texts: Are the magnetic field lines flowing from north to south _inside_ a bar magnet as well?

texts: It seems based on the magnetic field of ring magnets like the  magnetic field lines of a bar magnet actually runs from N to S also inside the magnet, yet schematic images tend to show the field lines running from N to S outside the magnet, then through south pole up to north pole inside magnet. That seems wrong, like it contradicts the behaviour of for example this axially magnetised ring magnet -->


texts:
Is the length of a steel dowel pin standardized to a certain tolerance? McMaster-Carr provides tolerances on the diameter of dowel pins but not the length. In the event where I want a dowel pin to fit into two blind locating holes, I'd like to know if I need to leave a little extra "wiggle room" in the hole depth.

For example, I have two parts that need to meet as close together as possible. One part has a 5 mm deep locating hole for a dowel pin. If I have a 10 mm dowel, can I specify a 5 mm deep locating hole on the second part (assuming the dowel is actually <10 mm long)? Or should I choose something deeper (5.5 or 6 mm perhaps)?


texts: How is Load Transferred in a fully supported base

texts:
Suppose, you put a point load on a plate that is completely supported. The pressure under this plate is Force divided by the area of the plate.
If I make this base very large, then pressure will be negligible.
There has to be a limit to the size of this base right, after which it becomes useless to increase the area.
Also, how does thickness of that plate come into play. Like at the top layer of the plate , the point load does engage the area completely , as we move vertically downwards does the area increases. The closest to reference I got was the force transfer under wheel surfaces in bridge design. How is this assumption made that the contact area increases with 45 deg. angle.


texts:
In a news article today the reporter claims that modern improvements in "ammunition design" have made long rife barrels unnecessary for assault weapons. Here is the paragraph:

  The 20-inch barrel isn’t needed anymore.

  One of the biggest differences between the M4 and the M16A4 is the
  barrel length: 14.5 inches versus 20 inches, respectively. The M16A4’s
  longer barrel allowed for a higher muzzle velocity and a longer
  effective range; conversely the shorter M4 barrel limited its
  performance in both categories. But improvements in ammunition design
  have enabled the M4 to close the gap with its longer forefather.

  The Marine Corps adopted a new 62-grain, 5.56×45 mm Special Operations
  Science and Technology round. The SOST round is designed to perform
  out of barrels as short as 10.5 inches, so the M4 has no difficulty
  shooting out to the extreme end of effective range, negating the
  advantage of the long M16A4 barrel.

What improvements in ammunition design are they referring to? Why would a bullet be equally accurate coming out of short barrel?


texts: FEA using abaqus, and it does not follow the trend

texts:
I am doing finite element analysis of a donut shape for my school work.

I'm increasing the thickness of the object with a 1 mm increment and run FEA each time, and then comparing the maximum displacement of the object. According to the mathematical relationship between the stiffness and thickness of this object ($k = 4Ebh^3/L^3$, where $h$ is the thickness), I should be getting a $k$ that increases with the cube of the thickness. Although it roughly follows the trend, it doesn't match the mathematical model perfectly... why is that? Is anything happening in that donut shape that I haven't caught, like buckling? And how would that affect the displacement or stiffness?


texts: How can I trust a K-type thermocouple purchased from a no-name company?

texts:
I am doing some temperature measurements for reliability testing, over an expected range of 16C to 45C.  I have an NIST traceable thermocouple thermometer (S220-T8), however it does not come with thermocouple probes.
Without a calibrated thermal reference, how can I be sure that K-type thermocouples purchased from Amazon are accurate?  Shouldn't thermocouples be subject to unit-to-unit variability and thus require some sort of voltage-to-temperature characteristic that is reported?  I am finding that sometimes even "name-brand" companies are not providing such a datasheet.
I understand that they work based on something called the Seebeck effect, and maybe the Voltage/Temp relation is intrinsic to the metal alloy used.  As long as the little pellet of metal is "K-type" and is in thermal equilibrium with the thing being measured then maybe that is good enough?
I have found an NIST traceable thermocouple probe for $100.  I assume this probe will be within some spec or that they will provide the voltage to temperature relation.  Is it advisable to purchase one of these NIST traceable probes and then use it to check the error of the remaining probes?


texts: What is the mechanism of adsorption-desorption on biochar obtained from slow pyrolysis/ torrefaction?

texts:
Biochar is a major by-product from pyrolysis along with bio-oil and it is considered an important chemical feed-stock because of many light oxygenates.

I have read some papers on using bio-char use as an adsorbent to remove furfural from bio-oil and use the acid rich liquid for anaerobic digestion. But I was wondering if someone has tried desorption of furfural from bio-char? This could help recover it as a pure chemical co-product.


texts: Proper storage of micrometer-adjustable torque wrenches

texts:
Sturtevant's website has the following warning:

Relieving the tension down to the lowest setting
on some micrometer adjustable torque wrenches
can cause the tool to go out of tolerance
and you won't know it.

I've always seen that practice recommended. What is that would cause some wrenches to go out of tolerance when they are stored with the tension at its lowest setting?


texts:
Can I inject plastic in a RTV mould?
Will the interior of the mould get deformed by pressure?


texts:
I'd like to ask an environemental question which has to do with waste packaging and the EU regulations that enclosure this subject

I'd like to package loads of different hazardous wastes in compliance with ADR. So, depending on the waste, I use the labels that are pictured in this link. https://conceptdraw.com/a1276c4/preview

How can I label the packages of some wastes that are not applicable to ADR?

These wastes are:

brake fluids (16 01 13*)
antifreeze (16 01 14*)
synthetic engine, gear and lubricating oils (13 02 06*)

A possible answer is to label them in compliance with the GHS (Globally Harmonized System of Classification and Labelling of Chemicals) which is the regulation for hazardous products but there is no a certain answer if this system is applied for hazardous wastes too.


texts: How to calculate tensile strength of braided steel wire?

texts:
I am working on project involving designing a recoil spring coil of diameter 10.2 mm and wire diameter 1.25 mm. I tried using a solid core wire but it failed due inadequate tensile strength. Dimensions can only be altered by 5 mm, which is not sufficient to make the solid core wire work.

My professor suggested looking into braided wire rather than a solid core wire. I considered 6x7 wire rope but they are too big. After some googling, I found out there are recoil springs with braided wires with 3 strands. I know it is going to be somewhat less than 3x the strength individual wires. I searched handbooks, reference books, etc. but I could not find any established relations/formulae between strands and tensile strength. How can I determine the tensile strength of a braided steel wire based on the number of strands?


texts: Is it still a bad idea to keep modern electronics plugged into the charger cable for longer than necessary?

texts:
I have an "DaVinci IQ" portable vaporizer. Since the battery quickly runs out of power, I often keep it lying next to me, plugging from the computer into its USB-to-Mini-USB (or maybe it's Micro-USB -- unsure about that detail), often beyond the point where all the five LEDs are lit, indicating that it's fully charged.

I don't know where I heard this, but growing up with "early" rechargeable batteries, it was always a "thing" that you were supposed to stop charging them as quickly as possible after they are fully charged, or else "bad things" supposedly happen. I don't know what exactly those bad things were, but I'm pretty sure this was true at some point.

The question is: is it still true? Should I unplug it ASAP once it's fully charged, or does it no longer make any difference whatsoever?

And, if the answer is that this still has to be done, why is this? Why can't the device "stop sending in electrons" once it's fully charged, since it clearly can detect that?


texts:
According to the following figure, boundary layer becomes progressively thicker with downstream distance x . Why?

I have an other question as follows:

When turbine blade thickness increases, what dose happen about blade boundary layer thickness? Dose BL thickness increase about blade?

I am grateful that guide me about this question and if it is possible, please give me useful links and papers about these questions.


texts: What materials could be used to make a strip that bends when wet?

texts:
A bimetallic strip is a band of two metals attached in parallel that expand at different rates in response to temperature changes, thus bending the band, often used for measuring temperature. A bike project I'm attempting would be greatly improved if I had a band that bent in response to moisture changes. Specifically, brake/rim dust being fed back into the braking system is considered the top factor for rim wear in wet weather riding, and I've attached a prototype sponge to my brake pads to clean the rim when I brake.

It works well but I don't have the sponge on all the time since it would just be rubbing a dry rim, and it's a pain to engage, so if I want to make it useful to more than just tinkerers it needs to auto-engage. There are a lot of other issues to consider even if I had a material that bent when wet, but this is the thing I know the least about how to design.

I would like to tinker with an arm that closes a 2-5mm gap when wet from rain. A separate sponge or squeegee will deal with brake dust primarily, but some possible contamination from brake dust and road salts should be expected.

The closest thing I've been able to find is a polymer sheet that dances around on a wet surface, which tells me it could be done, but there's got to be a simpler way.

Even using something like a strip of swellstop (a rubber+sand compound for sealing concrete) glued to a non-expanding rubber might work, but I suspect swellstop doesn't contract when dry, and probably doesn't dry quickly either.

It's relatively easy to find materials that expand when wet, but seems hard to find ones that return to their original shape when dry.

Do I really have to resort to "smart" polymers? Is anyone familiar with a material that is less exotic that could fill my need?

Finally, if I can't find one, what's my next step? I'm a dog flying an airplane when it comes to designing something like this from scratch, do I need a team of PhDs? Where would I even start?


texts: How do drag and downforce in a rear spoiler of a car vary with angle of attack?

texts: I ran an two aerodynamic simulations, one for a spoiler angle of 0 deg and the other for the same spoiler declined at 30 deg. The results showed a considerable increase in downforce, but only a slight change in drag. Is this the expected behavior of a spoiler?


texts: Can a boiler feedwater injector be used to compress air?

texts:
A steam injector effectively raises fresh water pressure above boiler pressure, otherwise it would not work. Replacing the steam by compressed air and condensation heat by a combustion, can an ejector be able to compress more air than consumed to a higher pressure?

The main objective is emulate an steam boiler feedwater injector. Take a bit of compressed air from a pressurized bottle and use it in some way to inject more air in the same bottle at a same (a little higher) pressure. In other words, an air compressor running from a jet pump.


texts: Is high pressure combustion hotter than atmospheric pressure combustion

texts: let's say i have the same quantity of coal and air. Will the combustion achieve higher temperature if the air is under pressure?


texts: How to bend iron pipe into a spiral guide rail for stair lifters

texts:
I need to bend one circular iron pipe with 4 cm diameter and 2 mm thickness
as a guide rail for an electric stair lifter similar to this picture (the spiral bending part of stair):

How could I bend the metal pipe as a continuous rail guide for the stair lifter device and a normal continuous stair? I tried ordinary bending devices like:

I have made one easy bending multilayer pipe (which I used for house thermal piping "The PEX-AL-PEX pipes") as a pattern for guiding the bending process, but we could not make correct bending diameters and the metal pipe does not fit as a continuous stair. I also tried changing its form from a circular  to elliptical cross-section. What mathematical equations must I consider for bending it (what force vectors for 30 cm diameter with 40 cm height?) and how I could make it practical?

I tried to bend my failed sample's metallic pipe with heat and hand pressure to make it fit to the pattern but finally its circular cross-section changed with a very hard process to make an ugly continues spiral sample stair as a guide rail!

Is there a way of welding the pipe so the circular cross-section doesn't change or some kind of professional pipe bending machine used for this application? I have no access to CNC machines or anything similar to this:


texts: Any books about design of complex machines?

texts:
I'm familiar with several books that deal with the analysis and design of simple mechanisms (such as Norton's Design of Machinery), including four-bar linkages, gear trains and cams. There are also books that deal with the design of machine elements, such as shafts, springs, gears, bearings and so on, taking mechanical properties of materials into considertion (like Shingley's mechanical engineering design).

However, I haven't been able to find a book about combining those individual machine elements into complex machines to perform a specific task. It seems very obvious to me that designing a milling machine, a wood chipper, a bottling machine or other such systems one would need more knowledge than simply the design of its individual elements. Many even require knowledge of thermodynamics, fluid mechanics or electronics to have been designed.

Is there any book you know of that deals with the design of machines that are more complex than simple four-bar mechanisms or gear trains, like the ones mentioned? Preferrably with the same mathematical rigor found in machine element books. I have also seen books dealing with engineering design in general (like Dieter's Engineering Design) but they are far too vague, only including a general oultine of design practices such as identifying customer needs, prototyping, documentation, etc. that apply to any engineering product, not only machines.


texts: What is the difference between an automatic transmission and an automated manual transmission?

texts: What is the difference between an automatic transmission (AT) and an automated manual transmission (AMT)?


texts:
Can someone help with this question ?
it's a thermodynamic question based upon Sonttage book 7th edition

(*)the question states :-

R-152a with a volume of 15 L and at 36 Celsius degrees with an equality of 80 %
can some one help to find the mass of the substance .

and there is another thing i need help with, (*when it comes to thermodynamic questions which includes springs.

(*)What is the balance point of a spring in a spring - piston -cylinder system

appreciate your help guys


texts: What's the name and purpose of this specific shape of hollows in a reinforced concrete slab?

texts:
Below is a stack of reinforced concrete slabs with hollows (camera is positioned along the hollows' axis). Such slabs are used for floors - you build walls of the next floor, then lay such slabs such that they rest onto walls with the end shown on the picture and the opposite end. The dark round dots are steel rebars covered in rust.

I've seen slabs with round hollows and with oval hollows but this shape is new to me. It's something like a rounded hexagon with an extra cavity on the bottom.

What's the name of this shape and why is it used for hollows in a reinforced concrete slab?


texts: How to determine which size of screw needed?

texts:
I am wondering how to determine screw size for a system.

Here is the attached pictures of an example system.

Lets say the mass of object, m = 10kg
distance, x = 0.5m, x2=0.5m

with moment = 0,
0 = F*1.0m - 100N*0.5m
F = 50N as the screw clamping force

is the calculation to determine required clamping force correct?
If its correct, how to determine the required size and number of screw?
(FYI, socket head cap screw is used)


texts: Plastic Injection Moulding a Piece with Undercuts

texts:
I am a newcomer to Plastic Injection Molding and would really appreciate some advice.

I have a prototype object that will be made from a type of polypropylene. I only need a maximum of 10 units initially to ensure that the product is satisfactory. The issue is that there are many undercuts in the design. Imagine if you will, a variety of different shaped trees growing randomly in a field. This will be the design. The trees and the field will need to be formed as a single object to maintain strength.

I printed a similar design which was aesthetically OK but due to material limitations was not suitable.

Maybe Plastic Injection Molding is not the approach I should be taking?


texts: Difference between perpendicular and transverse loads?

texts: What is the difference between perpendicular and transverse loads? I saw this on a forum for 3d printing, but I couldn't find any online explanations on what the difference between both measures of loading was.


texts: The differences between manipulated variables and control variables

texts: In control theory, are manipulated variables and control variables the same concept or is there a subtle difference between them?


texts:
Above is a picture I found online, showing a prestressed concrete beam. It mentions a "hyperstatic moment".
When a beam is prestressed, it deflects upwards. According to the picture, this deflection needs to be counteracted by an additional reaction at the center, which in turn creates the hyperstatic reactions at the ends. But isn't this upward deflection the whole idea of using prestressed concrete? Isn't this deflection counteracted by the working load on the beam? Isn't the idea to design the prestress so that when the intended load on the beam occurs, it balances the deflection from prestress and the beam is straight again? Why do we need to discuss this hyperstatic reaction as something separate?


texts: How to control a mechanical part using a button(on/off) on a motorcycle?

texts:
I don't know how to correctly write the question. I have no background knowledge of electronics engineering.
I was wondering for instance, How to open and close the Motorcycle Stand using the On/Off button? Just like the killswitch button or How can we open and close the rearview mirror?
I just want to have an idea. What I would need? How to approach? Parts? I know that I have to configure the ECU unit. But I want to move the mechanical using switches.
Happy to learn.


texts: All I know about welding is it is a technique in which electrode is connected to one terminal and the gripper connected to workpiece is in connection with the other terminal. As current passes and when the electrode is touched to the workpiece,an arc is generated which melts electrode and helps in the formation of a joint. As the circuit is completed with a conductor in-between,doesn't it result in short circuit?


texts: Why to compress the hydrogen + air mixture in Hydrogen ICE engines when combustion efficiency of hydrogen at 1 atm is already high?

texts: ICE Engines are designed to burn the fuel and air mixtures at high pressures to increase the combustion efficiency. But hydrogen combustion efficiency is already high at 1 atm and at constant Volume combustion, peak pressure may reach around 8 atm. So why compressing the hydrogen and air mixture in Hydrogen ICE engines? If we could avoid compression of fuel and air, we can design much simpler and cheaper Hydrogen engines.


texts:
I am designing a two dimensional cam profiles.  I want to use the "modified sine" method for drawing the position and angle changes.  (see attached sketch).   The modified sine curve is actually a combination of cycloidal curve at the first and last 1/8 of the curve and a sine curve in the middle 7/8 of the curve.  It is easily employed when the terminal velocities are zero.  However,  often times it is necessary for a cam profile to simply go from one velocity (perhaps zero) to a constant terminal velocity. The terminal velocity is simply an angle on the displacement diagram.

The profile is defined by:

$$ y=
\begin{cases}
\frac h{4+\pi}\left(\pi\frac\theta\beta-\frac14 \sin \left(4 \pi \frac\theta\beta \right) \right), & 0\lt\theta\lt\frac18\beta \\[2ex]
\frac h{4+\pi}\left(2+\pi\frac\theta\beta-\frac94 \sin \left(4\pi\frac\theta{3\beta}+\frac\pi3 \right) \right), & \frac18\beta\lt\theta\lt\frac78\beta \\[2ex]
\frac h{4+\pi} \left(4+\pi\frac\theta\beta-\frac14 \sin \left(4\pi\frac\theta\beta \right) \right), & \frac78\beta\lt\theta\lt\beta
\end{cases}$$

The maximum velocity which can be achieved is at $45\deg \left( \frac\pi4 \right)$ therefore, only the first half of the curve is usable for my need.

as an example,

what method would you employ to design a curve that would go from point $(0,0)$ at angle zero, to the point $(3,2)$ slope $30$ degrees.

What coefficients $h$ and $\beta$ in the above equations will create a curve such that the slope at point $(3,2)$ is equal to $\frac{30}{180}\pi$?


texts: Calculating torque needed to climb a graded hill

texts:
I've been designing an electric skateboard which is driven by only one of the rear wheels (for the moment). As I was picking out motors for the board, I soon realized I would need to find a balance between torque needed to climb hills, and RPM to get a good top speed.

So I'm searching for the best KV (RPM/v) motor/gearing ratio combination.

For all calculations I've assumed the following:

Total mass (board + rider) = 85 kg
Voltage = 12 Cells * 3.2V (LiFePo4) = 38.4 V
Max Speed = 40 km/h = 11.11 m/s
Hill Grade = 15%
Coefficient of friction between rubber and asphalt: 0.65
Diameter of wheel = 80 mm

I tried assuming maximum kinetic energy as being equal to maximum gravitational potential energy at the top of the hill.

$$E_{k,max} = \frac{1}{2}mv_{max}^2 = E_g = mgh_{max}$$

Then solving for $h$.

I'd take that and use $y/x = 0.2$, solve for $x$, then use some trigonometry to setup a Newton's Second Law problem and solve for force needed to overcome friction and gravity (Equilibrium problem).

Then using $T = F \times r$, find torque needed at the wheels, assume some gearing ratio that keeps that and the $V_{max}$. Then solve for RPM and divide by total voltage for motor KV.

My mechanics are rather rusty and I could use some help.


texts: Factors favoring crack propagation in the middle of a plate for an extensive length relative to plate thickness (Reasons for < marks on crack surface)

texts:
I have a scenario where we have encountered a cracked steel plate where the crack has propagated within the plate longitudinally for an extensive length. The plate thickness is 1", and the crack length is approximately 12" with somewhat of a bend horizontally, yet staying within maybe 3/8" max variation propagating right between the top and bottom of the plate. Stresses are complex but the highest load is likely a vertical load, and may be close to 10-20 tons. Impact factor typically ranges between 3.5-5.5 for this load case, but it is complex and not precisely known for the location for the crack, which is suspected to have received only perhaps loads upward to an impact factor of 2-3. Precise stresses for failure are unknown. Steels in question is 4140. Growth marks have been observed throughout most of the entire crack, with somewhat of a < shape, which seems to indicate that it cracked both top and bottom and then finally through perhaps? But that Seems strange that it would crack just right near the middle of the plate thickness for such an extensive length when loads are not applied linearly.

I would like to review the theories how the crack propagated based on the described observations. What can a < crack surface tell me? Can someone list that out and provide appropriate literature backup?


texts: What do I call this shaft that drives the rubber stopper into the glass vial in a vial stoppering machine?

texts:
I'm translating a Russian text about a drug product manufacturing process. The text mentions briefly the vial stoppering machine, in which rubber stoppers are first fed into the hopper and then directed towards vials, and a пуансон drives the stopper into the vial. Multitran provides multiple options for how to translate this "пуансон". It's basically some shaft-like member.

I googled and found a description of some stoppering machine in Russian, and it has a diagram, with "пуансон" under number 60:

The text there says that the axle (59) rotates, making the cam (58) rotate and push this.. plunger\piston\punch member (?) towards the vial and drive the rubber stopper into the vial.

I'm unsure which word to use for this part.


texts: Why does the ceiling have to be so high up in large supermarkets?

texts:
I just noticed this while watching a stream in Thailand, but this also seems to apply to the West (where I live) and the USA and everywhere because everything is globalized and standardized these days.

Basically, the ceiling/roof is way, way up there, seemingly for no reason. Why don't they put the ceiling much closer to the humans shopping for food? Why must it be so high up? Is this some kind of ventilation thing or something? Doesn't it cost much more to make a building so enormous in height and have to heat up a much larger volume of space?

I don't understand why it's not like a normal room. Then they could put another level on top or just save the money.


texts:
I had a quick question regarding a homework problem. I cannot seem to understand why we are using internal energy of evaporation for this problem, instead of just using the internal energy of vapour to find the dryness fraction? Any help is appreciated!
Thank you


texts: Closed loop response of a discrete system

texts:
I have trasfer functions of a plant and a controller in laplace domain. I checked for the closed loop response by applying a step response. The system is found to be stable.

I checked the response of the system for the same step reference in discrete domain. I can see that the closed loop response of the discrete system is unstable. The transfer function is converted to discrete form by c2d option in matlab with a sampling time of 1ms.

Shouldnt the response of the system be same in both continuous and discrete domain (atleast for high sampling frequency)?


texts: What is the pressure to secure certain temperature?

texts:
How to calculate the pressure needed for a pump to ensure a specific temperature in a pipe?

For example, there is a pipe 100m long. A booster pump is needed to pump water with supply temperature 70 deg C. I need to ensure a temperature of 65 deg C at the end of the pipe. How can I calculate the pump pressure needed to ensure 65 deg C at the outflow?


texts:
Is it possible, under current technology, to have an electronic filter in the microwave range (100 MHz to 300 GHz) with very low bandwidth , say 100 to 1000 Hz?

If yes,  then what is the basic technology behind it? Any example would be great. Smallest bandwidth filters I am aware is that of GSM mobiles at 200kHz.


texts:
Recently I have been researching torque and horsepower.  I know that the lower the car gear, the more the torque.  However, whenever I see specifications of a car, it says :

  X lb-ft of torque at Y rpm.

Now, shouldn't they specify the gear that was measured in? Or is this the torque the engine makes, measured before the gearbox?

I am a little confused, I would be happy if you could help me with some explanations.


texts: Conventions regarding sliding and press-fit tolerances for shafts and bearings

texts:
I often build things (3D printers, skateboard wheels, bicycle parts) that use off-the-shelf ball-bearings. These ball bearings are available in nominal mm sizes, and to the limit of my measuring tools, tend to be ground exactly to size. For example, a bearing with 15mm ID and 24mm OD will have ID and OD of exactly 15 and 24mm, to my ability to measure.
It's also easy to buy linear or rotary shafts ground to nominal diameters. For example, I can buy 15mm ground rotary shafts. These are usually ground to a +/- tolerance which means half of them won't fit the bearings, or the more precise ones are ground to an upper spec of 15mm and very small tolerance smaller. Usually, even with the 15mm upper spec, the size is too close to 15mm for a bearing to slide on. I have to polish the shaft down with sandpaper (destroying the nice finish) in order to get an bearing that can be assembled by sliding, such as for a bicycle hub axle.
In cases where you want a bearing to have a close sliding fit on a shaft, it seems two things are possible: Either you could buy special ball bearings with slightly over-nominal size (i.e. 15.15mm ID), or you could buy shafts with slightly under nominal size (14.85mm). However, there doesn't seem to be a common "standard undersize" shaft or "standard oversize" bearings for each nominal mm size; neither thing seems to be common. This leaves a world of 15mm shafts and 15mm bearings which don't fit each other except by interference fit.
To get a bearing and a shaft which fit each other with a close sliding fit, is it more normal to use an undersize shaft or an oversize bearing? If the former, why does it seem so hard to find shafts commonly available to fit nominal bearing sizes?


texts: Strength of a Vertical Round Aluminum Tube with load cantilevered off it?

texts:
Can a vertical round tube safely support a cantilevered arm mounted near the top of the tube?

ROUND VERTICAL TUBE:

6061 Aluminum
2 inch Outside diameter
0.25 inch wall thickness
3 feet height

ROUND VERTICAL TUBE / CANTILEVERED ARM INTERFACE:

this clamp

(I don’t know the weight of the interface clamp but it is aluminum)

CANTILEVERED ARM:

The Arm is 4 feet long with a working load of 100 lbs. at the end of the arm
The arm itself weighs 11.4 lbs

ADDITIONAL NOTES:

The manufacturer of the articulated cantilevered arm (dectron USA) sells a Steel 2 inch OD, 0.125 inch wall thickness tube for this purpose. But their solution won't work for my application.
I am not worried about the strength of the arm it is rated to support a 100 lb. working load.
Don’t think it matters but I have two 12” sections, one 6” and one 18” all rigid
The only limit I want is 100 lbs. at the end of the arm other than that I want to use this thing with confidence for decades:)
Should I consider High-Strength 2024 Aluminum with the same dimensions instead?
OR could I safely use THINNER walled tubing, 0.125 instead of 0.25 inch wall thickness, 6061 Aluminum, 2 inch OD?

Thank you very much for looking at this and your help


texts: What's the difference between simple and deep groove ball bearing

texts:
What's the difference between simple ball bearing and deep groove ball bearing?

EDIT:
  I read about them in my textbook of design. The book has only mentioned that there are teo types of ball bearings. One, simple and the other, deep groove. No images or explanation have been provided. When I search for their images on google, Images of both the types of ball bearings look the same.


texts: Design a part to straighten moment and reduce torsion

texts:
I have a configuration with two bolts and a point of force application (see figure).
I understand that, if perfectly rigid, the two parts depicted in the figure will behave identically in how they will transfer moment on the bolts from the point of force application.

In this specific case, there would be a torsion, that is moment on the upper bolt going forward and moment on the lower bolt going backward.

The question is: what options are there to keep the configuration (bolts, point of application of the force), but straighten the moment  on the bolts?

Would having a shape like the left one made of a flexible material change anything?

edit: to clarify, in the picture below i added, in red the resulting forces on the bolts using either of the two depicted rigid shapes, and the desired resulting forces on the bolts


texts: What procedure do steel plants use to recycle water vapor?

texts:
As you may know Steel plants and Tile Factories use a lot of water. I want to know how do these factories recycle water vapor which is mixed with flue gases to reuse it?
Do they take advantage of Heat Exchangers or other type of condensers?
If they do what kind of them?


texts: Axial compressor - change of temperature not proportional to number of blades and their geometrical properties?

texts:
I'm learning theory of axial compressors for my summer internship and I find some of the equations puzzling, although I do understand the way they were derived.

The equation bellow is for temperature increase on rotor.

Could someone elaborate on why isn't the $\Delta T$ proportional to other factors like the number of blades? Is it correct to assume that even one blade is considered to be able to accelerate all the fluid going through the compressor to the tangential velocity considered in this equation, given by $U =\omega$r? This would then mean that the number of blades and their geometry, except the main angles, will only play a role in energy losses and distribution of load on individual blades?


texts: How do split drawings from this without losing their dimension Autocad

texts:
I have a dxf file converted to dwg (unit: millimeters). There are 6 different drawings in the same file, How do I split those to different sheet. I wanted to take their consumption, as they are going to cut from a rexin 1.4 x 1 meter(w x h).
So I want to fill each drawing to sheet and get count.

Guide me a method, I am currently trying with autocad as they support the dxf file
Currently am trying with PATCH.dxf file (8x13 sizes in there)

https://gofile.io/?c=FL2JGj


texts: What's the benefit of copper plating paper clips?

texts:
(Sorry, not an engineer or student, just looking for the most metallurgically relevant stack.)
Recently I was in someone's office and, while playing with their paper clips, it occurred to me that copper is kind of a precious material for humble paper clips ... one look at the box, they're merely copper plated. But why even do that though?
Why not just leave them bare steel or aluminium or whatever they are made of (which, curiously, the box doesn't say)?


texts: Is the pressure of the gas identical to the static pressure of the liquid in the diagram?

texts: In my application the liquid would be tapped from a fast-varying flowrate, and I want to measure the static pressure change during this by measuring the air pressure above it. Will this work?


texts: Refrigerator temperature - compartment gas volume exchange, time to equilibrate?

texts:
I open the door for 30s of a 140L capacity 80W (240VAC, 0.8A) barfridge with a 20L freezer compartment (partition open to main compartment at one end) at a temperature of -5℃ with an internal main compartment temperature at 2℃, with initially 30L of 50-50 glass and plastic containers container mainly water inside, in a room at an ambient temperature of 41℃ and 85% humidity (Sydney today), to take out a 6-pack of medicinal beer.

Presumably, the cold, denser air from inside the fridge flows out,
   and is replaced by the hot, lighter air from the room.

How much of the fridge and freezer compartment air is exchanged in that time period?
How long does it take the exchanged air in the fridge to equilibrate
to its initial temperature of 2℃? What equation describes this? Is there an initial temperature rise?
How many grams of ice will precipitate from the exchanged air into
the freezer compartment?

EDIT UPDATE

After @Chris Johns' answer, I rolled the barfridge out and actually looked at the manufacturer's plate, and then updated my question from my original eyeball estimates.

Changed 40L to 140L
Added power info: "80W (240VAC, 0.8A)".

From my calculations, $ P = V_{rms} * I_{rms} $ = 240VAC * 0.8A = 192 W,

so efficiency,  $ \eta = P_{out} / P_{in} \%% $ $ = {80W \over 192W} = 41.7\%% $
Changed freezer compartment capacity eyeball estimate from 10L to 20L
The refrigerant is $CCl_2F_2-R12$, 85g.
Clarified the internal contents of the fridge as containing a total of 30L of plastic and glass containers (50-50) containing mostly water.
Clarified the temperature of the freezer compartment at -5℃.

I presume you can calculate the coefficient of performance (CoP) from this data?


texts: How to indicate standard screw thread in drawing

texts:
I have no experience with actual CAD drawings and CNC machines so please forgive me if this is a really stupid question...

Anyway I have a part which I have 3D printed and it contains some internal screw thread for an ISO metric screw. I modelled the threading myself so it will get 3D printed which took some trial and error. Now since I need it in high quality metal I want to CNC it. But I am wondering whether I have to let the screw thread stay in my model or indicate somehow this is actually ISO metric screw thread of this spec? Since I imagine there is special machinery/settings to make the threading.

Any help is appreciated


texts: Sudden increase in noise levels - subway noise -happend overnight

texts: This is  real life issue I am having currently and I am puzzled as to why it happened. I have lived over the subway lines (two actually each going in the opposite direction, two sets of tracks) for two years. The noise has always been a soft background hum, with an occasional louder train (that usually needs maintenance), hardly noticeable. One early morning near the end of January I was jolted out of bed by a loud noise. Turns out it is the subway. It is as if someone turned the volume up from 3 to 8 all of a sudden. Noise much louder (both tracks), last longer and there is shaking indoors too. Some small variances in the loudness of each train, but all much louder. The quietest train now is much loudest then the loudest one was before. I know that no changes were made to the tracks, trains, schedules or my building. What else could have caused it - noise from subway became much louder overnight?


texts: How do I calculate the force coming from the centrifugal compressor exhaust?

texts:
Let's say I have a centrifugal compressor as shown in the figure and I know the following parameters----1

Thrust
Inlet and outlet pressure
Power required to operate the compressor
Inlet and outlet velocity
Static pressure and pressure
The blade angle

Now I want to know how do I calculate the force exerted by the exhaust coming out?


texts: What thickness do I need for a 30x30 (cm) aluminium plate to hold 350Kg on three points?

texts:
I want to make a strong connected weight-scale Arduino project, for which I already own 3×350Kg sensors (red). I plan to make the plate (green) around 30cm×30cm in 99.5 Brut aluminum, with my three sensors placed in T (two on rear of left and right sides and the third one in the middle of the front side), and the local pressure on the plate should not exceed 5 Mega Pascal (Yellowish). However, I know nothing about strength of materials computation.

What minimal thickness would I need in order for my plate to bear such a load ?
I have read somewhere that I should avoid the deformation to be more that 0.1%×dimensions (i.e : 0.3mm), and, according with Wikipedia,

Young's modulus = 70 GPa
Shear modulus = 26 GPa
Bulk modulus = 76 GPa
Poisson ratio    = 0.35

However, I have no idea what to do with those numbers. All explanations I found on the net were much too complicated in regard with the problem and to know what to do with it.


texts: The formula for partial flow of Box Culvert

texts:
Refer to this document, and particular to Figure 2:

I wonder what is the formula that governs the box culvert partial flow with respect to full flow? In other words, base on what formula the above graph is generated?

The formula for pipe partial flow is as thus:

So essentially I'm trying to find the analogous formula for pipe culvert.


texts:
Given pressure is directly proportional to density, my understanding is that you can use the pressure of gas in a container to calculate the mass of the gas in the container. My reasoning being;

$p=k\rho$ ($p$ = pressure and $\rho$ = density)

Then;

$\rho = \frac{m}{V}$ ($m$ = mass and $V$ = Volume)

Therefore;

$\frac{p}{k} = \frac{m}{V} \rightarrow m = \frac{pV}{k}$.

This means that assuming $k$ is kept constant (i.e. constant temperature etc.) the pressure in the container should be directly proportional to the mass of the gas in the container, and therefore you can calculate the mass of gas in the container by using the pressure.

My first question is whether this is correct? And my second question is, assuming this is correct, would this still be accurate if the container is in use i.e. gas is being added/removed from the container, or would this only work when the container is sealed with no pipes in or out?


texts: I'm having a hard time finding an answer from the internet. What does starting torque mean?


texts: How to obtain transfer function of servo?

texts:
I am using a servo motor and controlling it via arduino. Servo motor is part of a control system and I have to use System Identification techniques in order to obtain the servo's transfer function. First step of the whole process is to collect input-output data of the servo's motion and use these data to perform system identification. I read and write data to the servo motor using the Hardware Package for Arduino of Matlab. My question is how to figure out the optimal test signals to enter as input to the servo due to the fact that servos are normally driven using PWM signals ?

UPDATE: I have connected the servo with an Arduino and I currently control it via Matlab (I also can do it with Arduino IDE but I am generally using Matlab for my project). I have created a sine wave with maximum value 0.924 and minimum value 0.111 because this is the range at which my servo responds and changes its position. I am feeding these values at my servo and it performs an oscillation. Now what I want to acquire is the angle of the rotation of the shaft in degrees for each one of the input values or maybe the sine of the angle of rotation of the shaft.


texts:
If this is the wrong place for this question, please migrate it to someplace where it's more suitable.

So one of my old teachers from my previous school sent me a contraption to try and figure out what it was and how it worked. Pictures here.

I've played around with it for a while. I tested to see if it did something when spinning really, really quickly by attaching a motor, tried taking it apart numerous ways, and plenty of things in-between.

As far as I've gathered, here's what I think it's doing. The propeller drives a shaft that is attached to something that converts the circular motion into linear motion. At this point the glass is frosted or there's some kind of glue on the inside that makes it very hard to see clearly what's going on. The top is connected to the bottle via two pipes that end in a hole in the side of the bottle. The cap itself has a hole in the top to which the top thing is screwed to, possibly also leaving space for water to go through -- it's unclear. The purple part is sticky on one side, suggesting that the whole thing sticks to the wall or maybe to something that moves like a car.

Or maybe the propeller isn't what does the driving at all. Maybe it's filled with water and stuck to a wall or something facing downwards, and gravity would cause the water to cause the whole thing to leap to life! But, I can't find any way of filling it up -- there's no existing holes as far as I can tell. I may be able to take off the whole red cap but that's made difficult with the yellow pipes.

So I'm stuck. Does anyone have any idea about what this mysterious thing is?

UPDATE:

The propellers have arrows on them indicating the direction they should turn. This suggests that the propeller is indeed the driver and not the drivee.


texts: Why is the Cape Elizabeth Fog Signal shaped like this?

texts:
On a recent trip to Cape Elizabeth, Maine, I came across this fog signal:

It appears to have an electromagnetic diaphragm in the middle, surrounded by concrete and some very curiously shaped steel pieces.  Why is the steel surrounding the horn shaped the way it is?

I've found some material on fog signal design, but nothing looks remotely close to what I see here.

Appendix:

US Lighthouse Society - Cape Elizabeth (last updated 2004)
https://www.us-lighthouses.com/images/archive/c/cape-elizabeth-lighthouse-and-fog-signal.jpg
https://en.wikipedia.org/wiki/Cape_Elizabeth_Lights


texts: I recently bought a servo whose torque is 2.2kg/cm, if i wanted to rotate (using the servo) an item that weighs 6.8KG (15lbs) at a length of 0.4572M (18 inches) 60 degrees would it be possible?


texts: Is the viscosity solution of Hamilton-Jacobi equation of practical use in optimal control?

texts:
My understanding is, given an optimal control problem, one can show that the optimal cost satisfies a Hamilton-Jacobi PDE and use dynamic programming to figure out the optimal control. However, sometimes this PDE has no strong solution, and the deep theory of viscosity solution was invented to make sense of a "solution" in this situation.
Does such "optimal" cost have any practical meaning? Phrased slightly differently, can one still figure out what the control should be, and implement it?
I feel like it has to be a function, not a distribution, in order to be implementable.


texts: What is the mathematical basis for the Ziegler-Nichols method for tuning a PID loop?

texts:
The Ziegler-Nichols method of tuning PID control loops has been around since the 1940's, and has been widely applied in many areas of engineering. I understand that it is really only a heuristic method of finding the right control parameters, and many others have been created over the years. However, when it was originally created, was there any mathematical reason for how the method worked. I am talking specifically about the open-loop step response method.

I cannot find any reason for why they decided upon the method they did. Is there any mathematical reason behind this?


texts: How to design a swivel connection for a single wheel trailer?

texts:
I'm trying to design a single wheel trailer for my underpowered VW, much like this one.

Unlike a conventional trailer, it is attached to the car at two points. To prevent the wheel from dragging, it has a swivelling mechanism. Those are hard to come by, so I'm going to build one myself.

I'm not a mechanical engineer by trade, so the questions I have are probably quite basic:

With caster wheel wobble in mind, should the wheel swivel freely, or is some friction desirable?
What kind of bearings should be used for the swivel point? There is definitely an axial load, but is the radial load considerable?
What would be the most effective geometry? How much trail/rake? Is this something I just have to experiment with?


texts: How can I transmit signals from pre-amplifiers to a laptop nearby using bluetooth?

texts: I am trying to collect signals from preamplifiers (Aquarian Audio preamps, PA-4) and have them sent to a laptop nearby wirelessly, I have not found a dedicated device for this process, and the preamplifiers have BNC connector. I need suggestions and this is the specs for the pre-amplifiers that I am trying to collect the data from http://www.aquarianaudio.com/pa4.html. If anyone has been into this similar situation, I need your advice.


texts: What is the purpose of these "steps" in rivers?

texts:
I have seen a number of structures within rivers, which resemble steps, and which allow the water to cascade down them instead of flowing naturally down the course of the river.

Example 1: River Avon in Bath

Example 2: River Seine in Paris (from Les Miserables (2012))

What is the purpose of these structures?


texts: Imposing/ensuring a constant mass flow rate in turbulent flow simulation

texts:
I'm trying to simulate using Finite Elements (non commercial software) the Tube Bundle benchmark problem:
http://cfd.mace.manchester.ac.uk/ercoftac/doku.php?id=cases:case078&s[]=tube&s[]=bundle
Many authors (e.g. Benchmark Simulation of Turbulent Flow through a Staggered Tube Bundle to Support CFD as a Reactor Design Tool. Part II: URANS CFD Simulation) have used a single periodic cell (the right picture in Fig. 1) as their computational domain, with periodic boundary conditions. To maintain the flow rate, they impose a constant, prescribed flow rate via pressure gradient/body source term.
Here is where I would appreciate some help. I have a math background, and I was not able to find any literature that explains how exactly this is done. The trial-and-error approach didn't help.


texts: Condition for equilibrium of a rigid body on a horizontal surface

texts:
The following question is from a past paper from Further Mechanics and it has been bothering me immensely I have spent hours cracking at a way to make sense of it, the question is in two parts

 Part 1:

An object consists of a uniform solid circular cone, of vertical height 4r and radius 3r, and a uniform solid cylinder, of height 4r and radius 3r. The circular base of the cone and one of the circular faces of the cylinder are joined together so that they coincide. The cone and the cylinder are made of the same material.
 Find the distance of the centre of mass of the object from the end of the cylinder that is not attached
to the cone.

I first roughly sketched the object as such

Then finding the $\bar{x}$ of each part seperately:

For the cone I used the standard result of the centre of mass being $\frac{1}{4}r$ away from the base:
$$\bar{x}_{Cone}=\frac{1}{4}.4r + 4r=5r$$

For the cylinder I derived $\bar{x}$ via integration:
$$y=3r$$
$$\bar{x}_{cylinder}=\frac{\int_0^{4r} xdV}{\int_0^{4r}dV}$$
$$\because dV=y^2 \pi dx $$
$$\implies \bar{x}_{cylinder}=\frac{\int_0^{4r} 9r^2 \pi x dx}{\int_0^{4r}9r^2 \pi dx}$$
$$\implies \bar{x}_{cylinder}=\frac{9r^2 \pi \int_0^{4r} x dx}{9r^2 \pi\int_0^{4r} 1 dx}$$
$$\implies \bar{x}_{cylinder}=\frac{\frac{1}{2}\left[x^2 \right]^{4r}_0}{\left[x \right]^{4r}_0}$$
$$\therefore  \bar{x}_{cylinder}=2r $$
Then by taking the weighted average of both objects I arrived at the correct value for the distance of the centre of gravity from the base of the cylinder which was
$$\bar{x}=\frac{11}{4}r$$
However the next part has had me at a complete loss for the better part of the day, it states that:

Show that the object can rest in equilibrium with the curved surface of the cone in contact with a horizontal surface.

I tried coming up with a rough sketch for this also

However I do not understand how to tackle this question at all, all I know is that for a body to be at equilibrium on such a surface, the centre of mass must pass through the point of suspension, however clearly this does not give an insight on how to answer this.
The condition for this question given in the marking scheme is that

Can someone explain what this means and why this is the case?


texts: How would you seal a hole in an HDPE container that's in -20C environment

texts:
I have a temperature sensor in a -20C freezer.  The probe is going into a bottle filled with propylene glycol solution.  I want to seal the hole where the probe is inserted into the bottle.

What's a good sealant for this?


texts:
I keep reading all over the internet that a torque converter multiplies torque at stall speed. Every explanation I have found sounded more like hand-waving than quantitative physical explanation. Essentially, the argument goes that the stator redirects flow which makes the torque converter "more efficient", thereby multiplying torque. This would not qualify as a demonstration to me.

As far as I understand it, the efficient slippage a torque converter allows lets the engine revolve faster and that alone can produce more torque due to the internal combustion engine output torque curve. But this is probably not the whole story: people and manufacturers insist that a torque converter does multiply torque.

Can anyone give a quantitative explanation of how torque can get multiplied in this context ? I assume this is physically possible since only energy conservation must be met in such a system. I expect the explanation to resemble somewhat the operation of a boost converter that can increase voltage to the expense of current.


texts: What are the elastic constants for tetragonal zirconia polycrystal (TZP)?

texts:
I have six known elastic constants of TZP. What is the relationship between the known and the unknown constants?

Known constants (GPa):

$c_{11}=327\\ c_{12}=100\\ c_{13}=62\\  c_{33}=264\\ c_{44}=59\\ c_{66}=64$

How can I find the others? Is $c_{22}=c_{11}$? Does TZP exibhit transverse isotropy?

Are the relationships between the tensor components and the coordinate axes given by: $c_{11}$ for x-direction, $c_{22}$ for y and $c_{33}$ for z; $c_{23}$ (4) for yz, $c_{31}$ (5) for zx, and $c_{12}$ (6) for xy?


texts: Formulation of problems and exercises in Mechanical Engineering

texts: I'd like to know how do the authors of Mechanical Engineering books(books of engineering dynamics, mechanics of materials, fluid mechanics...) and some university professors of Mechanical Engineering formulate those beautiful problems and exercises ? Especially those involving real situations. That is, where do they get those problem situations ? Almost always involving a real mechanical system, thermal system, fluid system...


texts: Calculating the force produced by acoustic levitation

texts:
I was reading some articles about acoustic levitation and I was wondering whether it is possible to lift a 100 kips load off the ground for about 0.5-1 inches with that. If it is, how should I calculate how much energy I need to deliver to a ultrasound speaker and effectively concentrate with a lens that can be used to produce such lift on an object.

I am not very familiar with this subject, so forgive me if I am asking some pretty dum question here. Thanks!!

Edit - Somebody apparently downvoted the question without saying why, I don't exactly know why. But I thought I should put some additional info to help people understand what I am referring to. Showing some "effort".... It is such a new field that there are not a lot of articles on how you calculate something like this and what is realistic.

Acoustic levitation made simple
Researchers demonstrate acoustic levitation of a large sphere


texts: Corrosion of a galvanic couple made with silver and gold

texts:
If a bangle is made out of gold and silver, connected with each-other would there be a corrosion happening? If so can it be explained using the galvanic series?

Also do those metals undergo oxidation under normal conditions?


texts: Is there a method to determine the runoff for arid areas in developing countries?

texts:
Note: this question was totally rephrased and expanded on, addressing the comments and questions posed to the first version.

The de-facto standard source for runoff calculations in South Africa is the "SANRAL Runoff Manual" (http://www.nra.co.za/content/Drain5.pdf)

I need to design a weir for a small earth dam in an arid area with a small (smaller than 200 ha), fairly flat catchment area in southern Africa. The idea behind the dam is to collect not more than 10 000 cubic metres of water for small stock watering purposes for the immediate time after the rainy season, somewhat reducing the dependency on ground water.

To design the dam wall and the spillway, one needs flow data through the catchment area in question. The rational method provides this formula:
 $Q=\frac{CIA}{3,6}$              ...(3.8)
where: $Q \hskip{1.5em}= $ peak flow (m3/s)
   $C \hskip{1.7em}= $ run-off coeficient (dimensionless)
   $I\hskip{2em} = $ average rainfall intensity over catchment (mm/hour)
   $A \hskip{1.7em}= $ effective area of catchment (km2)
   $3,6\quad = $ conversion factor

In arid areas rainfall events often are thunderstorms of fairly short duration, often less than an hour. These events are separated by long dry periods. Rainfall is generally measured on a daily basis. These recorded values are daily rainfall values, but they say nothing about the duration of the rainfall events.

Rainfall intensity is determined by dividing rainfall by the duration of the rainfall event. Thus, the shorter the rainfall event, the higher the rainfall intensity for the same amount of total rainfall. But since rainfall is not really measured by the second, minute or hour it is impossible to accurately determine rainfall intensity in areas where the rainfall events are short. In fact the margin for error increases tremendously as the duration of rainfall events decreases.

Using rainfall this data (with a large margin of error) for large catchment
areas is not recommended, since the rainfall does not have a "temporal distribution for at least a duration equal to the time of Concentration" (page 3.17). Q would be over-estimated and thus dams and spillways would be over-designed.

The opposite is true for small catchment areas, where the time of concentration is less than the duration of a rainfall event. The margin of error in the rainfall intensity calculation will become unacceptably critical. Especially for very small dams they will either be under designed, or they will be financially unfeasible.

Is there an alternative method to determine runoff in arid areas, where rainfall events are of short duration and accurate rainfall data (rainfall and duration of rainfall events) is not available?


texts: How to quickly equalize pressure in a low pressure container?

texts:
Background: This is for a science project I'm creating where I use an airpump connected to a sealed 5gal pail bucket to create a vacuum. That vacuum is then connected to water source to "suck" liquid into the bucket.

Problem: After I shut the airpump off, liquid continues to flow from the water source to the vacuum due to siphoning. Any lowcost ideas on how to prevent the siphoning from happening when I shut down the airpump? Preferably would like a passive solution, but if it has to be electronic, so be it. TIA!


texts: How do you apply fits and tolerances when designing hole and shaft?

texts:
I am familiar with the basic concepts of fits and tolerances, and I am aware of the various online calculators for determining them. However, I don't understand how to apply those numbers to my actual CAD design for the parts that I want to fit together. None of the calculators seem to account for the actual manufacturing tolerances of the shop I'm working with (in this case +/- 0.1 mm).

So, to be more specific, let's say I have a shaft and hole and I want to work with a nominal size of 6 mm. I want a "locational clearance" fit between them. The calculators tell me the maximum and minimum hole sizes, etc., but I don't know how to gather from this information what I should make the nominal sizes of the hole and shaft in my CAD model. And how can a calculator tell me that anyway, if it doesn't know what size my manufacturing tolerance is?

Can anybody elucidate?


texts: How maps of globe, country or region were created few decades/centuries ago when modern technology like today did not exists?

texts: What techniques were used to create the maps of a world, country or region when satellite or similar technology did not exists few decades or centuries ago?


texts: Is it possible to make very large diamonds using a pressure vessel at several GigaPascal pressure?

texts:
Nanocrystalline diamonds can be synthesized by direct conversion of graphite or carbon black mixed with low amount of boron (0.1%-10%) at 8-10 GPa, according to US patent No.20120255236.

If some scientists decided to make very large monolithic diamonds (tens of cm size) to make for example large diamond anvil cells with a centimeter sample size, would it be practical to use large pressure vessels with very thick steel walls to reach such very high hydrostatic pressures for such a large volume?

How to calculate the required material thickness to withstand such high pressures?


texts: My question is to calculate the electric field of a point in the Z axis of a empty hemisphere with a superficial density $\sigma$, but I have to do it from the formula of the electric field of a ring: $\vec{E}= \frac{\rho_l z a}{2 \epsilon_0 (z^2+a^2)} \hat{k}$, where $\rho_l$ is the lineal density, $z$ the z coordinate, $a$ the radius of the ring and $\epsilon_0$ is the electric constant. I have tried to express $\rho_l=\frac{dq}{dl}=\frac{\sigma dA}{dl}=\sigma dz'$ but if I change $a$ with $z'$ (because the radium of each ring changes) and I do the integral, I don't get the right answer. I know that I'm doing something wrong, and I'd appreciate if someone can help me.


texts: Making a mechanical device to measure the radius of the Earth

texts:
I want to design an experiment to show (in an educational context) how we can measure the radius of the Earth without using modern technology in order to demonstrate the engineering achievements of those who did it so long ago, and to show some practical uses for the maths involved.

The methods I know how to do this are:

Place a stick vertically in the ground and another one many kilometers North of it and measure the shadow of both at exactly noon.
Know the height of a mountain by a large lake or the sea and measure the distance you have to go until it disappears.
Watch the sunset lying down and then stand up and watch it again, measuring the time difference between them and know your height.

The first two are impractical to do with the kids, but the third one shows potential. However, is there a way to do this during the day using shadows cast by buildings, or must the shadow come from the horizon? How could I design some simple equipment to allow me to do this experiment and calculate the radius of the Earth during the day?

Note: I am happy to use a digital stopwatch as the kids can easily see how people in the past might have used a mechanical clock to do the same thing (including measuring the length of a full day).


texts: When do I need to consult a professional engineer during a home renovation?

texts:
I am a homeowner who likes to save money by performing DIY work. When possible, I prefer to serve as my own general contractor to reduce the cost of a project. However, when I talk with professionals about my plans and ask for advice, they often tell me that I need to consult with a professional engineer.

I want my home to be safe but hiring an engineer sounds like an expense I can't afford. How can I tell when it's really necessary to consult an engineer before performing work on my home? Why can't I just hire a licensed contractor instead?


texts: Identify bearing dimensions from its bearing number

texts:
In motors/pumps generally following bearings are used (ref: https://www.nke.at/en/bearings-applications/applications/electrical-motors):

Deep groove ball bearings
Cylindrical roller bearings
Angular contact ball bearings

All these bearings are designated with bearing number for example: Deep groove ball bearings: 6205.
Form this bearing no. we can easily have the information about its outer dimensions as given here:https://www.skf.com/in/products/rolling-bearings/ball-bearings/deep-groove-ball-bearings/productid-6205 OR from its catalogue.
Based on these outer dimensions, is there any way out to calculate the following specifications/dimensions:

Pitch diameter
Ball diameter
Number of balls in the bearing
Contact angle of the balls

Can somebody please let me know how can we go about this ?


texts: Understanding the RMS noise for a given bandwidth

texts:
I would like to ask a technical question regarding the current source Keithley Series 2400 Model 2450. I am looking for a high stability current source capable of feeding some Hall probes with a nominal current of 10 mA. According to the 2450's datasheet, for a current range of 100 mA, the RMS noise is 100 nA for the bandwidth below 10 Hz, as you can see below.

Could someone please help me to figure out in detail what this specification means? For example, if I set the 2450 with a current of 10 mA (100 mA range) and measure the current samples with a sampling rate of 10 Hz, should I expect a RMS value of 100 nA around the nominal 10 mA? Is that correct?
What if I measure the 2450's output with a sampling rate of 50 Hz? Can we estimate the RMS value as 100 nA * (50/10)^.5 = 223 nA? Would this be correct?
Thank you.


texts: What is best sensor & method to measure human height?

texts:
My application needed to measure human height on a standing kiosk. I need to attach the sensor on kiosk ceiling type top. I used different kind of ultrasonic sensor for this purpose but nothing proving reliable results.

First, general ultrasonic sensor have deadband within which the sensor doesn't work and second human head and should varies and thus the reflecting pattern. Can anyone suggest the best method and sensor to use for this purpose? I didn't use laser till now because of eye safety reasons.


texts: What is the process called for up-sizing a proof-of-concept prototype to full-scale?

texts:
What is the process called when you upscale your proof of concept to a full size prototype?

For example a traffic light circuit using LEDs to fill size lights and power supply?

That is if the term exists or if it is still prototyping as mentioned in the comments.


texts: What is name of clutch system in a roller shade?

texts:
I am trying to figure out what the exact term is for the clutch system used in a roll-up window shade.

I thought they were called centrifical clutches, but that typically gives me the opposite results like what is used in an automatic vehicle. Where speed causes it to engage.

Basically I want to look up some existing designs because I'm trying to create a product that uses one.


texts: How linear motion is getting converted into rotational motion in this early toy?

texts:
Can someone explain about the mechanism in this folk toy:

See Video here:
A "penny toy" of around 1900.

It has a spring and it converts linear motion in to rotational motion ( that drives the acrobat). Further the rotational motion is possible both anticlockwise and clockwise.

What exactly is going ne? I believe the mechanism is not  uncommon and someone from this background could throw some light.
Thanks in advance for your help.


texts: Understanding Bending and Twisting Moments in a Plate

texts:
I am trying to understand Kirchoff Plate  Theory and I am unable to understand the difference between bending and twisting moment for a plate. In a beam structure, if moment is along the axis of the beam, it creates twist, and if the moment is normal to the axis of the beam, it results in the bending of the beam. However, how do we differentiate between moments when dealing with plates.

Thank you.


texts: Exceed 'designed' speed ratio of timing belt

texts:
I'm trying to create a setup to transfer motion from a motor to a shaft that requires a much higher torque (bi-directional). The housing is about 6 inches long and the speed ratio needed will be around 1:10 or even 1:15 and I'm looking at using a GT3 belt with 14mm pitch. The reason for 14mm pitch is that the datasheet appears to suggest it is the GT3 that can achieve the highest speed ratio. However, according to the data sheet, the highest speed ratio specified is only 6.857 (28:192) - does that mean the belt isn't designed for running in setups with higher ratios? Also, the shortest centre distance between the pulleys is 27.9 inches:

https://www.gatesaustralia.com.au/~/media/files/gates-au/industrial/brochures-and-marketing-collateral/4963007--powergrip-gt3-brochure.pdf

If the speed ratio was to be pushed to ~10 (16:168) and the sprockets were just 5 or 6 inches apart, could idlers be fitted in between to give the belt and the sprockets better contact? Are there tips to setup such high ratio sprocket combination inside a small housing?

Thanks


texts: Use of 410 Stainless Steel for replacement of 420 Stainless Steel

texts:
Can we use Grade 410 Stainless Steel for replacement of Grade 420 Stainless Steel? The application is for engineering components which have torsional and fatigue load.

The reason for the substitution is that 420 is not commonly available in the Indian market. Can we use 410 stainless as a replacement for 420 stainless? Does it has any major differences with regard to chemical and mechanical properties?


texts: What needs to be considered when configuring the clock system for a MSP430F5xxx micro-controller?

texts:
I need to configure the clock systems for a MSP430F5528 microcontroller. The current development board has a 24MHZ crystal attach to XT2 pins (XT2IN/XT2OUT). The current design will need to support the follow peripherals.

UART
ADC
SPI
Timers

Few GPIO's will be need for system power up. The system is will part of a low power application. The power budget has not yet been determined.

About the MSP430 clock system

The MSP430 for the most part has three internal clocks

MCLK - Master Clock - CPU
SMCLK - Sub Master Clock - fast peripherals
ACLK - Auxiliary Clok - Slow peripherals

Question: What needs to be considered when configuring the clock system base on the above criteria?


texts: How are increasingly accurate machines made?

texts:
Making extremely accurate machines seems like a chicken and egg problem.  How do you make one if you don't already have one?

For example, how was the first indexing head made without an indexing head to make the indexing plate?  How was the first lathe made without a lathe to make the spindle?  Is it an iterative process where you start with something hand-made, and each machine can make one slightly better than the last?  I suppose that geometric constructions are the source of accuracy of some primitive machines.  But how do you get from there to something like the precision screw required for an accurate lathe or micrometer?


texts: How do engineers reduce vibration of system with multiple known natural frequencies? How do they design the isolation system for specific frequencies?

texts:
I have a system that is pretty much a chamber that needs to sit on the ground. I measured the transmissibility of the chamber vs the ground (output/chamber acceleration over input/ground acceleration) with accelerometers and plotted a transmissibility graph (is it also called transfer function plot...?). The steel chamber weighs about 100 kg.
From the graph, I found the natural frequencies (the spiking frequencies). Let's say I would like to reduce the vibration of the 3.2 Hz and 9 Hz vibration, what would be the real world approach to isolate this vibration as an mechanical engineer? Do they buy a specific set of materials online according to the natural frequency and then pad them under the system? Or do they come up with a spring + damper system that target these frequencies?


texts: Countersink bolt vs. Socket Head Cap bolt

texts: I know one advantage of using Contersink bolt is that the surface can be flat as the screw head gets embedded. If I want to join two parts together using bolts. What are the pros and cons of using Countersink Bolt vs. Socket Head Cap Screws? Which is more secure in combing the parts?


texts: Should I use brass compression fitting on brass tube?

texts:
I would like to use brass compression fitting on brass tube, I am confused because I have seen all the fittings that are used for copper and steel tube only.
Is there and disadvantages?


texts: Increasing Force Output on a Spring Return Pneumatic Cylinder

texts: The downside of using single-acting return spring pneumatic cylinders is the decreasing output force through a full stroke due to the opposing spring force. I'm wondering how would you design a spring return pneumatic cylinder which produces an increasing output force? Would you simply need to increase the input pressure?


texts: Finding the force in a cable of a rigid system

texts:
QUESTION (see attached image file):

I got stuck when trying to find tension for part A; see my working below.
and help me solve.


texts: How do you prevent ignition of the gas-air mixture before it reaches the burner nozzle?

texts:
I believed that the flame propagates over the place where fuel contacts the oxygen. If it contacts a fule+O2 mixture, the mixture inflames as well, and so on and on and on until there is no more inflammable material available around. If there is a gas comes to the surface, the flame stops and starts burning at the gas-air contact zone.

But, as it was explained yesterday, I can have the gas burning in my gas baking chamber because it gets mixed with air prior to getting into the chamber. This explain the mystery of having the flame in a sort of isolated chamber, but, what they refused to explain is that how it is possible that mixture does not blow up in the pipe as soon as you mix gas + air? Why don't you have the flame there, how do you prevent the mixture ignition until after it crosses the designed burner? How does the gas know how the burner/nozzle look like in order to inflame in the right place? My belief was that flame propagates in all directions over the fuel+oxygen mixture, so, it should propagate from the burner down the pipe until the gas-air mixer, right?

BTW, is it right that a hole in a gas pipe sucks the air despite gas in the pipe has pressure > 1 atm (it must be greater than 1 atm in order to be pushed out of the gas pipe instead of sucking the air into it)? How is it possible that gas flows from lower pressuire into the higher pressure area without violation of entropy principle?

I have noticed that there is a similar question on Quora. It is even more infomred than mine assumption -- it asks why no flahback arrestors are installed in the kitchen ovens? There should be absolutely no chance for the flame to go upstream over the explosive mixture! Why?

I keep asking my question because highly appreciated answer there is unsatisfactory. It just says that we use propane cooking cylinders

in our kitchens. These cillinders have much higher pressure than the air oxygen, and, therefore, backpropagation is not possible, says the answer.

However, it prevents the backward propagation of GAS whereas safety issue is propagation of flame.  how does it make the flame speed necessarily lower than the gas flow speed, what happens on the last days of cylinder exhaustion when pressure goes down and what about the centralized (natural) gas kitchens?


texts: I have a mechanism where two parts are screwed and unscrewed and I wish to incorporate a system by which the number of screwing and unscrewing can be indicated. I have thought of a method using the erosion of material. As part of that, I have two components which will have a "soft material" between them. So with each screwing and unscrewing cycle a certain amount of material is eroded. And once the the total amount of material has been removed, the user will know that the manufacturer guaranteed life is over. Can I get any suggestion for commonly available soft materials?


texts:
Does anyone know how this works? I hypothesize that the reason that the bullet shatters is that boron carbide is much harder than the copper of the bullet. Does anyone think that this may be made into a conventional armor design as some people are saying or is boron carbide too expensive for use in this application?
Link:  http://www.slate.com/articles/video/video/2016/04/metal_foam_armor_can_shatter_bullet_on_contact_video.html


texts: Stability of lattice or mesh supports for printing

texts:
Support structures like lattice supports, tree supports or wire supports are being widely used in metal printing or FDM as they minimise the wastage of material and power consumption. In addition, they are easy to remove.
But compared to volume support, are these structures stable enough to stand firm against the build tray during the printing process?
How these structures avoid buckling depending on the height of supported zones?


texts:
What is  meant by yield of isotropic plastic material?
How is yield of Isotropic plastic material different from the term normal yield which is referred as transition from elastic behaviour to plastic. I am bit confused of term Yield of Isotropic plastic material.
Edit: yes I am talking about Isotropic material and requesting for answers based on what graph of yield criteria explains
Please help, thanks!


texts: Can I neglect kinetic energy when modeling convective heat transfer for viscous, low mach airflow? Why or why not?

texts: I'm looking at convective heat transfer for air flow over a solid at Ma=0.2.  At this speed, it is plausible to model the flow as incompressible because of small density variations in the air.  Normally, when modeling compressible flow, we include the kinetic energy term in the energy equation.  But for viscous incompressible flow at this speed, is it necessary?  Can I neglect kinetic energy as a component of the energy equation due to the incompressibility assumption?


texts: Do any roller coasters actually use the brachistochrone curve?

texts:
Not sure if this is the right place to ask this. But I'm assuming roller coasters are related to engineering.
I know that in theory, the brachistochrone curve is the fastest way from point A to point B assuming no friction and air resistance, and I see a lot of articles talking about the brachistochrone curve and how it could be used for a roller coaster. But whenever I try to look for rollercoasters that use the brachistochrone curve, I can't find any. So that raises my question: do any rollercoasters use the brachistochrone curve?


texts: How to make a clamp for this motor to move it in two directions?

texts: I'm working on a disc brake balancing machine, as shown below this is a belt pulley drive and for alignment purposes I want motor to be able to move vertically as well as inwards outwards (to tighten the belt). Is there any clamp/adjuster design to achieve this?


texts: What is Design Element in the context of asset management

texts: In the context of physical asset management (BIM etc) what is a Design Element? I have come across the term several time but never in an official document - can anyone explain the term and provide a definition in case it is an actual professional term


texts: How can I determine the thermal conductivity of an open container?

texts: I want to know the heat conduction coefficient of a cup in order to investigate why tea cools at different rates in different containers. I know the cup is mostly plastic and paper. How do I determine the heat conduction? Do I use a known value?


texts:
What are the most popular and the most efficient ways to machine a fillet on an external edge of an object? If I were to use a CNC mill, what tools can I use for it, and how would the method change with the radius of the fillet?

I could imagine that internal fillets can be easily achieved by a ball-end to a mill, but I've never come across machining an external one.


texts: Liquid delivery to a pump based on viscosity

texts:
I have a tank that is filled with a viscous liquid (~3000 CPs). At the bottom of the tank there is a pipe that leads to a gear pump. There is 22" of pipe straight down from the tank followed by a slight bend (~ 20 degrees) and then 7" to the pump. The liquid level in the tank is variable (H).
It is very important that the pump is not starved on the inlet side. The flow-rate out of the pump is 3000 grams per minute. The liquid has a specific gravity of 0.93.
I want to know at what viscosity will I starve the pump. Conceptually, I can imagine that as the viscosity of the liquid increases there will be more and more resistance to it flowing from the tank through the pipe to the pump. To compensate for this the pump will have to work harder to pull the liquid through the pipe to achieve the same mass flow rate. At some point the pump will not be able to pull hard enough to overcome the resistance and it will starve. I found the following equations which seem to be the right way to go:
$$Q = \frac{\Delta P \pi  r^4}{8 \mu L}$$
The problem I have with the equation above is I do not know how to calculate the delta in the pressure. If I just use gravity ($\Delta P = \rho g \Delta H$) the flow rates I get are too small. I assume this is because it is not taking into consideration the negative pressure produced by the pump.
Is there a way for me to calculate the hydraulic vacuum force of the pump? Can I put it in terms of pressure? Can I assume there is a pure vacuum inside the pump and say the pressure difference is -1 atm + the contribution from gravity? Is this something I should be able to look up in the manual for the pump?
Any help or suggestions are appreciated. Thanks!


texts: How to minimize heat loss in an air extractor?

texts:
In an air-conditioned house equipped with an air extractor that removes for instance wet, smelly, etc. air from the bathrooms and kitchen, what are sensible cost-effective systems to prevent:

Heat loss during the winter by bringing in cold air and extracting hot air from inside the house
Heat gain during the summer by bringing in hot air and removing the chilled air inside

That is, I would like to minimize the energy cost of extracting chilled/heated air by somehow recycling that energy before the air is dumped outside.


texts: How to have a watertight or airtight pipe seal that is rotating at a radius, with a stationary junction tube?

texts: How would I have a watertight or airtight pipe that is rotating at a radius, if the main reservoir pipe is not? Since I'm pretty sure I didn't do a good job of describing what I mean, the image above shows the smaller pipe, at a radius from the center, yet the pipe, might carry water from the larger "reservoir" pipe, which is not rotating.


texts:
Honey dippers are often made of wood.  Is there a property of honey that drives this?
Honey dippers are shaped like ovoids with lateral grooves. Is there something about the viscosity of honey that caused this decision?  Is this design somehow superior to using a spoon?


texts:
I am looking for a way to generate a linear motion with a triangle motion profile for my hobby project. The travel distance should be 6cm (so 12 cm for round-trip) with constant speed 1.2 m/s or higher. The solution should be able to oscillate at 10 Hz for minutes at time.
The travel distance basically rules out the use solenoids, and the triangle motion profile requirement rules out basic slider-crank mechanism where the linear motion speed changes over time. I am hoping that this is a trivial problem for proper engineers, but as a hobbyist I am struggling to come up with a work-able solution.
Any suggestion will be appreciated.
Thanks


texts:
3d printing is a slow process and for my solution I need fast printing. So I print with no infill and I fill inside with a two part, 10 min drying polyurethane resin. I mix them in a disposable cup and use a syringe to put it inside. It gives super results as it is both sturdy and lightweight so I recommend this method.

My problem is that if the print has a high volume, the mixture begins solidifying inside syringe. So I need a device which can mix parts and apply it on the spot. Below is a crude drawing of what I need. Is there a name for such a device readily avaible or will I have to build it myself? Or any other advise is appreciated.

What I have tried so far:

If I use a slower drying formula then most of the solution leaks from small holes in printed object. In faster drying formulas it is managable.


texts: DC motor Magnetic axis of armature winding vs EMF

texts:
When considering the cross section of a DC motor we have:

I notice that the Magnetic axis of the armature winding is aligned with direction of the EMF that will cause the rotation. Is there a relationship between them? Also, will the direction of the magnetic axis of the armature winding change as the armature rotates?

Thank you


texts:
The thin steel float used in my car (which was built in the UK in the early 60s, which I'm assuming is why it's not originally plastic) has rusted to a point where it's leaking in fuel and therefore failing to operate as desired.

I'm planning to replace it with a plastic float, but obviously want to make sure I'm not using something that could dissolve in the petroleum. I notice that 5 litre plastic canisters are HDPE so I intend to use that, but I'm intrigued as to just how much it matters. Plenty of discussion around the net suggests that most plastic bottles are likely to dissolve, most of which in my experience are PET. But this chart suggests PET is as good as HDPE:

http://www.plasticsintl.com/plastics_chemical_resistence_chart.html

That chart doesn't have data on PP or PE interestingly (though I assume HDPE has the same properties as PE).

So my question, respecting that storing petroleum in plastic containers not explicitly rated for the task is a bad idea, which plastics will actually dissolve? If it's a grey area is there a minimum thickness?


texts: In what cases are the roughness values Rt and Ra used?

texts:
Roughness measurement instruments output those two values, where Rt is the distance  between the top of the highest peak and the bottom of the lowest valley, and Ra is the average distance of every point to the mean line.

In almost all technical specifications I see the Ra value being reported, so when is the Rt value used/why is it measured?


texts: How would I get my hands on something I designed in Solid works?

texts:
Lets pretend I designed a plastic Lunchbox, like the ones pictured below in solid-works.

What processes or options are involved in obtaining a physical sample of my design?


texts: I was given a challenge question from my teacher that I need some assistance in solving. The problem is to merely identify the two-force members. I understand the ideas of how to determine a two-force member (colinear forces, equal magnitude, etc.), but in this problem, they just aren't clicking for me. Thanks in advance for the help!


texts: Method to extract closed curve from 3D CAD into CSV or TXT

texts:
I have engineering data emerging from more or less complex constructions.

On a regular base I need outlines from construction data to perform geometric calculations on them. The construction data comes from different CAD packages (e.g. Inventor or SolidWorks). I basically need certain closed polygons stored in a way I can read it with primitive methods like sloppy designed PERL programs.

Edit: The polygons are planar. I.e. the data I want to process is 2D. Basically it often is an outline of a 3D object, e.g. a housing.

So my favourite input format for such extracted polygon data is a CSV-file or plain text with whatever separators are available.

As most CAD-SW can import 3D-Models saved in STEP, I practically can choose which software I use to save the polygon data. The outcome is, I will probably end up having DXF or DWG files, which are the most primitive CAD-files I can get from that.

This leaves me with getting my polygons out of that goddamn DXF into a CSV file. Does anyone have an (preferably) easy way to do that?

Addendum: For increased clarificaiton, I describe my task. I have to design PCBs which fit nicely into oddly shaped housings. While my EDA-sw exhibits a fairly usable routine for importing DXF-data, my self programmed autoplacer does not. So in my EDA file, I may have a nice outline, but this does not help me with placing the components inside that polygon. Hence I need the polygon data separately in my autoplacer.


texts: Trying to find this exact type of T Ruler?

texts:
I am trying to find the exact tool which i assume is a modified t ruler to purchase but i cannot see any exactly like it. Any help would be appreciated:

Picture attached:

It is adjustable and has a fixed right angle piece on top so it is square with the material you are marking. All the t rulers i find only are essentially a standard ruler with an adjustable moving piece. I need the T ruler with the t at the top and then the adjustable moving part.


texts: Could 3D printing be done at a distance e.g. by pointing laser?

texts:
Could 3D objects be printed from a distance? Say, by pointing a laser at a stone wall?

I'm not concerned with whether the requisite technology already exists or would be difficult to build, but rather, whether something like this could be built in principle, or if there is either a law of physics or a massive intractability that would prevent it.

If it is possible, I'm interested in the theoretical limits. How far away can the material be (e.g. can we print something on the moon with a laser stationed on earth)? Can any material be used? Etc.


texts:
If you have a look at the car's wheels, you'll notice that they have holes which can be of different forms (mostly circular or rectangular).

Why do they have such holes?  Doesn't that reduce the stiffness of the wheels?


texts: Pole placement with damping ratio and natural frequency

texts:
how can I find out the poles of a system if I have the damping ratio $ ζ = 0.707$ and the natural frequency $ω_n = 2.3\text{ rad/sec}$?
$A = \begin{bmatrix} -0.02 & 0.1 & 0 & -9.81 \\
-0.23 & -0.134 & 120 & 0 \\
0.0006645 & -0.019598 & -0.97 & 0\\
0 & 0 & 1 & 0 \end{bmatrix}$
$B = \begin{bmatrix} 0.14  \\
-2.9  \\
-0.6313 \\
0 \end{bmatrix}$
$C = \begin{bmatrix} 0 & 0 & 0 & 1 \end{bmatrix}$
$D = 0$


texts: How to design a shelving unit out of McMaster Carr Struts?

texts:
I apologize for the complete beginner question.

I'm an Undergraduate Research Assistant trying to design a shelving 8'tall  by 10' Long, 4' wide shelving unit to support about 200 lbs. I'm designing this to go over 4' 8' table, so the folks in the lab can reach up and grab any of our optical equipment easily.

My question, is how to get started? I've had luck finding components on McMaster-Carr for Struts(https://www.mcmaster.com/#struts/=1b21hmv) and braces, but I'm completely new to building things in general, and I'm trying to avoid any stupid mistakes.

Can anyone point me to any resources or tips to get started? Any help would be greatly appreciated.

This is an example of the thing I'm trying to build


texts: How should the assignment to test software for a vehicle’s VCU be aproached?

texts:
As a graduation project, I was assigned to solve the following problem:

How can the vehicle’s behaviour be simulated in the form of a testing programme, with which the VCU software can be fully tested for correct functioning?

The VCU here is the central control unit that monitors the Engine control unit and the Transmission control unit. Additionally, it controls the Power Distribution Modules. These power and measure various sensors and systems around the vehicle. The VCU also contains the vehicle’s main interface to the driver by means of a display and buttons.

The VCU is a complete display and controller package from Murphy, the manufacturer. It communicates with the connected devices via 2 CAN busses. The VCU is not directly programmed with code, but configured by PowerVision, a design program for the display, made available also by Murphy.

In PowerVision, control and check loops, functions and systems are designed. Errors can be made during designing though, which makes them not having the intended effects on the connected hardware. This is what must be tested with the testing programme mentioned in the assignment above.

Since my experience with software testing is quite non-existent, I’m not sure how to approach this correctly, most efficiently, or most effectively. Hence my question:

How should the assignment to test software for a vehicle’s VCU be approached?

VCU in question: https://www.enovationcontrols.com/products/displays/powerview-780


texts: Concrete pad over filled, in-ground pool better with or without wall support?

texts:
We are currently having a project done in our backyard to: (1) fill an in-ground pool and (2) build a "sport court" (with a large concrete pad and some tiles) over top.
The pool demolition is underway, but we're having our doubts about the contractors' approach.

As you can see, the pool has been emptied and the deck has been removed. What remains is the aluminum walls that are sunk into the concrete base.
My general understanding of proper pool removal is that the walls should be removed, at least a couple of feet below the surface. Mainly so they don't stick up anywhere. Also, that the concrete based should be broken up. The contractor, having drilled a few small holes in the bottom of the concrete, is planning on:

Leaving the walls, as is, and filling the pool with dirt (compacted)
Levelling out the dirt to be level with or just above where the pool walls come up
Placing the 5" concrete pad (roughly 30'x25') on top of that

He claims he has done it this way before and that the pool wall is actually a structural benefit (used the term "rebar"). This doesn't feel right to me, and I thought that rebar meant steel that is embedded in the concrete. My worry is that the pad ends up resting on the aluminum wall with the dirt underneath shifting away.
He also has drilled a few small holes (you can see some) in the pool bottom for drainage, but again, I thought you're supposed to break it up more; it doesn't seem like it would drain well to me.
This contractor is an experienced concrete contractor and has done large jobs around our municipality, so I hope I'm wrong on this one, but would love a second opinion: is this approach alright for something we want to last a long time?


texts: Hydrocyclone effectiveness vs. absolute pressure

texts:
Some sources say that higher pressure in hydrocyclones implies better performance it leads to a finer filtration. But why?

Is it because water is almost incompressible and the particles can be pressured and their density increased?


texts: How far can my FM transmitter signal reach?

texts:
I have a working FM transmitter on a raspberry pi2. I'm running my FM raido at 103.3MHz, and the antenna that I connected to the GPIO4 is a 70cm copper wire.

More data:(checked with a multimeter between GPIO4 and pin6-ground)

DC voltage: 1.2V
AC voltage: 1.8V
Current: 18.4mA

update: I manually checked the distance by tunning cell phone fm to 103.3MHz. it was around 20 meter.

My question:

1.How far is my FM transmitter signal going?(Is there a formula?)

2.How do i increase the transmitting distance?(amplify the signal)


texts: How is fire risk reduced in dense contemporary timber neighbourhoods?

texts:
In the Middle Ages most buildings were made from timber. After large fires timber was restricted or outlawed altogether and brick and stone became the preferred building materials, e.g. in London after the Great Fire in 1666 (Source), or Lübeck after 1251 (Source).
Today fairly dense new neighbourhoods are designed using exclusively timber construction, e.g. Berlin Schumacher-Quartier (Source).
How is the fire risk reduced in these dense contemporary timber neighbourhoods?


texts:
Hello everyone :) This is my first post here so please excuse any of my mistakes.

I’m having some difficulty with solving the following problem. Let us have a thin-walled square pipe exposed to bending, torsion and stretching (picture below). On the left side of the pipe, where sits the rivet, we will have shearing stress due to the twisting moment and the shearing force coming from the bending moment. At the exact same point we will also have normal stress coming from the streching and bending moment.

While calculating the force in each rivet, why do we only consider shearing stress without the normal one? I tried asking my professor. He replied with the second attached picture, which I don’t seem to understand. Any help is appreciated :)


texts:
I need to accurately measure (+/-0.25mm) the bolt hole circle drilled into a heavy metal plate.  There are three holes on one plate and nine holes on a second plate. The plates are approximately 300mm diameter. The holes are approximately 18mm diameter tapped M20 and the bolt hole circle is about 200mm diameter.

When known, I will create a mating part on the CNC mill and lathe. The finished part rotates at around 2000 RPM, so the accuracy of the machining and fitment will determine the vibration of the finished system.

How can I measure the hole circle?  Tools? Technique? Calculations?


texts: How to model projectile motion using dynamical system matrices

texts:
I'm trying to figure out how to model projectile motion which can be defined using a simple [quadratic] equation which defines projectile parabola:

$$y = y_0 + v_{0y}t - \dfrac{1}{2} gt^2$$

I came across some slides from Brown University which model the motion as follows:

$$\begin{align}
\text{Matrix form: }& \begin{pmatrix} 0 & 100 & -10\end{pmatrix} \\ \\
\text{state: }& \begin{matrix}y & y' & y'' \\ p & v & a\end{matrix} \\ \\
&\begin{pmatrix}
1 & 0 & 0 \\
1 & 1 & 0 \\
0 & 2 & 1 \\
\end{pmatrix}
\end{align}$$

But I'm not quite sure how they came up with that transition matrix. Can anyone shed some light how to pick the state variables and how to model the motion?