texts:
Statement

In a crank system, as described in the picture, we know the values of: the width of the connecting rod ($m$), the width of the crank ($b$), the torque in the crank ($M$) and the angular velocity $\omega$ which we apply to this torque. We want to know the result force ($F_2$) of the system.

Note: the diagram is missing $\gamma$, which is the angle between $F_1$ and $F$. Also, $F_1$ and $F$ are poorly drawn; they should verify $(1)$ below. It is just an error in the diagram, not in the concept of the question.

Solution

My attempt was the following:

  By the diagram, we can see:
   \begin{align}
 F_1 &= F \cos \gamma&&(1) \\
 \frac{b}{\sin \alpha} &= \frac{m}{\sin \beta} &&(2)\\
 \alpha + \beta + \gamma + 90 &= 180 &&(3)\\
 F_2 &= F_1 \cos \beta &&(4)
 \end{align}

  Puting $(1)$ in $(4)$: \begin{align} F_2 = F \cos \gamma \cos \beta && (5)
 \end{align}

  First of all, we need a relation between $\cos \beta$ and $\alpha$.
  The only one is $(2)$, where we can get $\cos \beta$ in function of
  $\alpha$ by isolating $\cos \beta$ after having applied $\sin \beta =
 \sqrt{1-\cos^2 \beta}$, so:
   \begin{align}
 \frac{b}{\sin \alpha} &= \frac{m}{\sin \beta} \nonumber\\
 \sin \beta &= \frac{m \cdot \sin \alpha}{b}\\
 \sqrt{1-\cos^2 \beta} &= \frac{m \cdot \sin \alpha}{b}\nonumber\\
 1 - \cos^2 \beta &= \frac{m^2 \cdot \sin^2 \alpha}{b^2}\nonumber\\
 \cos^2 \beta &= \frac{b^2 - m^2\cdot \sin^2\alpha}{b^2}\nonumber\\
 \cos\beta &=  \sqrt{\frac{b^2 - m^2\cdot \sin^2\alpha}{b^2}}\nonumber\\
 \cos \beta &= \frac{\sqrt{b^2 - m^2\cdot \sin^2\alpha}}{b}\nonumber
 \end{align}

  Puting this in $(5)$: \begin{align} F_2 = F \cos \gamma \cdot
 \frac{\sqrt{b^2 - m^2\cdot \sin^2\alpha}}{b} && (7) \end{align}

  Now, we need a relation between $\gamma$ and $\alpha$. From $(3)$, we've
  got: \begin{align} \gamma = 90 - \alpha - \beta && (8) \end{align}

  However, We want $\gamma$ only in function of $\alpha$, without $\beta$. So we go to $(2)$ again to calculate $\beta$ in function of $\alpha$. By
  applying $\arcsin$, we've got: \begin{align}\beta = \arcsin
 \left(\frac{m \cdot \sin \alpha}{b}\right) && (9)\end{align}

  So, putting it into $(8)$: \begin{align*} \gamma = 90 - \alpha -
 \arcsin \left(\frac{m \cdot \sin \alpha}{b}\right) \end{align*}

  And putting it inside $(7)$: \begin{align*} F_2 = F \cos  \left[90 -
 \alpha - \arcsin \left(\frac{m \cdot \sin \alpha}{b}\right)\right]
 \cdot \frac{\sqrt{b^2 - m^2\cdot \sin^2\alpha}}{b} \end{align*}

  We can even go further. We know that $\cos(90^\circ - x) = \sin x$.
  So: \begin{align} F_2 = F \sin  \left[\alpha + \arcsin \left(\frac{m
 \cdot \sin \alpha}{b}\right)\right]  \cdot \frac{\sqrt{b^2 - m^2\cdot
 \sin^2\alpha}}{b} \end{align}

  Simplifying with Wolfram Alpha:  \begin{align*} F_2 &= F \left(
 \sin(\alpha) \sqrt{1-\frac{m^2}{b^2}\sin^2(\alpha)} + \frac{m}{b}
 \sin{\alpha } \cos { \alpha} \right) \cdot \frac{\sqrt{b^2 - m^2\cdot
 \sin^2\alpha}}{b}\\  F_2 &= F \cdot \sin\alpha \cdot \frac{ m\cos
 \alpha \sqrt{b^2 - m^2 \sin^2\alpha} + b^2 - m^2 \sin^2 \alpha }{b^2}
 \end{align*}

  Finally, if we want to express this identity in function of $\omega$,
  $t$ and $M$ we just have to substitute $\alpha$ by $\omega t$ and $F$
  by $M/m$, so:

  \begin{align*}  \boxed{F_2 = \frac{M}{m} \cdot \sin(\omega t) \cdot
 \frac{ m\cos(\omega t) \sqrt{b^2 - m^2 \sin^2(\omega t)} + b^2 - m^2
 \sin^2 (\omega t) }{b^2}} \end{align*}

Question

Is this solution correct?

PS: my level of physics studies is quite low, so, please, restrict to this level of difficulty.


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Problem outline:
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Known:

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The diameter of each wheel.

I have a timeseries of RPM/articulation angle data with a 2Hz sampling rate, but if I can get some help with the general equations, I'm more than comfortable doing this bit.
I've done similar instant centre problems with non-articulated vehicles in the past, but my uni years are now a fair bit behind me and these days I spend most of my time programming, so my engineering skills are a bit rusty. Unfortunately, "reasonable" accuracy is important here (still making allowable assumptions such as disregarding slip, etc) so I can't use the assumption of linear distance. Any help would be very much appreciated!
Rough idea:


texts:
I have a tiny plastic disc of dia 1cm submerged inside water in a container in the halfway.
I have to make the disc to oscillate sinusoidal with a frequency(1Hz to 10Hz) and amplitude (1 cm to 5 cm).

I got an answer for similar question based on a mechanical method using a loud speaker. But this does not serve the purpose as a vibrating connector creates ripples and affect my observations.

How can I produce such oscillation and control externally without any wires?
I made a failed attempt using Lego gears owing to mechanical instability and interference with other moving parts.
I can use magnetic electric or any other means and I can replace plastic with any other material that can respond to external field variation. Therefore looking for a non mechanical method


texts: At what point does an I-beam becomes a H-beam?

texts:
According to BS5950, a beam section can be classified as plastic, semi-compact, compact or slender. For the same section area, a H-beam can take axial compression (without buckling) better than an I-beam, and as such, uses a different strut curve in the code:

Now, I understand that a H-beam has a wider flange compared to an I-beam, but at what point, precisely, does this transition from I- to H- occurs? For example, is a 400x300 (depth x width) beam considered a H- or an I-beam?

Update:

Extracted from BS5950 guide, the following table shows H-beams (also known as universal columns, some of which with depth greater than width. This is the reason why I don't believe the differentiation is so straight forward.


texts: Emulate normally closed relay with 2 normally open relays

texts:
Good afternoon, I have recently ordered a normally closed relay to fix on my car's daylight-running lights. When the main lights come on the DLR should switch-off. Unfortunately amazon has delivered instead of a normally closed 2 normally open relays (!!?). Is there a clever way to emulate the normally closed relays functionality with two normally open relays?
Thanks in advance.

regards
perry


texts: What does 'easily reversed' mean in the NIST spectral database?

texts: I'm trying to do some processing of optical emission spectra from sputtering plasmas, and am confused by what NIST means by 'easily reversed' in their notation. Anyone have a clue?


texts: Orientation of wire in linear position wire sensors

texts:
Talking about a wire potentiometer, I was wondering about the way it could be used after installation. as you know, wire sensors have a roll of wire inside them that come out of a hole, and it sounds like that the wire should always remain direct and in the same orientation as it comes out.
for example in this link
you can see that the wire is always held along one axis , let's say X axis to verify the length of the wire:

if my interest is the length change ( not the absolute current value) of the wire, and the wire does move not only in X direction, but let's say also in Y (and or) Z direction , while my interest is in $\delta L$ of the wire, not only in one certain axis, how much error would we introduce to the measurement ? is there a way to approximate that ?


texts: We are working to design a lock mechanism and need to hold a square plunger out of a hole for extended periods of time (potentially years). The square plunger is under pressure from springs to return to the hole. Initial testing with a friction pawl has been positive, but we wonder about maintaining grip over a longer period of time. The pawl is lightly spring actuated to maintain forced contact with the plunger surface at all times. Does anyone have experience with friction pawls and in particular why these are not as commonly used as ratcheting pawls? They seem to grip quickly and if angled correctly seem to hold on. Are there pitfalls we are not aware of over the longer term? Thank you for any thoughts.


texts: Reduce and compute flow in self designed pen

texts:
I am currently designing a simple pen for drawing with different types of liquid varnishes. My current design has a tip at the bottom side of the pen (blue) and a tank at the top side where the varnish is filled in (red). This varnish flows through a 0.7 mm hole in the tip. The drawing works so far. But the problem is, that it flows too quickly such that I have to draw extremely fast to prevent it from dripping. The main goal is now to reduce the flow/pressure in the tip. Unfortunately, the tip is not manufactured by me so that I cannot change it. But everything else is printed with a 3D printer and can be changed.

I thought about two different design changes. Option 1 includes a small channel between the tank and the tip. I printed this option with a channel size of 1mm, but I didn't help. Maybe the channel was too big. Option 2 added cap on the top side of the pen. I hoped that it would reduce the pressure by letting less air in, but again this did not really help. The size was 1mm which is maybe still too big. My question is if these changes help to reduce the pressure on the tip. Are there any other physical tricks to reduce the pressure/flow? Would it help to make the tank wider/narrower?

In addition, I wanted to ask if it is possible and how to compute the pressure on the tip with these designs.


texts: Efficiency and NOx emission of lean burn gas engines

texts:
I have a question regarding the efficiency of lean burn gas engines. Maybe it is just a confusion concerning the terminology of "thermal efficiency", "brake mean pressure", "brake thermal efficiency" etc. but let's see.

Stationary gas engines in combined heat and power plants are usually run at a very high air-fuel-ratio in order maximize efficiency and reduce NOx-emission at the same time. With the introduction of more air, thermal efficiency is increased due to a higher heat capacity ratio of the gas mixture. At the same time this also results in reduced temperatures in the combustion chamber which reduceds the oxidation of nitrogen and therefore lowers nitrogenoxide emissions.

However, in literature a tradeoff between low NOx-emissions and a high engine efficiency is often mentioned.

Also, I assumed that higher temperatures in a combustion chamber were indicative of an efficient combustion, which is also not in accordance with the first paragraph.

Other papers that I have read also indicate a maximum of brake thermal efficiency at the same air-fuel-ratio as the maximum NOx-emissions, which is also not in accordance with the first paragraph.

Does anyone here have a good understanding of lean burn engine mechanisms and can help me understand this? I can also provide more details regarding my own misunderstandings.

Follow up questions:

Once again, thank you for your answer, Mark. Here are some further thoughts including the graphs that confused me initially. Most notably the graph "otto cycle efficiency vs. compression ratio".

Regarding the beforementioned graph: With the increase of lambda, the isentropic exponent gamma is also increased, resulting in a higher thermal efficiency. Does this increase in efficiency also imply an increase of the available power at the crank shaft? My assumption is that the increase in efficiency also increases the available work in the p-V-diagramm of an Otto cycle (area between the 4 points of the different steps of an otto cycle). One thought experiment would be increasing lambda to infinity, therefore maximizing thermal efficiency as the isentropic exponent approaches that of air. However, this does not make much sense now as there will not be any power at the crank shaft.
Or to put this whole paragraph briefly: What do I gain by an increase in thermal efficiency? Where does the statement "lean burn engines are efficient and reduce NOx-emission" originate from, when the minimum of the brake specific fuel consumption is at the same lambda as maximum NOx-emissions?

The argument of the efficiency of a lean burn engine is often used in literature, however the lowest brake specific fuel consumption occurs at a lambda only slightly higher than the stochiometric operation of the engine and quickly rises then. This is very confusing as the previos investigation of gamma would lead to the assumption that I can simply "increase lambda to get more efficiency". What is the motivation behind an increase in thermal efficiency when it cannot be used as mechanical power at the crank shaft?

Please excuse that my questions seem a little naive.

And one last very important question: When investigating lambda, is it correct that with an increase of lambda the mass of the actual fuel is reduced? Or is the mass of fuel usually held constant in such experiments and lambda is increased by adding more oxygen, effectively increasing the total mass of gas in the combustion chamber? (To make a long question short: Is the convention that total mass in the combustion chamber is held constant when varying lambda or is the fuel mass held constant and lambda is varied by adding more oxygen)


texts: Is a metal Prince Rupert's drop possible?

texts: Can a Prince Rupert's drop be made of metal instead of glass?


texts: What is reason of low axial velocity at tip and hub of an axial turbine?

texts:
I am analyzing results of my turbine simulation. I have created one line from hub to casing at downstream of the flow...please see the following figures. I want to investigate along this line how the axial velocity changes. In one of my results, my new blade(VT in last Figure or blue line in last figure) has the lower axial velocity than to base blade(CT) at hub and tip. (Please see attachment.) What does this mean? I think that this is due to low separation in downstream of flow of new blade(VT). Am I right?

Another question:

According to the following picture, Is axial velocity equal to velocity V in my case?


texts:
As my kids are counting down to Christmas, I came to wonder how did people measure time through history. More precisely I wonder about unit systems for  precision time keeping of years past gone.
I am wondering this, because the other two most prominent units (length and mass), have had many systems of units, which still echo from the past (some louder some less so). So even though I know of fathoms and leagues or slugs and stones, I don't ever remember encountering any other unit system other than that of second, hour, day, month, year.
I've checked Wikipedia  at History of timekeeping devices, but only devices are mentioned (see hourglasses, burning incenses etc). However, nothing I could find about the actual names of units.
Has anyone else found the names of the actual units?
UPDATE: Thanks everybody for their responses. All of the answers so far for me had merit, even though on hindsight the question was not strictly engineering - it is more on measuring, which I perceive as a vital part of engineering. I've got to admit that the response is even better that I had hoped. I learned a lot of new things. Hopefully, there will be in time even more informational answers.


texts: A question on non-destructive testing and evaluation

texts: In most geometry inverse problem, information like the temperature measurement on the surface is use to detect the shape and location of a defect. My question is: is it possible to measure the temperature distribution or temperature gradient of a material up to certain depth? What kind of device is used for this kind of problem? Can you recommend a study that deals with such kind of problem?


texts: What is the mechanism of transition in applications of finite state automata?

texts:
Just began studying automata. I've already seen several examples of the applications of finite automata: pattern matching, automatic doors, etc. And so far, I understand the logical connection between those mechanisms and state diagrams and formal definitions. But I'm curious, what thing is implementing time steps—if that's what they're called—allowing states to transition. I know a tiny bit about computer architecture so I'm thinking it's like a processor clock, you know, something just ticking on and off very rapidly. Then the automata takes input on every "tick" of said clock. But with different devices using different current types (AC/DC) how is this actually being accomplished in an arbitrary physical device?

Now that I'm writing this out, it seems clear there are multiple ways to accomplish that ticking depending on what we're talking about, but I'm just looking for the most common examples found in real-life. For example what is allowing the sequence of input signals to occur in an automatic door?


texts: Through which medium is most of the heat transferred down (downwards) a glass tube filled with water: the glass walls or the water column?

texts:
If a much hotter object is attached to the tube from the outside, and the heat in question is transferred to the part of the tube that is below the source of heat, so there is no convection.
The conductivity of glass is a bit higher than that of water (0.8 to 0.6), but the area of water perpendicular to the flow of heat is way larger than that of the glass, so I think that almost all of the heat will be transferred through the water column. Is my reasoning correct?
Is Fourier's law applicable in this case?


texts: What is the material requirement for Van der Graff generator sphere?

texts: I would like to make a Van der Graff generator for my science fair project out of aluminized mylar. Do you think this might be feasable or do I need to use thick stainless steel ball? Is there some sort of charge or conductivity limit that I need to consider?


texts:
I was just reading about the anti-lock brake system example on the wiki page for fuzzy control system. The principle seems to be simple: instead of just assigning a SINGLE category (cold, cool, nominal, warm or hot) to the temperature of the brake, it translates the temperature into a continuous scale (fuzzy set), like 70% cold and 30% cool.

I can see the advantage of this over the 0-1 logic because now the input is smoother than the 0-1 logic and so the output will also be smoother. But if you have the temperature available, which is already in a continuous scale, why not just control directly based on the temperature? Why do you need the extra step to convert the temperature into fuzzy set and then do the control?

I noticed fuzzy control seems to be a hot topic a couple of decades ago. So maybe it's just because the controllers (in applications like cars and washing machines) were only capable of controlling based on rules rather than doing PID control?


texts:
The switches are so high it's not possible to see how they function on the ground. I really tried to look up information about this on the internet, but there's very little info available, and the info that is there is incomplete. I saw this diagram but still don't understand how the switch works.

It seem simple to have a trolley pole follow the wire, it is simply U shaped and a spring pulls it up, so that force is applied against the wire. However I cannot possibly imagine how does the switches function, mechanically speaking. Also, how do they prevent a short-circuit at the switches' frog where both poles touches each other.

Also, back when tramways (UK: tram, US: streetcar or trolley) also had a trolley pole, did they have switches using the same mechanics as in a trolleybus switch?


texts: Number of layers in a laminated steel transplant, using Young's Modulus

texts:
I'm not sure if my calculations are correct for the above question.
$$
E = \frac{\sigma}{\epsilon} = \frac{\frac{My}{I}}{\frac{\delta}{L}} = k. \frac{1}{I}
$$
Where k is constant for both beams, therefore:
$$
E_1I_1 = E_2I_2
$$

$$
\frac{I_1}{I_2} = \frac{1}{10}
$$

$$
\frac{\frac{W(H/n)^3}{12}}{\frac{WH^3}{12}} = \frac{1}{n^3} = \frac{1}{10}
$$

$$
n = 10^{\frac{1}{3}}
$$
Is this correct? If so should I round up or down for the number of layers? Also any comments on part (b) are welcome :)


texts:
I want to create a Pneumatic cylinder, The purpose is, Inside it will will contain a Nylon piston, and one end will be filled with clay. Cylinder will be closed from either side using end caps, which also has Push-in connectors(1/4" BSP). Compressed Air from a cylinder(Max. pressure of Cylinder 10 Bar) will be given to Piston side through a Non return valve and a Regulator. Which will push the Clay out through other end.

What should be the Wall thickness of Cylinder? It should safely handle Maximum pressure that might arise.
I have already provided a Safety valve calibrated at 6 Bar in my prototype that I made from a GI water Pipe, which has thickness of 3.85 mm. Is there any way the pressure inside the tank could reach a pressure higher than the maximum pressure Compressor can deliver (Compressor is rated for 10 Bar, with cutoff at 8 Bar)
I'm thinking about making the cylinder using a 100 x 5.75 mm Aluminium Pipe and End caps from Aluminum Rods. Would this be enough?
Should I give more thickness for End caps than cylinder?
How to find the maximum pressure rating of the cylinder if material, Wall thickness and diameter are known?


texts: What are left justified and right justified ADC results?

texts:
The TI MSP430F20XX series has a 12-bit internal ADC output, which is right-justified.

What is the difference between a left-justified output and a right-justified output? What are their pros and cons?


texts:
It is easy to find a very flat surface, "perfect" straight edge, or squares for ensuring things are perpendicular. The machines that make these need to be flat/orthogonal to do so, but how were the first squares and straight edges that were fairly accurate made?

"Fairly accurate" is subjective, and I don't know exactly how to define it, but in my mind I am imagining measurements made in a time before the age of heavy machinery and modern manufacturing.


texts: How do I build a miniature concrete house?

texts:
Our teacher gave us a project before Christmas break, it was to build a miniature house, she didn't state what specific materials should be used, so I built a cardboard house. She didn't accept it because it wasn't firm enough for her. Now I want to know if it is possible to build a miniature concrete house?
Considering I can't find any tutorials online I'm guessing it has a high chance of collapsing, but I don't know, that's why I came here.


texts: Are thermal (LWIR) lenses as capable as visible-wavelength optics?

texts:
I'm trying to figure out whether lenses for thermal (long-wave infrared, i.e.,  7-14µm) cameras are inherently more expensive or less capable than the lenses for visible cameras.

Production lenses for digital cameras often incorporate a dozen or more individual glass elements up to perhaps 50mm in diameter.  With surface coatings these systems still transmit over 90% of light in the visible spectrum, and are able to nearly eliminate all forms of distortion while providing a wide focal (zoom) range.  These systems can be mass produced for a few hundred dollars per unit.

In the limit (i.e., assuming the same economies of scale were provided), is similar performance and/or price possible with current uncooled thermal lens technology?

I am having trouble determining the state of the art in thermal lenses.  I know that for production cameras at least the front element is typically made of coated Germanium, or Ge-As, and a single Ge element in real-world temperatures (i.e., below 50°C) transmits over 90% across the LWIR spectrum.  (My understanding is that Zn-Se and Zn-S are also very good in the thermal spectrum, but they are too soft to be exposed, so they could work as interior elements, but not the front element.)  But I don't know, for example:

Is transmission through these materials so low that using more than a couple of elements is not practical?
Are these materials inherently significantly more expensive to manufacture than the glasses used in visible light lenses?
Are the physics of refraction in these materials in the LWIR spectrum too variable to build lenses with many elements, or with "zoom" capabilities?


texts: Is it safe to use a 1/2" NPT connection for thermowells when the process  pressure is  70 bar and temperature is about 85°C  ?


texts: Issues creating a high pressure chamber for corrosive solution

texts:
I'm trying to do an experiment on high pressure's effect on the electrical impedance of a really corrosive solution. I'm aiming for at least 2,000 psi with a pressure chamber but the only material I found that's chemically inert is PTFE and it's really limiting. One of my design is to use a PTFE diaphragm at the opening of the tube and press it inside the chamber to create pressure, and the other one is to push a PTFE piston into a tube directly but I don't know if it will hold much pressure.

The problem is that I can't really find a pre-made diaphragm that's under $500 that suits my chamber. Also, I can't find a way to fit a pressure gauge into the chamber and seal it properly. If you have an idea where to find these parts or any suggestions on how I should improve my design to better accommodate these challenges, that would be a great help. Thanks in advance!


texts: Deviation of Ideal Rankine Cycle from Actual Rankine Cycle

texts:
I'd been having difficulty with a problem from Cengel and Boles, Thermodynamics An engineering approach. The problem is about the deviated Rankine cycle from Idealised ones.

The question I would like to ask is how to obtain the enthalpy at state 3 and at state 6. The image attached shows the data for the problem.

I would also like to know is there a need to use the T-S diagram in obtaining the enthalpies in state 3 and state 6.

This is what I got so far:

The enthalpy at state 1 is obtained from the steam table and is h1 = 182.586 kJ/kg.
The actual work done by the pump is calculated using the isentropic efficiency value for pump and the value is w(pump, actual) = 18.986 kJ/kg
To calculate the heat input, the enthalpy at state 3 and state 4 must be known. The problem is I do not know how to get the enthalpy at state 3.
Similarly for the work done by the turbine, w(turbine,actual) the enthalpy at state 5 and 6 needs to be know. The problem is that I do not know how to obtain for enthalpy at state 6.

Updates:

I managed to obtain the work done by actual turbine with the method described by @algo.
The problem that I still have is how to obtain the enthalpy at state 3. I need it to obtain the heat input to the boiler. Can considering irreversibilities in the pipes (State 2 to 3) actually help in obtaining the enthalpy at state 3? Currently, I have no clue on how to start.

Any helpful reply would be appreciated.

Thanks


texts: Measuring pipe bolt torque without a torque wrench

texts:
I've had trouble with leaky pipe flanges, since my flanges are made of plastic. The problem comes down to the fact that sealing a flange is based on torque. Torque relies on bolt friction, which can change even between different bolt diameters. Therefore, it's a terrible indicator of the clamping force.

Is there any other way to measure flange sealing force than by using a torque wrench? I'm interested in any method that works, whether it's a known system or something crazy.

Ideal solutions would take around the same time to measure as the torque wrench (maybe double), can be used to check flanges that are currently in operation as well as new installations, and can work with a wide variety of flange, bolt and gasket materials.


texts: Lifting a 100 gram load vertically - Best combination of motor/s, battery/ies and gearing?

texts:
A hobby question. I have a load of 100 grams. The load incorporates all the components necessary to lift itself. I want to lift the load vertically (i.e. against gravity) at a speed of, say, 1 metre per second. I intend to use a small, hobby, toy-car type micro-motor/s, probably with some type of built in reduction gearbox, so as to increase torque.

Operating Range: 6 - 12VDC
Torque @ Stall: 7 oz-in.@ 6VDC
Torque @ Stall: 20 oz-in.@ 12VDC. Gear train damage can occur if stalled (locked)
0.118” (3mm) Diameter “D” Shaft
No load current: 40mA (6VDC)
No load current: 100mA (12VDC)
Stall current: 360mA (6VDC)
Stall current: 1600mA (12VDC)
No load speed: 240 RPM @ 6VDC
No load speed: 460 RPM @ 12VDC
Gear ratio: 50:1
Motor size: See Schematics
Shaft size: 0.118" (3mm) Dia. x 0.393” (10mm) L
Weight: 0.3 oz (8.5g)
DC reversible motors

I intend to use Lithium Ion batteries (TangsFire 18350 3.7V 1500mAh Eco - friendly Li - HP Rechargeable Batteries).

I'm trying to find a workable or perhaps optimal combination of motor(s), gear reduction, and battery supply that can do the job.

The total weight of 100 grams would include the weight of the components - batteries, motor(s) etc.

The motors with a built in gearbox already attached weigh about 8.5 grams each.
The Lithium Ion batteries weigh about 15 grams each.

Motors
Specifications a likely motors (they have the reduction gearing already built in). I will likely use three of these micro-motors working together to provide more pulling power (i.e. torque?).
460 RPM Micro GearmotorBlocks
Batteries
I plan to use 2 or 3 of these batteries: TangsFire 18350 3.7V 1500mAh Eco - friendly Li - HP Rechargeable Battery -  YELLOW 10

Questions:

Doable at all? Will it pull a 100 gram load vertically upwards?
The device will be attached to a string and it will hang down from a fixed point above the device. A bit like a mini-elevator.
If it is doable, what would be the maximum speed that it could travel at in an upwards direction?


texts: What standards apply when specifying coating/painting in a mechanical part drawing?

texts: I have produced a part drawing which calls up a machined mark on a flat surface, and the supplier has manufactured the part with this surface painted. I haven't added a note to the drawing that says that machined surfaces are not to be painted. Can I ask for the part to be re-worked by the supplier based on a generic 'drawing to BS 8888' note in the drawing border?


texts: Tornado Safety: Basement or first floor interior room?

texts:
Bulding

I live in a new (~10 years old) 2 story duplex home in the Eastern United States.

We have a completely interior bathroom on the first floor. It is between 2 other (exterior) rooms, the garage, and the firewall. It has a shower (plastic covering, not tile) but no tub.

We also have an unfinished basement. The foundation is concrete slab with CMU walls, which extend about 18 inches above ground level. There is a small (I think it's called a "port") window in one corner. At the opposite corner is a steel door that opens to a poured concrete stairwell topped with Bilco doors. It's an open space, I'd estimate a little under 1500ft2. We use about 2/3 of the space for general storage (decorations, unused furniture, food, the usual stuff) and 1/3 for my woodshop (hand tools, power tools, lumber, etc).

Risk

According to http://www.tornadohistoryproject.com, my County has seen 31 recorded tornadoes since 1950, with the following breakdown by scale:

| Fujita Scale | Number |
| ------------ | ------ |
| 3            | 1      |
| 2            | 11     |
| 1            | 13     |
| 0            | 6      |

(the Tornado History Project gets it's data directly from NOAA but uses the term "Fujita Scale" consistently - I don't know whether that means all their data after 2007 is actually scaled on EF or not - they don't seem to specify).

Advice

The general advice is always "get to a basement or an internal room on the lowest floor."

This makes sense. Roofs and exterior walls are for obvious reasons the first surfaces to be damaged and destroyed. Upper floors are more susceptible to structural damage. Direct wind and debris from tornadoes also is much less likely to extend below ground level, making basements in general a good place to be. In a lot of cases (as in mine) the basement is used as storage for  food and/or provisions - helpful in the event of being trapped.

It's also clear why fully interior rooms are an acceptable alternative - they put more structure between you and the storm. Since wind-induced structural failures happen from the outside in, they're also the rooms most likely to be left standing.

Questions

Are there any other factors to consider? What are some other risk/benefits that I've not considered?
Speaking in the most general sense, if you have both options, does one tend to be ubiquitously safer, overall?
Speaking specifically to my home, given that A) the historical risk of major structural failure is low and B) the basement is wide open and filled with sharp would-be missiles, which would you recommend for my family, and why?


texts:
Some cameras have a pattern similar to stairs close to their lens.  For example:

Such a system absorbs and/or reflects undesired light rays in order to improve image quality.
How would you call such a mechanical part?


texts: How come my calculated engine torque is so much less than the manufacturer's specifications?

texts: Here are my calculations. Am I doing anything wrong?


texts: Properties of an hexagonal shape vs round tube shape

texts:
In a bike frame build, are there any differences between hexagonal cross-section tube instead of the typical round tubes?

Assuming that both are made from the same aluminium alloy and have the same wall thickness, are there differences in weight, strength, or durability? Does the hexagonal shape have any particular advantages over round tube?


texts: Replicate stepper motor with gasoline engine

texts:
For those unaware of what a DC stepper motor is, it boils down to an electronic motor where the rotation can be precisely controlled, i.e. you can control the rotation of the motor in fractions of a degree. For example the motors I have currently allow you to move the motor just 1/2048 of a full rotation. This enables very precise movement.
I am trying to achieve the same thing, however with a motor, that is not powered by electricity but by gasoline. This motor is connected to a large and heavy flywheel that enables more or less constant RPM once the motor has settled. Using gear reduction I can get a very constant very low RPM which works fine for precisely moving a piece of machinery, however the problem is that I cannot really engage and disengage that movement reliably.
Since the gasoline engine also powers a 500W DC generator obviously the first choice would be to just use that electricity for a stepper motor, but that would take the fun out of the project (its a fun project, nothing serious). So far my ideas were the following:

Use strong electromagnets to simulate a controlled clutch where the energized electromagnets would engage the clutch more or less immediately and have some powerful springs to retract it once the electromagnets are no longer energized. Combined with more or less constant RPM this would make it possible to create precise movement by engaging the magnets for a defined time. Problem is that while I am able to create the clutch and circuit I don't have electromagnets that are able to push that much weight and dont overheat after a minute or two (literally).
Use some hydraulic oil with an oil pump powered by the gasoline engine. On the surface this is perfect, however it has some issues: I would be using a geared oil pump which needs to be engaged on demand, essentially just transferring the problem downstream. Using a DC motor to control the geared oil pump seems like cheating...

So long story short, does anyone have any ideas how to replicate a DC stepper motor with a gasoline engine (assuming constant low RPM) that does not require any DC motor on its own?


texts: Capacitors available in the market have a lower bound around 1 pF or 0.1 pF. Why is it difficult to manufacture capacitors in femtoFarad or lower range?


texts: What are the career growth opportunities for an Engineer with Product Testing Experience?

texts:
I studied Medical Engineering and previously worked as a test engineer for flow measuring instruments (for three years now) and find myself in a dead-end job. There are virtually no matching jobs.

While I can program quite well, I can't get a job as a programmer, because the companies prefer "full-fledged" programmers.

Is there an engineering work which is a mixture of Programming and measuring technology | physics | electrical engineering | medical engineering?

For example, PLC and automation technology you can not learn at home apparently. Therefore this is no choice for me.

As an engineer I like logical systems. And I like to improve measurement systems or products. I like programming of course. Therefore automation technology sounds good. But it is difficult to enter this field. Maybe I should apply as an software engineer (C#) and demand less salary.


texts: How to Build waterless non composting toilets?

texts: I am a CEO of New Beginning Homes. I am looking into building a waterless non composting toilet. This toilet will be run using gears and a handle that turns the gears to push the waste through a decomposing process where the waste will then be able to be used again for agricultural purposes. I am already aware of incinerating toilets. Any ideas on what could be used to break down the waste and on what types of gears would be best for this type of thing?


texts:
I would like to know what I am doing wrong for this PID controller design problem. I have all the parameters calculated ($\zeta$,$\omega_n$,$\sigma$...) and I have my target point set up. But now I need to find the zeros for the PID controller. I am have the equation

$$\sum \text{angles from zeros} - \sum \text{angles from poles} = (2k-1)\times 180 $$
where k = #poles - # zeros of the open loop system....I think.

In my case with the PID controller and the Plant function I have 4 poles and 2 zeros (unknown).

So using geometry I find the angles of all the the open loop transfer function and then I am given the the hint "either set both zeros at the same location or set one close to the origin and calculate the location of the other I chose the latter. So I picked a point close to the origin found its angle and then found the angle of the new zero by subtracting the angle of the poles from the angle of the zero and then subtract that from 180 to get the angle for the new zero. The root locus for this doesn't even come close to my desired point so I assume I am doing this completely wrong.


texts: Can we collide two Nano Spacecraft moving at 20% speed of light?

texts:
Nano spacecrafts are gram level silicon chips that will be accelerated to 20% of the speed of light to reach Alpha Centauri in 20 years.
I wonder if we can break the weight limitation by shooting multiple spacecraft and connecting them after the acceleration. To test this idea, I need your help with calculating the numbers. Let's assume that we want to connect two spacecraft, $A$ and $B$.

$A$ is accelerated before $B$.
$B$ is accelerated to a speed slightly bigger than $A$
it takes $t$ days for $B$ to catch up $A$

As $B$ will get closer to $A$ it will have better precision aligning on $A$ collision path, but it will also require more energy to navigate $B$
Please calculate what precision is needed to collide with $A$ and what maneuvering speed $B$ needs to do it.
This question doesn't contain all the details for making this calculation. I am looking for a realistic example to understand if such a mission is even possible, so please feel the gaps with realistic assumptions about the problem.


texts: How much is the braking torque of this belt brake?

texts:
I just thought of a mechanism that has a belt brake, but I cannot calculate the braking torque.
On the picture, the middle black shaft is stationary, and the blue is rotating with ω1 speed. The green one is the belt brake, the friction coefficient between the belt brake and the stationary black shaft is μ = 0,4. The right side of the brake is fixed to the blue shaft.
You can change the braking force with the screw colored red. In this example you add 9 Nm torque to the screw.
Could you help me find the braking torque of this braking system?
Here is the picture:

Thanks for your help!


texts: Is it possible design a portable high powered vacuum cleaner from a 12V DC motor?

texts:
I am currently designing a device that can pick up 20 kid's plastic balls from one box and transfer them all into another box. I have decided to use a vacuuming method to vacuum up the balls as my way of picking up the balls. Right now I'm just testing if my idea can just pick up one ball. But anyway, I'm planning to use a 12V DC motor that comes with 18,800 RPM and 4.9kg/cm torque connected to a 120mm diameter centrifugal impeller made of plastic to provide suction. This is all then attached to the top of an L shape pvc pipe of 120mm diameter at the top to fit the impeller and motor, and 80mm diameter at the bottom for the ball fit through. I am also powering this device with 8 1.5V AA batteries and won't be able to use other sources.

At this point I've been doubting if this potential vacuum would even have the sucking power to even vacuum up just one of these 65mm diameter balls. If this device fails which it likely will, would it be that my 12V DC motor isn't powerful enough, or my pvc pipe is too wide or something else. I've read online that it's something to do with a good CFM volume or airflow volume for good suction power, but I'm not too sure what component of the vacuum cleaner would provide this. Any suggestions would be really appreciated!

Picture of ball: (https://hiphiphooray.com.sg/product/colourful-air-filled-balls/)

Basic prototype of vacuum: https://ibb.co/q183PCM


texts:
Recently I visited the steel industry, I discover contract workers trimming loops of head and tail side of every coil:

For 12mm rebar coils, they have to trim 8 loops at head and 3 loops at tail side.

What's the purpose of trimming loops at ends of every coil?


texts: Simple EEPROM Code for Arduino to act as a Boolean

texts:
So I'm new to using Arduino's in general and just want to have my code by reversed each subsequent startup using the eeprom on my Arduino uno. I've been trying to read up on how to use the eeprom but I'm kind of confused so I've posted below a picture of some sample code that I think should work (but it's probably wrong). Basically I want to on start-up, execute some code, and next startup it executes some other code (the reverse of the original. Then the next startup to execute the original code. I'm unsure of how to fit my Boolean system into the loop part though, so any help would be greatly appreciated!

So What I want this code to do is the first time I power the Arduino to print "Code A". Then after its shutdown, and restarted again to print "Code B" But what I get at the moment is


texts: Printable and reusable whiteboard material

texts:
I'm trying to find a material suitable to be printed and with the properties of whiteboard, easy to clean and reusable. I'm having difficulties to find alternative materials, or providers.

As far as I know magic whiteboard is an alternative but it isn't reusable, only last two times.

EDIT

When I say printable I mean than I can print on it, lines or other shapes and images like on paper and I want this to be permanent. I didn't mean that it needs to be printed in a 3D printer, sorry.

Maybe I'm looking for simple whiteboard, but I need to print on it and make it lightweight and handy (mobile phone size). In addition I would like to be able to use different and thinner pens on it.


texts:
Is miter joint in welding - butt joint or corner joint ?

My example includes 45 degrees miter (90 degrees) angle on two SHS (Square Hollow Sections) - 50x50x3 [mm] Working with EN/ISO norms regarding welding and joint preparation.

My opinion is that horizontal welds are butt welds and vertical corner welds (fillet) - Just my opinion. I am not sure about it, that is why I seek guidance. See image:

How will these welds be designated and shown on a technical drawing ?


texts:
Relying on my past knowledge on how to attack the problem, I should use the equation
Moment of B about AC = $r_{AB} \times B • n^ AC$
To find the least force on B.
I just don't know what position vector  I should use for B, I am certain that I should not use points A OR C as a reference to get its position vector. That's what I believe. Or should I use it? Or the way I know is not the right way of solving? Is there any other way?
Sharing what I've done so far, I tried solving the midpoint of line AC, thinking force B could be from point B to the midpoint of line AC. Say, I've got my position vector for force B, I continued solving for $r×B$, then the dot product of the answer and unit vector AC,  and I've got force B as 28 lb., and since my process is unclear surely my answer was wrong, too.


texts: Building a steel footbridge over a railway line and its catenary

texts:
I'm doing an investigation about building a bridge over a railway line and its catenary system. I'm mainly interested in the electromagnetic environment on the bridge as it is affected by the presence of the catenary.

Is this an issue that I need to be concerned with?

I have no experience in either of these fields and that is exactly why I would like to get insight from people who do work in these particular fields. To answer some of the questions that have been raised in the comments section:

  What order of distance, what voltage? AC/DC? | South Africa or ...? | I'd expect regulatory requirements for unrelated reasons would place you well outside EM interaction range.

Ideally I would like the bridge to be of reasonable height such that the pedestrians wouldn't mind taking the stairs. I have freedom to reduce the height of the catenary system for exactly this reason. It is a 25 kV AC catenary system. What is the standard EM interaction range?

  What electromagnetic enviroment? You haven't specified any. Will this bridge parallel a power line? Be near a large radio transmitter? What makes you think there are electromagnetic issues here at all?

According to this Wikipedia article, AC high voltage lines "give off" electromagnetic radiation. The bridge is not close to anything really (no power line or large radio transmitter), it just goes over the train track and its catenary.


texts: Is it Possible to Automatically Transform an Image of an Object into a Line Drawing in AutoCAD?

texts:
I have many photos of devices which must be traced into AutoCAD. Is there any software for tracing object edges/outlines automatically so that a Primary Plan of the object can be made in AutoCAD?

For example: the photo below, shows an object I would like to have a line drawing of in AutoCad.

I need to trace the object's edge/outline from a top view and create a line drawing in AutoCAD.

I tried Photoshop by using it's Magic Wand Tool and made this:

The method I used was from How To Transform an Image into Lines to AutoCAD by youtube

I found this site and made this photo by using it's edge detection function:

My photo is in www.photo-kako.com/en/edge.cgi:

So after this how could I change the main edge/outline to a line drawing in AutoCAD automatically?

Or how could I do this better, any help or instruction for saving time and getting a better result would be appreciated?

Because the lack of time, I have made that work by my hand  similar to this :


texts: What is the difference between $K$ ,$K_{IC}$ and $K_t$?

texts: I have seen three representation of stress concentration factor values $K$,$K_{IC}$ and $K_t$ now all that I know is $_I$ in suffix represents opening mode of crack.The suffix $t$ stands for tip.However I do not understand how the three are factually different.I would require some fundamental advice on the three.


texts: Vertical component of force for rigid wheel hitting a step

texts:
My question relates to finding the vertical component of force due to a rigid wheel hitting a rigid step. I know the details of the step and I know the horizontal velocity of the wheel. I'm using the result to try and determine a damper of some sort to react this vertical force.

With reference to the image below, the shallow angle of the step is, a = 9.1° with the sides of the triangle being, x = 62.4 mm, y = 10 mm.
Horizontal velocity of the wheel is, $V_x = 8,33 \frac{m}{s} [8330 \frac{mm}{s}]$
The unsprung mass on this wheel is, M = 150 kg.

Time taken to cover the distance of the x dimension:
$t = \frac{62,43mm}{8330\frac{mm}{s}} = 0,0075 s $

Acceleration, $A_x = \frac{V_x}{t} = \frac{8,33\frac{m}{s}}{0,0075s} = 1110,67\frac{m}{s^2}$

So I reckon the horizontal force component is, $F_x = MA_x = 166 kN$

And so the vertical force component should be, $F_y = F_x\sin(9,1°) = 26,25 kN$

Please review my method and determine if this is a plausible method.

If I've made any errors I would appreciate any advice on how to correct this.


texts: Is is possible to form a 3D object from the front, side, top views with a triangle, a square and a circle respectively?

texts: A friend of mine asked me this question, but I don't know if it is possible or not. If it is possible, please show me how to construct it. If it is not possible, please prove it. Thanks.


texts: What is this circular metal object embedded in spalled concrete?

texts:
Consider the piece of spalled concrete shown in the attached image. It has spalled due to the corrosion of the reinforcement bar. There is a small circular piece of metal embedded within the spalled concrete. What is it?

Additional image of circular objects still in-situ in reinforced concrete air tower structures:

Additional close up image of concrete plug containing metalic horseshoe like object from another part of the wall.


texts: Is the use of direct-expansion split systems to heat or cool exit enclosures permitted under the US model building Codes?

texts:
Most multistory buildings have enclosed exit stairways somewhere within them to provide safe egress from their non-discharge floors.  In a building that relies on hydronic heating/cooling, steam heating, or direct (resistance) electrical heating, the US model building Codes are rather clear that the heating/cooling equipment for the stair can live within the stair enclosure, in addition to having the ventilation equipment for that stair enclosure placed within the stair enclosure, connected directly to outside air.
This is as per the penetration rules in NFPA 101 7.1.3.2.1(10), which explicitly permit steam and water heating and cooling lines to serve the stairshaft in addition to electrical conduits, as well as IBC 1023.6 point 2, which permits exit stair ventilation equipment (in my case, a "single room" or "decentralized" type HRV or ERV in addition to an air handler/indoor unit) to be located within the stair enclosure.  Furthermore, the IBC's definition of ventilation includes means for supplying conditioned air to the space being ventilated, which supports interpreting 1023.6 point 2 to permit the placement of an air handler dedicated to an exit enclosure within that exit enclosure.
However, it seems to me that this argument falls down as soon as you provision direct-expansion air conditioning to the exit enclosure using a traditional split-system architecture.  This is due to NFPA 101 7.1.3.2.1(10) not permitting refrigerant lines to enter stairshfts, the Handbook commentary stating that 7.1.3.2.1(10) is intended to be a comprehensive list of permitted exit enclosure penetrations, and IMC 1109.2.3 prohibiting refrigerant lines from entering exit enclosures (exit passageways and exit stairs).
This, however, has the effect of forcing the air handler for the exit enclosure to be moved outside the exit enclosure, or to be migrated into a unitary system such as a through-the-wall or rooftop terminal type unit.  However, through-the-wall and packaged terminal units struggle with unwanted air leaks between the unit chassis and the wall sleeve, and RTUs have efficiency issues as well due to the entire unit living outside, forcing ducts to penetrate walls into exterior space.  Furthermore, there may not be adjacent indoor spaces available to house said air handler if it is desired to place it indoors.  Even if such spaces are available, that requires fire dampers on the duct penetrations thru the stairshaft as well as shaft-rated construction around the ducts and the air handler itself, which makes maintenance access to said air handler much more difficult.
This leaves me wondering: is it the intent of the model Codes to prohibit exit enclosures from being served by direct-expansion air handlers (split system indoor units) located within them?  It seems to me that the combination of a small ductless mini-split heat pump and a distributed-type HRV or ERV would provide an inexpensive way to fully service an exit enclosure in a fashion that's compatible with a low-load, high-efficiency building design, yet on their face, the IMC's refrigeration rules seem to apply to all split refrigeration systems, from a one-ton minisplit heat pump to a massive supermarket's remote chiller system, despite the vast difference in risk between the two.  Furthermore, hydronic and steam lines can leak too; worse yet, some heating systems that are allowed, such as one-pipe steam radiators, are more prone to fluids leakage during common malfunction conditions (any sort of stuck radiator vent on a one-pipe system will cause the radiator in question to spit cruddy water on a regular basis) than modern direct-expansion split systems ever are.


texts: How does the demapping/demultiplexing of transport channels to logical channels work?

texts:
I am trying to model WCDMA MAC, but I cannot figure out how to demultiplex HS-DSCH unto DCCH, DTCH.
Also, since I am using E-DCH/HS-DSCH transport channel scheme, how does the data of DCCH  and DTCH mapped to E-DCH on transmitter side would be demapped on the receiver side?
The respective MAC headers do not seem to provide a clue to tell just by looking at the message which part belongs to DTCH and which part belongs to DCCH.


texts:
Suppose we have the following truss-like structure, with a load of 1N on the middle joint and two reactions on the bottom joints.

If I try to analyze this using a Cremona diagram, I run into the problem that I do not know how to handle a load on a joint inside the structure. Is it possible to analyze this with a Cremoda diagram, and if so, how does the naming of the different faces and panels work? Because we can only depict forces on joints between faces, right?

Is there even a solution?


texts:
I currently need to paint a steel structure with galvanizing primer.  The primer is an epoxy with >90% Zinc content.  The TDS for the primer states that intimate contact with the substrate is needed to achieve full effect.

This makes sense to me...

However, the paint spec and certification for the paint mandates an iron phosphate coating as pretreatment for the primer.  Does this not prevent intimate contact?  Or am I missing something?


texts:
I have been melting aluminum in a DIY furnace for a few months in order to make lost wax casts. I was thinking that since bismuth has a much lower melting point than aluminum, that I could add a small amount of bismuth to lower the melting point (9 parts Al, 1 part Bi). Qualitatively this seems to be working. But I am confused.
Looking up a phase diagram for Al-Bi, I find:

Which if I understand it correctly seems to mean that the melting point actually went up. Am I reading it correctly? If both metals separately have a lower melting point than the alloy at that ratio (and I am not reaching the new melting point), then what am I making?
Besides lowering the melting point, my hope was also to lower the viscosity so that the mix fills in my mold better. Will adding bismuth help accomplish this goal? Should I be adding tin instead? Is there a tin-bis-al ratio that would yield minimum viscosity at temperatures below 1500 °F (ideally mostly made out of Al)?


texts: How to vary the force output of a motor while stalled?

texts:
I want to provide a gradual increase in force provided to a piston (perhaps 0-100N over the space of a couple of seconds maximum), up till the point it begins moving, and then drive it to a varying speed after that.

I was thinking of using a linear actuator and applying a variable voltage to control the speed and force, but apparently using such motors in stall like this is generally a bad idea due to burning out the coils. However stepper motors and solenoid actuators are both designed for holding loads in place while applying a certain torque - would a stepper motor be able to do this without damage? Or could a solenoid actuator provide the gradual force increase in stall, and then the rest of the movement be accomplished using a seperate motor?

Many thanks in advance


texts: Why are phones not getting charged when I supply 5 V and 0.3 A?

texts: I'm using thermoelectric module to get the voltage. With the help of it, I'm getting 3 volts Open circuit voltage. I've attached DC-DC converter which regulates this voltage to 5 volts. I've attached USB at the output of the converter to connect my phone for charging. The thing is a basic cell phone is getting charged some 20% and then it doesn't progress even after 2 to 3 hours of connecting to USB. And whenever I connect smartphone, for a second charging symbol pops up and then charging stops.


texts: Boundary condition for a parallelogram-shaped excavation on an embankment

texts:
What we learn in engineering school is often idealistic, with textbook examples showing typical prismatic steel beams with a plastic section classification or excavation in a perfect sand or clay geology. However, in the real world nothing is perfect and engineers will face complex problems not taught in school, where there is little referencing literature and where the design codes do not provide clear guidelines.

One of the tasks I was assigned when I started out as an engineer was to design cofferdams for both abutments of a river bridge with a 30 degree skew across the river due to site constraints. As a result, the abutments at both side of the river are skewed. As a designer for the contractor, often we do not get to dictate the shape of the excavation. Material cost is always a source of great consternation, even more so in temporary works design.

I built a 2D frame for each strut level to do a structural analysis for the odd-shaped cofferdam. However, as the excavation is on a 35 degree slope, the sheet pile wall on the land side has greater lateral earth pressure than the river side. Also, due to the parallelogram shape, I have difficulty balancing the forces.

How should you model the boundary conditions for such an irregularly-shaped cofferdam, where the lateral earth pressure acting at the strut level is not balanced?


texts: How to pull on one side, while keeping an angle?

texts:
I have the following setup, consisting of a bar attached to another bar via a ball joint (indicated by a circle, and attached to the wall over a pulley with a weight at the end (the small "kg" symbol). I want to pull on one side of the bar. This is sort of like a one-handed cable row at a gym.
Top view:

Side view:

But when I pull, indicated by the black arrow, the angle (in red) between the force and the bar gets wider than the 90 degrees before the pull.
Top view:

I thought of adding a blocking element:
Top view:

But this would not help, as the pulley always aligns with the pulling force vector.
Top view:

How can I pull, while keeping everything (the angle between the two bars, but at least the angle between the back bar and the force vector) at 90 degrees? I hope this makes sense. I am thinking about something between the two bars, such as a spring.


texts: Installing satellite dish to point to local zenith

texts:
After receiving help on my previous post (Stopping/reducing wobbliness in threaded rod), I've decided to come back and ask another question: how can I actually hold the satellite dish into place? I don't wish to have the dish steerable (as this will probably require too much work considering the size of the dish), but I want it to at least be able to point ("look") directly upwards (to local zenith). The dish weights 16kg and has a diameter of 1.5 meters.

This is where I plan on installing the dish:

As it seems, there's nothing the dish has to offer for this kind of things (I got it used from someone who no longer needed it):

Any ideas on how to hold the dish in place to point to local zenith would be appreciated!


texts: Thrust consideration in sprinkler and irrigation systems

texts: In commercial fire sprinkler systems or large farm irrigation systems, is the thrust produced by the water a major design consideration? At what stage in the design process is this taken into account?


texts: How do fiber optic sensors detect strains in a structure?

texts: I am working on a project on detecting damage in structures using fiber optic sensors. I read the paper Structural Health Monitoring in Composite Structures by Fiber-Optic Sensors and found out that fiber optic sensors can not only detect strains but also locate them; how is this possible? Do they measure the intensity of the reflected light or something?


texts: Nastran / Frequency Response / Free-Free

texts:
There are examples of using SOL 108 and SOL 111 to create a frequency response.  In Siemens Simcenter (NX Nastran), the examples focus on a tower with a seismic mass.  The model drives the mass with an acceleration, attaching the mass to the structure using rigid elements.

This creates a model that adds (?) stiffness at the mass attachment points.

What if I want to simulate the frequency response function (FRF) of a structure that is unconstrained?

The test I conducted was to hang my part on a wire and tap (laterally) it with an impulse hammer.

This might be equivalent to constraining the support point as:

Fixed in DOF's 1, 2 (Tx and Ty)

I could apply a lateral acceleration (in the direction of the hammer tap).

Is this the conventional way to produce the FRF?  If not, what is?


texts: Can we make a motor without a permanent magnet and with wireless energy transfer?

texts:
If we could transfer energy wirelessly with 100% at short range. Then what if we create a motor that have both stator and rotor be an electromagnet? By putting a magnetic coupling to transmit energy from stator and rotor would have a coupling receiver that output energy to magnetic winding
The design would be exactly the same as a DC motor. Maybe a design like a brush DC motor that replaces the brush with a wireless energy receiver and electronics controller. Or a brushless DC motor with only a wireless energy receiver.
Unlike induction motor or conventional DC motor, both stator and rotor are electromagnet pushing and pulling each other directly
So we wouldn't need a permanent magnet at all but I think it would provide more torque and efficiency than an induction motor, and more comparable with a DC motor
But I can't find anyone who designs a motor this way. Is there any problem or disadvantage of this concept?


texts: What were the technical reasons for type bar designs being more common than type wheels for manual typewriters?

texts:
During the era of the typewriter there were a few kinds of basic designs. The (afaik) most well known is the type bar design, where each key is connected to an individual type bar that hits the paper when the key is pressed, each type bar carries the uppercase and lowercase shapes of a single letter. The other variant is the type wheel or type ball design, where a single ball or wheel shaped element contains all the letters. The mechanism rotates and/or tilts the wheel/ball before it strikes the paper so that the right letter is imprinted.

Type wheel/balls have some advantages over type bars: They cannot get stuck, and the entire wheel/ball can be replaced to change the font. The Blickensderfer, one of the early wheel operated typewriters, is often described as being much simpler than other contemporary (often type bar operated) machines, containing only a quarter of the moving parts of other contemporary typtewriters, so the type wheel mechanism appears to not necessarily be more complex than type bars.

During the last decades of the typewriter era, the electric type ball operated Selectric machines where very popular as higher end typewriters, but I have the impression that type bars were more common in manually operated lower end machines.

Were there technical reasons for type bars being more popular in simpler typewriters? If so what were they?

(This question is based on a few assumptions, which may be wrong. Please tell me if that is the case. And it may be that nontechnical reasons were more important in why type bar designs were more popular. I'm also interested in those, but in that case this is not the right site.)


texts: In what ways could coastal cities like New York/Boston/Miami mitigate future sea level rises and maintain current dry land area?

texts:
We've all read articles on rising sea levels and the impact it will have on coastal cities in the coming decades. There are even maps that illustrate how varying levels of rising seas will impact the dry land in and around these cities.

My question is, aside from deep carbon cuts that can help postpone or reverse rising sea level trends, what sorts of engineering proposals could these cities undertake to maintain their current areas of dry land? Whether its constructing massive gates around the shores of the city limits or something else entirely, could we avoid large portions of these urban areas going underwater in the future?

I'm gonna go ahead and say spare no expense when it comes to strategies.


texts: Where to output the colder air from a "heat-pump boiler"?

texts:
In an average family house, where should we let the colder air from a "heat-pump boiler" out?

1) - to the inside of the family house (ex.: heated in winter, so letting cold air in it..)

2) - to the outside of the family house?


texts: Can a DC voltage booster be connected directly to a DC to AC inverter?

texts: I am doing a project on a generator. Instead of using an alternator I am using a dynamo. I then amplify the voltage produced using a DC to DC voltage booster. However, can I get a higher AC voltage by connecting it directly to a DC to AC inverter? I am still green in this topic, I hope you guys could explain it clearly and perhaps you could give some helpful resources.


texts: How would I use a laser to cut a moving solid object?

texts:
Using a laser to cut sections out of a small moving solid has been suggested for a manufacturing problem. However, usually lasers come as a point, which means that we'd have to make the laser head move in quite an exotic curve, which will slow down our cut rate.
Is there a known solution to this? In my head, if the beam was instead focused as a blade and not as a point this would solve this, but I'm unable to find any existing solutions.
Ideally we don't want to move the laser head, or move it as little as possible to get our number of cuts per second as high as possible.


texts: How do I measure max oscillation of building using accelerometer?

texts:
For my school project, I am trying to measure the effect of a mass damper by changing the length of the string (that carries the mass), my setup is similar to the following video:
 https://youtu.be/f1U4SAgy60c?t=4m4s

I am trying to find a relationship between the length of the string and the oscillation of the "building". But I don't know exactly what the guy in the video is trying to measure and if it is related to what I'm trying to do.

Is it possible to use an accelerometer to map the oscillation of the "building" and if so, is there a relationship between the accelerometer data and the displacement of the oscillation?

My aim is to find the maximum amplitude for different lengths of string, so does a larger amplitude from the accelerometer data correspond to a larger amplitude in the displacement time graph?

I am desperate for help as I would much rather use accelerometer data rather than use a ruler in the background to measure the displacement of the oscillation.

Thank you in advance!!!


texts: Is there a specific name for diagonally braced truss members like those on the Queensboro Bridge?

texts: I am wondering about this specific type of truss in particular, any links to further source information and images regarding this particular geometry would be much appreciated.


texts: How to calculate Average temperature from area under the curve?

texts:
Let us say I have a graph of temperature against time for a material as shown here.

I want to calculate the average temperature. Will it be simple mean of the curve or rms of the curve?
Edit: The material is some metal.


texts:
Do off-the-shelf air compressors have minimum driving speeds, below which they cannot build the necessary pressure? Reciprocating compressors and scroll compressors are available—is there a difference in minimum working speed?
In my application, I would like to drive a compressor at very slow speeds (1–10 rpm) to store wind energy over a long period of time, but I'm concerned internal leakage inside the compressor may make that nonviable.


texts:
I'm trying to figure out what size of round tube to use for a tensegrity structure that'll probably have people climbing on it.

The rigid elements are 21' steel tubes, and in normal cases they undergo ~800 lbf of compression.

Assuming it's horizontal and pinned at both ends, and is under ~4000 lbf of compression (design * safety factor 5) -- I want to know how much load it can withstand at the center, given the inner and outer diameters.

Approximate answers are fine, but I'm not sure how to approach this.


texts: Why does a motor lockup at low RPM in my simulation?

texts:
I'm running a simulation in a CAD on a rather simple assembly with several parts in which a motor effectively rotates a part. If the motor is set to constant 10RPM, the part rotates fine and the max. motor torque is around 500N-mm. However, if it's set to 5RPM, it gets stuck and the motor torque reaches 8000N-mm.

How come a higher RPM could avoid a lock-up? Isn't a higher torque less susceptible to rotational lock-ups, since it's the force to rotate an object?