texts: Maximum shear force of metric steel bolt

texts:
I'm struggling to calculate with any confidence the allowable shear force for a metric bolt holding two aluminium pieces together.

I only need an approximate figure, since I will allow a very large margin of safety.

Assume that the pieces being joined are sufficiently strong. Assume the bolt is threaded throughout its length. It is acceptable for the thread to be damaged, but no permanent deformation to the bolt core. Assume a single bolt holds the two pieces such that the pieces can freely rotate, but that they won't.

The two pieces being joined are are 5mm and 3mm thick. The bolt is M8 with 1mm thread. Assume the bolt is made of a weaker steel.

What is the value of the shear force for the above?

So far, the most progress I have made is by using this online calculator, but I think it's for tension strength. Nevertheless, the "proof load" comes out at 8.82kN for for "property grade" 4.6. I'm guessing the area strength is of similar magnitude.


texts: Ryzen 5 2600x Rev. A versus Rev. F: What is difference in revs?

texts:
My son built a computer a few months ago with Gigabyte m/b and Ryzen 5 2600x. He bought the parts at a local Computer Super-Store and built it.

I liked it so much I bought the parts at the same local Computer Super-Store and built one for myself. Had some trouble with bad h/w but Super-Store allowed returns and now my computer runs great.

When we were attempting to determine why my computer might be having trouble we noticed only one difference: his Ryzen 5 2600x was marked Rev. F and mine was marked as Rev. A.

When I returned the m/b and CPU I thought maybe I'd get a Rev. F also but again it just so happened that it was a Rev. A and everything does work fine.

Now I'm very curious as to what the differences might be in those two Revs.

Do you know what the differences are? Do you know where I might find the differences listed?

Yes, I Googled (actually duckduckgo) but didn't find anything even mentioning the Revs.

Even on the official site on the specific CPU details I don't see anything: https://www.amd.com/en/support/cpu/amd-ryzen-processors/amd-ryzen-5-desktop-processors/amd-ryzen-5-2600x


texts: In a diesel engine, does more heat leave the engine through the tailpipe or the radiator?

texts:
Diesel exhaust is hot, and there's a lot of it.

Diesel radiators also get pretty hot.

In a typical diesel engine, which one is dissipating more heat?

EDIT: In response to a request for specificity below, I am specifically interested in heat losses on five different gensets I operate. The engines are a 0.7L Kubota D722 (no turbo), two Lister Petter LPW4 engines (also no turbos), a 2.216L Perkins 404D-22 (also no turbo), and a 4.5L John Deere 4045TF151 (turbocharged). These engines are run at 1800 RPM (except for the kubota, which is 3600 RPM), under roughly half of rated continuous load.

That is my specific situation, but I am looking for a general understanding of the matter, not just situation-specific advice.


texts: How can I absorb shock on an existing steel structure?

texts:
I'm currently trying to extend the shock-absorbing capabilities of a welded steel structure that is shown in the following image. It is a structure that supports a slat conveyor. A load is to fall approximately in the middle half of the structure. The base of the structure rests in a concrete foundation.

I need to expand the shock-absorbing capabilities because I'm worried about the structure failing due to pure impact forces. I'm not as worried by vibrations as by the maximum force exerted on it due to the impact. The load impact is difficult to quantify, even for a worst case scenario, but it is safe to say that the structure has resisted an impact force that is 25% lower than the one that is to fall now.

I would prefer not to change all the beam sizes, since the slat conveyor that rests on top of it is already assembled, but I could add some supports if needed.

According to Design of Welded Structures, however, making the beam span between supports shorter raises the impact stresses suffered by the structure, even if it lowers the static stresses (once the load is in place).Is there anything I can do to minimize these impact stresses?


texts: What would a track in a culvert be used for?

texts:
A colleague works in a closed (no public access) watershed and came across this culvert today. These smooth "tracks" down the center of the culvert are something we have never seen before. Any idea what they may be for?

Some details that may afford clues:

Culvert installation date is unknown (so 30+ years).
The culvert runs underneath an access road.
There are no other utilities or structures anywhere near (within a mile) of this culvert.
The channel upstream and downstream of the culvert are still in their natural state.
Logging use to occur in the watershed in the past, but there are no known logging zones next to this culvert.
The culvert is massively over sized (serves an area of 150 acres which typically does not receive significant snow-pack).
This stream empties into a main tributary which is about another 1/3 mile downstream.
Surface road was originally used for access to the upper part of the watershed, and for logging vehicles/equipment.
This culvert is located near Portland, Oregon


texts: What thickness of aluminium sheet do I need to achieve the same strength of a 1/8" steel sheet?

texts:
I want to use a boat with an aluminium hull. The authorities wants me to prove by calculation that the hull strength (longitudinal, lateral and local strength) equals at least the strength that would result from the use of steel plate of a thickness of 0.11811 inches. So what I'm looking for is:

A gross idea of the aluminium plate thickness I need;
A method for showing that the aluminum plate is strong enough to be substituted for the steel one.

How can I calculate that thickness?


texts: How to distinguish primary and secondary beam in FEM formulation?

texts:
Assume that I am writing a new FEM software for structural analysis, it shouldn't really matter whether this is a frame or frame+shell element analysis tool.

I understand that primary and secondary beams have their own function, and are designed for different use.

  Primary Beam: A horizontal beam connecting columns (simply supported
  or shear connected.) Function: It will transfer the load from
  secondary beam(if present) to the columns.

  Secondary Beam: A horizontal beam connecting primary beams (simply
  supported or shear connected.) Function: It will transfer the load to
  the primary beam and not directly connected to the columns.

In FEM, everything is just frame element, and all the beams and columns are equal, so whether one beam should resist more loads ( ie primary beam) than the other is completely up to the outcome of FEM procedure. But as engineers, sometimes we just want this one beam to take more loads than the neighboring ones.

How can I modify my FEM engine to do what I want?


texts: Is there a material that returns to original, curled form when straightened?

texts: Is there a material that 'wants' to be curled up but can be straightened an indefinite number of times without failing?


texts: How much does human tissue attenuate radio frequency signal of a given frequency?

texts: Attenuation of radio frequency (rf) signals in a medium depends upon medium characteristics and frequency of the signal. How much does human tissue attenuate rf signal of a given frequency?


texts: Why is it when taking the moment coefficient relative to c.o.p., the weight is ignored?

texts:
I have been working on a question, and my lecturer has hinted me with this equation that doesn't include forces due to weight?

$C_{M_x}=C_{M_{ac}}+C_L(x/c−x_{ac}/c)$

What he told us was that due to the derivation of the equation we can ignore weight with this equation? However when taking the moment of course one must take weight into account correct? Is it included in the lift coefficient?


texts: Base Driven Tuning Fork Mechanical Response Spectrum

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I am new to vibration analysis/simulation etc. so I may be missing something very basic here so please forgive me if I'm explaining things poorly or not making sense.

To familiarize myself with vibration simulation I am trying to simulate the frequency response spectrum for a tuning fork. I am using Solidworks.
I have

created the geometry for a tuning fork
fixed the base and calculated the eigenfrequencies eigenmode shapes
Applied a uniform base displacement excitation (same magnitude for all frequencies)
Plotted the lateral displacement of one of the tines as a function of excitation frequency
The part is made from copper (young modulus supplied by software) and I am using a modal damping ratio of 0.02 for all modes.
The excitation amplitude is 1mm

Here is an image of the main "tuning fork" mode showing the fixed base (green arrows) and excitation vector (purple arrow).

Here is a plot of the magnitude lateral displacement (x direction) of a node at the tip of one of tines of the tuning force versus excitation frequency.

The peak at ~500 Hz corresponds to the mode shown above. The peak at ~2.5 kHz corresponds to a higher frequency vibrational mode.

Question

I am confused about the high frequency response of the tuning fork. At low frequency I see that the response is falling off from the two resonances towards lower frequencies. This makes sense. If you slowly move the tuning fork up and down (from the base) there will be no stress or deflection since everything is slow so there will be no lateral displacement.

However, I would ALSO expect the response to drop off at high frequencies as well.. I guess my intuition here is motivated by the following. Consider a mass attached to a base by a spring and a damper. If the base is shaken then at high frequencies the response of the mass falls off, it is as if there is nothing connecting the mass and the base at high frequency. I guess I expect something similar for the tuning fork. If I drive at high enough frequency the tuning forks can't even tell there is a drive..

Can someone please explain to me:

1) If it is correct that this response function should be constant versus frequency above the tuning fork resonance frequencies and

2) Whether it is correct or incorrect can you give me any intuition for why we should expect whatever is the correct behavior?


texts: Why do small displacement engines have higher RPM ranges?

texts:
So lets compare my dirt bike and my daily driver:

My dirtbike is a single 350cc cylinder 4 stroke engine. It has a redline at 12.1k RPM.

My daily driver is a six cylinder 3.6L V6. The redline on it is 6.5k RPM.

On my daily driver, and without much mechanical knowledge, I understand that at 6000 RPM, each cylinder would be moving at 1/6th of the total RPM as its a "team effort"
My motorcycle piston would be working alone, so it has to reach the 12.1k on its own.
Is the bottleneck not the piston, but in the crankshaft? How can a single cylinder work faster alone as opposed to working with other cylinders?


texts: why do we need state feedback in H-infinity concept instead of output feedback

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I have faced control of a flexible manipulator which have a zero dynamic related to flexible parts dynamic. the zero dynamic states (generalized states) are not observable in input-output dynamic and usually use observer to estimate them in state feedback applications.
I see in the manuscripts that in H-infinity based controller, in penalty/performance vector definition, the internal dynamic states are participated.
I have a question: is it possible to have output feedback (containing just external dynamic states)? is there any controller based on H-infinity which leads to output feedback? assuming the C matrix in y=Cx is not full rank.


texts: Can gravity be a driving force for a spring-mass system?

texts:
If a spring-mass system is undergoing free vibration (oscillating up and down), then does it imply that there is no gravity?
My tutor always consider gravity when finding the Equation of Motion for such a system. But isn't gravity is an external force? If so, wouldn't the system be technically undergoing forced vibration as it is experiencing an external force in its direction of displacement?


texts:
This is a basic question but for some reason it has me stumped. I am modeling a continuous load on a soil layer on a commercial FEA package. This is a plane strain problem where the layer is modelled 20m wide by 10m deep.

I am trying 2 variations with 0.2 m  thickness and 1 m thickness. The load the software is applying is 1 kN/m/m for the 1m thickness variation. I would like to find an equivalent loading (i.e one which will give me equivalent stresses and strains throughout the layer) for the 0.2 m thickness case.

I am hesitating between using 0.2 kN/m/m and 5 kN/m/m. The reasoning behind these two numbers is either 1/0.2 = 5 or 1*0.2 = 0.2. Can anyone please explain what 1kN/m/m actually means? and how do we convert it for different thicknesses?


texts: Which of these propeller configurations is most efficient?

texts:
All propellers shown in the figure above are identical and are operated at identical speeds with four separate (numbered 1 through 4 vertically) configurations illustrated. The physical distance between the cross sections of any two propellers is small and is close to the diameter of a propeller.
Each configuration is open to the air (for instance mounted on a common axis in the lab) and not enclosed within a pipe or a container.
In the top figure, $\bar{P}<\underline{P}$, with similar air pressure relationships for all the propellers shown in the rest of the figures which correspond to the directions of thrust obtained from each propeller shown in the figure. Using Bernoulli's equation we can state the relationship $\underline{v}<\bar{v}$ between the speeds corresponding to $\bar{P}$ and $\underline{P}$.
Using Bernoulli's principle or other intuitive fluid flow concepts, we would like to understand the relative efficiency of the configurations, where the metric of efficiency is the ratio of the sum of the magnitudes of the thrusts of both propellers (in any of the configurations 2 through 4) to twice the thrust of the propeller in configuration 1.

We're mostly concerned with the comparison of the second, third and fourth configurations. Using Bernoulli's equation, the second configuration seems to be non-degrading if not beneficial to the performance (sum of individual thrusts) while the third and fourth are difficult to analyze by this approach since the flow reverses in the region between the two propellers. If we look at the speed of the air flow (air is thrown with high speed on the propeller side opposite to the direction of thrust), the propellers in configuration four affect each other's performance the most perversely. However, it is difficult to assess the comparison of the second and third configurations. The propellers are co-axial although powered by distinct motors and are open to the air. We can assume still air at atmospheric pressure and density with zero ambient flow rate for the purposes of the question. The back-pressure between the propellers is the object of analysis since knowing it would mean we know (at least a part of) the thrust magnitudes.

Which configurations will generate the maximum sum of the individual thrusts? Can we explain the reasoning intuitively (using Bernoulli's equation or other fluid flow concepts) for the higher efficiency obtained in some of the configurations?


texts: What practical geographical and engineering constraints limit the depth to which you can build underground?

texts:
Similarly, does there exist an index with the maximum building depths and heights in the United States?

I found this map of soil types in California by UC Davis, but I don't think this directly translates into maximal building depths: http://casoilresource.lawr.ucdavis.edu/gmap/


texts: Sizing a motor for a floor jack-like mechanism

texts:
I've been trying, as a thought exercise, to run some calculations on a floor jack-like mechanism that is expected to lift 130kg (287 lbs). Dimensions and setup are as per the image below.

The 130kg load is to be positioned at the end of the boom, to simplify things, I assume the load would be at 90 degrees relative to the boom. My understanding, is that the force would be greatest then, anyway...

Here's my approach to try and size the motor:
1. Find the torque at point A, due to the load on the end of the boom.

$$F = ma = 130\cdot10 = 1300\text{ N}$$

I specify $A$ as 10, rather than 9.8. So, 130 kg load exerts a force of 1300 N.

The torque, then at point A would be

$$\tau = rF\sin\theta = 0.5 \cdot 1300 \sin(90) = 650\text{ Nm}$$

I don't know what force the linear actuator needs to produce - x. I proceed to calculate what applied force at point B would yield a torque greater than 650 Nm. Let's assume a 10% safety margin, so 715 Nm needed at point B.

The angle will go from 90 degrees down, let's say to 30 degrees at the max lift point of the boom.

With reduced angle, the torque is also diminished, so at the highest point, the linear actuator's force applied will need to be (at 30 degree angle relative to the boom)

$$715 = rF\sin\theta = 0.1F\sin(30°) \therefore F = 23,833\text{ N}$$

This sounds like a ridiculously high force rating for an electric linear actuator.

Is my approach correct? I'm quite certain I'm missing something important. Your help will be greatly appreciated.

EDIT
Clearly, the above setup isn't ideal for an electrical linear actuator. The other lifting setup I can think of, is a mobile crane, like in the pic below.

Taking the same size and parameters as above, the force needed by the actuator is much more palatable.

Let's assume force is applied at a distance of 40cm from the point of rotation and an initial 30 degree angle. The lifting mechanism needs to counter a torque of 715Nm (calculated above).

$$715 = rF\cos\theta = 0.4F\cos(30°) \therefore F = 2,102.94\text{ N}$$

Is this correct? (ignoring the counter-weights on the actual crane)


texts: Flap disc vs sand paper vs grinding disc

texts:
Assuming a notional 4.5" disc, on a common 4.5" angle grinder:

Which abrasive cuts faster, a flap disc, a sanding disc or a grinding wheel of common grit (I believe 36 or 40)?

Assume, at least for the sanding disc, and the flap disc that the abrasive material are similar, for example, aluminum oxide.  Ditto for the grinding disc, however they do not seem to be as clearly marked as to the abrasive material.


texts: Export simulink sdi dataset from MATLAB 2015b

texts:
I have used the Simulation Data Inspector in Simulink to log a dataset of two time varying signals.
The only option I see concerning exporting is to .mat or to workspace, which basically produce the same type of output:

Simulink.sdi.Dataset

I have no way of opening this file or dataset, and I need to export it to Excel or to a simple text file with this format:

Time  Var1  Var2
0  53  34
1  47  78
2  67  24
3  54  87
4  45  54

(tab separated values).

My goal is to use the logged data in LaTeX for a report, but as of now I am stuck with a 1x1 Dataset in the Workspace which I cannot use or read.
I have checked the MATLAB manual online, but the export-function they refer to does not work with this simulink.sdi.dataset:

>> export(voutyngve2,'XLSfile','data.xls')
Undefined function 'export' for input arguments of type 'Simulink.sdi.Dataset'.

Can someone please give me a tip?


texts:
How do FE solvers solve the case of panel buckling under pure shear?
The main problem is that global matrix of initial stess is singular in that case. One method is to apply some forces that shear is not so pure. But I think there should be some alternatives. So what do you think?


texts: How are IFC file material relationships maintained across platforms

texts:
IFC files have an IFCMATERIAL property which names a material and is referenced by other components in the model.

The IFC file doesn't point to a materials library, doesn't indicate a system variable that points to a library and uses very general names such as "concrete".

How are these relations managed across multiple interfaces and systems? For example, I have an IFC exported from Revit, where I to import this into xBIM on a system without Revit, how would xBIM know what materials to bind to the objects?

Thanks.


texts: What is the connection between PID and feedforward controllers?

texts: They are tightly connected as some concepts of feedforward is based on PID algorithms, and both of them are control systems. But when I see a phrase such as "Feed forwards augment PID control", I'm confused. Can they be used at the same time?


texts: Power distribution problem in multi-camera usb array

texts:
Problem Summary
My MacBook Pro (development system) can successfully capture images from 24 cameras in the multi camera assembly we have assembled. But when our assembly is attached to a new Raspberry Pi 400 (target deployment system), Linux only mounts up to 18  of the 24 available cameras.
The RPi system log sometimes shows:
“USB Device over current status detected”
at boot up time if the assembly is already connected,  or at attachment time if the USB cable is connected after boot up.
I suspect that this problem may be a power related problem, but I don't know how to diagnose this problem, nor which steps I must take to repair the problem.
In trial and error Attempts to access more of the cameras on the Pi, I have tested configurations in which additional power input is provided to the hubs.  But these trials have not succeeded.
Details and Research
Our multi-camera array is made of 24 or 18 USB cameras and 4 to 5 USB 7-port hubs, that are attached to a controlling computer (Mac or RPi400) via a single USB cable.
The hubs can be optionally powered using USB-c cables.
I have attached this assembly to both my MacBook Pro (development system), and to a Raspberry Pi 400 (target deployment system). While all 24 cameras are accessible when connected to the Mac, The RPI will only detect up to 18 cameras, and sometimes it won't even find that many.
USB Camera array configurations:
Note that all cameras, hubs, cables and the USB port on the computers are all rated  USB3.

What I’ve tried:
I have tried connecting external power to zero up to all of the hubs.  I have tried them arranged in both spoke and daisy chain configurations shown for both 24 and 18 cameras.
I can put USB amp-voltmeters between any 2 USB devices, as well as on the power inputs to the hubs when they are receiving external power.
With external power to all hubs, the meter between the master hub and the computer reads a steady 5.15V and 0amps.
I am guessing that the difference between the Mac and the RPi response may have something to do with how much voltage or amperage the RPi USB port can handle, and that those values are different for the MacBook Pro.
What suggestions can you offer as to what Voltage and Amperage measurements should be measured, and where to measure them to determine what is causing the hardware errors.


texts:
In a conventional nuclear reactor the amount of neutrons 'flying around' is maintained with control rods and water is usually used as a moderator. From a certain point of view the control rods keep the nuclear fuel just critical enough.

In a molten salt reactor where the fuel is dissolved in the salt irrelevant of this is thorium, plutonium or uranium. And in a reactor where the nuclear fuel is solved into the salt :

How is it possible to maintain the mass critical enough in a molten salt reactor?

I can understand that they use control rods in the reactor itself, but if the salt is dropped into the safety reservoir below the reactor isn't the mass getting uncontrolled supercritical?

Thanks!


texts:
I dont understand how the diagram of M/EI of conjugate beam drawn , can someone explain about it ?
According to conjugate beam theorem , i know that the M/EI represent the w(x) , which is force per unit length of the beam . I dont understand why the author draw in in 2 directions ( upwards and downwards) ...


texts: two parameter equation to approximate torque v.s rotor speed curve of AC induction motors

texts:
Like the title states, I am looking for a way to approximate the torque vs rotor speed curve of an AC induction motor using the standard specs given in a specs sheet:

LRA
Pull-up torque
break down torque
rated torque
torque = 0 at synchronous speed

I am trying to approximate with least squares. I don't know what two parameter equation would be the best way to go with.


texts: What settings to set to weld aluminum with TIG?

texts:
I bought a Everlast 205 AC/DC and I am new to welding. I would like to experiment with aluminum welding but my electrode doesn't last very long. The arc-cone is pretty wide and I cannot establish a nice weld pot and I don't understand why.

My welder is set on AC with 40% cleaning and 140 A, 80 Hz. If I set the cleaning above 60% my electrode last only 2 seconds, but below 50% it lasts about 10-15 seconds.

Here a picture of my experiment aluminum which is a 4 mm thick plate:

What's wrong with my setting?


texts: Assessment of steel beam for lifting to Eurocode 3

texts:
A client wishes to use an existing steel beam to lift a 1 tonne load using a sling. The 3 m long beam is measured as UB 203x133 visually observed at both ends to be secure with end-plates with all four bolts present.

calculation

For conservatism assume the lowest credible strength steel i.e. S275 steel and the lightest section i.e. UB 203 x 133 x 25. From the Blue Book for $L_{ef}$ = 3 m, the design moment capacity $M_{Rd}$ = 54.6 kNm ($c_1$ = 1.00).

There is no dead load on the beam. Use partial safety factor $\gamma$ = 1.6 for imposed load.

Design load $F_{Ed}$ = 10 kN x 1.6 = 16

By inspection beam is OK in shear. All 4 bolts present in each end plate so connection is OK. Check beam in bending.

Treat the beam as simply supported and assuming sling midspan:

$M_{Ed} = \frac{PL}{4} = \frac{16 \times 3}{4} = 12$ kNm < 54.6 kNm $\therefore$ lift OK

Please provide feedback on this assessment with a criticism or suggestions for improvement.


texts: Is there a possibility to shield CMOS-chips from light but still be current sensitive?

texts:
Since I am not from the field of physics or engineering, the next question may seem a bit naive. I would like to measure an electric current with a CMOS sensor, which is practically directly applied to the sensor by a conductive solution. However, it should be prevented that a (changing) illumination with blue light also leads to a signal on the sensor. Is there a possibility to make this shielding in a way that ions can continue to flow, but no photoelectric effect occurs?
Maybe there is something like a conductive, light-absorbing coating or something similar?
Or other physical principles that I can't come up with?
Or could you point me to a principle that I can investigate further?
Thanks in Advance!


texts: Running Hydraulic Pump with High Torque Motor

texts:
It's my understanding that hydraulics are merely a means of gear reduction to move a given object. So then I'm wondering why I can't find a formula or way to determine the following issue:
I want to run a gear pump (specifically a hydraulic motor as a pump; I know it will be more inefficient) with a DC electric motor. The system is meant to run intermittently so will not be subject to constant load like one would find in industry. I can't utilize a large bulky large HP motor so I am trying to run it with a below-spec HP motor that has a large amount of torque. Everything I've managed to find though seems to read as torque is insignificant, the HP rating is the determining factor. Is this correct? If horsepower=torque * RPM, wouldn't a small HP/large torque motor work, just at a lower RPM/speed?


texts: What are the key differences between the X-Band and the S-Band radars?

texts: They differ in frequency of about 6000 Mhz. What are the practical differences of these devices. What are the ups and downs vs the other?


texts: Internal differences between latching solenoid and Stepper Motor

texts:
It is my understanding that basic latching solenoid consist of coil, magnet, spring, two electrical wire, electrical connector, enclosure and armature plunger. My assumptions are based on Latching Solenoid Theory

A basic 4 wire stepper motor consist of 2 additional coils, magnet, four electrical wire, enclosure and electrical connector. My assumptions are based on Intro to Stepper Motors.

The above are my basic understanding with regard to internal differences and similarities between the two components. I understand vendors will include addition feature to differentiate themselves from competition.

Questions: Are there any other standard subcompacts that are missing in this basic analysis?


texts:
I've noticed that aluminum squeeze tubes have a fold at the end. The fold is not the seal of the tube, as I can unfold and see the seal on the very end of the tube once unfolded. Wikipedia states that

  Aluminium tubes generally have the far end folded several times after the contents have been added. The tube is thus hermetically sealed and nearly germ-free due to the high temperatures during the production process. The inside of the tube can be coated to prevent the material from reacting with the contents.

I don't understand why the 2nd sentence follows from the first, especially in my case where the seal is not the fold, rather it looks like the seal was made, then it was folded. Shouldn't the seal be enough to hermetically seal the tube?

Why are aluminum tubes folded at the end? How does the folding relate to hermetically sealing the tube?


texts: Heat transfer characteristics in narrow rectangular channel

texts:
Please take a look at following figure:

System considered is a narrow rectangular channel of 2.5 mm depth (W x L is 60 mm x 150 mm). Since channel has low depth, it can be considered as mini-channel. Bottom surface is hot and at $~ 100\,^o \text{C}$, top surface is initially at ambient $20\,^o \text{C}$. Air flow enters channel at $20\,^o \text{C}$.
I want to know how for such narrow channel heat transfer is defined for air as working fluid. Specifically:
$$ Nu = f(Re, Pr)$$
a correlation of Nusselt number as function of Reynolds and Prandtl number. Re range is in 500 - 2000.
Any suggestion of literature reference are welcome.


texts:
How can I measure changes in liquid level of the order of 50 μm?

The tank is cylindrical with a radius of about 12.5 mm and a total volume of about 45 ml. The fluid is water-based. The technique needs to be optical or similar because no external body can touch the solution.

I looked at ultrasonic sensors but they don't seem to reach such high precision. Now I'm checking laser sensors as well, but it seems that they don't satisfy the required precision either.


texts: How to improve reference tracking using state feedback?

texts:
Suppose that I have a state-space system $A, B, C, D$ and a gains matrix $K$ computed via LQR. I would like to track a reference signal $x_{cmd}$. I do so by using the control law:

$$ u = -K(x - x_{cmd})$$

where $x$ is the system state.

How do I develop a feed-forward term as a function of $x_{cmd}$ to encourage the system to follow the reference more closely, particularly in the case of time-varying $t_{cmd}$?


texts: Is the flow same in parallel pipes feeding into a water container?

texts:
I have 2 questions.
I am aware that the headloss is the same in all intakes into a water container.
My question is, is this illustration correct that the flow is different for different outlets?

And when you calculate the headloss for this system, how do you go to calculate the splits?
As 1 pipe which has the surface of the 2 pipes or is there something I'm missing?


texts: USB sound on PC when plugging laptop charger into the socket

texts:
Sometimes I hear my PC making the USB - connected device sound when I plug in my laptop charger into the socket.
By USB connected device I mean the sound that it usually makes when I connect something through the USB port.
I am not exactly sure what causes this sound.


texts: Orthonormalization of Damping Matrix -- modal analysis

texts:
In my mechanical vibrations class we studied the method to orthonormalize a set of differential equations by the mass matrix (principle coordinates). This is where you take the matrix of eigenvectors from the un-damped system and normalize it by the mass matrix.

Multiplying the mass matrix by the modal matrix gives:

X'MX = I

And multiplying the stiffness matrix by the modal matrix gives:

X'KX = W^2(ii)

Where W^2(ii) is the matrix of squared natural frequencies.

My question is: is it appropriate to try and orthonormalize the damping matrix in the same fashion?

X'CX = 2*zeta*omega(ii)

Should this transform the system's damping into principle coordinates?


texts: How to reinforce concrete over a circular span

texts:
Last year we poured a RC suspended slab according to designs of a structural engineer. (Note we are just DIY home builders but have taken professional advice throughout.)

The slab was cast with three little 300mm diameter port-holes which we had planned to use for light, but for various reasons we wish to cover these up now.

Of course, a steel plate over the top would be fine, but for waterproofing purposes I'd like to set a concrete square over the top, using a slurry to bond new to old concrete, and waterproofing the whole lot.

My concrete square would perform two functions: to provide an upstand to waterproof, and to cover the hole.

From a structural point of view, a piece of plywood would (hypothetically) be adequate, because over the top we will add 100mm insulation then hard finish like paving.

But I'm aware I may need to consider the mass of the concrete itself, so will need to add rebar.

There are other possible solutions, like trying to seal a steel plate, then screeding over the top - but as we will be applying quite an expensive liquid membrane, then setting hard finish which I hope to last for 50 years on top, I'd like this to be a bullet-proof solution in terms of waterproofing. The fact they stick out of the ground is not a problem, as we will be adding insulation over the top of the remaining area before the paving stones. Although my idea would mean a reduction in area of insulation which is not idea.

Here's a pic of the formwork (not complete) which shows square sides and the circle inside the hole is propped from underneath (NOTE: I have not yet adjusted prop height, when I do, the circles will be flush with the top of the concrete)

I have also cut and bent rebar into 400mm lengths, with a right angle bend at each end and a further 100mm that could be doweled into the existing concrete to provide both reinforcement and prevent movement. I was going to use 4x lengths laid parallel per hole.

I've made no calculations, as I think this may be a trivial "onsite solution". But I'm aware there will be an (albeit small) amount of suspended concrete here.

Can someone tell me if this is a sensible plan so far?

Another option might be to place a steel plate over the holes then add concrete as per my plan above.


texts: Two angular velocities on two segments connected by a hinge joint differ only by the joint angle velocity

texts:
I was reading this article called "Joint Axis and Position Estimation from Inertial Measurement Data by Exploiting Kinematic Constraints", but I'm not understanding one part, which doesn't let me proceed in the reading of the same.

From the physical point of view, we have the following situation:

Two segments (one orange and the other green) connected by a hinge joint. The 3-axis coordinate systems that you see in the picture (the one on segment orange and the other on the segment green) are the local coordinate systems of two 3-dimensional gyroscopes.

The dashed line that you see in the hinge should be the coordinate axis of the same joint. Since the joint can only move in one dimension, we have just one axis.

Now, given this setting, the authors say (first page, column at the right, at the end of the same):

  ... let the angular velocities of the gyroscopes, in the coordinates of
  their local frames, be $g_1(t)$ and $g_2(t)$ for the first and the second segment, respectively. Then it is a geometrical fact, that $g_1(t)$ and $g_2(t)$ differ only by the joint angle velocity and a (time-variant) rotation matrix

Questions

What is the joint angle velocity?
What is this time-variant rotation matrix?
Why do the angular velocities differ only by the joint angle velocity and a time-variant rotation matrix? What does it even mean, actually?


texts: How to design the right input to obtain a desired output for a linear system?

texts:
If I have a state-space model, so that matrices $A$, $B$, $C$ and $D$ are known, how can I design the right input $u$, so that $y$ is a desired signal, say, a sine wave with constant amplitude?

$$\begin{aligned} \dot{x} &= A x + B u \\ y &= C x + D u \end{aligned}$$


texts: How does single-phase AC synchronous motor work?

texts:
In a recent question of mine about microwave plates, jpa correctly identified the type of motor used for microwave plates as a specific variant of AC synchronous motor, equipped with gears that reduce the speed to some 5RPM.

  A single-phase (or two-phase derived from single phase) stator winding is possible, but in this case the direction of rotation is not defined and the machine may start in either direction unless prevented from doing so by the starting arrangements.

What I am unclear on - what is the principle of operation of such motors?
What construction property of the motor is responsible for the start direction being unpredictable but the motor never being stuck and unable to start?


texts: Feasibility of additively manufacturing large metal objects in microgravity/high vacuum (space)

texts:
This a somewhat speculative question; I would like to know whether it is feasible to additively manufacture large (>100m) metal objects - from for example aluminum alloys - in a space environment.

Methods could include 3d-printing or hot/cold spray techniques, or perhaps a fine spray of molten metal onto a thin sheet.

Simple shapes like spheres, cylinders, plates, beams are of interest.

There is some existing work, e.g. https://www.nasa.gov/content/spiderfab, but nothing I can find focuses on manufacture of large simple objects using additive techniques.


texts:
I'm trying to control my 12V fan with a 5V fan controller.
With this circuit the fan run at full speed.
When I measure the voltage on PWM and ground I obtain 5V.

Which circuit can I use to adapt the 5V PWM on the 12V PWM ?


texts: Inverter + Direct drive vs. Belt drive motor in washing machines?

texts:
What should I choose from today.

I am looking at washing machines, and I see that LG has this Inverter Direct Drive (6 motion cleaning) technology in their machines, I see that its not like a year old one, but I am also wondering how long do these last?

So can someone tell me how does direct drive perform nowadays, especially in LG products;

If its more reliable then how cheaper is belt drive fixing?
Are there more stuff to go wrong with that technology?
I see some manufacturers use only inverter technology, what does that
mean to the average consumer, should I choose that over non-inverter?


texts: Thermal Capacitance - Convention for Modeling of Electrical Equivalent

texts:
As an EE, I am very comfortable with the mapping of thermal quantities to their electrical equivalents. However, understanding how thermal capacitances should be connected is driving me crazy.
this example:

Shows a "room" with a thermal resistance and capacitance. There is an external temperature excitation upon which the ambient temperature "rides". Why is it that when the system is modeled electrically, the bottom nodes for the R and C aren't common to one another? Why is it that the C is to the ambient reference, and the R is to the excitation? Shouldn't the C also connect to this excitation?


texts: Is engineering still a good career for Americans?

texts: Obviously it is a good career for indians. But it seems like ME is becoming EE and the adoption of various technologies has deskilled the job to the point where 90% of the available positions are outsourced or taken by h1bs. Is engineering still a good career with viable employment?


texts: Are Scientific Calculators still current?

texts:
I've been a civil/structural engineer for 20 years now. My HP 48GX has recently done its last calculation. So I looked for a replacement and it seems that the market for scientific/graphing calculators has changed.

My question: Could it be that smartphones are replacing calculators in the engineering world and all one needs to do is buy an "graphing calculator" app?

(I am not referring to the open sourced HP48 app)


texts: Using Density Correction Factors for Fans and Blowers

texts:
I've been researching fans/blowers and their use in pneumatic systems (particularly conveying systems), and I'm confused by the application of density correction factors. Let me describe a sample situation:
I have a wood processing plant in which I will be using a centrifugal fan to move material through a pneumatic system. My pneumatic system is characterized by the system curve $$P_s = K_{sys} Q^2$$
where Q is the volumetric flow (CFM) and $P_s$ is the static pressure. In order to move the material through my system, I need a minimum CFM of (say) 10,000. Via my system curve, I find that this corresponds to a static pressure of (say) 7 inWC.
So, I need a fan that can supply 10,000 CFM at 7 inWC. I will do this by superimposing my system curve on the fan curves for the various fans I might select to determine the HP and RMP requirements. Here is where the density correction comes in:
My Understanding:
Ultimately, what I want is material to be moved through my system. The fan gives energy (i.e. does work) to the air, and the air in turn gives energy to the material it moves. At a given volumetric flow rate, denser air will have more energy and thus be able to do more work. Now, the 10,000 CFM I need is the flow rate needed under actual conditions (ACFM). Fan curves are calculated at standard conditions, so I should convert my ACFM to SCFM before comparing to the charts. I do this by simply multiplying by the standard/actual air density ratio.
My Question

Do I also need to correct static pressure? Physically speaking, I don't think the pressure generated by the fan is a function of the air density. Particularly because this pressure is just measured relative to ambient air pressure.
Is it wrong of me to correct flow rate? Some pages I found online said that CFM should not be adjusted, as centrifugal fans are "constant volume devices" (volumetric flow at a particular RPM does not depend on air density). However, I believe that this reasoning neglects the work/energy considerations I made above.

Any references to pages/papers explaining the underlying physics would be greatly appreciated!


texts:
Suppose the fit for a rod and a hole in a gear is supposed to be free running and the fit is 3mm H9/d9. For the specification of the hole for the manufacturing of the gear, is "3mm H9" already adequate since d9 only refers to the shaft tolerance which may not be pertinent to the manufacturing of the gear? Sometimes I see the fit specified on drawing sheets for some reasons, e.g., "10mm H9/d9".

If my understanding is correct, 3mm H9 essentially means 3mm - 3.025mm and 3mm d9 means min. 2.955mm - 2.98mm. So the clearance ranges from 0.02mm to 0.07mm - am I right?


texts: What does an E in a circle after a diameter mean?

texts:
I’m pretty sure it’s something to do with the fitting, possibly specifying to use the minimum circumscribed or maximum inscribed circle to tolerance the diameter but I can’t remember.

The tolerance would be in the form

  ⌀123 ± 0.01 Ⓔ

In case the Unicode doesn’t work correctly that’s

  [Diameter Symbol] [value] [plus minus symbol] [value] [E in a circle]


texts: Does the volume change under the tensile or compressive stress?

texts:
This confusion arise because my teacher says that volume does not change under tensile/compressive stress within the elastic limit of the material ( consider metal here). But as far as I can see via applying Poisson's ratio it does ( otherwise lateral strain would be proportional to square root of longitudinal strain). So does the volume chaneg under tensile stress ? What might be the molecular basis of such?

I defined a quantity (cause it was simple to calculate) $ \frac {\Delta A}{A}$ and then found that

via **Poisson's ratio

$$ \frac {\Delta A}{A} = \alpha \epsilon _{lon}( \alpha \epsilon _{lon} +2)$$

whereas the one derived via assuming the volume to be constant (i.e., $AL = A_0 L_0$) was
 $$ \frac {\Delta A}{A} = \frac {\epsilon _{lon}}{\epsilon _{lon} +1}$$

Here $ \alpha = \frac {\epsilon_{lat}}{\epsilon_{lon}}$


texts: Is there a miniture atmospheric water vapor condenser?

texts:
I am looking to add a condenser for a plant preserving container. The plants need water and I was wondering if I can have a passive method to condense atmospheric moisture to water. My container is small and I would like the condenser to be as small as 30 cm$^3$ (but I can be flexible). Is there a current passive miniature air well (condenser)?
My container design can be changed to fit the condenser (so it is irrelevant). Therefore I would like to find a passive condenser that is small enough but enough to water a plant continuously.
(note: I am not asking for a product, I am asking for a mechanism or a technology or a method)


texts: Why is this construction site pouring gravel over a wire mesh, and then covering it with dirt?

texts:
My office is afforded a prime view of a construction project where the workers are currently covering the leveled ground in a wire mesh, raking gravel across the entire mesh, and then covering that gravel layer in another layer of dirt.

What is the function of this, engineering-wise? I know gravel in a foundation typically is used to help with water runoff, but I can't guess why the mesh is being rolled out underneath, and this is going to become the foundation of a 3-story health pavilion, not some single-family house or storage shed (the entire footprint here with gravel and mesh will have a building on top of it, not a parking deck or a parking lot).

Is this simply a base layer of some kind, upon which concrete and rebar will be placed?

I am in the United States, in Georgia.


texts:
I have set up a peltier module with an aluminium heat sink, cooling fan, 12v, 7ah battery supply and thermal paste for the purpose of cooling water. At first, it performed well. It dropped down to 3.5°c in 2 hours. However, after the 2 hour mark, it had suddenly started increasing in temperature. I didn't move it or change the room temperature at all.
I decided to change the cooling fan to a liquid coolant, which didn't work either. I bought another set up, but this time I noticed the peltier module and cooling fan would only perform seperately when tied to the battery unlike before when both performed well even when the wires were tied together. So I brought back the previous set up, and tested it with the battery again. The same problem occurred.
Can anyone explain why this is happening and what I should do to get it to perform again?


texts: How were horizontal and vertical structures ensured in old times?

texts:
In modern times bubble levels and water levels are used to check if a surface if strictly horizontal/vertical.

How did people ensure vertical/horizontal surfaces in older times?


texts: How long can a chair sit before wearing out?

texts:
I'm mainly interested in aluminum or steel chairs here, as they're what I have lying around, but other materials could also be interesting to hear about if anyone has the data.
As I understand it, the chair exerts effort on the floor and the floor pushes back against the chair when it exists. So unlike a teapot orbiting Mars, for example, surely the surface must wear out over time.
I can't find anything that gives any sort of ballpark figure, but obviously they last long enough for nobody to complain about it. Not referring to long-term comfort while being used here ─ that's a different matter.
I doubt anyone is going to leave a chair in their garage for however long it takes to answer this question, so I'm also cool with anecdotal evidence. I've never put more than a few decades into a single chair before, so I don't have much personal evidence to go off.


texts: Oxygen sensors in trace gas environments

texts:
Do Oxygen lambda sensors (used in automotive applications) work in trace gas environments?

My requirements for a trace Oxygen gas sensor:

The sensor must be capable of working in an inert gas environment of either Nitrogen or Argon.
The sensor's operating temperature is not more than 40-50 degrees Celsius.
The sensor is capable of sensing an Oxygen gas concentration as low as 10 ppm to an Oxygen gas concentration as high as (19-25%, that is, an Oxygen concentration of regular air).

Could anybody who is working with such sensors suggest some sensor that I can use in such environments?


texts: How many batteries can I charge and how long would it take?

texts:
Using a hydro generator which gives an output of 4.838KW, I am trying to figure out how many batteries I can charge and how long it would take.

I am doing the calculations based on 12V, 17Ah batteries. this is for a theoretical large scale operation so i am therefore looking to charge between 25 and 100 batteries.

If an extra generator is necessary this can be factored in, however the core of this question is to figure out the ration between power output it watts and charging of multiple batteries in V & Ah.

If anyone could help it would be very much appreciated.


texts: I'd like to prototype a kind of device to move a rope like a sinusoidal, or similar waveform, it doesn't have to be precise about the waveform, the goal is hide this mechanism in order to show a floating waveform in space for an exhibition. I think to use an electric motor to vibrate one side of the robe and to fix the other side, but I'm not an expert in this field. How to convert the rotatory movement to vibrate the rope? Any hints on how to do this? Thank you


texts:
We are using a load cell as shown below, the data sheet for which can be found on this link.

The load cell needs to coupled with a plunger as shown below.

The plunger is supposed to measure the axial force acting on it. Initially, we had just stuck the plunger with the help of glue on top of the load cell. But with this setup, if the force acting is not completely axial, it tends to cause a moment which leads to incorrect measurement of the force.

We are interested in knowing a reliable way of coupling to solve the issue.
Also, we would like to know if there is some reading reference available regarding this.


texts:
Consider the movement in the vertical plane of an $AB$ bar with a mass of $20 kg$, $0.8 m$ long and supported by two cursors: one at the end A and the other at point G coinciding with the center of mass of the bar.
Cursor A slides on the vertical guide at a constant speed $vA = 0.5 m / s$ (zero acceleration) due to a vertical force $F$ applied at point $A$. Cursor $G$ slides on a guide inclined at $45º$ to the horizontal.
For the instant when the bar is in the vertical position $(Θ = 0)$ calculate the force $ F $ and the reactions on the supports $A$ and $G$.
The solution is $F = 167.14 N; RA = 4.16N; RG = 23.5 N$

I already know that:
the angular velocity of the AB bar is $1.25 rad / s$
the acceleration of the center of mass is $0.88 m / s2$ and the angular acceleration of the $AB$ bar is $1.56 rad / s2$ (anticlockwise)
However i cant get the correct results for the reactions
$\sum M_{c}= I \alpha$ <=> $R_Gcos(45)*0.4=16/15*(1.56)$ <=>$R_G=5.88N$
$\sum F_{y}= (F(y))ef$ <=> $R_{Ax}+R_Gcos(45)=20*(-0.625)$
$\sum F_{x}= (F(x))ef$ <=> $R_Gsen(45)+F=20*(-0.625)$
then i got the wrong walues: $R_{Ax}=-16,657$, $R_{G}=5.88N$ and $F=-16.66N$


texts: How is a plank able to stop a spring door

texts:
So , here we have door which can get closed on its own due to spring. Agenda of Q is to put sth beside the door so that the door does not close.
The Q tells us that when we put a brick of 0.5kg. Door  is able push the block. But if I keep a plank of mass 20g if which touches the door and the planks end touches the walls. The door remains closed. FRICTION is present
My solution to why does the door is able to push the block is because F=M*a. So , as the force becomes large due to acceleration of the door. The block is not able to apply enough counterattacking force on the door at that time and then kinetic friction happens due to it.
In case of plank , since it touches the door even before the plank moves. Therefore , acc of plank=0 and F by plank is also 0.
If my solution is correct , then why does in the case of a plastic bag or rod which is long and is touch the door and the wall same as plank. Then , why does the plastic gets deformed even though F of door is 0.


texts:
$$\propto  \dfrac {\text {Cross-Sectional Area}}{\text {Volume}} $$

I've seen this equation on my textbook (physics).

Let us imagine that there are two pen with $7$ and $3$ lenght. Which is harder to break? According to the equation, $3$ is harder to break. Can you explain it?

Kindest Regards!


texts:
does anyone have any idea what standard shaft size / adapter this is?
the motor is NEMA 56C and the socket size it self is 27.8 mm in diameter and 32 overall with the key.


texts:
I have been struggling with the following problem for a few days now and would greatly appreciate some assistance.

I'm new to control systems and have very little experience with PD controllers and never heard of the pole placement method so please correct me where I'm wrong.

The main problem I seem to be having is that there are three poles $\ s(s+2)(s+5) $ all other examples i have done have had only two $\ (s+2)(s+5) $.

So I don't see how I can you the standard formulas I have been using:

$$ s^2+2ζω_ns+ω_n^2 $$

$$ s^2+(K_d-1)s+(K_p+1) $$

Like I said I'm very new to this so please forgive me if anything I've said is completely wrong.

Thanks in advance for any assistance.


texts: Mechanism for controlling the clamping force

texts:
I am working on upgrading a research project on wind energy. They are trying to measure the performance of wind blade designs in a small wind tunnel (i.e. their models are relatively small).
What they were doing was measure the torque generated by the wind by mounting on the axis of the wind blade a bicycle discbrake and engaging it. (They have gone through many mechanical iterations)

Currently they are using a servo motor to pull a bike cable that activates the clamps. What they do is: blade is accelerated, and then the brakes are applied and bring the blade to a halt. While the blase is slowing down, they are measuring the torque and rpm. In order to maintain a constant force on the clamp they are using a spring to maintain a constant tension of the bike cable.
I am upgrading the measurement software side, and two of the wishlist feature requests were :

to control the system to apply enough clamping force that will maintain the number or rpms. (apparently they had tried that in the past with a PID but it did not work out).
to maintain a constant torque on the design (i.e. clamping force on the discbrake).

When I saw the system I could see the following issues:

given the discbrake design, the available travel between engaging and free running is very small (a few hundred microns). That makes the system the system very non linear and very difficult to control (in a few microns you go from 0 to max braking power - even with a lever).
there is a lot of play on the discbrake (its wobbly) - due to the mounting of the shaft- , however because the shaft is spinning at 3000 to 10000 rpm it tends to self align.

Overall, I wasn't hopeful that I could achieve the level of control with their current system.
So my question (inspired while I was reading this question) is what mechanisms can I look into to apply a controllable clamping force (or equivalenly clamping torque) on a 3[mm] spinning shaft which is rotating at 3000-10000 rpm?


texts: How can I keep a Zippo lighter from losing fluid to evaporation or leaks?

texts:
Zippo lighters are notorious for needing regular refilling. The fuel evaporates from the cotton regularly.
Some people put a bit of rubber around the seal.

What atmospheric conditions keep fuel from evaporating? Temperature, humidity, etc.
Should I keep the lighter near my body  (for heat) or in an outside pocket?

Should I keep it topped off, or will fuel evaporate faster that way?


texts: What is the difference (if any) in capacity factors and efficiency between reservoir hydropower and run-of-river power plants?

texts:
My question is about differences between reservoir-hydropower and run-of-river power plants. Are run-of-river plants less efficient? what would be an approximate guess of the differences? (assuming they are placed in the same catchment). Would annual capacity factors (% of time in operation) differ? by how much?

This answer makes me think that reservoir hydropower would be more efficient because it can capture a larger % of the kinetic energy than wind power. Arguably the run-of-river plants would be in a similar situation, because they are less able to slow down the water flow in comparison with reservoir hydropower. Obviously water and air are very different fluids and I can't just translate the efficiencies from windpower.

Regarding capacity factors, in principle I have no reason to think ROR has lower capacity factors. Water throughput would depend on the catchment area and I guess both have similar maintenance requirements. However, all these are intuitions, I have not found real data to corroborate my hypothesis.


texts: What's the widest spectrum a single camera could process?

texts:
I saw this question, which was too broad, and I thought of a more specific question that can hopefully be answered.

There are "normal" (visible light spectrum) cameras, infrared cameras, and UV cameras, and there are also specialized VNIR cameras that capture the visible spectrum plus some of the near-infrared range. As I understand it, the typical application of VNIR cameras use filters to shift the NIR frequencies into the visible spectrum, to be captured by red, green, and blue sensors, producing false-color images that are essentially a composite of the NIR color information and the visible.

But what if, instead of concerning ourselves with the ability to compress the range of frequencies down into the visible spectrum for the sake of human eyesight, we designed the camera with the goal of recording the widest possible range of frequencies (for example, inventing a new image format with more than 3 channels per pixel - say, R, G, B, IR-A, IR-B, IR-C, UV-A, UV-B, UV-C, designing a sensor matrix of subpixels sensitive to those channels, etc.)? Accepting that we would have to substantially improve the manufacturing of the sensor array to achieve the same resolution as an ordinary RGB matrix, let's prioritize the minimizing of chromatic aberration over maximizing detail.

How far can we extend the frequency range of a single camera? If all the light (or electromagnetic radiation) we capture still has to pass through the same aperture and lens(es) at the same time, could we get all of the infrared, visible, and UV spectra at once? Could we go further than that? What factors impose the hardest limitations on such an endeavor? If possible, please differentiate between something that's definitely, completely impossible, vs. just prohibitively expensive.


texts: How to calculate lever force when lever has uniformed distributed load?

texts:
We have a simple class 1 lever:

$$\begin {array}{c}
\text {5,000 kg} \\
\downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \\
==================== \\
\hphantom {==} \triangle \hphantom {==============} \\
\vdash  \text{1 m} \dashv \vdash \hphantom {======} \text{4 m} \hphantom {======} \dashv \\
\end {array}
$$

The lever ($===$) is 5 m long. The fulcrum ($\triangle$) is 1 m from one end of the lever. The lever has a object sitting uniformly upon it weighing 5,000 kg.

How do I compute the upward force that needs to be exerted at the end of the 1 m side of the lever to keep the lever stationary? $F = (W \times X)/L$ is simple when the weight is applied at the very end of the lever. But what happens if the weight is distributed along the lever?

Our final goal is to tether the free end (on the 1m side) to keep the lever level and we need to know how strong the tether should be.


texts: Why does concentrated shear force on a beam influence the whole beam?

texts:
This might be a silly question but can someone explain how this shear force on the right side of the beam causes Qy throught the whole beam?

I understand it mathematically but not conceptually so I would be grateful is someone could help me understand this via an analogy or something, because when I solve mechanics I am often stuck on such simple problems because intuitively it feels incorrect to me.

I'm aware there is also the M force on the beam but I left it out of the picture because that one I can visualize and I understand it.

In other words, why does the whole beam "feel" this force (if we ignore bending for a moment)? if you press down on my hand I don't feel that pressure anywhere else on my arm.


texts: How to build a pivot linkage for a robot.

texts:
I have asked this question in 3DPrinting.stackexchange forum but got no answer answer. Please take a minute to see if you can help.

I am building a simple RWD vehicle using 3d printer parts. See the picture below.

As you can see from the picture, I am using 3d printed linkages for steering mechanism and I used regular bolt and lock nuts to secure them together (thats what I had laying around the house at the moment). The problem here is that, holes in the linkages are not exactly the size of the bolt, and because the bolts are threaded, it generates a lot of friction. Other than that, the bolt seems to sit loose inside the hole and creates an unstable pivot.

If I tighten the nut more, it just presses them together making it hard for the servo to operate. I am looking for a solution that will use simple bolts, nuts and washers which can be bought easily off the shelf (or even with the bolts and screws everyone has around there house). What can be done to make this joint stable in xy plane, rotating freely around the bolt. By the way, even though I used nylon lock nuts, it seems to loosen after couple of repetitive rotations.

Thanks for your help in advance and I hope ya'll have a great day.


texts: How do I correctly model a building to determine effectiveness of a heat source?

texts:
The problem domain

You have a shelter that you use in a cold climate, and you want to provide it with some heat to take the edge off the chill.

You already have a structure in a location which gets cold winters, let's say in the -15C to -30C range. When it gets down to -30C you are used to turning on a heater, whose fire usually increases the temperature by approximately 10 degrees (to -20C).

You want to construct a similar structure - exactly like the first, or as close as possible - except this one will be in an even colder area near one of the planetary poles and getting winters that might reach temperatures as low as -80C. Similar to before, you plan to turn on the heater if you wake up to the lowest expected temperature of -80C.

I want to figure out how much the heater will warm the structure in the colder area. It very well may just heat the structure by 10 degrees as before up to -70C, but I do not know for sure.

The question

This question does not seem to be as straightforward as I originally thought it would be, and there have been other comments and posts probing some specifics here and not getting me to a satisfactory answer, so the question is this...

What are all the non-negligible forces at play here which should be considered to decide if the secondary structure will be heated by the same amount (10 degrees) as the first structure, and in what way does each of these affect the result?

In case it matters: The building will likely be either a cold-weather tent or a human-made cave made from snow which is designed with the floor higher than the doorway to trap the warmer air inside. If the specific choice matters, feel free to either say so in comment or assume one or the other for your answer.

See also

I think the primary concern might be the heat capacity (ie: the number of heat units needed to raise the temperature of a body by one degree) of air. See also my question Physics.SE: If two objects of different temperatures have the same heat source applied, do they heat up by the same amount? for the Q&A which led me to this (hopefully correct) assumption. One of the answers even seemed to suggest that the heat capacity change may be significant, assuming I read the complicated answer correctly (maybe not).

I tried to Google up whether the heat capacity of air changes with temperature. I found an interesting table labeled "Specific Heat Capacities of Air", though that does not go down far enough, and a calculator which does. I get 1.005 kJ/(kgK) for 0C and 1.009 kJ/(kgK) for -80C. In my naivety, I would guess that means the heat source might work 0.4% better at the colder temperature (making this tree I'm barking up a negligible one), but I would not be surprised if I am way off base.


texts: Steam sterilization of whey in a bioreactor

texts:
I'm trying to design a bioreactor to produce citric acid with whey and Aspergillus Niger.

The first step in the process would be to put whey into the reactor with some dextrose (approx. 10%). Then, this solution should be sterilized, and I was thinking of using batch steam sterilization by direct injection of the steam in the reactor.  The sterilization should be done at 121°C.

I'm not sure how to calculate the sterilization time and the amount of steam required for a given reactor volume (approx. 600 m3).  I was thinking of calculating it as if I had a 600 m3 autoclave, but I doubt the approximation holds. In that case, the death kinetics would be given by the Arrhenius equation:

$$
 k = Ae^{\frac{-E}{RT}}
$$

I'd need to determine the activation energy, $E$, the pre-exponential factor $A$, or some approximation for $k$. Then, I'd just have to integrate the equations for the heat and hold energy required:

$$
\begin{align}
\nabla heat &= ln(\frac{N_0 V_0}{N_1 V_1}) = \int_{t_0}^{t_1} k(t) dt \\
\nabla hold &= ln(\frac{N_1 V_1}{N_2 V_2}) = k(t2_-t_1) dt
\end{align}
$$

To figure out $t_1$ and $t_2$.

Am I approaching this problem correctly?


texts: How do I hold a end milling tool in a rod which is smaller than the tool(smaller efers to the diameter of the rod).


texts: Transducers in cuff-style blood pressure monitors

texts: I have been doing research into blood pressure monitors, and I was wondering when the cuff tightens, how do the transducers actually measure the systolic/diastolic pressure in the arteries.


texts: What is a reason that handlebars fit to a motorcycle and steering wheel fit to a car?

texts:
What is the reason that handlebars are installed on motorcycles and steering wheels are installed on cars?

Notice that the way to use both handlebars and steering wheels are quite similar, but a steering wheel allows for much more rotation than a handle bar when you control a vehicle.

Please give me a reason why a massive vehicle should use a steering wheel and a light weight vehicle should use a handlebar?

The reason maybe involve scientific reasons, safety reasons or designing reasons.


texts: Three-phase versus single-phase operation of a generator

texts:
My generator (a Fermont MEP-803A, 4 cyl diesel, 10kW rated) can run in three distinct modes:

Single-phase 120V, in which one terminal is hot, and another is neutral
Single-phase 120V/240V, in which two terminals are hot, and another is neutral. The difference between the terminals is 240V, and each one to neutral is 120V.
Three-phase 208Y, in which three hot terminals are each 208V apart from each other, and each one is 120V from the neutral terminal.

I need to run a bunch of lights that all need 120V. So the obvious thing would be to just use the 120V mode. But I'm thinking it may be better (more efficient maybe? less vibration maybe?) to run it in three-phase mode, with the load balanced among the three hot terminals.

My thinking, based on my coarse understanding of generators, is that in three phase operation, the torque should be more homogeneously distributed over the course of a single turn of the engine, so there should be less vibration and more equality in effort among the cylinders. In short, I'm guessing that three-phase generator operation would have the same advantages three-phase motors have over single-phase motors.

Is my thinking correct here? If not, why not? Conversely, are there any disadvantages to three-phase operation over single-phase operation?


texts: How to obtain the $dC_d/dC_l^2$ value from the drag polar of an airfoil for Xrotor?

texts:
I'm currently trying to do an initial design for a propeller. In order to do this I'm trying to use Xrotor. Xrotor allows the user to enter certain information about both the propeller geometry, flight conditions and the airfoil lift and drag data after which it performs its calculations. Xrotor requires the following values for the lift and drag data (example values are given):

========================================================================
1) Zero-lift alpha (deg):   0.00       7) Minimum Cd           : 0.0070
2) d(Cl)/d(alpha)       :  6.280       8) Cl at minimum Cd     : 0.150
3) d(Cl)/d(alpha)@stall :  0.100       9) d(Cd)/d(Cl**2)       : 0.0040
4) Maximum Cl           :  2.00       10) Reference Re number  : 2000000.
5) Minimum Cl           : -1.50       11) Re scaling exponent  : -0.2000
6) Cl increment to stall:  0.200      12) Cm                   : -0.100
                                      13) Mcrit                :  0.620
========================================================================

This information can be obtained from the drag polars of the airfoil.

$\alpha,C_l$ plot">

$C_d,C_l$ plot">

[

The 360 degree polar was made using JBlade. The only value that Xrotor requests that I am not sure on how to calculate is the d(Cd)/d(Cl^2) figure. I'm fairly confident that this can be obtained using the $C_d,C_l$ drag polar, but I'm not completely confident on how I should go about it. What is the correct way of determining this value?


texts: Silicone paste vs. silicone grease vs. silicone spray lube

texts:
For purposes of usage in home/auto and light industrial circumstances, what are the differences? What are the pros and cons, and suited uses, of each?

Thanks!


texts: Does a motor suffer damage when resistance to the intended motion is met?

texts:
I'd like to create something similar to a hydraulic press. I know I need some sort of motor, but I was curious about a fundamental question about motors when used in a system where the force required to continue motion increases.

General question: if a motor is under stress and the intended motion is impeded to some degree, does the motor get damaged?

Literal example: what happens to the motor of a ceiling fan if you grab the fan to immediately stop it? Does this damage the motor? Are there motors that expect resistance and either increase the torque or stop immediately?


texts: Deflection of a cantilever beam composed of separate (not bonded) planks Uniform load

texts:
This is related to this question
It is the case of a simple cantilever beam having a uniform rectangular cross-section.
cantilever beam composed of separate planks - taken from
The question in the original post was What happens if we split it along its longitudinal axis?
@sudhir asked What would happen if the beam was loaded uniformly


texts:
I'm currently designing some small-scale robots capable of both melee and laser-tag combat. For the melee component, I'd like to create small, ejectable panels that hide the laser-tag receivers. When hit, these panels would pop off exposing the receivers.
However, I'm having trouble finding a suitable mechanism to fit my constraints. Ideally the mechanism would be: small/shallow, so as not to stick out too far from the robot and either 3D-printable or low-cost. My first thought was the mechanisms in pens which don't seem accessible without disassembling a ton of pens, or push-to-open cabinet latches which are too large to use. I've also ruled out something like an electromagnet and push-button as that would add unwanted circuit complexity. Is there another mechanism that would serve this purpose?


texts: Does every engineering design needs to have a complete theoretical backing or may experimental data suffice?

texts:
This may sound rather vague on its own so I will explain with examples.

The solid booster rockets used by NASA space shuttle used a central bore design because it had a certain characteristic on burn rate and thrust.

If this data was to be acquired only form experimentation like burning test rockets and not deriving any mathematical relation between bore design and thrust then would it be considered sound engineering?

Are any designs based solely on data from trial and error used in  critical mainstream engineering?

Like we use it just because it works and do not investigate why it works like that because it's very complex to understand but still easier to implement.


texts: Are all advanced methods used in FEM, other than the Direct Stiffness Method, also ultimately based on Direct Stiffness Method? If not is there still a common starting point? Why did other methods emerge on top of direct stiffness method? In theory Direct stiffness methods seems to solve all indeterminate structures


texts: Why does the Channel Tunnel enter the ground around 10 km from the coast?

texts:
I know that digging tunnels is always much more costly than building ways or train above ground.

Why doesn't the Channel Tunnel start around the coastline? Why does it have an around 10 km long portion under land on the British side?


texts: Dose adapter sleeve hinder the axial displacement of inner ring of spherical roller bearings?

texts:
This is supposed to be the locating bearing in my design, the outer ring is supported by the housing and a taconite seal (taconite seal is hidden). So it is fixed in place and can't move at all.

There is no significant axial forces working on the bearing system. I want to know if the inner ring can move to the left side due to thermal expansion of the shaft while it is not supported axially by anything else ? (same direction as the red arrow)

I think the conical shape of the sleeves adapter prevents any movement of inner ring anyway am i right? The length of the shaft is 50 inches and the diameter is 4.5 inches


texts: Manually Attempting Empirical Measurement of Flour Dough Compressive Strength

texts:
I want to make a DIY dough press, so need to know how much pressure I would need to apply. I don't have mechanical engg background, so based on some googling, I think this is what I need to do, but wanted to validate here.

I took a small dough ball, and placed a very light flat surface on its top, and then put a 16.9 fl oz water bottle (weighing 1.1 lbs) on top of it. It squished the dough ball to a thick circle of 2.09 inch diameter. (3.145 sq inch area).

Then I put 7 more water bottles on top of it (total 8.8 lbs approx), and the dough squished flatter to a circle of 2.91 inch (6.647 sq inch).

Now my questions are,

a) Is this correct way to calculate compressive strength of this dough ball by dividing force / area, where it came to rest. So with 1 bottle on top, when it squished somewhat flatter, the PSI = 1.1/3.145 = 0.349 lbs/sq inch

b) If so, then shouldn't the compressive strength be constant as it is tied to the material. So dividing the final area after adding more weight should yield the same value? The second value, 8.8/6.647 =  1.323 lbs/sq inch.


texts:
We have all seen PVT diagrams. From my understanding one should measure pressure, volume and temperature on or near the outside of the system.

Volume: maybe by displacing water initially and then cameras.
Temperature: I have some thermometers lying around. But since the system can have different temperatures on different parts of its boundary I don't know how many places I need to measure it.
Pressure. I don't know how to measure this. Maybe if I hang the system on a hook I can know the pressure at the point it was hung from, but all the other points have me stumped.

Have someone made PVT diagrams and know how it is done?

I found some methods to measure pressure in fluids:

fiber optical submersible pressure sensor
pitot tube + manometer
prandtl tube + manometer


texts:
I have been trying to create a machine to climb coconuts as the existing machines are very slow and strenuous to use and frankly, most climbers prefer to climb it manually than use the existing machine, which all more or less use the same concept of the image given below

(Search Google for more).

I wanted to automate that process to make it easier and faster.

I have been experimenting with machines and designs like using circular drums and powering them, using raised platforms attached to vehicles but none of them have properly materialized. So now after many futile attempts, I turn to the engineering community to help me and suggest new ideas on their own.

I am new to this and I don't know if I can ask such a question.
But still I just wanted to try. Give me any ideas if you can. If you feel that this is not appropriate, please comment below and I will correct it.

Thank You


texts: Do Car Safety (Colision) Regulations Depend on Max Speed?

texts: To what degree is a Car's crash worthiness dependent on max speed? If a car could only reach a max speed of 45 mph, would it require less protective measures than your average car that goes 60+ easily? I am interested particularly in the US and the World Forum for Harmonization of Vehicle Regulations.


texts: How much do these bolts hold? Marked 10.9, with shank area of 153 sq mm

texts:
A certain truck has 5 (per side) *2 sides= 10 bolts holding the body to the frame. The bolts are marked 10.9 and the area of the shank is 153 sq mm. From my math I got 3e8 lbs for all 10 bolts together.
From a mechanical engineering point of view, how would you describe the mechanical characteristics of these bolts?

Edit:
Thank you for the discussion. I was dividing by the bolt section area; I should have been multiplying. Now the answers make much more sense.
Each bolt has a tensile strength of about 32,000 lbs * 10 bolts = 320k lbs.
Of course the more interesting tests in a vehicle application are the shear loads you would encounter in a collision, but that is also a MUCH more complicated question.


texts: How can one go about aligning the dead and the live centers of a lathe ?


texts: How to subtract a region where two solids intersect?

texts: In Autocad 2015 for Mac, I have created a cylinder with a torus wrapped around it. The torus is 2 mm thick, with 1 mm embedded inside the cylinder and 1 mm outside. I want to subtract the torus from the cylinder, so I will be left with a semicircular groove around the cylinder. I have already done this once, but I had to remake the object so I deleted the original and started again - and now when I try to subtract the torus, it simply deletes the torus and leaves the cylinder untouched. What is going wrong, and how can I fix it?


texts: How much space should I leave between round bushing and the rotating parts to minimize the play?

texts:
Hello everyone I am designing a parts that needs to rotate so I am planning to  insert a round bushing.

But I am curious of how much space I need to leave between the round bushing and the parts that need to rotate? (Assuming the round bushing will be fixed by tighten the screw)

The outer diameter of the round bushing is 3.5mm so how many mm hole should I design for that 3.5mm round bushing? If produce by a CNC machine how accurate can it mill?

Thank you very much


texts: Trying to reduce RPM of a combustion motor

texts:
I'm trying to reduce the rpm of a combustion motor. It operates at 2000 rpm with 3HP, and I need it to work at around 12 rpm (no matter the power). I've made the math with sprocket and chains, but the biggest sprocket is of 472 mm of diameter, which is too big.
Is there any cheap and easier way to achieve this?
Thanks!


texts:
I'm designing something with a vertical linear actuator. It is a quite large actuator lifting a load. I'm anticipating sway from the actuator as it moves up and down so I'm creating a support structure. What is the best way to determine how much this sway will be? I can figure out the weight of the load and the acceleration of the actuator

Thanks for the help!


texts: Trying to determine the name of a filter set up

texts:
I am having an issue with caking in a process.  I am already trying to figure out ways to prevent the caking in the first place but I need a short term solution that will allow the line to continue running.

My idea is to take two filters and have them piped to run in parallel with one another.  However, I want a valve on the inlet of each individual filter.  I want this so while in production I can have Valve A open (allowing fluid through Filter A) while keeping Valve B closed (no fluid through Filter B).  Then when Filter A's mesh becomes clogged open Valve B, close Valve A, and remove and clean Filter A.  This way the fluid is still being constantly filtered and we do not have to stop the line for a filter change.

I am struggling with a name for this arrangement of filters as in my mind its a simple enough set up that a commercial version should already exist (I could be wrong about that).  All I am able to find on line are filter arrangements that allow series or parallel flow but not the ability to turn off flow to individual filters.  It could also be an option while ordering that maybe I am not catching.

Thanks in advance for any advice.


texts:
I have an assignment for my Mobile Robotics course to design the drive mechanism for a legged hexapod and demonstrate its gait in motion.
The idea is to design the hexapod as per the following schematic:

There are 2 motors in the mechanism, each driving 3 sets of wheels. Wheels 1,3 & 5 are connected to one motor and wheels 2,4 & 6 are connected to the other. The wheels work as sort of a crank to produce motion in the legs and both the motors are 180 degrees out of phase to enable a working gait.
The part where I am having trouble is designing a gear mechanism that connects the 3 wheels in this triangular configuration to a single motor. If anyone has ideas for that, or further suggestions, it will indeed be very helpful.


texts: What are the possible implications of the heating of the structural stonework of Notre-Dame cathedral during the fire?

texts:
Yesterday, Notre Dame cathedral caught fire. The roof and the central spire were destroyed and some of the stonework was subjected to high temperatures for an extended period.

What are the likely implications for the strength of the individual stones, the walls and other structures?


texts: Limits of Euler-Bernoulli Beam Theory for Wide Plate in Flexure?

texts:
I'm looking for established limits or rules of thumb for the validity/accuracy of Euler-Bernoulli beam equations for particularly wide "beams". For example, a simply supported rectangular plate where the breadth(b) is much larger than the height (h) [e.g. b=120 inches, h=1 inch].
Is there a point at which a simply supported beam where b >> h would deflect more like a plate in plate theory rather than a beam in beam theory? If you can, please provide references. Thank you!


texts:
I'm looking for advice on how to attach a thermocouple to a metal surface in a fashion that's relatively temperature resistant (more-so than) glue.

I've got some very fine gauge wire on hand to make the thermocouples and specialized spot welder that will join them to form a bead. My goal is to attach them to a 3-7 mm thick sheet some kind of metal. Could be steel, aluminum, copper etc. I don't have a strong preference on either the metal used or the exact thickness. I have access most commonplace metalworking equipment and can purchase basic tools and materials but can't justify the expense of a purpose-built welder for this kind of thing.

So far I've tried two things (unsuccessfully):

Soldering: I used a gas torch to heat copper plate enough to get a nice puddle of solder on it and then tried to dip the (already welded) TC. The wire simply would not wet, it would just push the solder out of the way and couldn't make a connection.
TIG welding: I tried to weld a both TC and bare TC wire to an aluminum plate by forming a small puddle on the plate and then attempting to dip the wire into the puddle while quickly extinguishing the arc. Mostly the wire just melted and "ran away" from the arc. Other times it just didn't fuse to the surface.  I also tried putting the wire in contact with the surface in advance and starting the arc on it.

I know that I've heard mention of doing this, but haven't been able to find any good information about how to actually do it. I could use anything from a definitive answer to comments on how to improve the techniques that I've attempted already.

p.s. I weld semi-regularly but have very little experience soldering (esp. with a torch), so don't assume a lot of skill or knowledge in that department.


texts: Does the rack for a rack and pinion often have or need to have the involute profile?

texts:
I am looking at designing a rack and pinion system that will be laser cut out of some plastic. While the cad system that I am using has a spur gear generator, I was looking at the design of the rack gears. I thought that it needed an involute type profile, but many of the references that I see have a flat profile instead of an involute type profile. For example, this metal rack gear from McMastercarr has a seemingly flat profile.

Is this common? Is the reason that it has a flat profile due to the fact that the radius of the base circle for racks is theoretically infinite?


texts: How to calculate a tripod table's stability?

texts:
I have designed a circular, 800 mm (31.5") diameter tripod table. The top is made of stone and weighs 40 kg (88 lbs). The height of the table is 750 mm (29.5").  There is a central column with tripod feet lower down which touch the floor 108 mm (4.25") in from the outer edge of the table top if looking in plan. The fulcrum created by two of the feet is a line 240 mm (9.5") to the table edge at its widest point.

Question: How much weight can be put on the edge of the table top before the table tips over, and how much can this weight increase if the feet touchdown 90 mm (3.5") from the outer edge? (In this case the fulcrum line would now be approx 230 mm (9"))


texts:
I'm looking for examples of mechanisms that can constrain a hub rotating around a shaft from 0 to 360 degrees.  Rotation between 0 and 360 should be free.  Rotation < 0 and > 360 should be stopped.

A few things I think could work but I am not not sure what this is called and searching on google has not helped.

a simple pin would allow for 0..(360 - pin_width)

a spiral would allow hard stops 0..360 but the pin would need to float radially.

a gear set of 2:1 would allow for pins but would add some complexity.

thanks for any ideas folks might have and/or any names i might be able to use in a google search


texts: Transformation of 8mm straight motion to 210 degree motion

texts:
Everyone.
I want to make the transformation form Straight motion to Rotational motion ,like [this].1

So I made .

But it did not work.
Probably, this was mistake of Groove size　on spiral groove.
But I thought I must  know the formula  between red arrow and blue arrow of this mechanism.
So Would you tell me the formula of this?
And Any clue for this mechanism welcome.
Thank you & Sorry for poor English in advance .


texts: What is the effect of annealing on the defects present in the sample? Does it remove defects in the sample? Is there any chance that due to annealing the point defects present in the sample combine to form a large size void?


texts:
My body weight and that of the skateboard is $M = 90\text{ kg}$

I want to move 10 meters in 4 seconds.

$$\begin{align}
x(t) &= (at^2)/2 \\
x(4) &= (a\cdot4^2)/2 = 10 \\
 &= a\cdot16/2 = a\cdot8 = 10 \\
\therefore a &= 10/8 = 1.25\text{ m/s}^2
\end{align}$$

The wheels of the skateboard have a radius $r = 0.027\text{ m}$. I want a maximum velocity of $v = 30\text{ km/h} = 8.333\text{ m/s}$.

$$\omega = \dfrac{V}{r} = \dfrac{8.333}{0.027} = 308\text{ rad/s} = 2941\text{ rpm}$$

$$F = ma = 1.25\cdot90 = 112.5\text{ N}$$

The torque needed $C = Fr = 112.5\cdot0.027 = 3.03\text{ Nm}$.

Therefore the power $P = C\omega = 933\text{ W}$.

But I'm not really sure if it is correct because I only need 3.03 Nm when I start moving, same for 2941 rpm is just the maximum velocity.

$C\omega = P$ but I'm not sure that it is the torque at start multiplied by $\omega_{max}$.

If I am right I need then to buy a DC Motor with 933 W and at least 3.03 Nm and at least 2941 rpm?


texts: Why is the functional of an elastic system equal to it's total potential energy and why is it stationary at it's minimum?

texts:
Okay this was even quite difficult to formulate but let's start with some statement's in my FEM book:

Elastic continuum has a functional which is equal to it's total potential energy
Elastic system is in balance when the stationary value of it's functional equals the minimum of potential energy

I understand nothing about it but I will try to form some more exact questions:

a) Is there any physical interpretation of a functional? All I can find is that a functional it's an integral of a function and the arguments of that function are also functions. But that doesn't tell me how it is derived and what is it's meaning

b) Connected with a), why is this functional equal to total potential energy in elastic systems?

c) Why is the elastic system in balance when the stationary value of the functional is equal to the minimum of potential energy? Why not maximum or any other state?


texts: Charging a Li-po battery (battery output current)

texts:
I would like to design a buck converter to use a PV panel to charge a 11.1V 3000mAh 3S 30C Lipo battery.

I want to choose the minimum inductance for a CCM ($L=\dfrac{V_{out}T_s}{2I_{out}}$), what is the output current that I need to charge this battery? should $V_{out}=11.1\text{ V}$ and $I_{out}=3000\text{ mAh}$?


texts: How does tractor achieve constant PTO speed?

texts:
Tractors have a PTO shaft which supplies power to implements. Most implements are rated 540 or 1000 RPM.
I'd like to know more about transmission that is used to convert variable motor shaft rotation to constant PTO rotation? If you can give me a hint about the right search keywords, that would be great.


texts: While going downhill, does my car consume less fuel when in neutral or in gear?

texts:
I once meditated on the fact that a car, in downhill, would consume more fuel when in neutral to keep the engine on, rather than in gear. To keep the engine on when in gear, in fact, you mostly need the gravity and enough thrust to keep it rotating, and therefore no fuel (just motor oil).

This is what I'd expect cars to do but I'm probably missing something. How's actually the story? And if it's not like this, would/could my idea work somehow? (note: patent pending :P)


texts: How do I determine the output equation in the state-space representation?

texts:
In the state space representation, the state equation for a linear time-invariant system is:
$$
\dot{\mathbf{x}}(t) = \mathbf{A}\mathbf{x}(t)+\mathbf{B}\mathbf{u}(t)
$$
This state equation can be derived by decomposing an $n^{th}$ order differential equation into $n$ first-order differential equations and then choosing the state variables $x_1(t),x_2(t),...,x_n(t)$ and their derivatives $\dot{x}_1(t),\dot{x}_2(t),...,\dot{x}_n(t)$. The state equation essentially describes the relationship between the state variables and the inputs in $\mathbf{u}(t)$.
Additionally, the output equation for a linear time-invariant system is:
$$
\mathbf{y}(t) = \mathbf{C}\mathbf{x}(t)+\mathbf{D}\mathbf{u}(t)
$$
However, I am not sure how this output equation is derived. More precisely, what is an "output"? Is it the set of state variables and inputs that need to be observed by the engineer or another system downstream? If that is true, then if I have a mass-spring-damper system, where the displacement of the mass is represented by the state variable $x_1(t)$, the velocity of the mass is represented by the state variable $x_2(t)$, and an externally applied force on the mass is represented by the input variable $u_1(t)$, and I was interested in observing/measuring the displacement of the mass, would my output equation then be:
$$
y(t) = x_1(t)
$$
Alternatively, if I was interested in observing both the displacement of the mass and the externally applied force, then would my output equation be:
$$
\mathbf{y}(t) = \begin{bmatrix} y_1(t) \\ y_2(t) \end{bmatrix} = \begin{bmatrix} x_1(t) \\ u_1(t) \end{bmatrix}
$$
So far, neither the state variables nor the inputs have been scaled in my output equation. Because of this, I don't understand the purpose of the $\mathbf{C}$ and $\mathbf{D}$ matrices. Could they be used to linearly transform the state variables and inputs for another system downstream? From this image on a typical state space representation:
$\hskip2in$
It seems that what I am saying is correct, but I would prefer a better explanation.


texts: How are perfectly square blocks made from scratch?

texts:
So I'm looking into how stuff is made from scratch, starting with a surface plate which has been lapped flat using the three plate method. But almost everything I read on the subject on "the history of precision" and such stops there and glosses over the rest by simply stating that it's possible. How does one go about making perfect 90 degree corners from simply a flat surface?
To clarify, when I say "from scratch" I mean going from no tools at all to a perfectly square block. I'm asking about the history of machining, how the first precision machines were made.
If anyone has any good resources on the subject which explains it in further detail I would appreciate it very much :)


texts: Does the speed of Heavy Vehicles make more potholes

texts:
Should Heavy Trucks drive more slowly on weak (bitumen) roads to reduce potholes in the road surface?

I am discussing with a feasibility engineer what causes more potholes.  He says it is simply the 'Weight' on the road (ie of the vehicle touching the road), and I argue that it is the acceleration AND weight combined...(Perhaps the Work to be a little more exact... Something that relates to acceleration/direction, mass and time).  My thoughts are, that a truck travelling fast will bounce and produce more short term weight, and also accelerating back and forth will put more pressure on the road surface - more than the truck weighs in fact, all combining to create potholes or enlarge existing potholes.

(What 'he' means by Weight Only - is that they can predict how a road will wear down simply by a factor of the Weight of the trucks that will drive on it.  They do not consider the speed (limit), and I also have no real idea of how accurate they are but it seems roads wear out a little faster than they think)

Can anyone explain how I am wrong?  Or why the feasibility engineer is correct?  (Or please let me know if this question is not in the correct forum, for which I apologise in advance)

NB:  We have forestry trucks running on our small road, which 'seems' to be tearing it up - and they drive fast!  Faster than the 30 km/h recommended limit (legal limit 50...People, dogs, kids, deer, moose, bikes around).  So I would like to argue that the forestry trucks should drive super slowly to preserve our precious roads, which are ostensibly for local traffic only.  Not that I mind the trucks on the roads every now and then, I just want them to reduce impact.  The roads are probably only 'made' for local car traffic, and the odd tractor.


texts: Using a rotational latch to restrain an object under a horizontal force

texts:
So hypothetically, I'd like a to build a latching system to prevent a steel block experiencing a horizontal force from moving  until another upwards force releases a latch, at which point it would allowed to move. Not shown, downward force is applied to the latch by a spring.
So obviously, this design will not work because releasing the latch would require pushing the steel block in the opposite direction of the force, but there is another object in the way preventing that motion.
Perhaps the latch could flex? But that does not seem durable given a large horizontal force?
Is there a simple soltuion to allow this basic design to work as intended without requiring the moving object to move counter to the resisted horizontal force when the latch is released?
I am not a professional mechanical engineer, so I apologize if I have not worded this in an easily understandable way; please feel free to suggest edits to make things more clear.


texts: How do I interpret states in the MATLAB System Identification Toolbox?

texts:
I am using the MATLAB System Identification Toolbox to estimate a 3rd order state space plant model. More precisely, the plant is a car with an Arduino mounted on it. The car takes in a PWM duty cycle as an input and outputs a distance measured by the ultrasonic sensor attached to the car. This is the car in question.
I can measure both the input and output. However, when I try to estimate a state space model, giving the $A,B,C,$ and $D$ matrices, there is no way of telling what the state variables $x_1,x_2,$ and $x_3$ mean. Ideally, these should be displacement, velocity, and acceleration, so that I can implement the corresponding difference equation on the Arduino. Is there a way of finding out what MATLAB uses as the states in these models?
Thanks for the help.