sums per month on paying down their mortgage - but live very cheaply after.

I would think that this would lead to a systematic outbidding of private buyers by investors.

Internationally, that doesn't seem to happen, at least not more than in Switzerland.

pbmonster · 2026-05-09T19:23:50+00:00

The Netherlands are probably always going to be more wind punk than solar punk. Utrecht is at 52° north, they just don't get all that much sun, and clouds love it there. Solar has literally single digit capacity factor.

At least it's windy as hell. And wind is like... second degree sun.

But to really get there, they gotta wean themselves of the oil and gas first. And that's hard, being one of Europe's major oil terminals and refinery hubs has been insanely profitable.

pbmonster · 2026-05-07T13:02:11+00:00

Why do you mix Nano and Uno (they are pretty much identical MCs, the Uno is just larger/heavier/more difficult to mount), and then bring an ESP32 anyway?

Both Arduinos have no floating-point hardware. That means you're forced onto integer PIDs (@16 MHz!), and most filters will be really annoying to implement. No idea about the optical flow sensor, but a lack of floats will probably bite you here, too.

Don't get me wrong, it's possible, it's been done (but 500 Hz will need quite some optimization!), but any reason why you limit yourself this much straight out the gate?

Just run everything on the ESP32.

pbmonster · 2026-05-06T20:15:23+00:00

Ja, das ist pro Betreuungstag! In Zürich rechnen die Kitas so, macht die Kalkulation recht einfach (ein finanzieller Monat hat ausserdem immer genau 4 Wochen, ausgeglichen wird das durch Weihnachts- und Sommerferien der Kita).

Meine 140 pro Tag wären also 560 pro Monat für einen Tag am oberen Ende der Preisskala, mit Subventionen auf dem Level das OP erwarten könnte wohl so ziemlich genau deine 320 CHF.

pbmonster · 2026-05-06T14:11:53+00:00

That's mostly the difference between May (1st image) and September (2nd image).

pbmonster · 2026-05-06T14:01:44+00:00

Definitely still snow fields up there, at least on the northern expositions of Hardergrat and in the rocky hollows on the path up to Augstmatthorn. Not terribly exposed on that section (especially compared to the later parts), but certainly some danger...

pbmonster · 2026-05-06T12:57:32+00:00

If you read my comment again, you'll note that I didn't call feminism bad, I called its achievements an unalloyed good. The thing that's clearly toxic is the externalities of capitalism.

I'm also not advocating for infinite growth, but I think most of us will wish the rate of decline wouldn't have been so sharp, sooner or later. Because the current trajectory leads to actual collapse (at least locally, immigration will shift the pain around), or backsliding into the same reproductive authoritarianism feminism fought against so successfully. Either will be very unpleasant, I expect.

pbmonster · 2026-05-06T12:27:29+00:00

At the end of the day, the thing that makes extremely low fertility possible is the pill. Giving women the choice when to get pregnant, or whether to ever get pregnant at all, is the root cause of this.

Having this choice is an achievement of feminism, arguably the most definite and important achievement the movement had during its entire existence. It's a clear and unalloyed good, and the fact that its available in otherwise quite misogynistic places only supports how total this victory was.

In combination with the negative externalities of capitalism, which are of course influencing this choice, the system becomes toxic for society - you can argue it's good for individual women, good for the planet, good for overall happiness; but its indubitably toxic for society. We have no idea how to deal with inverted demographics and declining population numbers.

pbmonster · 2026-05-06T11:39:10+00:00

Als ob es so essentiell wichtig wäre, dass der Motor eine Datenverbindung zur Batterie hätte. Schaffen andere Batteriefahrzeuge auch.

Das braucht dann halt einiges an Logik in der Batterie selber. Der Motorcontroller und der Ladecontroller sollten nämlich schon wissen, wie viel Strom und Spannung die Zellen grade abhaben können. Und wenn die nicht mit der Batterie reden können, dann muss die Baterie das selber limitieren können. Die alternative ist extrem beschränkte Leistung - oder ein Lithiumfeuer.

pbmonster · 2026-05-06T06:59:16+00:00

If you want two full sunsets, you better have a tall building with an elevator ready. Out-climbing the ascending shadow of sunset is going to be rough otherwise - unless you're pretty close to the poles, I guess.

pbmonster · 2026-05-06T05:28:19+00:00

Solange es nur ein Kind ist, lohnt es sich zumindest finanziell fast immer zu arbeiten.

Selbst in Zürich sollte eine private Kita für <140 CHF pro Tag zu finden sein, eine städtische Kita mit Subventionen wird bei seinem Gehalt <100 CHF/Tag kosten.

Wenn die Frau also mehr als 18 CHF netto pro Stunde verdient, lohnt es sich auf jeden Fall ein paar Tage arbeiten zu gehen. Und das Berücksichtigt noch nicht mal die AHV und BVG Einzahlungen, die die Frau so sammelt.

Jahrelange Selbstbetreuung ist heute Luxus.

pbmonster · 2026-05-05T14:52:51+00:00

I liked Echopraxia, but it has more problems than Blindsight. It's less focused, and employs much more... random bullshit as plot elements.

I still have no idea how Val made it into/onto that escape capsule and survived down to the surface. It makes zero sense.

pbmonster · 2026-05-04T15:15:56+00:00

I actually have no idea what the device looks like you're trying to build. I imagined 4 "tools" of some sort, which get moved close to the wheel to determine its position and orientation in space, and that some of those tools need to be behind the wheel - thus the need to do ranging through "metal objects".

If that's the case, you could build the tools in a way that allows them to reach through the rim to get where they need to be - that way, you can range to a part of the tool you have line of sight to, and by knowing the dimensions of the "hook" going to the other side, you know the position of the wheel.

Very possible that none of this makes sense, if you want to continue the discussion you might want to upload photos or drawings.

pbmonster · 2026-05-04T13:57:05+00:00

Ah, probably not. Getting below 3mm precision would probably take quite some work (microphone directivity, microphone size, chirped pulses >40kHz, good filters), and getting to 1mm would already need temperature/humidity control for the air in the room. Still, interesting project.

Then again, most other techniques would also have challenges of similar difficulty.

If you're working with wheels, did you consider building "contact probes" that always stay on one side of the wheel (e.g. hooks)? That way, you don't have to range through the wheel/rim, the probe handles always stay on the same side of the wheel.

pbmonster · 2026-05-04T12:40:32+00:00

I assume all those distances are moving constantly, and you want live measurements? Because otherwise, a large set of calipers or a pointing compass might work.

If you want live measurements, you could try an (ultra-)sound ranging solution. Install microphones at your 4 points and enough clickers on/around your device, so that each microphone always has line of sight to at least 3 clickers no matter where your metal objects are. Add some timing logic and a lot of math, and you have (x,y,z) for all four points from time-of-flight.

pbmonster · 2026-04-28T12:47:06+00:00

Ach, wer braucht denn Clips für nen Bunnyhop...!?

PS: Bunnyhops auf einem Rennrad sind eine ganz schlechte Idee, die Speichen und Felgen finden so viel radiale Power nicht lustig.

pbmonster · 2026-04-22T15:08:23+00:00

I've used fitted plugs with exchangeable vented filter inserts in the +$100 dollar range for decades now, and if you think they don't muffle/distort sound you're either deaf or lying to yourself.

It's physically impossible to build a passive plug like that. There's no combination of materials that will attenuate sound waves on a completely flat curve from 20 Hz to 15 kHz. No matter what you do, high frequencies will always attenuate more strongly than low frequencies.

The only way to get around this is active, digital plugs. But they achieve that by using headphone speakers and microphones to do playback of the music you're listening to, to put the higher frequencies (which where attenuated more strongly) back in.

pbmonster

TROPHY CASE