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1500 questions
11
votes
6 answers
Why isn't heatpump technology used for solar collector panels and boiler tanks?
All solar collector and boiler tank systems that I can find on the market use a liquid to circulate the heat between solar collector panels (or PVT panels) and boiler tanks. Is there a reason why they do not use expandable gas and a compressor…
Louis Somers
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11
votes
9 answers
Aluminum weight saving
"Aluminum saves weight! Its 3 times lighter than steel!"
Also its 3 times weaker and 3 times softer. When comparing stiffness and strenght to weight ratio, aluminum isnt any better than steel of comparable grade.
Yes, 7000 grade expensive aluminum…
Soliton
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11
votes
3 answers
Could a gold/{second metal} crown be created that would pass the Archimedes test cost effectively?
Many people are familiar with the story of Archimedes submerging a crown in water to identify if the volume of the crown was consistent with the volume of the same amount of gold. The test was to see if a lighter cheaper metal (like silver) was…
James Jenkins
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11
votes
4 answers
Extending USB cable makes it not work
I have a camera that uses a USB cable to connect to my computer. I want to extend the cable from 3ft to about 6ft. Originally I just created my own cable, soldering 4 26AWG wires to a blank USB connector and connecting the other side to the correct…
Jack Campbell
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11
votes
3 answers
How do vending machines prevent people from stealing goods?
I never understood mechanically how a vending machine prevents people from accessing goods through the dispensing panel. From what I understand it's not a locked door that unlocks only upon payment, dispenses goods and then re-locks. In my…
Sidharth Ghoshal
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11
votes
2 answers
Soil swelling and mass/volume relationships
Given moisture content, Specific gravity of solids, initial volume, and weight. I'm asked to compute the moist unit weight, dry unit weight, and degree of saturation of this compacted soil. This is already done. This compacted soil sample was then…
Gon
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11
votes
2 answers
Why do air entrainment admixtures improve the freeze-thaw resistance of concrete?
It is stated on here that:
Air-entraining admixtures cause small stable bubbles of air to form uniformly through a concrete mix. The bubbles are mostly below 1 mm diameter with a high proportion below 0.3 mm. The benefits of entraining air in the…
egg
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11
votes
1 answer
How do Thumb instructions compare to ARM instructions for performance?
A colleague mentioned that Thumb instructions were significantly slower than ARM instructions (this was for an AT91SAM7S32 processor). Is this true? What are the performance benefits of one instruction set over another?
Patrick
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11
votes
1 answer
How fast should I sample with a logic analyzer?
If I have a 10 MHz digital signal, how fast do I need to sample with a logic analyzer to avoid any bit errors? Does the minimum sample rate increase if I want to attach a protocol decoder (e.g. SPI)?
I am aware of the Nyquist-Shannon sampling…
Patrick
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11
votes
4 answers
Why are most jigsaw blades designed to cut on the up stroke and have teeth that point towards the shank?
Why are most jigsaw blades designed to cut on the up stroke with teeth that point towards the shank? Why are reverse teeth jigsaw blades less popular?
Adam
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11
votes
3 answers
Why doesn't stovetop glass crack from thermal shock?
I have a feeling that if my stovetop was made out of regular glass, it would have cracked from rapid cooling/heating a long time ago – especially if you consider accidental water spills. What kind of glass is able to withstand such abuse?
(I am just…
Vasiliy Sharapov
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11
votes
3 answers
Why are mass-produced metal parts machined by rotating the part against a stationary tool?
There's a TV programme called "How It's Made" which often shows automation of mass-produced machined parts. Very often, it seems that metal parts are machined (especially drilled) by rotating the part against a stationary tool rather than holding…
Lefty
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11
votes
2 answers
Why are three way bridges rare?
It's true that most bridges are "two directional."
But three way bridges are pretty rare, globally. I can understand why there wouldn't be many for rivers, but if bridges are designed based on the lie of the surrounding ground, why wouldn't there be…
Tom Au
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11
votes
1 answer
Avoid snapping an electric cable from too much rotation
I recently built the basic construction for a crane out of lightweight material. Basically the head of the crane contains an electric servo motor which spins the head of the crane by pushing itself away from the tower (the rotor is fixed to the axis…
Mast
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11
votes
5 answers
How is lift related to airspeed?
Lift produced by an airplane wing is related to airspeed - this much is clear; a plane moving too slowly will stall. But what is that relation? Linear? Quadratic? Exponential? I don't need the exact equation, which is surely quite complex, just the…
SF.
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