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1500 questions
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Waterproof Case Time Limits

Some cell phone cases have a waterproof rating of IP-68, often specifying that they can tolerate immersion to 6 feet for 30 minutes or 3 feet for 60 minutes. My understanding, however, is that a good seal (like an o-ring) would fail near a certain…
bobuhito
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∂p / ∂s ds Component in Euler's Fluids Equation

For the last hour I have been trying to understand what $\dfrac{\partial p}{\partial s}ds$ is in Euler's equation but I have a problem. You can see this image: I know that $p\ dA = \text{Force}$ $γ ds dA = mg$ but what is $\left(p +…
Arief saladdin
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Speed Control of Quadcopter along with Position Control Using PID with Simulink

Within MATLAB Community, I found an example of a simple quadcopter model control built with Simulik and SimMechanics, The controllers handle position and orientation control. I want to extend this controller and add a speed controller (Quadcopter…
mozcelikors
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Are ABS/PLA too volatile to be used in cryo vacuum?

I need to use a custom part inside high vacuum (cryo vacuum), for example as a shadow mask. If PLA/ABS are not volatile, I could just print the part I need. The question is, are ABS or PLA too volatile to be used in cryo vacuum chambers?
Sparkler
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At How Many RPMs Would Aluminum HDD Platters Shatter?

I'm using hard drive platters to create a Tesla Turbine. I'd like to get as much efficiency out of it as possible. That being said, for safety concerns, I'd need to know a generic range at which they'd shatter. If there's no range that anyone has…
user4142
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Are Rolling-Element Bearings Practical for Light Loads?

I have a 5" x 4" x 3/8" plastic panel (wall thickness of 1/8", ribbed). I need to slide the panel over a 12" plastic track that is U-shaped (like a skateboard ramp). This motion could be repeated 2 million+ times. The panel is rigid and maintains…
skibulk
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Uncertainty Calculation of LVDT displacement transducers for length measurement

I have to calculate the uncertainty of measurement for an LVDT Linear displacement transducer used for measuring length. Uncertainty calculations are ruled by ISO 17025 but there are no (at least haven't found) specific guidelines for the…
spe4ker
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Clamping force of a bicycle quick release skewer

In brief: between a standard quick-release skewer and a bolt-on skewer, which will provide greater clamping force? More detail: Modern bicycle wheels are held in place by clamping skewers that run through hollow axles. The typical "quick release"…
Carl
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What surface temperature (rise) is required to (dis)qualify a combustion appliance from obtaining a "zero clearance to combustibles" rating?

How far must the surface temperature of a UL-listed combustion appliance rise to prohibit the manufacturer from specifying it for a zero clearance to combustibles installation? (I looked in UL 127 but was unable to find a straightforward answer…
ThreePhaseEel
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How to model elastic support in FEM?

I need a 8 m x 4 m x 0.6 m RC plinth (mechanical requirement) which needs to be built onto loose gravel. Obviously I am going to over excavate, back fill with selected material and bed my plinth on that. The plinth accommodates 2 x 65 m3 water…
SlydeRule
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Modifying a fixed camera lens for close focus

I found this article on hacking macro lenses. The author used a lens extension tube to allow closer focusing. IE The lens's Minimum Object Distance (MOD) was significantly reduced. I cannot find an affordable lens that suits my requirements, so I…
skibulk
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How to size a fan for open air application?

Assume that you have an axial fan placed in open air with no duct. How can I go about calculating the air speed at a distance x from the fan? The fan is about 1 m above the ground in an open space. I want to use the fan to generate power from a wind…
e.hassouny
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Derivation of beam slope for a cantilever beam

I am trying to derive the maximum beam slope formula $\theta = \dfrac{wL^3}{24EI}$ for this cantilever beam: What method can I use for this derivation? So far I can only find simply supported beams and derivations for the $\theta_{max}$ formula at…
cheeseefungu
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Negative feedback Gain and Phase Margin

Consider the system with unitary negative feedback such that the open loop transfer function is $$G(s) = \frac{as + 1}{s^2}$$ a) Determine the value of $a$ such that the phase margin is 45º b) Determine the stationary state error for the unitary…
Giiovanna
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Turning an engine over with engine compression

When you compress a bicycle pump and seal the opening, the pump will automatically return to it's initial position when you release it. I suppose this is how air suspension works as well? if you have a internal combustion engine without any gas and…
Erik
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