texts: Plugging a 25A device (Welder) on 10A house plug

texts:
I would like to plug a 25A welder on a 10A house plug. I understand that it will not accept full power or the circuit breaker would switch.
However, my question is if I may run under some lower power setting: for instance setting 70A out of 200A on the welder.

From a very simplistic point of view:
A welding machine with a maximum of 200A for 25A@220V mean, the welder at 60A would require about 10A@220V

However, a welding machine is not such a simplistic situation and uses several variants of waves, AC or DC, several frequencies, etc. which make all more complex.

Question
May I plug this 25A Welder on a 10A-protected house plug?


texts:
I just modded my Basetech BT-305 laboratory power supply to become an IoT device.

Everything works as planned, except the volt display in the multimeter-part of the supply, which is directly shown below. I disassembled the display part and saw a missing resistor, but am unable to find out how many ohms it had, as I am not an electrical engineer, so I hoped you guys could help me.

This is the problematic part:

I also found the circuit diagram PDF on the page I bought this device

I bought the above from Basetech BT-305 Labornetzgerät, einstellbar 0 - 30 V/DC 0 - 5 A 150 W Anzahl Ausgänge 1 x

In case anyone has the same device and has a picture of this part, that would solve the problem of searching for the right resistor immediately.

EDIT:

A high-enough resistor that would fit in there is 0.5 kilo Ohms. This was measured by using a very high potentiometer and slowly decreasing the resistance until it worked as it should. Thanks to William for the idea in the comments below.

EDIT 2:

As there seems to be interest in how i modded this device for iot in the comments.

the goal is to switch the output on/off over the internet (app/http requests)

In short: disassembled the device, added a second AC power plug (female) into the bt-305, so that a 5v wallcharger could be powered in the case. The 5v charger is used to power a "Sonoff SV"  which is an esp-based smart switch from itead. The sonoff sv supports a so called "isolated mode", which means it input is 5v, and the 2 output pins just short each other when getting the command to switch, acting like a normal switch on 2 cables. Those output pins are soldered to the pins of the "output" button of bt-305, so sonoff is just simulating a button press. Sonoff has an app to communicate with the switch, or you can connect it to IFTTT and send http requests to a rest-url via web-hooks to set the state of the switch. I generally use the app, as it supports "inching mode" which means the switch-output gets shorted for just 0.5 seconds, which is necessary to simulate a button press.


texts: How to measure electro-mechanical coupling?

texts:
I have mounted a piezo-ceramic ultrasonic transducer (MODEL # SMD10T2R111WL, Vendor Website: PIEZO CERAMIC DISC 10X2MM R 215 KHZ WIRE LEADS) under a plastic tank using epoxy. Please see the picture below.

Is there a way to measure the electro-mechanical coupling of the transducer under the tank?

From the specs of the transducer, the electro-mechanical coupling coefficient is >= 60%. What is the meaning of it? Is there a way to measure it?


texts: At what efficiency does a fan cool a PC case?

texts:
A PC case is basically a rectangular pathaway for air to flow through but at the places where the air enters and exits there are solid plastic or metal panels commonly with meshes and little holes.

When a fan is rated at 50cfm or 80m3/h at 100% speed by how much is this figure decreased when taking into account the characteristics of the volume of the case?

Is it 20% or 80% for example?


texts: Relationship between particle size and wave parameters in acoustic levitation

texts: Can you tell me in acoustic (ultrasonic) levitation if a relationship between the acoustic sound wave parameters (frequency or amplitude or other) and the particle size that can be levitated is known? If yes what is the relationship?


texts: Do I need to mention every dimension on a to-scale drawing?

texts: I'm my engineering drawing course, do I need to mention and show every dimension in the diagram if I've drawn everything to scale and also written the scale below?


texts: Does a TXV completely close when there's no thermal load whatsoever?

texts:
How is a TXV supposed to behave in a no evaporator thermal load situation (for example, evaporator fan completely off)? Would it completely close, not letting any liquid refrigerant get through (and reach the pump still in the liquid phase), would it still let some liquid refrigerant leak past into the evaporator coil, eventually overcome by the pressure building up in the high pressure line, but not enough to manage to reach the evaporator's outlet without having turned into superheated vapor, or would it behave differently? Would the evaporator coil still be able to develop frost in that situation (and potentially end up making the evaporator completely unable to turn the liquid into superheated vapor)?

Thanks


texts: My professor told us that If we spray water in dry air the process is on an Isenthalpic line of the Mollier diagram. Is it always true? if yes, can you explain me why?


texts:
I'm designing a 3d print model of a ring that you can wear, but the outer surface of the ring can be dialed like a watch bezel.
Check this video to see how the bezel moves in grades so it stops on every minute.

https://www.youtube.com/watch?v=JQDZipgtan0

I started a draft model as you see in this picture:

Those are the inner parts of the ring, but it doesn't seem to work as I expect because the inner gear is a bit loose and also hard to rotate because of friction.

What I'm looking for, is the name of this mechanism (if it is known) or a link to a reference that explains such thing or even similar ready schematic that I can copy.

PS: I found similar ring but I don't know how it works


texts:
A uniform square beam of sides 200mm is to be used as one side of a ladder chassis of a commercial truck. The beam is to be constructed of steel, E=205Gpa and yield stress,320Mpa. A load analysis of the chassis reveals that the beam is uniformly varying from 30kN/m to 90kN/m spreading along the whole span. The design length of the beam is 6m and it's to be bolt fastened at the ends , hence can be treated as jointed ends. The design standard requires a design with Factor of safety of at least 2.0 and central deflection not more than 40mm.
 a) Determine the maximum bending moment in the beam and hence the maximum stress in the beam.
 b) The maximum deflection that occurs in the beam
 c) Does the design meet both standard requirements of the chassis design? Clearly show the working.


texts: Position of Spring to support Vibrating feeder

texts:
So I have to design a vibrating feeder of 55kg which moves the material (light objects eg. olives) on it in forward direction (linear motion). I am stucked on the positon of the spring. I mean which arrangement of spring will be better:
1. Spring can be placed at 4 corner of the vibrating feeder.
2. 2 in back corners and 2 in middle.

Is there any calculation or relation regarding this topic...?
I have attached the simple arrangment of what I have explained above.


texts: Equal power transmission in 4x4 vehicles?

texts: If a 4x4 (true 4x4 not AWD) has 3 wheels slipping, does the one tire with traction receive all the torque available from the transmission? Is there typically a reduction in power transmission in 4x4 systems to the wheels that are not normally powered (i.e. front wheels on a pickup)?


texts: I want to calculate the density of CO2 using a cubic equation of state in order to plot the P-v diagram. From theory I know that I get one real root when the substance is in single-phase region and two when it is in two-phase region. In the latter case the smaller volume is associated to liquid while the other to vapor. I'm using Matlab to solve the cubic eos, incrementing the pressure and the temperature at fixed intervals. How can I merge the two solutions to represent the actual Pv plot?


texts: How to find the center of mass of a robot?

texts:
I have been wondering about the different methods of finding the center of mass of a robot? Mine is a balancing robot, so it has two wheels and a chassis on top. I need to find the center of mass so that I can tune the robot to balance. I have done some research but I have only been able to find the following 2 ways:

Use the conventional method of finding the center of mass an irregular object with weighted lines and then the junction of all these lines would give the center of mass. But I don't know how reliable this method is? Since the robot is a 3D object, so its center of mass will lie somewhere at a depth inside the robot chassis?
Design the whole robot, part by part in a CAD software, like Inventor and then use the software's features to let it automatically find the center of mass. Unfortunately, my CAD skills are not good enough.

Any help and suggestions are appreciated.


texts: Could someone explain to me the process described in this quote from G.B. Shaw (fragile load transfer system of some sort)?

texts:
The idea, as I understand it, is to transfer fragile material (glass bulbs in this case, I believe) from one moving something to another, or over to a platform. This is taking place in the 1920's, I think. Anyway, here's the quote:

  However, I suffered myself to be taken to Battersea; and there, sure
  enough, I found a workshop, duly labelled as the premises of The New
  Transport Company, Limited, and spacious enough to accommodate a
  double railway line with a platform.  The affair was unquestionably
  real, so far.

  The platform was not provided with a station: its sole equipment was a
  table with a row of buttons on it for making electrical contacts. Each
  line of railway had on it a truck with a steel lid. The practical part
  of the proceedings began by placing an armchair on the lid of one of
  the trucks and seating me in it.  A brimming glass of water was then
  set at my feet.  I could not imagine what I was expected to do with
  the water or what was going to happen; and there was a suggestion of
  electrocution about the chair which made me nervous.

  Gattie then sat down majestically at the table on the platform with
  his hand hovering over the buttons.  Intimating that the miracle would
  take place when my truck passed the other truck, he asked me to choose
  whether it should occur at the first passage or later, and to dictate
  the order in which it should be repeated.

  I was by that time incapable of choosing; so I said the sooner the
  better; and the two trucks started.  When the other truck had passed
  mine I found myself magically sitting on it, chair and all, with the
  glass of water unspilled at my feet.

Does "a double railway line" mean two tracks running parallel to each other? Are they linked? Is a switch involved?
Are the trucks - trucks (i.e. bogies) that look like this:

or are they flatbed freight cars that look like this:

Most important: how was the author (G.B. Shaw) transferred (along with the glass of water) over to the other - moving - whatever it was?


texts: Why/when is AC-DC-AC conversion superior to direct AC-AC conversion?

texts:
I am currently studying wind power and the power electronics used for it. In wind power a generator is driven by wind, thus the resulting power is of widely varying frequency and amplitude. The power grid, in turn, has strict requirements for the input power in terms of frequency, phaseshift and sinusoidal form. For this reason, power converters are today used routinely in wind power.

The predominant way to get the power into the grid is to use an AC-DC converter followed by a DC-DC converter and a DC-AC converter. This seems rather complicated instead of using a single direct AC-AC converter. Why is the indirect conversion via the DC "in-between" route preferable?


texts: Why people always say K-Jetronic will not work with high performance high duration cams and because of this the K-Jetronic equipped engines will not be making lots of power. In Bruce Andersons book "Porsche 911 Performance Handbook" he says that get rid of K-Jetronic and replace it with Weber carburettors or modern EFI if you want to make power. But then there are race cars like Porsche 934 RSR Turbo that used K-Jetronic it made 485HP @7000RPM , Ferrari 308 GTB Group 4 it used K-Jet and it made 310HP @8000RPM , Peugeot 205 T16 E1/E2 both E1 and E2 used K-jet and they made 350HP @8000RPM and 550HP @7600RPM respectively , Audi Quattro Group 4 also used K-Jet and it made 320HP @6500RPM. If K-Jet sucks so much in terms of making power , then how did these cars accomplish these powers at these high rpms? them making their peak power at 7-8k rpm suggests that they are using high performance high duration cams but people say k-jet doesnt work with them. How did they managed to make K-Jet work in race cars with high performance cams etc back in those days?


texts:
As far as I know, moments/torques occur when forces applied are not in line. However, I often see moments/torques being applied at a single point in free body diagrams.

How can moment/torque be applied at a single point?

Illustration Below:

Caption: The above image shows an ideal moment acting at the center of a beam. An ideal moment is one which is not associated with a force.
Link for the page


texts: Saving RAM Memory when writing to 2K page size NAND flash

texts:
I am writing a driver for the Samsung K9WAG08U1D NAND flash chip. The specification of the memory chip mentions it has a page size of 2048 bytes (2kB). I am using a TI MSP430F2619 which has 4096 Bytes (4kB) of RAM. This means I need to allocate a 2k memory buffer just to write to flash. My application is a protocol converter and hence requires an additional buffer for handling to and fro transmission.
Please suggest me better approach to reduce the RAM requirement due to flash page size.


texts: Solidworks motionstudy/motion study causes parts to "jump"

texts:
(solidworks files here)

I've made a small assembly thet mooves smoothly manually, but when I try to moove it the same way is motion study, it collides is a strange way... what can be the cause of that?


texts: Have there been/is there a scale about the difficulty of a ground for using a pickaxe?

texts:
One of the worldbuilding questions was asking about the efficiency
of a possible siege and I wondered if there was something like a scale
in former times (when they did not have machines) how difficult a ground
is for using a pickaxe (Something like 1 = compacted earth and 6 = granite).

So the question is:

Does one/several qualitative scale(s) exist (comparable like the Mohs scale for hardness) which judges the difficulty of the ground for a pickaxe?
If not, are there some qualitative tables how difficult a specific ground is for using a pickaxe?


texts: Constant on multiply-connected boundaries for Saint-Venant torsion

texts:
I am trying to solve the Saint-Venant torsion problem with FEA.

I have read some classic text and stuck in finding the constant value of stress function on multiple boundaries (i.e. closed section with holes).

In many classic texts, it is shown that the value of constant can be determined by evaluate the following equation at each boundary.

Can anyone show me how to compute Phi at each boundary based on above equations?
Thanks!


texts: Understanding oversampling in control system

texts:
Oversampling means to sample at significantly more than the Nyquist Rate. I can well understand it in signal re-construction: more samples can improve the ADC's resolution, signal-to-error ratio, etc.

However, when in a control system, I have some difficulities understanding it. Assume that the frequency of the process variable is $f$, so the Nyquist Rate is $2f$, and we sample at $2f$ (the controller will take action upon each sample). Maybe we don't get a stable process variable, so we decide to improve the sampling rate.

Next, we sample at $20f$, a sampling frequency 10 times higher (also the controller takes action upon each sample), and this time we obtain a stable process variable. However, because the controller action is also 10 times faster, the frequency of the process variable is no longer $f$, but much higher, say $f'$.  Now the Nyquist Rate becomes $2f'$.

Comparing sampling frequency $20f$ and new Nyquist rate $2f'$, they may be very close, so we cannot call it "oversampling".

Is my understanding towards oversampling and Nyquist rate correct?


texts: How does a multimeter protect itself from high voltages?

texts:
I have used a cheap multimeter to measure voltages in simple DC circuits, but I have seen pictures of them plugged straight into the mains and used to measure various home-built generators.

Why doesn't the higher voltage fry the multimeter, and also in theory could a small cheapo multimeter be safely used to measure very high voltages? If you get the setting wrong on the dial, does this matter?

I'm not planning to plug one in, nor would I recommend anyone who doesn't know what they're doing to do this either, I'm just wondering how it works.


texts: What are the advantages of different types of groove in welding?

texts: In welding, we have different types of grooves like V-shaped groove, U-shaped groove, Double V, Double U, J and Double J. What is the advantage of each kind over the other?


texts:
Why is the atmospheric pressure given as the value of length of mercury column in barometer. Since the density for the both the cases are different.
Is it that by experiment we found the value to be same or it has some scientific relation with mercury and atmosphere


texts: I'm supposed to be finding the reaction forces first but from the FBD of the entire truss where am I supposed to start. If I take the moment at A then I get 3 unknowns at Bx Dy and Dx. If I get the sum of forces in x direction equals to 0 then I get 3 unknowns again. Same thing with the Y direction, I get two unknowns.


texts: For a tangent ogive, given a radius, can you determine it's length?

texts: A tangent ogive body has a specific radius for a given length, so how would you determine length if only given the radius?


texts: Solidworks Extrude Base/Boss - Base Extrude Doesn't Seem to Exist Anymore?

texts:
I've started using SolidWorks migrating from other software, Creo Parametric (formerly Pro/E) and the Base/Boss terminology confused me. After significant research, I've found that a "base feature" represents the starting feature and a "boss feature" represents any features built off of that - http://help.solidworks.com/2020/english/solidworks/acadhelp/c_feature_based_models.htm.
However, through using SolidWorks 2020, and from many different tutorials, I have never been able to make the first feature a base feature, e.g. "Base-Extrude1", but rather it alway shows as a boss feature, e.g. "Boss-Extrude1". Has the "Extrude Base" been deprecated from SolidWorks and Extrudes are always boss extrudes now or am I just doing it wrong? Are there any differences in the Property Manager for base features vs boss features?


texts: Difference between AD630 'Phase Comparator' and 'Lock-in Amplifier' modes

texts:
The datasheet of the AD630 mentions that the device can be used as a Precision Phase Comparator or as a Lock-in Amplifier.

What's the difference? They both seem to map the amplitude of a modulated signal to around DC. That is, the output of both circuits is the demodulated signal. (Assuming the reference signal is the modulated signal)

Why would I want to pick one circuit over the other?


texts:
I am conducting research to determine vibration limits for cultural heritage objects (e.g. art, small sculpture, ceramics). The vibration source can be, for example, transport, construction in or next to a museum, or rock concerts in or next to a museum. As a former materials scientist and engineer in the aircraft industry working on component lifing, I am fully aware that vibrations are a form of cyclic load, and that such damage is cumulative. The limits have to be based on some form of an S-N (Wöhler) diagram for fatigue life. S is normally given in stress amplitude, but one could also use displacement/strain, which can be converted to stress. However, in the vibration monitoring world, vibrations are given either in velocity or acceleration, and sometimes power density spectra.

For buildings, vibration criteria are generally given in units of velocity, but in transportation, they are often given in g, and sometimes PDS.

I have been using velocity as a measure for S in the S-N diagrams, since that is what building engineers use, and it is the closest I can get to deformation (one derivative). If I give a vibration limit in velocity (and duration) and the frequency range in which it is valid, then I am indirectly giving a deformation, which is what one sees in building codes.

In the transport industry, acceleration (g) appears to be used more often. I assume that this has to do with the fact that the cause of damage is more likely to be shock than continuous vibrations.

So my question: which unit, velocity or acceleration, correlates better to damage due to vibrations, and why?


texts: Calculate mobile base weight to support adjustable arm

texts:
I want to calculate how heavy a mobile hydraulic post table base must be to support an adjustable monitor arm and monitor.

Monitor (iMac) Specs:

Height: 20.3 inches (51.6 cm)
Width: 25.6 inches (65.0 cm)
Weight: 30 pounds (9.54 kg)

Mobile Hydraulic Post Table Specs:

Ship Weight: 120.0 lbs
Load Capacity: 300 lbs
Platform Size: 16 x 16 in
Raised Height: 49 in
Lowered Height: 31 in

Monitor Arm Specs:

Product Weight: 17.5 lbs (8 kg)
20 inches (51 cm) of vertical adjustment
62 inches (157 cm) of side-to-side motion
Screen ≤ 46"
Capacity 14–30 lbs
Lift 20"
Tilt 80°, Pan 360°, Rotation 90˚

The one capability that I think could cause the post table to collapse is the 62 inches (157 cm) of side-to-side motion. I've included a drawing.


texts: What is the name used for this type of connectors?

texts:
I am trying to identify the following connector used in an outdoor lighting product. Dimensions are length of 30mm and diameter of approximately 8 mm. I have done several google searches without much success.
Does anyone in this forum have experience using this type of connector or similar connector? If so please share appropriate search terms. Thanks!


texts: Forward and Inverse Kinematics of PUMA 560

texts:
I am currently coding a Forward and Inverse Kinematics solver for a PUMA 560 robot. For the Inverse Kinematics part I am using the closed for solution given in this paper. But my issue is, my solution for IK for a given set of (x,y,z) does not return the same values returned by my FK values. The reason I am doing this is to verify my code accurately computes the FK and IK.

These are the DH parameters for my robot (These are Python code, since I was testing my algorithm on Spyder IDE before implementing on C++).

DH Parameters

  Link lengths
   a = [0, 650, 0, 0, 0, 0]

  Link offsets
  d = [0, 190, 0, 600, 0, 125]

  Link twist angle
  alpha = [-pi/2, 0, pi/2, -pi/2, pi/2, 0]

So basically I finding the T transformation matrix for each link from the the base frame {B} to wrist frame {W}. This is my code;

 Function to compute Forward Kinematics

def forwardK(q):

#T06 is the location of Wrist frame, {W}, relative to Base frame, {B}
T01 = genT(q[0],0,d[0],0)
T12 = genT(q[1],a[0],d[1],alpha[0])
T23 = genT(q[2],a[1],d[2],alpha[1])
T34 = genT(q[3],a[2],d[3],alpha[2])
T45 = genT(q[4],a[3],d[4],alpha[3])
T56 = genT(q[5],a[4],d[5],alpha[4])

#Tool frame {T}
#T67 = genT(0,0,d[5],0)

T03 = matmul(T01,T12,T23)
T36 = matmul(T34,T45,T56)
T06 = matmul(T03,T36)
#T07 = matmul(T06,T67)

x = T[0][3]
y = T[1][3]
z = T[2][3]

print("X: ",x)
print("Y: ",y)
print("Z: ",z,"\n")
print("T: ",T,"\n")

return T06

 The function to compute  T Matrix

def genT(theta, a, d, alpha):
T =  array([[cos(theta), (-sin(theta)), 0, a],
    [sin(theta)*cos(alpha), (cos(theta)*cos(alpha)), -sin(alpha), (-   d*sin(alpha))],
    [sin(theta)*sin(alpha), cos(theta)*sin(alpha), cos(alpha), cos(alpha)*d],
    [0, 0, 0, 1]])

return T

from the T Matrix relating the {B} frame to the {W} frame position vector of the {w} [x y z] is extracted. R Matrix (orientation) of the {W} relative to the {B} is obtained by the following piece of code;

T = forwardK([30,-110,-30,0,0,0])
x = T[0][3]
y = T[1][3]
z = T[2][3]
R = T[0:3,0:3]

Where T is the transformation matrix relating {W} to {B}. Then this information is fed in to the invK(x,y,z,R,ARM,ELOBOW,WRIST) function to check if the algorithm returns the same set of angles fed to the forwardK(q1,q2,q3,q4,q5,q6) function.

  In the invK(x,y,z,R,ARM,ELOBOW,WRIST)
      - ARM, ELBOW, WRIST are orientation specifiers to describe various possible configurations of the manipulator. Each of these parameters are either {+1,-1}. These values are then used in the closed form geometrical solution presented by the afore-mentioned paper.

I did not post the code for the invK(x,y,z,R,ARM,ELOBOW,WRIST) since it is a direct implementation of the closed form solution presented in the paper and also it significantly long hence making it highly unreadable.

What do you think I am doing wrong? I am quite sure the way I am computing the FK is correct but I could be wrong. The matrix multiplications of my Python code are correct since I double checked them with Matlab. Any advice is appreciated.

I already asked this question on robotics.stackexchange.com, but could not get a proper answer. That's why I am here. Thanks


texts: Raspberry pi, Stepper Motor and level shifter

texts:
It is my understanding that a Rasperry Pi cant handle 5V on the GND-pin.
For that reason I got myself a level-shifter which is supposed to be able to change the output from 3.3V to 5V. I need it to be 5V because that's what the stepper driver operates on.

I don't know if the 5v-output is programmable or if its just a steady stream of power.
If it's programmable i assume i could plug pin2 directly into the stepper driver and send it back through the level shifter making it 3.3v that i can connect to a GND-pin.
The connection from the stepper driver to the motor should be fine.
This is the code im using trying to activate the stepper driver
import RPi.GPIO as GPIO # Import Raspberry Pi GPIO library
from time import sleep # Import the sleep function from the time module
GPIO.setwarnings(False) # Ignore warning for now
GPIO.setmode(GPIO.BOARD) # Use physical pin numbering
GPIO.setup(3, GPIO.OUT, initial=GPIO.LOW) # Set pin 3 to be an output pin and
set initial value to low (off)
for x in range(0,100):
GPIO.output(3, GPIO.HIGH) # Turn on
sleep(0.1) # Sleep for 0.1 second
GPIO.output(3, GPIO.LOW) # Turn off
sleep(0.1) # Sleep for 1 second

Stepper driver: http://sahel.rs/media/sah/techdocs/hb860h_manual.pdf
Level shifter: https://www.spikenzielabs.com/Catalog/adafruit/breakouts/4-channel-i2c-safe-bi-directional-logic-level-converter-bss138


texts:
Predict the diffusion coefficient for nitrogen through a mixture containing 50% hydrogen, 30% ammonia, 15% nitrogen, and 5% water at 25°C and 1 atm. This was my thought process on which equation to start with but do I assume I'm dealing with water and ammonia in a gas phase? Would this even be a correct equation to use?.

Assumptions: Stagnant mixture

$$D_{AM} = \frac {1-x_A}{\sum_{i=1}^n \frac{x_i}{D_{Ai}}} = \frac{1-x_A}{\frac{x_B}{D_{AB}}+\frac{x_C}{D_{AC}}+\frac{x_D}{D_{AD}}}$$
$A=\text{N}_2$

$B=\text{H}_2$

$C=\text{NH}_3$

$D=\text{H}_2\text{O}$


texts:
Screen protectors are supposed to protect your devices from nicks and scratches, as well as the stress of impacts which might otherwise lead to cracks or shattering. The fundamental principle behind their operation is that screen-protector glass or plastic "gives easier", in a sense, than the glass on, say, a phone or smartwatch, acting analogously to the "crumple zone" in a car.
It's well-known how screen protectors work (and, indeed, there are several such questions on SE), and its certainly arguable that they must, in fact, provide some protection, but how effective are they, actually?

We reduce the problem to the following:
Consider a phone and smartwatch, with "standard" chemically-strengthened glass or equivalent (Gorilla Glass, e.g.), at something like 0.1-0.3mm thick (I wasn't able to find much data on this, surprisingly)
Obviously, screen protectors aid in preventing nicks and scratches (anything between the screen and the outside world is bound to). So, instead, we focus on the protection they offer from cracking/shattering. Most screen protectors are 0.1-0.3mm thick, and are made of tempered glass or plastic.

I've tried running the numbers, however this involves some science I'm entirely unfamiliar with. I can think of a few complications, as well. Protection certainly depends upon the angle at which impact occurs. Similarly, many phones and smartwatches have curved edges (we can assume that the screen protector covers these), which may be weak-points. Also, phones require cut-outs for speakers, microphones, etc.

Note: originally posted on Physics SE. I received some answers regarding how screen protectors work, but bothing on their effectiveness. For those questions, I was directed here.


texts: Evaluating bonding integrity of piezoceramic transducer

texts:
Currently I am working on a Structural Health Monitoring system utilizing piezoceramic transducers. The proof of concepts have worked very well. But we are in the process of working small scale manufacturing. We have observed inconsistency in the electrical response and trying to root cause the issues. In our design the piezoceramic transducer is attached to a host structure with cyanoacrylate adhesive. One of our concerns is the integrity of the adhesive. What are the possible non invasive methods to evaluate the integrity of the bonding?

Note 1: We are looking at X-ray as an option.
Note 2: This questions is related to How to measure electro-mechanical coupling?


texts: Using strain energy to calculate deflection

texts:
I have a solids problem I cannot solve, I have the answer and I have attempted the question. I just need to know where I am going off track, (perhaps there was an issue setting up my deflection equations?). Any assistance would be highly appreciated.

Question:

My work is as follows:

Castigliano's theorem: deflection = partial derivative of strain energy U wrt a force F

I split the beam into two parts, A - B and C - B (So I don't have to
deal with the reaction forces at C)

Edit:

X is the distance from the free end for Mab and Uab

And it is the distance from F for Mbc and Ubc

My first moment:

Mab = Fx

2nd moment:

Mbc = F(x-b)

U = integral from o to x of (M^2/(2EI))

Uab = integral from 0 to b of ((f^2*x^2)/2EI) = (f^2/2EI)*[x^3/3] (0-b)

Uab = (f^2/2EI)*(b^3/3) = ((F^2*b^3)/6EI)

Ubc = integral from 0 to b of ((F^2*(x-b)^2)/2EI) = (F^2/2EI)*[(x -
b)^3/3] (L-b)

Ubc = ((F^2*(L^3 - (3b(L^2))+(3L(b^2)) - b^3))/6EI)

Therefore

Utot = ((F^2*b^3)/6EI) + ((F^2*(L^3 - (3b(L^2))+(3L(b^2)) - b^3))/6EI)

Utot = ((F^2*(b^3+L^3 - (3b(L^2))+(3L(b^2)) - b^3))/6EI)

Utot = ((F^2*(L^3 - (3b(L^2))+(3L(b^2))))/6EI)

Deflection = dUtot/dF = ((2*F*(L^3 - (3b(L^2))+(3L(b^2))))/6EI)

Deflection = ((F*(L^3 - (3b(L^2))+(3L(b^2))))/3EI)

Clearly not the answer, I am not sure but maybe I went wrong somewhere in the first
couple of steps, perhaps either setting up my moment equations or setting them
up in the integral. But I can't figure it out. Can someone please help ID my error and let me know what I did wrong?


texts:
What would the adhesive strength of chewing gum be? Would it be enough to support a car bumper? I'm more interested in how much tensile strength chewing gum has. I'm working on a project regarding the used cars movie, and in the movie, the salesman repaired a bumper that was unconnected with chewing gum.

The bumper I'm thinking of is the one featured in the beginning of the movie, a '57 Chevy sedan. I want to see if it is even plausible for chewing gum to support a car bumper, so assume a fixed load of just the bumper. Since it was the '50s I would guess the bumper would be 25 pounds at least.


texts: Deriving a Time-Dependent Equation from a Surge Arrester for Transient Voltage Analysis

texts:
After looking through dozens upon dozens of IEEE papers, it seems that no one has really developed a simplified formula for a surge arrester.

What I would like to be able to do is perform a transient voltage study, and would like to be able to determine how the transient voltage would be impacted with the addition of a surge arrester, purely mathematically.

Is there a method of developing a "cutoff" equation for a surge arrester given its V-I data from a manufacturer?

For example:
$$\begin{array}{c}
 & \text{Vrated (kV)}\\ \hline
\ 15kV\\ \hline
\end{array}
\begin{array}{c}
 & \text{I(kA) (8/20µs), (kV)} \\ \hline
\ 1 (33.1) & 2.5(37.8) & 5(41.3) & 10(45.6) \\ \hline
\end{array}$$

In the table above, 15kV is the rating of the surge arrester, and to the right is the characteristic curve (V-I) of the arrester, where the number on the outside is the current in kA and the number in parenthesis is the residual voltage in kV.

Does anybody know how to take a curve, such as the one above, and transform it into a time-dependent equation that I would 'subtract' from a sinusoidal transient voltage,

$$V(t) = [transient-waveform]-[surge -arrester-curve]$$

The only formula I've come across that characterizes manufacturer data and is used in EMTP software is:
$$I=p(V/Vref)^q$$

But it is not time dependent and absolutely no mentions how the 'p', 'q' and 'Vref' variables are calculated.


texts: How do I calculate final equilibrium temperature of a pot of water on a stovetop vs. after I add food to it?

texts:
So I'm trying to come up with a simple hack to heat up food in a water bath to hopefully +-1ºC of a target temperature, but I really don't understand the physics of it all so much. I'm pretty sure I can keep a hot plate at a somewhat steady temperature by cycling it on an off at regular intervals, but I'm not sure what that means for the food itself.
Here's what I'm thinking: If I can get the hot plate to stay steady at a temperature of my choice, when will place a pot of water on it and the water will stop heating up after it hits some lower temperature point, say at 75ºC. That means it has reached thermal equilibrium and is heating up at the same rate as it loses heat to the environment - and as long as the heat output of the plate is the same and the environment is stable, the water shouldn't drastically change temperature.
What I want to know is: will the final equilibrium temperature will be significantly different after putting some food in it?
I did some googling and managed to come with the following, probably wildly incorrect reasoning:
Most foods' specific heat is around 3 kJ/KgºC, and waters' is around 4 kJ/KgºC. I suppose that means given the same heat input, food will heat up about 1.33x more than water?
And thus a pot with, say, 3kg water and 1kg of meat (assuming a specific heat of 3 kJ/KgºC for the meat), all the stuff in the pot will have an average specific heat of 3.25 kJ/KgºC (3+3+3+4=13, divided by 4kg = 3.25), so it will all heat up 1.08x more?
What exactly does heating up 1.08x more mean, though? Do I just multiply 75ºC by 1.08? Surely not, right? Do I need to stick 1.08 in some formula or convert it to kelvin or something? What even are numbers, really? Thanks!
Just to clarify, what I'm concerned here is the final temperature once the pot reaches equilibrium again, not how much the temperature will drop when the food is added.
EDIT: To further clarify - what I want to calculate is what the final equilibrium temperature of a pot of water will be after placing some food in it, knowing only the final equilibrium temperature of the water before placing the food.


texts: How to measure turbulence parameters experimentally?

texts:
When running CFD simulations with turbulence on, I often need to specify inlet parameters such as the turbulent intensity, turbulent viscosity ratio and/or the turbulent length scale.  If these parameters are already known for a given experiment, I have no problems validating experimental data.

But I'm curious to know how these parameters are measured experimentally.  How can I directly measure the turbulent kinetic energy and turbulent viscosity from a single experiment?  Due to the inherent randomness of turbulence,  would I need a lot of repeated experiments to measure it or can it be done in a single experiment?

How is this typically done in practice? Knowing that there is a trade-off between accuracy and cost, what would be a low cost measurement technique that is minimally intrusive to the overall flow while providing accuracy to within an order of magnitude with the fewest number of repeated experiments?


texts: Can you make the magnets rotate inside the coils of Brushless motor?

texts:
I know that current brushless motors, have a non rotating core made of copper coils, with permanent magnets on the outside rotating around it, and eventually connected to a shaft.  But i was wondering, if it was possible to make the exact opposite ?
I mean having a rotating core made of magnets around a shaft, with non rotating coils around it. Would it work? Hallback arrays of magnets would still work ?
I mean, phases are the same, and Magnetic field are not unidirectional. I don't see why it couldn't.
Thank you in advance.


texts: Meaning of quasi-axisymmetric case in 2D elasticity

texts:
A couple of books on elasticity, e.g. Gould and Soutas-Little, in the section on 2d elasticity in cylindrical coordinates, mention the case of 'quasi-axisymmetric' problems. These are problems where the stress and strain retain and axial symmetry (i.e., no dependence on the angular coordinate $\theta$), whereas the displacements $u_r$ and $u_\theta$ may carry $\theta$ dependence.

In particular, on writing the expression for $u_\theta$:
$$
u_\theta = A*r\theta + B*\cos\theta + C*\sin\theta + D*r
$$
with A,B,C,D constants, both mention that the last three terms rigid body motions, and hence do not contribute to any strain.

This statement per se I understand. Rigid body motions cannot give rise to strains or stresses. However, while I can imagine that the $\cos\theta$ and $\sin\theta$ represent rotations, I do not see how the $r$ term cannot give rise to strains! If $u_\theta$ is (say) zero at the inner radius and finite at the outer radius, it must surely give rise to strains! What is going on? What am I misunderstanding?

Addition to answer below --

Please see my comment to the answer for an explanation of the $r\theta$ term as well.


texts: How can I determine air speed in an exhaust pipe?

texts:
I have a vertical exhaust pipe with an air inlet at the bottom. Biofuel is burnt also at the bottom of the exhaust pipe.

This means air is drafted from the bottom of the pipe through the inlet, burning the biofuel, then out from the top of the pipe.

How can I determine the air speed?

Should I use Bernoulli's equation?


texts: Formula (or heuristic) for calculating force required for incremental change in angle of attack of an airfoil

texts:
Assume I have a system comprising of an airfoil A immersed in a fluid.

Further assume, that the airfoil is affixed via two bolts at one end, and is untethered at the other end.

The system can be parametised as follows:

S is the span of the airfoil
C is the chord of the airfoil
V (vega) is the relative velocity of the fluid passing over the airfoil
$\rho$ is the density of the fluid in which the airfoil is is immersed
$\theta$ is the current angle of attack of the airfoil (in radians)
L the distance between two bolts affixing the airfoil at one end (< C)

[[Question]]

Given a new angle $\theta_i$, what would be the formula for calculating the force required to be exerted on the two bolts to change the current angle of attack of the airfoil from $\theta$ to $\theta_i$? (assuming all other variables held constant)

[[Notes]]

From the lift characteristics of an airfoil, I think its fair to assume that a greater force will be required to be exerted as the angle of attack increases (up until the stall angle)

Additionally, since the force required is likely to be monotonically increasing (up until stall angle), I would prefer if the function actually returned the supremum of the the forces required to increase the angle of attack from:

$\theta$ $\rightarrow$ $\theta$ + $\delta$$\omega$

where $\delta$$\omega$ is the change in radians divided into an infinitesimal number of steps.

Ideally, the formula should derived from first principles (or the answer be provided as pseudocode for an algorithm), so that I can follow the logic, and apply it to an airfoil of non-rectangular shape.


texts:
I want to convert rotary motion (the orange propeller) onto a square path (the dark gray path). Is this a valid way to go about it? Would it be possible to use a square peg instead of a round one (the red circle) in order to keep the peg level as it travels? If not how could I keep it level? I'm a noob.

Update 2015/11/16 - Posted another option as an answer below


texts:
I got a position error measured by a linear encoder like in the picture below.

Could anyone explain some possible reasons for this kind of shape to occur in control theory?

My system looks like table with four legs.

The four legs move up and down by using motors and have a linear encoder as control reference.

The table should stay in its position after moving up.

The four servo motors actuating the four legs control the position by using linear encoder signals, respectively.

But after moving the table up around 10 mm ~ 20 mm, a strange symptom has happened. One or two encoder signals look like square waves (sometimes one encoder signal, sometimes two, sometimes none).

A simple setup diagram is as below.


texts: Calculate Efficiency Loss of a Leak in a Hydraulic Cylinder

texts:
I am trying to figure out what the efficiency loss of a leaking hydraulic cylinder is.  This master's thesis found that a controllable pitch propeller (essentially a hydraulic cylinder inside a rotating shaft to control the pitch of the propeller) had external leakage of  0.5 ltr/min at 40 bar and internal leakage of 3 ltr/min at 100 bar.  I was wondering if it would be possible to convert these numbers into a rough efficiency loss?

I have been google searching for days to try to find a reference to indicate how to make this calculation.  I also went all out and went to a local university library to use Engineering Village -- hoping to find some paper that did an analogous study but couldn't find much to help.

This seems relevant but not sure how to use it: Losses through holes drilled in a pipe


texts: Why do we write T cos theta = mg for this Q instead of mg cos theta = T

texts:
For this Q , the author of the textbook writes that T cos 45 =mg
but it also states  that mg cos 45 is not equal to T. I got to know about this because this is the way , I solved it first.
My Q :1 is that why mg cos 45 is not equal to tension or T.
The main point to noice is that Tcos 45 = mg doesn’t give same value of T as T=mg cos 45.
According to me why I think mg cos 45 should be equal to T :

There is no acceleration along T. Therefore acc=0.

T and mg cos 45 also come at the same vertical line.

Also as Q2: can we say there is $a_t$ is along z axis for this question ?
Name of author: Dc pandey


texts: How rubber and other ductile materials absorb impact energy

texts:
I learnt that, there are two types of weight plates in strength training, cast iron plates and bumper plates.

The bumper plates are coated with rubber material so that if dropped comparatively lesser damage is caused. I know this has something to do with the rubber absorbing energy but can't understand it.

If we take one in each type with same mass and drop it from the same height (neglecting air resistance and assume same contact area during impact), what is the difference between the two impacts?


texts:
How do those mechanisms such as the ones in cars work - when you open a tray or glove-box, and it opens slowly by "easing in".

I would like to build my own compartment with a sliding cover that would slowly open by with the push of a button.

Thanks


texts: How to predict out wavelength emitted from gasses

texts:
I'm trying to figure out which gas emits a specific wavelength when excited.

Say I want to develop an LED that emits a certain wavelength.

How would I figure out which gas emits that specific wavelength?


texts:
I am doing this daylighting project for which we must bring the light far down into a bunker. I have found .

I have heard and read that the quantity of light that you bring in a cable decreases, 60% of light for 10m cable, 40% for 20m cable etc.

Will a thicker cable bring more light in ?
If yes, does it make sense to start, where we capture the light, with a thick cable, as the distance increases, use thinner cables. The light from the thicker cable is concentrated into the thinner cables with convex lenses out of the thicker cable and then into the thinner cable using concave lenses. The final are where we want to put the light might need thin cables.


texts: Best glue option for laminated Kevlar  birch plywood for not peeling off

texts:
I have a problem where I glue a laminated sheet of Kevlar to birch plywood and it peels off easily
I tried:

Laminating the Kevlar directly on the plywood with lamenting epoxy
Using the laminating epoxy to glue Kevlar (with peel ply surface) to the plywood

Both options are peeling off and I need a strong bond
Any recommendations?


texts: Calculating the torque required to move and hold an arm parallel to the floor

texts:
I'm a computer scientist doing a dissertation in robotics and I'm designing a mechanical arm that mirrors a humans, as such I am wanting to pivot the entire arm from a "shoulder" using a stepper motor and some gearing, I was looking at holding torques for different stepper motors and realised that I'm not actually sure how to calculate the force that is going to be put on the arm and the motor when the arm is straight out perpendicular, is this the same as the holding torque?

I think part of my confusion is I am not to sure what terms to actually search, so sorry if this has already been answered before.


texts: Is there any material that has a higher kinetic friction than static friction?

texts:
Is there a material that has higher kinetic friction than static friction?

You can assume it's sliding on any surface you want.

Better if you come up with one that has this property on a standard flooring material: steel, wood, smooth concrete, tile, asphalt, etc.

Also better if the material has this property at a macro scale.


texts: How can I make a tee connection on a wire rope?

texts:
I want to fix a wire rope horizontally between two trees with a T-connector in the middle of the wire rope to hang a tire swing from.

Something like this:

tree-------wire rope------???-----------------------tree
  I                        I                         I
  I                        I                         I
  I                        I                         I
  I                        I                         I
  I                        I                         I
  I                    tire swing                    I
  I                                                  I
  I                                                  I

I looked for a T-shaped connector but have not found a solution.

What kind of connection can I use to hang the tire swing from the middle of the wire rope? I need something that will not deteriorate during the use of the swing.


texts: Derive a formula for the propulsion force - verification request

texts:
I'm having some difficulty with the following problem:

Derive a formula for the propulsion force containing $\rho, Q,S, u$ (pic below)

The propeller is moving left with the speed u. My only idea was to use Bernoulli as well as put an observer on the propeller and look into the flow from his perspective. I'd be grateful for verifciation of my solution as well as any hints

My attempt:


texts: Why do gimballed gyroscopes platforms need drive motors in order to maintain it's fixed orientation?

texts:
I have a fundamental misunderstanding about the role of gimbals and gyroscopes in determination of angular rotation rates (in inertial measurement units). A set of three gimbals enables an object mounted on it's innermost gimbal to assume an arbitart orientation in space. Viewed differently, a three axis gimbals set enables full freedom (3 degrees of freedom) of relative motion between the object mounted on them and it's support, what paves the way for the design of stabilized platforms.

In particular, one can mount three orthogonal gyroscopes on a gimballed stabilized platform, so that the gimbals isolate the gyros from any external torques and the three gyros will maintain a fixed orientation relative to the inertial space.

Up to this point, i agree with the chains of reasoning. What i don't understand is why one can't simply incorporate angle sensors in order to measure the angles between the axes of the gyros and spacecraft axes?

I now quote the wikipedia article on "gimbal":

  In inertial navigation, as applied to ships and submarines, a minimum of three gimbals are needed to allow an inertial navigation system (stable table) to remain fixed in inertial space, compensating for changes in the ship's yaw, pitch, and roll. In this application, the inertial measurement unit (IMU) is equipped with three orthogonally mounted gyros to sense rotation about all axes in three-dimensional space. The gyro outputs are kept to a null through drive motors on each gimbal axis, to maintain the orientation of the IMU. To accomplish this, the gyro error signals are passed through "resolvers" mounted on the three gimbals, roll, pitch and yaw. These resolvers perform an automatic matrix transformation according to each gimbal angle, so that the required torques are delivered to the appropriate gimbal axis. The yaw torques must be resolved by roll and pitch transformations. The gimbal angle is never measured. Similar sensing platforms are used on aircraft.

So if the initial purpose of the stabilizes gimballed platform was to isolate the gyros from any external torques, why do we now need a complicated drive motors system and a matrix calculator in order to apply torques to the components of this platform?

My question might result from a lack of knowledge on practical engineering issues, or maybe from a basic misunderstanding of the mechanics involved here. Anyway, my attempts at reading other sources than wikipedia didn't help me a lot, so i'll be glad to get an exhaustive answer.


texts: Definition of non saturated thermodynamic mixture?

texts:
In steam, when we say it's 0.9 quality, we mean that 90% is gas and 10% is liquid. But, as for specific volumes, will the specific volume of the gas be the inverse of the mass of the gas over the volume of the whole mixture or of the part of the mixture that the gas occupies? What is that part? In other words, is it correct to say,

$\large{\frac{V_{total}}{m_{(total)}}\ =\ \frac{V_{total}}{m_{(gas)}}+\frac{V_{total}}{m_{(liquid)}}}$

or what? What is the equation?


texts: Is the efficiency of a reciprocating air compressor constant for all allowable values of Pressure?

texts:
Efficiency = Actual Mass displaced by the compressor divided by the theoretical mass displaced.

If we continuously increase the pressure in the compressor tank, will the efficiency stay roughly constant or is there another relationship between Pressure in the tank and efficiency of the compressor?


texts: Is continuous beam design deemed "unsafe" by any code of practice/design practice for reinforced concrete building structures?

texts:
I am asking this because some of my engineer friends said that they won't want to analyze beam as continuous beam for RC building structures, because it is "unsafe" to do so, whether it has anything to do with less deflection or no, I don't know.

His logic is that continuous beam predicts less deflection ( and hence gives more economical design), is his claim valid?

I wonder how does practicing engineers view the modelling and analyzing/designing beam spans as continuous beams ( instead of beams with many supports) when it comes to reinforced concrete building structures? Do they generally feel that it is OK to design beam spans as continuous beam ( and hence more economical because the reinforcement bars used will be less), or do they share my friend's opinion?

What does the building code of practice ( or common design practice) across the world say about continuous beam design, do they discourage or encourage it? Any reason not to design beam spans as continuous beam?


texts: Heat Conduction/Convection Along discontinuous tube

texts:
I have a question regarding heat conduction/convection. I have a metallic tube over which a rope heater is wound, supplying power. A glass tube and a 2nd metallic tube lies at the exit of the first tube. The inlet thermocouple is placed at the inlet of the first metallic section, and exit thermocouple is placed at the end of the 2nd metallic tube.  Assuming I am supplying 500 W of heat to the rope heater, would I be getting 500 W of heat at the exit of the first metallic section (before the glass tube and second metallic tube) or is the 500 W only available at end of the 2nd metallic tube (meaning significantly less power available at the exit of the 1st metallic tube)? The discontinuity with the heater and glass section in the middle has me confused.
Thanks!


texts: Looking to design a cantilever support to hold up an 80kg projector

texts:
I need to make a support (preferably metal) for a projector to be fixed on the wall. The projector size is:

Width: 0.7m

Length: 1.1m

Weight: 80kg

If anyone knows how i can solve this please let me know!
Thank you so much!

Note: This will be going to the back of the Musical theatre, the wall of the theatre is made of concrete block.

Many thanks


texts: How should the public raise questions about unsafe structures in the United States?

texts:
In a program on NPR that I was listening to, there was a bit about a bridge that from the description sounded to a layman as unsound and is still in use. The program described it as an old wooden railway (and I'm aware that has its own set of challenges) bridge with rotting timbers.

In the United Sates, if a member of the public sees a bridge (railway, tramway, car/truck, foot, bike, etc...) that is of questionable soundness, what is the process for him or her to determine who us responsible for it, and if they (the responsible parties) should look at it and have it evaluated?

Is there a particular agency that is responsible for regulating bridges and ascertaining their safety?


texts: Mini mini line-in input latency - Real-time audio spectrum

texts:
I'm trying to build a fancy audio visualizer with an old Mac mini. Here's the idea:
I have an Atoll ST200 streamer as an audio source which I'd like to connect to my mac mini's line input to forward the song to an audio visualizer.
Now, when using the headphone jack output on the streamer and connect it straight to the line-in of the mac mini, I'm experiencing no delay at all. Unfortunately though, when using the headphone jack of the streamer, it no longer sends audio to my amp (and thus to my speakers).
As I have a headphone pre-amp, the Fostex HPA8 MK2, I tried connecting the streamer to the pre-amp with an optical cable, and then tried connecting the pre-amp headphone output to the Mac mini's line-in input. When doing that, I'm experiencing audio delay, of roughly 200ms, which causes the audio spectrum to get out of sync with the audio getting out of my speakers.
I also tried using the analog RCA output of the pre-amp (using an RCA to jack cable), but the result is the same.
You might then immediately think that the delay then comes from the pre-amp, however, when connecting my headphones to the pre-amp and comparing it with my speakers, there's no delay experienced at all.
All of this makes me think there's some kind of buffer issue on the line-in input, but that still doesn't explain why I'm not experiencing such delay when connecting the mac mini straight to the headphone jack output of the streamer.
Do you folks have any idea what might be the cause? Do you think I could solve the problem by using a dumb USB sound card? Is there any way to increase the line-in buffer, if that's even the cause? I know there are ways to do that via logic pro and all, but the use-case's different here.
Thanks a ton for your help, I'm quite desperate right now, the result is astonishing but the delay is soooooo frustrating :(


texts: How to calculate of Second-order system Frequency and Time domain values?

texts:
$\frac{0.25}{s^2+0.5s}$

Can I use formulas for 2nd order systems in this pdf?

If not, how can I understand if this sytem is underdamped, damped, etc?


texts: How to specify plumbing fixtures so models are not immediately out of date

texts:
Rock-solid guide specifications are the ultimate pipe-dream of consulting engineers because they minimize the amount of time that needs to be repeatedly spent on the minutiae of tiny details from project to project.

In specifications for items that are commercially available, I often see specific models listed in the specifications.  On one hand, this is great because if an alternate item is proposed by a contractor during the submittal process, the similarities can easily be compared.  Putting model numbers in a specification, however runs the risk that by the time someone uses the specification again, that model might have been discontinued.  Plumbing fixtures are the absolute worst for this.

Every single manufacturer seems to have products that run the gamut from low end to high end products, and they ALL seem to change model numbers constantly.  Is there a brand of plumbing fixtures (for any or all fixture types) that maintains consistent models for long periods of time or is there a better way to avoid spending time constantly updating specs without contractors trying to sneak the cheapest builder-grade fixtures through submittals?


texts:
I am doing a Finite Element analysis of a continuum. In my problem definition I use these units:
mm for length, kPa for applied stress, and MPa for material stifness (Young's modulus).

With these units, I get my output in: kPa for stress and micron for displacement, which is what I prefer.

Now I have to add Mass Density information to my problem. To benchmark my setup, I am trying to reproduce an old textbook example, in which the Mass Density is given in units of:
$$
\\lb-sec^2 / in^4\,
$$
What would be the equivalent of this in my adopted SI unit system.

My impulse is to use:

$$
\\kN / mm^3\,
$$

Any suggestions or advice will be appreciated!


texts: Is interference between aircraft an issue for fly-by-wireless technology?

texts:
I was reading up on fly-by-wire development, and I saw a short section about fly-by-wireless technology. It seems like a great idea, with the potential to lower costs, weight and complexity. I can see a possible scenario where it could be an issue, though:

Two aircraft are very close together (e.g. on a runway or flying in formation).
One pilot transmits commands through the aircraft's fly-by-wire system to other parts of the aircraft.
The other aircraft accidentally receives the signal because it is so close.
Things get very bad very quickly.

The thing is, I haven't been able to find any technical specifications regarding fly-by-wireless systems, and I have no idea if the transmission would be powerful enough to reach the other craft, nor if it would then be interpreted as actual data sent from that aircraft's pilot.

Is this cross-interference between fly-by-wireless systems possible? If so, how can it be mitigated?


texts:
I am looking for a solution to monitor and log ambient He levels down to 50-100ppm.

The detector is meant to be installed in an experimental hall where a large number of Photo Multiplier Tubes are in use. PMTs ageing speed increases with the He concentration. We consider 100-50ppm a safe limit for the PMTs and we want to make sure that the ambient level of He does not exceed that threshold.
Unfortunately there is a (normally sealed) device in the same area that could leak Helium so we need to actively monitor the He level.

The only solution I could think of is to look for a Thermal Conductivity Detector, such as those used in handheld gas sniffers. But a TCD will give only a reading related to the overall difference between sample and reference. Can you suggest any other solutions?


texts: How to solve analytically this equation?

texts:
I need to solve the next equation and to find $x_1$:

$$\dfrac{d(x_0x_1)}{dz}=-\beta\dfrac{dx_0}{dz}\dfrac{1}{r-z(r-1)}$$

where $x_0$, $x_1$, $z$ are variables, and $r$, $\beta$ are constants.

At this point is it possible to multiply whole equation with $dz$, will I lose some information because of the therm $\dfrac{1}{r-z(r-1)}$?

On the other side, I have expression for $x_0=f(z)$, it is dependent on $z$:

$x_0=\left(1+\dfrac{\beta}{r-1}\left(  1-\dfrac{1}{(r-z(r-1))^3} \right)\right)^{0.5}$

On which side I need to go to integrate this equation?


texts: Considerations for planet carrier design

texts:
I need to design a planet carrier for a planetary gearbox to which I'm gonna be doing some simple vibration experiments. It basically consists of the ring, sun and 3 planets and the ring it's no more than 20cm diameter.
I've seen many types of designs for planet carriers surfing the web, mainly star type or triangle. I only need the carriers to keep the planets in place but eventually I will need it as the input or the output, so a shaft is needed.

Also, I don't know what kind of bearings I should use on each end of the carrier for the shaft that will go into the planet gears. I'm not a mechanical designer so I don't know about the tolerances either. I was thinking of just measuring the inner diameter of the planets, and design a small shaft to fit very tightly into the gear and the bearing, and have the bearing fit into a bore in the carrier by pressure also, but I don't know if that's also the correct design to go with. I will send everything to be manufactured so I won't have opportunity to mend any mistakes.

Sun = 32 teeth (1.5 module), 48 PD, Ring = 80T 120 PD & Planets = 24T 36 PD


texts:
I'm asking this here because I really cannot find a better place to ask this.

Near my house (in the US), there is a pair of parallel train tracks operated by Union Pacific, primarily for cargo-carrying trains.

Along the track, there are various types of signals (for the trains): some are circular with three lights, some are linear with three lights (like a traffic light), and I think I've seen some with two lights. There's one pole on each side of the track, each with its own lights. Sometimes, on a pole, there are two sets of the lights - one above the other (I.e. Two traffic lights on the same vertical pole, and another identical one for the other set of tracks).

What do these signals mean? Why do they vary? How do I read them?


texts: For a Venturi, I calculated total head theoretically and experimentally. I noticed that the last point along the Venturi has not got the same as the start point total head? Shouldn’t it be the same due to Conservation of energy?


texts: Does filter surface area affect resistance?

texts:
I am in the process of designing the enclosure for a small kiosk like project, and intend on having two fans (Noctua NF-A12x25, chosen for their high runtime rating, quietness, as well as other factors). I want to filter the air to prevent dust accumulation over many years of operation, and have tried searching for a way to choose a filter, but I am too inexperienced in this topic and cant seem to find the right keywords.
What I want to know is, given a filter that filters smaller particles, and thus causes more resistance to the air, can "two" of them be placed in "parallel" to increase airflow? is there a limiting factor, or can we possibly use a small fan with a very large strong filter?
My apologies if my question is too basic or if my tags are wrong


texts: Would a car slip down on a frictionless banked road and situation for friction road

texts:
Here , we have a car on a banking road. Considering two cases:

Frictionless and friction surface of the road.
I give an initial velocity to the car by a push for a second. Then , the cases discuss about the direction of friction and motion of the car.
Case 1: Frictionless road surface
We will have an $N*sin$$\theta$ force acting towards the circle. Initial direction of motion was along the road but isn’t it that due to the banking of road and frictionless road. The car would slowly start to slip down $? $Is this case also uniform circular motion $? $
non uniform circular motion is not possible here since friction is not present. Therefore , no acceleration.
Also , can we say no centripetal and tangential acceleration is present$ ?$
_____ 1)N cos $\theta$ = mg
_____ 2)N sin $\theta$ = $\frac{Mv^2}{r}$ . From this , we can say the car moves down $?$.
Case 2: Friction is present between road surface and car.
All directions are same as the above except for friction. So , can I say that friction also acts in the same direction as $Nsin$$\theta$ ? in case of uniform circular motion.
In non uniform , friction force will be at an angle alpha to the centripetal acceleration $?$
By the $?$, I wish to understand what would happen.


texts:
there
I installed SINO 942 tracker in my bike, it works well, but then my bike's self start has stopped working (it works when I ride bike for around an hour), so
I think the tracker is eating up battery when the bike is parked for long hours.

I am already thinking about installing a manual switch, or a rechargable
12 V battery (so it wont need to connect to main battery), but all of these
are manual and regularly to-be-interacted-with solutions.

Please suggest best solution I can use to rectify this issue.


texts: I am designing a savonius type wind pump for low wind speeds(avg speed = 2.7 m/s), with these speeds and rotor area of about 2 m2. Acc. to my calculations, I am getting a volume flow rate of 50 ml/s at 10 m lift head, for this flow rate, is it feasible to build a piston pump of diameter 1.5 inch and stroke of about 4 cm. Is there a minimum limit on stroke length of a piston pump which is feasible?


texts: I am a first year engineering student and I am currently struggling with the dynamics prt of my course. It’s not that I don’t understand the theory behind it’s just that every problem I tackle seems to be different from the last one and brings with it different tricks and methods that need to be used. Any advice on how to get good at it?


texts: Gear switching for simple differential steering

texts:
I'm rather new to the field of gear systems, and to the field of RC models to which this case applies. I'm trying to design a system where a single variable speed engine would drive two different propulsion systems (in this case, rows of oars on a model galley). I want to be able to steer the galley by means of differential rowing.

I could use a double differential like in a tank, but it seems unnecessarily complicated, as I don't need to vary the turning radius continuously, in fact I only need three fixed configurations, RC-ed by a selector switch: both sides rowing, left only (turning right), right only (turning left). It could be go up to five if adding neutral turns left and right (the two sides rowing in opposite directions).

A major additional difficulty is the need for synchronization: although it would only minimally affect performance, visually it's quite important to have both sides rowing together when going forward - this is also a point where a double differential would fail, in my understanding.

Can anyone think of a relatively simple gear system to solve this problem?


texts: I want to determine the flow rate and required turbine size for an offshore hydroelectric scheme and need help

texts:
I'm creating a report on the possible implementation of a sub hydro system and need some help. I've attached the image of what I'm proposing, where I've essentially created a head via a riser B with a water inlet just below sea level, which will then flow down into the hydraulic turbine and fill up the pipeline and Riser A to create electrical energy.
In it's initial state, the entire system is full of water. When power isn't in demand I've incorporated an ESP to then evacuate the pipeline and Riser A back out of Riser B (Riser B is still filled after). Initially I calculated the required energy needed to evacuate Riser A and the pipeline which would act as potential energy using the simple energy equation E=mgh. That potential energy would then be converted into electrical energy upon subsequent flooding of the system again.
I'm having trouble in determining the ideal size of the turbine though because I'm not sure how to calculate the flow rate that will be coming into Riser B and subsequently into the turbine itself since Riser B is never completely empty. I assume that I won't need that large a one due to the the large head, but I'm not sure of the appropriate governing equations or if they're even needed given my potential energy calculations.
I'll be testing multiple values of pipe diameter and pipeline length but original values were:
Riser A = 500m
Riser B = 50m
Pipeline L = 10000m
Pipeline, Riser A/B Diameter = 500mm
Any help would be appreciated, because I'm stuck in a bit of a rut finding the connection between the two as I'm using two different ideas and joining them.
Also for reference the ESP will be powered using excess energy from a wind turbine (not shown).


texts: How to detect whether a bus is in motion or not

texts:
I am a university student and I need some help in a project. For the past few years now, many accidents have occurred whereby in overcrowded buses, passengers are accidentally propelled from the back emergency door. Or, sometimes because the rear door is not properly closed.The driver are unaware when this incident occurs as he has no control on the rear door. And after a deep analysis, I found that accidents like these have occurred in US and in European countries as well.
Hence, I wanted to find a solution which can be implemented in any buses which will prevent these type of accidents in the future.

An automated system which will prevent the rear door from opening while the bus is in motion and will automatically unlock when the bus is at rest.

Here are some links describing accidents that have occurred:

Boy opens exit door on moving school bus, falls out
Family calls for tighter safety rules after son, nine, falls out of 60mph coach and is only saved by a passing surgeon and nurse

Actually my problem is that I can't find a device which can tell me if the bus is in motion or not.

I did some initial tests with an accelerometer. But when the bus moves at constant speed, its acceleration is zero and hence the device assumes the bus has stopped.

I can use an RPM sensor but I need a solution which can be easily plugged-in in any buses. That is, the system can be implemented by anyone... something which can easily be mass produced.


texts:
A subsequent question stemming from here A massless motor is attached to a massless pulley(the blue circle) with a fixed rotational inertia and they are all attached to a mass X (the green platform). A cable (in orange) with spring constant K is attached to the pulley from the black rigid ceiling, the cable could be at the top of the pulley at t=0, or it could be at the side as shown in the picture.

Assume it is a motor supplying the torque to the pulley. What torque should the motor (assume it has the same outer diameter with the pulley) output to move the mass up? Should the torque produce a force that is the same as the weight of the platform and the cable would experience a tension two times the weight of the platform? If this is so, it could be said that it is the tension from the cable that is pulling up the mass with an acceleration of g, right? But if the motor rpm is constant, then why would there be acceleration?


texts: how would one calculate the % of heat not absorbed by a heat sink?

texts:
I'm planning on building a plant growth chamber inside a sealed/insulated 55 g rain barrel, and I'm trying to figure out how much of the heat from my lights will enter the chamber, and how much will leave through the heat sinks.

I plan on attracting 3x3000k 80cri Vero 29 gen 7 COB LEDs to the lid and running around 120-150 W/h total through them. According to their datasheet, their efficiency runs around 130-190 lumens/W depending on how hard you drive them which I have read is around 40-55% efficient (although Wiki seems to disagree with that). I believe this means that they will produce 54-82.5 W/h of heat.

I will be attaching both COBs to their own Arctic apline 11 plus active heatsinks rated for 100 W (see datasheet). They are aluminium and the fan moves 37.8cfm over its fins, but surface area and mass values for the aluminum portions are not provided by the manufacturer. That being said it’s total mass is 428 g.

I really would like to know what fraction of heat will be diverted into the growth chamber vs what fraction of heat will exit through the heat sink, so I can figure out if using DIY thermoelectric cooling is a viable option to combat this heat and keep the inside of the chamber no warmer than 85°F/30°C.

If so this will allow me to build a sweet 55 gallon growth chamber that can utilize CO2 injection while being temperature controlled.

Other variables:

Max ambient temperature 35°C
Inside walls of container have an Emissivity value of 0.044


texts: Parameter fitting in transistor simulations

texts:
What are good methods for black box model fitting? I have a set of experimental data, and a mathematical model (basically a set of differential equations) with adjustable parameters. The parameters should be adjusted so that the model reproduces the experimental data. I have some literature values to start, but simply with these values the curves produced by the model don't fit to the curves of the experiment (the literature values are to be regarded with a certain error anyway; the experimental data that I have to fit my model to is fortunately barely noisy).

I've been trying to get some results for two months, with results more than nothing but far from satisfactory. Lately what I've tried is an evolution algorithm, called CMA-ES, but it takes a lot of time, becasue it needs a few hundred iterations, and one iteration involves solving the set of DEs several times, which takes at least 15 minutes. (Now that the better server at the lab died, it takes 50 minutes per iteration...) It gave the best results so far, but these were again not satisfactory.

Can you suggest some good methods to do the fitting?


texts: Determining change of object over time ( diameter )

texts:
I am currently attempting to solve the following problem. Say that I have an object that can expand and contract, given some external force. What I want to know is how much it has expanded, or contracted, over time. ( the diameter difference ) In addition, while this expansion or contraction is occurring, the object is free to move around. ( Example, object rolling around on the floor while wearing these sensors on itself )

I am considering of solving this problem by using two sensors, where one lies at the front of the object and one on its complete opposite ( back of the object ). An example of this can be seen below:

When the object expands, here is the size difference:

Obviously, the diameter of the second object is substantially bigger, and it is something I'd like to record as it increases / decreases.

Are there some good sensors that I can use to record this change over time? ( Note, sensors that can attached to a Raspberry pi board, or wirelessly connected to, that is ). I'd also like to stay away from sensors that would easily be lost if movement of the object was introduced, or require cords. ( i.e Capacitance belts, conductive yarns, etc. as they can easily give false readings of "contraction" and "expansion" given that the movement is too large. ex: Capacitative sensor gets stuck on the side of the object, and gives enormous diameter readings )


texts: How do I relate Grab Strength and Grab Tear to the real world?

texts:
I'm looking at a spec sheet for a high density polyethylene woven fabric and I'm seeing the following parameters on it

  Tensile Grab Strength: Warp 155 / Weft 170 - tested ASTM D-5034-09
  Grab Tear: Warp 30 / Weft 25 - tested ASTM D-751

I understand how warp and weft are the horizontal and vertical so clearly they're running these tests twice, once for each dimension, but I tried reading the papers on the tests that were run and they were quite dense (no pun intended) and I quickly got confused.

How can I translate this into something I can use? Is there a standard unit these are in? What is the difference between grab strength and grab tear?

I'm putting my products in these bags and I need to understand what these terms mean!


texts:
What type of mechanism can I use to connect 2 coaxial pipes of unequal diameters, where the outer pipe can slide over the inner pipe? I was thinking about splines, is there any better way...?
Also, if I want the connection to be leakproof, what are the options that I have ?


texts: What is the process for qualifying a weld between structural steel and stainless steel?

texts:
In the US, typical structural steel welding is covered by either AWS D1.1 or AWS D1.5 (bridges). Both of these codes cover a wide range of carbon steels.

AWS has a separate code for welding stainless steels, AWS D1.6. There is some mention of welding to carbon steels, but this is mostly talking about choosing the filler metal and not the testing.

Neither D1.1 nor D1.5 cover stainless steel.

In this specific situation, I am looking at a fillet weld between a carbon steel plate and a stainless steel plate.

What is the procedure for qualifying (PQR and WPS) a weld between the two materials? Does one code control over the other? Would the weld have to be qualified per both specifications?


texts: How does the location of a mass affect its dampening performance?

texts:
I'm looking at something called at a Steadicam that stabilizes cameras. It looks like this

Clearly, the weights at the bottom are used for dampening/stabilizing. If the arm holding the weights were shorter/longer, would the stabilizing effect be affected? Would the centre of gravity change if the arm lengths were different (and thus affecting stability)?


texts:
My washing machine broke down recently, and they replaced the motor. The old motor was not broken,
as far as I could tell; the sensor that told the CPU that the drum was balanced was what was out of
order. At any rate now I have a perfectly decent rotor and stator, and I started thinking about how to
recycle them. Apropos of not much of anything, I started thinking about a one‐man hovercraft.

What I have so far;

The washer service manual specifies a max RPM. I assume this is completely useless because it refers to
the motor and drum assembly and I’m not going to dismantle my washing machine to weigh the drum. I can call the repair guy and find out how much the drum weighs, but I'll only do so if I find that the calculation takes too long (I don't want to bother him on the weekend).
The required lift force is equal to a > 9.8*(mass of hovercraft + mass of rider), where a is some
acceleration over a time T. Where T is simply the amount of time necessary to move vertically from rest to a
position above the ground equal to the height of the deployed skirt. In other words solve
$Y=Y_{0}+V_{0}T+0.5aT^{2}$ for a known Y, zero initial velocity, and $a=\frac{F}{m}$.
The friction and air resistance are negligible, however since increasing horizontal component of motion
reduces vertical component, thrust should be higher than what is required to simply achieve lift by some
factor.

Questions;

How can I evaluate the power of the motor? I have not been able to find specs online so far. Does it even make sense to talk about the power of the motor without knowing the power
supply? Is there a maximum and minimum power output? Alternately, is power even a relevant
parameter, or should I be concerned solely with RPM?
The friction and air resistance are negligible, however since increasing horizontal component of motion
reduces vertical component, thrust should be higher than what is required to simply achieve lift by some
factor.
What factor must I exceed vertical thrust by in order to move horizontally?


texts: Converting nonlinear system into equivalent nonlinear of the Byrnes-Isidori normal form

texts:
I have a nonlinear system (Ball & Beam) which is described by the following equations of motion:

$$ \ddot{y} + \frac{mg}{a} \sin(θ) -\frac{m}{a}y\dot{θ}^2 = 0 $$

$$ \ddot{θ} + \frac{2m}{b}y\dot{y}\dot{θ}+\frac{mg}{b}y\cos(θ) = u $$

where the letters stand for:

$y \rightarrow $ Ball Position
$ θ \rightarrow $ Angle of Beam
$ u \rightarrow $ External Torque Applied
$ b = my^2+J$
$a, m, g, J \rightarrow $ Positive Constants

Now, my final goal is to convert this nonlinear system into an equivalent nonlinear system of the Byrnes-Isidori normal form.  The state-space representation ($\dot{x} = f(x)+g(x)u)$ of the system by considering the state variables $x_1 = y$, $x_2 = \dot{y}$, $x_3 = θ$ and $x_4 = \dot{θ}$ is:

\begin{gather*}
\dot{x_1} = x_2 \\
\dot{x_2} = \frac{m}{a}x_1x_4^2-\frac{mg}{a}\sin(x_3) \\
\dot{x_3} = x_4 \\
\dot{x_4} = -\frac{2m}{b}x_1x_2x_4-\frac{mg}{b}x_1\cos(x_3)+\frac{1}{b}u \\
y = x_1 \rightarrow Output
\end{gather*}

The relative degree of the system is $r=3 < n=4$ (resticted to the region where $D_o = \{x\epsilon R^4 \ | \ x_1 \neq 0 \ \& \ x_4 \neq 0\}$ ), so we have the internal states $μ_1$, $μ_2$ and $μ_3$, which are:

$μ_1 = y \Rightarrow \dot{μ_1} = μ_2$
$μ_2 = \dot{y} \Rightarrow \dot{μ_2} = μ_3 $
$μ_3 = \ddot{y} \Rightarrow \dot{μ_3} = \dddot{y} $

Now, in order to find the internal dynamics we need a function $ψ$ which validates the expression:

$$ \nabla{ψ}\cdot g(x) = 0 \Rightarrow \frac{\partial ψ}{\partial x_4}\cdot \frac{1}{mx_1^2+J} = 0 \Rightarrow $$

$$ \frac{\partial ψ}{\partial x_4} = 0, \ \text{since} \ \frac{1}{mx_1^2+J} > 0 $$

where $g = [0 \ \ 0 \ \ 0 \ \ \frac{1}{mx_1^2+J}]^T$. I chose the function to be $ψ(x) = x_1 + x_2 + x_3$. And now, the internal dynamics by differentiating this function is:

$$ \dot{ψ} = \dot{x_1}+\dot{x_2}+\dot{x_3} \Leftrightarrow \dot{ψ} = y + \dot{y} + x_4 $$

$$ \dot{ψ} = μ_1 + μ_2 + x_4 $$

Now, what's left to do is to express the term $x_4$ as a function of $ψ$ and $μ$. In order to do so, I followed the below procedure:

$$ μ_3 = \ddot{y} \Rightarrow μ_3 = \dot{x_2} = \frac{m}{a}x_1x_4^2-\frac{mg}{a}\sin(x_3)  $$

The term $x_3 = ψ - x_1 - x_2 = ψ - μ_1 - μ_2$ and combibning these I obtained an expression for $x_4$:

$$ x_4 = [\frac{a}{m}\frac{μ_3}{μ_1}+g\frac{\sin(ψ-μ_1-μ_2)}{μ_1}]^{\frac{1}{2}} $$

My question is regarding the zero dynamics that can be found by $\dot{ψ} = w(0,ψ)$ meaning that I should set $μ_1=μ_2=μ_3=0$ while $μ_1 \neq 0$ (which also validates restriction for the relative degree to be well-defined). I am stuck at this point and considering what to do. I also considered to take a simpler $ψ$ function such as:

$$ ψ = x_1 + x_2 \Rightarrow \dot{ψ} = μ_2 + μ_3 $$

but this means that $\dot{ψ}$ only depends on $μ_1$ & $μ_2$ resulting the zero dynamics to be $\dot{ψ}(0,ψ) = 0$. Do I miss something regarding the procedure or maybe am I somewhere wrong ? Could use any help.


texts: For a bridge/beam, how will the Young's modulus affect the susceptibility of it buckling?

texts: I originally thought that a higher Young's modulus would increase susceptibility, but now I'm thinking it might be independent.


texts: In Engineering fields, how often do you find yourself being asked to be a "salesperson", and what is your reaction?

texts:
I have recently been told that my "salesmanship" is lacking when it comes to getting my ideas implemented.  I receive the feedback that my ideas are sound and the data to implement is compelling, and even that the ideas are presented in a way that management can understand, but I am not doing a good job of "selling" the idea when it comes time to implement.

I feel a little odd about this because on the one hand I can understand that, as an engineer, I haven't honed this skill.  However, on the other hand I feel almost blindsided that this is a skill I am expected to have; the decision-makers have already said, "go implement", but when I go to implement, the people with whom I am supposed to partner put up barriers to progress.

I'm wondering how others deal with this.


texts: How can electrical noise be isolated in an Embedded System?

texts:
An input device sends a 20ms positive signal to perform an action. The signal is captured using an interrupt triggered on the rising edge of the positive signal. It appears that there might be some electrical noise on the signal line. I suspect this because the interrupt is getting trigger inadvertently. I currently don’t have access to an oscilloscope to verify the signal integrity.  I am using MSP430 microcontroller.

Question:  What is the most effective/simple way for the micro-controller to capture the 20ms positive signal with out modifying electrical hardware?


texts: How to represent floating point numbers using logic gates?

texts:
Using the formula given at the start of the question, I had to convert the numbers in part (a) to floating point notation.

My answers for part (a) were:
(i) 1111.2^11 + 111
(ii) 1111.2^11 + 000
(iii) 0000.2^00 + 000
(iv) 1100.2^00 + 000
(v) 1010.2^11 + 101

But now i have no clue on what to write for 2(b), because I didn't really use a specific formula for finding out the answers for part (a).
Any help would be greatly


texts: What is the Technical Term for this kind of slot?

texts:
I am looking for the technical term which describes the kind of slot one finds commonly in modern phones to hold SIM cards. More specifically, what does one call a slot that one pushes the SIM card into once and it is secured there, and then pushes on the SIM card once again so that it pops out and allows it to be removed.

If there is no technical term, does somebody know where I may find information on how such a slot works so I may attempt to replicate it in a design?


texts: Does the bearing stress vary along the bolt?

texts: I'm currently working on problems for my mechanics of material course, and I just learned how to calculate the shear stress on a bolt holding stacked plates. That whether it be a single or double shear, I have to account for every shear plane. However, what happens for the bearing stress? I know that it depends on the area of contact, which is diameter * thickness of the plate. If there were three plates (double shear) and I looked at only the portion of the bolt in each plate, would the bearing stress not differ? Do I have to look at the entire bolt at once to calculate the bearing stress?


texts:
I’m in a position where I need to order high volumes of nuts and bolts for a project.

I read through a South African National Standard, SANS 2001-CS1, in which it states that when I use hot dip galvanized fasteners the nut should be of a higher class than the associated bolt.

Could you please specify whether this is accurate and what the reason will be for this?

Your assistance will be greatly appreciated.


texts: Adsorption - what models are used for dry scrubbing?

texts:
For scrubbing with activated carbon, air is generally brought through a dry adsorption media, where the contaminant is adsorbed onto the media.

I would like to know what mathematical model is used for this process.  I presume the rate of adsorption is proportional to the concentration of the contaminant, and can utilize a plugged flow reactor model - but the carbon has a finite amount of capacity it can adsorb.  So, how does this change the equation?  After t = 5 days if the first 0.1 mm is completely saturated, how would it take for a 1m long bed to reach breakthrough (i.e. detectable concentrations)?  There has been rules of thumb used in industry (such as if the first 2/3 are saturation, change out the media), but I would like to see a more thorough mathematical derivation.


texts: Equation driven conical spring not rebuilding properly in Solidworks 2019

texts:
I'm trying to make an equation driven conical spiral, you can download the file here. I know that I can use the spiral tool to achieve this but there are reasons why I want to do it like this. I have five global variables that control the characteristics of the spring: the initial radius ri, the final radius rf, height H, number of coils nc, and diameter of wire d (it's a square wire so the diameter is the width/height of the square). The equations for generating the coil are:

x=("ri"-t*(("rf"-"ri")/"H"))*cos(t*((2*pi*"nc")/"H"))

y=("ri"-t*(("rf"-"ri")/"H"))*sin(t*((2*pi*"nc")/"H"))

z=t

with limits from t=0 to t=H. The problem is that when I change the variables, the spring does not rebuild, even when I use Ctrl+Q several times. I have no idea why this is. I have another small coil above the spring which I'm going to use to make an end coil and it seems to update ok but the main coil doesn't. Any help would be appreciated.


texts: How does gear reduction affect a stepper motor's holding torque?

texts:
I'm new to mechanical engineering, gears, and motors. Coming from a software/hardware background, I am trying to understand how to leverage gear reduction to maximize the torque output of a stepper motor for an equatorial mount. The speed can be very slow so I would like to focus on maximizing torque for a heavy payload.

By my understanding, the output torque is the product of the input torque and the gear ratio. Is this the same for the "holding torque" of a gear system? Is the output holding torque the product of the input holding torque and the gear ratio?


texts: Can you make a decision on where is defect if you have the frequency spatially?

texts: Let's say for a steel bar, you have the frequency information on each spatial location along the steel bar, could you make a decision that a defect/crack is exist on the specific location without having to inspect the steel bar first?


texts: Relationship Between Gear Ratio and DC Motor Power Consumption

texts:
In my class, we are currently trying to understand the relationship between gear ratio and motor power consumption.

Given two gears, one attached to a motor, and the other attached to a string carrying a mass, I am trying to identify the gear ratio that minimizes the power consumption of the motor given a vertical distance travelled by the mass.

We analytically determined the motor constant, the motor resistance, the radius of the gear about the motor, and mass to be lifted, and the voltage applied to the motor, and the goal is to use this information to determine the gear ratio.

I understand the two relevant motor equations as well as the various relationships provided by the gear ratio, but I am unsure where to begin with this problem.  If someone could provide a push in the right direction, I have a bunch of ideas in my head and could hopefully take it from there.

The two motor equations are:

$$\begin{align}
V &= iR + K\omega \\
T &= \left(i-i_0\right)K
\end{align}$$


texts: I want to know something about the mechanical properties of the MAX phases. How ductile can $\text{Ti}_3\text{SiC}_2$ for example be at elevated temperatures? Can it be as ductile as Zinc or Aluminium?


texts:
I know that a hydronic system forms a closed loop. When the boiler is turned on, the water temperature will increase and expand. Since this system forms a closed loop, there is no volume for the hot water to expand. Therefore, the pressure inside the system will increase and explosion might occur if the pressure increases significantly. To maintain a constant pressure, an expansion vessel is installed to contain the increase in the water volume as it expands as it heats up.

The expansion vessel is divided into two compartments separated by a diaphragm. There is water on one side and air on the other side. Initially the air pressure equals the system pressure. When the water heats up its pressure increases. Eventually, the pressure exceeds that of the air causing the diaphragm to bend back in the air space, compressing the air. Since the water is allowed to expand, this means the system pressure is maintained constant. On the other hand, the air pressure has been increased because its volume decreases. Now, more increase in the water temperature will increase its pressure. The hot water will not be able to push the diaphragm more unless the pressure water becomes greater than the air pressure, which means the system pressure is not maintained constant. Am I wrong?


texts: Hold height constant. Then a Rectangular Prism, with length and width = radius of the cylinder, has greater volume! So why aren't tank wagons (railroad vehicles that transport gas and liquid)  Rectangular Prisms?


texts: Autodesk Inventor Make Holes on Different Edges Based on One Line

texts:
I need to invent a construction based on standard square tubes with holes placed in certain distance from each other and from ends of the tubes:

I also need to imagine the tube with holes as a parametric part. Therefore I want to base all the holes on alone sketch line with points, something like the following:

How can I base all the tube holes on the above sketch line?


texts: How to find resisting moment with rebars of different yield strengths?

texts: When designing a concrete slab or rectangular beam, how would you compute the Mn value if there were two rows of rebars one with a yield strenght of 40 ksi and the other with the yield strenght at 60 ksi?


texts: Can't Find Regulator for 16G CO2 Cartridge (800 PSI to 400-200PSI)

texts:
I am trying to make a Paintball Gun that works off of 16G CO2 Cartridges(800 PSI). I can't find a compact regulator that drops 800 PSI down to 400-200 PSI. If anyone knows of such a regulator could you please comment it below?
Also I wanted to try using a Ninja Regulator, but I don't know if the 4500 PSI or 3000 PSI input pressure would work with 800 PSI.


texts: How do you attach something temporary to a smooth metal shaft?

texts:
I want to attach something small to the smooth metal shaft of a small motor (2-3 mm in diameter), like fan blades, but I want it to be temporary.

If I make it too loose, then the fan won't turn at all, but if I glue or solder it on, then it will be too permanent and I want to be able to take it off.

Is there a way to firmly attach something temporary to a smooth, small shaft that has low friction while still being able to remove it when it needs to be?


texts: Why is it more convenient to express stress tensor in Material rather than Spatial coordinates?

texts:
I was reading chapter introduction about Stress and the author wrote the following about stress tensors:
"Since the current configuration of many problems, especially those involving solids, is not known, it is therefore not convenient to work with stress tensors which are expressed in terms of spatial coordinates. For some cases it is more convenient to work with stress tensors referred to the reference configuration or an intermediate configuration."
Is the material coordinates more useful since its hard to determine the current configuration? If yes,then why is it complicated?


texts: What components are needed to reverse the direction of a belt conveyor using one reversible motor, and how do they change the tension on the belt?

texts:
On regular conveyor belts, motors are usually placed on the head shaft where material is discharged, and tension is highest at the entrance of this head shaft. However, if the motor were to be simply reversed, it seems as if the load-carrying side would lose tension, turn slack, and the material handled could fall out.

In order to reverse a conveyor belt without having two separate motors, and simply having a reversible one, what sort of system do you need to maintain the tension?


texts: How much force can an acme lead screw handle?

texts:
I have a stepper motor that claims 425 oz*inches torque. I want the lead screw to span 2' supported on both sides. I'm trying to decide what diameter lead screw is strong enough to not be damaged by the motor, in other words I'd rather the motor started skipping steps before it caused damage to the lead screw. Equations and handy calculators for what force I could apply with a given lead screw are readily available. I suspect my motor would skip steps before it damaged any t8 lead screw if it were pushing against an unstoppable barrier.
However all the lead screws I've been browsing don't have a listed metric that says how much force it can handl.
From what I've read, the longer the unsupported stretch of lead screw, the less force it can push before it bends instead of moving. I also gather that a longer stretch of contact between the nut and lead screw increases the amount of force that can be withstood before the threads break.
Is there some way of estimating what the maximum force a lead screw can safely push at a given length, lead length, diameter, etc?