texts: 2 motors on same shaft but 1 is off. How does that work?

texts:
I've been thinking about hybrid drivetrains. One thing that is bugging me is operation when one motor is off while the other is on. In a scenario in which the motors are connected with all the rotors on the same axis, I can easily see how the velocities would add up. But if one motor was turned off, wouldn't the motor just cause the other one to spin in reverse and not put out much power to the shaft (assuming there is a large load on the shaft)?  The whole equal and opposite thing. If the load is much bigger than the drag of the motor running now backward, then all your effort would be going into spinning the off motor backward.

If the motors were hooked up in parallel through some gear and one was turned off, I can see how the power output would be decreased by at least half. The single motor that is on is losing power because of back EMF from the off motor.

Is the only way to overcome this is through some sort of clutch? Thanks!


texts: Calculating Gearing Ratio from Constrained Rotational Linear Arc and Horizontally Opposed Rotation

texts:
I'm 3D printing an aircraft throttle unit as a POC and am trying to calculate the gearing ratios that are required in order transfer the full range of linear motion into a directionally opposed sensor whilst being constrained by certain design factors.
In the attached image, each throttle unit (L&R) will have a total articulation of 70° (35° each way from centre) and I'm trying to work out how to transfer/translate that linear motion into a rotational force that'll drive input into a potentiometer with a rotational constraint of 295°
I've tried calculating the ratio myself using the following expression 'm=a/r' where 'm' is equal to the articulation of linear motion divided by rotational constraint to gives me 1:4.2 but I have a feeling that's incorrect.
Also, once I have the correct gear ratio I'm unsure of how to work out the number of teeth required on both the spur gear and drive gear (is it as simple as for each tooth on the drive gear, 4 (rounding down) are required on the spur gear?)
Thanks in advance!


texts:
As I understand, a steam machine needs a pressurised gas to work. This can be compressed air but it used to be steam. Energy was provided to the steam engine by heating up water. I don't understand why it used water as the pressurised gas could have been generated only by heating air in a closed tank.

Is the design of heating air in a tank instead of heating water to generate steam feasible? If so, why do steam engine work with steam instead of hot air?


texts: Modeling Friction-reduced Pressure Drop in Natural Gas Flowing along a Horizontal Cylindrical Trunkline (Pipe)

texts:
I am seeking some help related to part of a project I am currently working on, where I require to (data-driven) model the pressure drop due to friction for natural gas flowing along a horizontal pipeline (not underground). I have data for the following variables:

P1: Pressure at the entry side.
P2 : Pressure at the exit side, P1>P2
Q: Volumetric Flow Rate at the entry side
T1: Temperature at the entry side.
T2: Temperature at the exit side.
Z: Compressibility of the natural gas
M: Molar Mass of the natural gas.
D: Density of the natural gas at the entry side.

I found out that a linear regression fit between [(P1)^0.5 - (P2)^0.5]^0.5 vs Q can be used to obtain an empirical model for the pressure drop because the scatter plot converges acceptable well to a 'straight' line. I am showing the scatter plot below based on the real data here.

Can someone kindly suggest me how can I improve the convergence towards a linear plot more by including more variables and hence improving the accuracy of the model? I would be grateful for any insightful help or a general suggestion.


texts: Identification of control system type? Open loop or close loop,

texts: What is the type of control system of door closer in attached photo?


texts: How does the SRI "Abacus" rotary transmission work?

texts:
I'd like to understand the new SRI "Abacus" transmission, recently reported at
http://spectrum.ieee.org/automaton/robotics/robotics-hardware/sri-demonstrates-abacus-rotary-transmission

I haven't been able to find any information on it that doesn't seem derivative of the IEEE story.

I'm curious about how one determines the reduction ratio, and what the "grooves" look like mathematically (for example, the function from angle to width).

Judging from the pictures, this one seems to have
    6 setscrews on the inner race,
    7 "beads", and
    8 setscrews on the outer race.

It's hard to tell the number of cycles for the grooves, but the ones in the outer race seem to be aligned with the setscrews.

They say the beads can have any profile you like; it seems that must then determine the groove profiles, but how would you get from one to the other?

I've tried to reason out the relationship between number of groove cycles on each race, diameter profile of the beads, offset of the driveshaft's attachment to the inner cam, and the resulting reduction ratio. But my intuition is failing even after watching the video many times.

Can anyone explain the relationships involved here?

Thanks!!!


texts: Someone please explain how to get the FAx and FEx because both support are pin.. I only got the FAy and FEy

texts: Can someone explain how to get the Fx for the support A and E


texts: FEA: What is the difference between a spider of RBE2s and multiple SPCs

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I am not sure what the difference is between using a spider of RBE2s. and multiple SPCs across a face. I've heard that the spider is the more accurate method as multiple SPCs make the model overly stiff but I am not sure why. In this particular instance I am trying to model the shown face being thru-bolted to a much larger plate. I've included 2 images for further clarification of my definitions.

Spider of RBE2s

Multiple SPCs


texts:
Does having multiple angular contact bearings together increase the total dynamic loading of the system linearly?

Example: Angular contact bearing with rated dynamic loading at 50kN, thus 3 of them setup together will result in a dynamic loading of 150kN.

See picture for reference.


texts: Understanding net torque from an actuator

texts:
This will probably sound like a silly question, but here goes....

Let's say I have an actuator, with a torque rating of 1 Nm. I then connect it to a wheel, which starts rotating at a constant speed. From Newton's second law, I know that Net Force = Mass * Acceleration, or in this case, Net Torque = Mass * Angular Acceleration. Given the input torque of 1 Nm, this would mean that the wheel would have a net torque of 1 Nm applied to it. Therefore, the wheel should experience an acceleration of 1 Nm/mass. However, the wheel doesn't keep on accelerating -- it just rotates at a constant speed. So why doesn't the wheel accelerate, when the actuator is applying a fixed torque?


texts:
When we apply a vertical shear force Sy and the structure is symmetric about x axis, then why is it logical to have the position of shear center at the location of intersection of line of action of shear force and x axis?

If we go by basic definition then the moment about the shear center due to shear forces should be 0, so the line of action of external shear force is logical, but when we consider moment about x- axis, rather than getting cancelled, I think they get added.

eg. This is the situation.

Now look at the final solution depicting the shear flows

So as I suggested, instead of moments being equal and opposite, I think they exactly equal in magnitude and direction. So where am I getting a wrong interpretation?

EDIT:- I tried to keep the question general and explained accordingly, to be specific the question is as follows:-

The thin-walled single cell beam shown in Fig. 20.11 has been idealized into a combination
of direct stress carrying booms and shear stress only carrying walls. If the
section supports a vertical shear load of 10 kN acting in a vertical plane through booms
3 and 6, calculate the distribution of shear flow around the section.

Boom areas: B1 =B8 =200mm2, B2 =B7 =250mm2, B3 =B6 =400mm2, B4 =
B5 =100mm2.

x is horizontal and y is vertical

It is a closed section beam. An idealized version of an airplane wing


texts: How would an electromagnet function within an MRI?

texts:
For the purpose of this situation. Lets say there are 4 small electromagnets within a MRI. All of them activate at the same time. The entire setup is comprised up of non ferrous metals. The metals within the core of each solenoid are only magnetized when the current is applied to the electromagnet. The MRI is on.

What would happen to the non ferrous metal when it is suddenly magnetized? Would it immediately succumb to the power of the MRI? Could the current be turned off quickly enough for the MRI to not immediately pull the non ferrous metal towards it?

From my understanding, the non ferrous metal would instantly lose its magnetic properties once current is no longer affecting the electromagnet so the MRI would have no affect on the metal.


texts: How is the design life of a reinforced concrete structure calculated?

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The specifications for large structural projects typically call for the structure to have a specific design life. This can be 50 years, 100 years, etc.

Accommodating the design life for steel can be as simple as adding additional thickness to account for the expected corrosion over this time period. This calculation would also take into consideration any variations based on coatings or type of steel.

History has shown that unreinforced concrete structures can last hundreds of years. The Romans have some examples of this such as the Pantheon.

The problem with reinforced concrete is that eventually the reinforcing will corrode, expand in size, and cause the concrete to crack. There can also be issues with the aggregates that are used.

How can a designer calculate and, by contract, guarantee the life of a reinforced concrete structure?


texts:
Say I have a light source at a distance of 1Km from a  light detector (photo detector). Right in front of the sensor, I keep a rotating reticle with some sort of pattern.

To better appreciate the situation take a look at the image below.

Now I want to simulate the detector output signal for various patterns on the reticle. For example "reticle B" from the above image would produce a square wave, and the "reticle A" would produce a  pulse train.

Is there any tool for doing such kind of simulation? Is there any python/matlab library?


texts: Derivation of the equation of the work done in a polytropic process

texts: I am completing a question that is requiring calculation of the work done in a polytropic process. In the worked solutions the work equation seems to be reversed for the answer, as can be seen in the screenshot- the top row is p1v1-p2v2 insted of p2v2-p1v1. Any clue why?


texts: How to calculate deflection of a simple beam with a load in the center?

texts:
Given this type of arrangement:

- image by Hermanoere

Where the beam is of rectangular cross-section.

I am specifically thinking of a wooden beam where I can look up some material characteristics (e.g. modulus of elasticity) from places such as here

If I only know

Force
Length between supports
Width and thickness(height) of beam
Modulus of elasticity of beam material

Wikipedia suggests I also need to know "Area moment of inertia of cross section" but I have no idea how to obtain this.

Do I have enough information to calculate deflection?

Footnote: I ultimately want to know how thick the beam should be so that
it won't break if I sit on it - but to avoid asking unacceptably many
questions at once, I have broken my problem up into simpler and more general questions.


texts:
I am just starting in Autocad 2018, under 3D Basics tools.
I have created a BOX, and then I am trying to apply the FILLETEDGE command, and after selecting any edge, the message "No fillet to be computed" results, since I cannot select any edge, nor any fillet is displayed as preview when hovering over any box edge, though the edges highlight when hovered over. The radius is already set to a proper value (Edge: 50, Radius: 3). X-Ray Visual Style do shows the box in blue-grey transparency.
Should I made some previous conversion on the BOX (which I understand already is a 3D Solid) object for the FILLETEDGE command (which too should work on 3D Solids?) to work?


texts: Can you shape a buoyant object stuck to the bottom of a body of water such that it floats?

texts: I understand that an object, say a closed plastic cube full of air, stuck to the bottom of an aquarium with a smooth glass bottom will not float if you firmly place it such that no water can get underneath. What if you change the shape such that you add surfaces that water CAN get under to provide lift? Take the cube and change it into a T shape for instance. Now the horizontal part at the top DOES have area under which water can provide lift. Will this break the suction holding the bottom of the T to the bottom of the aquarium and cause it to float?


texts: How to calculate minimum and maximum cross-section of a compression clip

texts:
I am trying to design and 3D a custom snap in fastener, and I am having a hard time figuring out what cross section it needs to have so that it does not break when compressed, but also isn't so that it is not too hard to compress to push in the clip.
This illustration shows the over all device, including a "cylinder" (gray with white line) that is inserted into the blue "clamp" component.  The green "e-clip" is supposed to snap onto the blue clamp, as shown.  With this clip in place, the center section of the e-clip should push the cylinder tightly against the blue clamp to impede both rotational movement of the cylinder and radial (in/out) movement.
Finally this entire assembly is pushed into a cylindrical hole in a panel to hold the assembly in place.  on either side of the part that is inserted there are fingers with a nub at the end. When inserting these will need to be compressed to fit through the hole, and once they reach the other side of the panel they should spring back out, and the nub prevents the assembly from slipping back out.
I am having two problems that are causing 3d printed versions of this design from being reliable.
The first problem is with the e-clip. If the center part of the clip isn't long enough, it won't push the cylinder tightly to the other side, and the cylinder easily turns.
If the center clip is long enough, and too strong and stiff, it may actually make it impossibly hard to get the clips on the prongs to open enough to slip all the way past the retaining edges of the blue clamp.
If the center key is not strong and stiff enough it can snap off.
If the prongs are not thin enough to flex open to go around the retention part of the clamp they can't be pushed over the retaining edges.  And if they are too thin, the ends of the prongs break off.
The second problem is with the clamp itself. It also has two fingers to hold the clamp in place.  These will need to be thin and flexible enough to compress and allow the assembly to be pushed into a hole, but they also can't be too thin so that they fracture when compressed.
What I have tried:
I have tried 3d printing using a number of different materials including PLA, PETG, ABS and Nylon.
I have tried to increase the thickness of the parts that fracture, and to decrease the thickness of those that are too rigid to compress or expand enough.
I don't seem to be dialing into a workable solution through this trial and error method.  How can I determine thickness/cross section needed to prevent fracturing during insertion, but still be bendable enough to "snap" in place.
Are there analytical methods that can tell me in advance which solutions will/won't work for a given material?


texts: What is the difference between a diffuser and a duct in turbines?

texts:
I have been reading this paper, which addresses the advantages of diffusers in cross flow turbines.

The abstract says (emphasis is mine):

  A CP’s extraordinary improving resulted when yaw increased up to 22.5° for the hydrofoil shaped and up to 30° for the symmetrical diffuser. Similar behaviour in yawed flows also occurred in case of a ducted single rotor, demonstrating that it is a characteristic of CFTs.

I am confused as to the difference between a duct and a diffuser in terms of turbines.

According to Wikipedia, the diffuser sounds similar to a duct.

  a wind turbine modified with a cone-shaped wind diffuser that is used to increase the efficiency of converting wind power to electrical power. The increased efficiency is possible due to the increased wind speeds the diffuser can provide.

My question is, what is the difference between the two? Do they have different functions?

I ask because it seems like the author is implying that the two are different.


texts: Is there any link between tensile strength and endurance limit for steel ?

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I'm designing a shaft, and i have to choose a material.

I deal with cyclic stress in my machine, so i set up an expression for all the possible stresses and combined it with von Mises criteria for plastic deformation, it gives me the so called comparison stress.

This comparison stress should be lower than the endurance limit of the material. I don't have the endurance limit, but instead the tensile strength.
Is there any connection between endurance limit and the tensile strength ?


texts:
Recently we put 500 feet borewell in our area, it's hot summer season now. Person who drilled the borewell told me that we can get 1.5 inch of water now. During winter season we can expect at least 2 inch of water. Now we are planning to install the motor at 410 feet and buy 5hp motor with 2 inch mouth.

My question is
Can I put 2 inch pipe inside borewell and control water outlet at the end of borewell with 1.5 inch? Whenever water level increase can I increase outlet with 2 inch? Can I control water outlet at the end?

Question rephrased:

Can we adjust water outlet of the submersible motor at the ground surface or edge of the pipe? Usually people adjust water outlet at the end of motor mouth section which is inside the borewell not at the ground. Is there any signigficance where the reducer kept?


texts: I am looking for a mechanism that would allow me to support a fixture attached to a 3-axis motorized stage. I have attached a picture of my current design. I trying to design/incorporate some sort of hardware that will support the green fixture to travel in the z-axis as the grey stage moves during its analysis procedure. I originally tried a lab top scissor lift but that requires me to manually adjust the stage. I was thinking of a gas spring platform but wasn't sure how to incorporate it properly. Any ideas?


texts: Why use different specific heat capacities in the energy equations for incompressible and compressible fluid flow?

texts:
Background:

I notice that there is quite a bit of similarity between the standard heat equation and the energy equation (from the navier stokes equations).  The heat equation is given as

$$\frac{\partial\left(\rho h\right)}{\partial t} + \nabla\cdot\left(u\rho h \right) - \nabla\cdot\left(k\nabla T \right)=0$$

with $\rho,h,u,k,T,$ are the density, total specific enthalpy, fluid velocity, thermal conductivity, and temperature, respectively.  Note that for many applications, it suffices to write the total specific enthalpy as $h=c_pT$, where $c_p$ is the constant pressure specific heat capacity.

On the other hand, the energy equation (from the navier stokes system) is given as

$$\frac{\partial\left(\rho E\right)}{\partial t}+\nabla\cdot\left(u\rho E\right)-\nabla\cdot(k\nabla T)+\nabla\cdot(\sigma u)=0$$

where $E,\sigma$ are the total energy and stress tensor, respectively.  Here, the total energy E is the sum of internal and kinetic energy $E=e+K$, with $=e=c_vT$ and $K\frac{1}{2}|u|^2$.

Since both equations are derived from the conservation of energy, it is no surprise that both equations share the following terms:

Rate of change in Enthalpy (time derivative term)
Advection of internal heat (divergence term)
Heat diffusion (laplacian term)

The energy equation has additional terms which are not found in the heat equation.  These additional terms are specific to compressible fluid flow and account for

Rate of change in & advection of kinetic energy (K)
Stress contributions to energy ($\sigma$)

In many situations, the kinetic energy and stress contributions are very small when the fluid flow is incompressible, and thus can be neglected.  This results in the energy equation and heat equation being almost identical except for one subtle difference:

A subtle difference
The heat equation is formulated with the constant pressure specific heat capacity $c_p$ while the energy equation uses the constant volume heat capacity $c_v$.  Yet, I assume that they are derived from the same principle of conservation of energy.  If so, I would expect the two expressions to use the same specific heat capacity.

This becomes more important when dealing with different types of fluid flows.  I have seen models for incompressible flow where the energy equation is simply formulated in terms of the standard heat equation (as above) with the constant pressure heat capacity $c_p$. Since the temperature does not affect incompressible fluid flow, one can think of this as a "scalar transport" which depends on the resolved fluid velocity $u$.

Application: Solidification & Melting
In my particular case, I want to model phase change (solidification and melting).  For incompressible flow, it suffices to rewrite the total specific enthalpy as the sum of internal and latent heat ($h=c_pT+h_L$) and substitute h in the equation.  For compressible flows, the equation is written in terms of internal energy $c_vT$, not enthalpy.  So, I'm not 100% sure that it would suffice to simply add the latent heat term as if it were a part of the total internal energy.

The only way to know for sure is if I understand why the incompressible energy equation is written in terms of $c_p$ while the compressible energy equation is written in terms of $c_v$.

My Question

If the energy equation for incompressible flow is formulated in terms of constant pressure heat capacity $c_p$, why isn't the energy equation compressible flow also formulated in terms of constant pressure heat capacity $c_p$.  Why is the heat capacity different for incompressible and compressible flow?  What accounts for the difference?

Furthermore, for my specific application, how do these differences affect how to add latent heat effects for solidification and melting of a compressible fluid?   Can I simply add the latent heat to internal energy term $e$?  Or do I need to completely reformulate the compressible energy equation in terms of enthalpy in order to add latent heat effects?


texts: How can I drill a long, narrow hole into the end of a steel circular bar?

texts:
I'd like to drill several very small (~0.015") but relatively long (~1") holes into a bar of stainless steel, as shown in the diagram below.

I did a quick check on McMaster and all the drilling lengths are much shorter (<<0.5") than I need. I'm not sure if it's feasible after all. How can I source this part, or machine it myself?


texts:
I have a warehouse ( 36m x 14.4m x 10m ) that I want to keep it under 30 degrees Celsius but everyday the temperature will goes above that. It has two turbine ventilator that I don't know the specification and for the ventilation it only relies to two rolling doors ( 3x2m ).

I have a thought that it is caused by bad airflow in the warehouse so
I have an idea to add 3pcs of 8ft HVLS Fan and adding 5 more turbine ventilators. But will it works because I will have to do a big investments to that fans.

I live in Jakarta, Indonesia. And the ambient temperature ranges from 28 - 35 degree C in the afternoon.


texts:
I'm new to plasma cutting with a hand-held plasma cutter (as opposed to CNC). Its straightforward to cut with a fence/guide and I am getting good results that way.

However, when I want to freehand a rough shape without setting up a complicated jig, I can't figure out a way to see a line I want to cut. I wear a welding mask on a low setting for eye safety and once it dims I can't see any lines I've drawn on the part.

Does anyone have a good way to safely see a cut line when plasma cutting with a dimming mask?


texts:
My background is more Chemistry and Biology, not Physics, or specifically engineering with fluid dynamics, so bear with me! Also, this is a little long, so I will do my best to make it easy to follow.

The Problem:

I am trying to derive a formula to calculate air flow rates (in CFM) based on the static pressure (inches W.C.) of the HEPA filter I am blowing through for a laminar flow hood that I am building. Link I am trying to figure this out because many HVAC application fans have ratings of their output at certain static pressures, many, many more do not, and it would be really helpful to beable to derive this information on my own.

Information I have available to use:

Standard fan information, from the manufacturer (Brake Horsepower, Fan wheel dimensions, RPM &/or CFM).
Volume of the Plenum Chamber, Link, in this case >= 4 ft$^3$. (12" x 24" x 24" as it is generally accepted that the size of an adequate plenum must be >= the volume of the filter).
The Static Pressure of the HEPA filter, in my case 1" w.g., and although I don’t know how it relates to anything or what it means, I also have the resistance range of, 0.69.
The desired volume/rate of air on the intake of the filter, calculated out to 400 CFM @ 1.00" w.g. SP. ( Based upon this formula (Desired FPM Output) x (Volume of HEPA Filter) = Required CFM Input. Link. --The desired output of the entire unit, 100-200 FPM, ideally.

Questions developed from research & attempts to solve:

Some fans are rated at 0.00” SP all the way up through +1.5” SP. What are the standard conditions for these specs? I.E. in chemistry you have SC = 1.0 ATM @ 0$^{\circ}$C. If a fan is rated at 500 CFM without any information given about Static Pressure, what would be the static pressure? Is it 0.00” w.c.? above, or below?
I have stared at the Affinity, or Fan Laws, Link, for countless hours now. Specifically Law #2. SP$_2$ = SP$_1$( CFM$_2$ / CFM$_1$)$^2$. I was hoping that this would solve my problems, but I have been trying to solve for CFM$_1$, since I know I want SP$_2$ to equal 1.0” and I know I want CFM$_2$ to equal 400 @ SP$_2$. I have been operating under the assumption that a fan, at it’s highest RPM/CFM is operating at 0.0” SP. But then you can’t calculate for the obvious reasons, so this has to be wrong. So back to standard conditions for fans.


texts: Analysis Of Planar Frame Using Hardy Cross Method (Moment Distribution) With Sway

texts:
The image shown below is a sketch of the structure/frame that I am attempting to analyse using the Hardy Cross (Moment Distribution) Method. I need to find the bending moments, axial forces and shear forces on each of the individual members. After that, I am planning to apply the design equations according to codes.

The main reason I am stuck is due to the sway generated by the unsymmetric nature of the structure. I am unsure about where to apply the arbitrary sway load and also how the joint rotations are related (using displacement triangles). I need these details in order to analyse the structure using Moment Distribution with Sway. Software is not an option as I do not have access to it.

Please demonstrate how to solve the structure (mainly find the bending moments).


texts: Can all electromagnetic spectra be focused like a laser?

texts:
Lasers have a wide range of applications, but can be very costly to produce at high power/intensity.  Since light is nothing more than a narrow band of the electromagnetic spectrum, it makes me wonder if the same high power/intensity applications can be achieved at a lower cost by concentrating  other wavelengths (e.g. Infrared, radio, etc.)

A cursory google search revealed nothing of this sort, which makes me suspect that i this is not possible.  But i just want a clear answer as to whether other electromagnetic waves (besides light) can be concentrated and propagated as a beam invthe same way as a laser.  If possible, i'd also like to understand if/why larger wavelengths hinder our ability to concentrate these waves into high power/intensity applications.


texts: failure point of flat panel under pressure

texts:
Generally, how would I go about finding the maximum distributed pressure which a flat rectangular panel of material, say glass or acrylic, can withstand given thickness, length, and width?

For example, a glass panel 10cm by 10cm by 1cm thick. How much pressure in Pa could the panel withstand before failing? Something like a door on a vacuum chamber.


texts: Axially loaded member with a spring / Mechanic of Materials

texts:
i've been struggling with this problem i made up. It is about a cylindrical copper member (diameter $d=20$ mm and length $L=250$ mm) with a spring (stiffness $k=166,5$ kN/mm) fixed on a wall, as the figure shows:

The copper member, initially at $20 ºC$, is submitted to a temperature difference of $\Delta T=50ºC$, and the elasticity modulus and the thermal expansion coefficient of copper are $E=110$ GPa and $\alpha = 1,7\cdot 10^{-5} \frac{1}{ºC} $, respectively.
The problem is about calculating the reactions at A and C.
Im not sure how to approach this problem with superposition or the 3 step method (equilibrium, geometric compatibility and force/displacement relation).
I know the  temperature gradient of $\Delta T=50ºC$ will cause the member to expand $\delta_T=0.2125$ mm , exceeding the $0,08$ mm gap between the wall and the copper member. Leaving a "residual expansion" of $\delta_{res}=  \delta_T - gap = 0.2125 - 0,08 = 0,1325$ mm, unable to expand beyond the wall, therefore, once the member touches the right wall, the spring starts compressing.
So the question is, how do i write down the correct geometrical compatibility of displacement?
Thank you for your patience (im not native speaker)


texts: Is there an intuitive explanation for the Kinematic Viscosity unit of mm^2/s?

texts:
I've learned that a high viscosity means that the fluid is more thick. Dynamic Viscosity thus represents the resistance to shear forces. Presumably, higher resistances are represented by higher numbers in the relevant ISO spec.

Thus I'm puzzled about the unit of Kinematic Viscosity (which is basically Dynamic Viscosity modulated by a measure of the density of the fluid). The unit is:

  m^2/s

But how can this unit be understood intuitively? The higher the viscosity, the lesser the flow-rate and thus less m^2 fluid should flow per second in whatever measurement setup they are using.
Looking at the unit for kinematic viscosity, it seems that a higher value means that the fluid has a lower viscosity (i.e. is less thich), because, well, more square meters of fluid seems to flow per second.

How can the unit of kinematic viscosity be understood intuitively, when seen in relation to the definition of viscosity?


texts: angle of twist of gear relative to another

texts:
why we need to consider 2 moment caused by the 85Nm in this question ? The question ask for the determine the angle of twist of gear A relative to D .

Why shouldnt the angle of twist = (85)(0.4) / (      (0.5pi)( 0.015^4- 0.01^4)(75)(10^9)  )  + (85)(0.25) / (0.5pi)(0.02^4)(75)(10^9) only ?


texts: How should I go about adding holes to laser or water jet cut sheet metal?

texts:
I’ve been working on an electric Dirtsurfer project that has many parts to be made from folded sheet aluminium.

Obviously the sheet metal needs holes in it for bolts. The sheet aluminium will be either CNC laser cut or CNC water jet cut.

I’ve got three options:

Add holes to my design at the exact dimensions that I need them to be. I am placing myself at the mercy of the accuracy of the CNC cutter to ensure I have no slop which might let the bolts move. But no drilling!
Leave the holes out of the design. I measure the cut patterns to find the right places for the holes and drill them myself. Using a drill will give me a clean hole that I can fully trust the dimensions of. This is what I’ve done in the past, but I haven’t been accurate enough with my placement.
Undersize the holes in my design, and drill them out to the correct size later. I don’t have to measure anything, but still get a clean accurate drill hole.

Any practical advice from someone who’s done this before?


texts: So here I have a cantilever beam and I have the shear force diagram. When we are talking about the maximum shear force diagram. Should I take 40kN? Or I need to absolute the value and take 60kN. I am new to mechanical engineering and I am so confuse on these kind of problem.


texts: How can I calculate the power to drive a water pump based on discharge from two hoses?

texts:
I am trying to solve the following problem:

  A pump feeds two hoses, each of which is 45 m long and is fitted with a nozzle. Each nozzle has a coefficient of velocity of 0.97 and discharges a 37.5 mm diameter jet of water at 24 m/s when the nozzle is at the same level as the pump. If the power lost in overcoming friction in the hoses is not to exceed 20 per cent of the hydraulic power available at the inlet end of the hoses,
  calculate (a) the diameter of the hoses, taking f = 0.007, and (b) the power required to drive the pump if its efficiency is 70 percent and it draws its water supply from a level 3 m below the nozzle.

Here are my workings for part (a) of the question.

Head lost at nozzle $H_p = H - 4fLv^2/ D2g$
or Hp = Head at inlet to hoses - frictional head loss in each hose.
$C_v = 0.97$ and Jet Velocity $V = C_v \sqrt {2g * Hp}$,
so then I worked out $H_p$ from this to be 31.208 m.
For continuity of flow, flow from hoses = flow from nozzle, so $v = V (d^2/ D^2)$ and $v = 0.03375/ D^2$.
I have then put this in the frictional head loss formula $4fLV^2/ D2g$ and this gives $1.43521875 * 10^-3/ D^5 * 19.62$.
Note $2g = 19.62$ and $H = 5 * \text{frictional head loss}$.

So lastly I put this in the formula $H_p = H - 4fLv^2/ D2g$. I solved for $D$ and I got 98.7 mm for the hose diameter.

Is this on the correct path for Part (a) of the question?

How can I work out the power for Part (b)?


texts: What signals are expected on the connectors for this 12V Volkswagen Scirroco wiper motor circuit

texts:
EDIT: added a picture of a very similar unit.

I picked up a used VW rear? wiper motor that I want to use for a simple motion experiment.

Having no idea how to power the thing I popped open the case and looked inside.

Not really wanting to break it (and not being extremely motor savvy) I am asking if my assumptions are correct.

A) The large ground looking plane on the left side of the board is likely ground
B) The voltage is likely 12V or less.  Some of these components look a bit tiny for 12v though?

This is just an exercise in guesswork that may or may not fit into the meta of this beta site but it seemed a good place to ask sensible questions about the circuit.

I did try to find the docs for the part but had no joy.
Appreciate any help. I have a limited current power source that I can test out any guesses with.
Thanks.

I am also assuming that the various connections could be i) common ground ii) slow speed iii) fast speed iiii) common +ve

I have no idea if that is correct of the likely order based on the diagram. would also appreciate any insight on those assumptions.

Noting the possible current limiting resistors on two of the channels might this indicate they are the loom switching pins? The center ones?


texts:
I am working on a project for college, and I am stuck on one idea that I don't really know how to represent it.

Basically what I want to do is something like a pipe, that if a put a kind of cylinder on inside from the top side, the cylinder will reach the end by force of gravity.

So something like this:

But, if I turn the pipe, so I put the bottom on top and the top on the bottom, that cylinder must be stopped/blocked.

So something like this:

So my idea was to put some-kind of corrugated pipe as follows:

In this way the pipe will be one way only. As creating a pipe like this for a school project will be too hard, my questions is if is there already a pipe like this, if not if you have any other idea to achieve this.


texts:
Why does increasing derivative gain $K_d$ in a  PID controller loop lead to a reduction in overshoot and an increase in rise time?

This is not a homework question, it is a question to improve my understanding. I know that the output of the derivative path of the controller is $K_d \times \frac{de}{dt}$, but I don't understand why increasing $K_d$ would lead to the rise time increasing and less of an overshoot as when $\ K_d $ is greater, the controller output would be greater, thus leading to an increased overshoot?


texts: Max torque allowed on cypress wooden beam

texts:
I am trying to calculate the maximum torque that a piece of cypress wooden beam can handle before it snaps or becomes structurally unsound. I know this will depend on the thickness and width of the wooden beam.

Does anyone know where I can lookup the property value (coefficient or some other value) that will allow me to calculate the max tolerable torque given the thickness and width? I am looking for the value for cypress wood, but if there is a database for other types of woods, that'd be even better.

For reference, I am trying to design a bathtub bench for sitting that will hold up to 300 pounds. The current plank is 1 inch thick x 3.5 inches wide x 30 inches long.

Thanks,


texts:
Hoping this is the best area to ask this, mostly in the DIY and hobby world I've seen 2 engines coupled together to make a twin engine some so this for the zen of doing, but others do it to align the pistons I've noticed particularly in RC aircraft rather than buy a twin engine where the pistons operate at exactly the same time and I supposed matched this  Introduces a reciprocating vibration that causes issues.

I've been hearing if you take 2 two stroke engines and couple them together with 1 at TDC and the other at BDC they cancel each other out and a guy on YouTube showed a video of one with a glass of water next to it barely moving.

What is the name for such an arrangement? Is there any disadvantage of doing this? Links to more information? I shall search for YouTube video as described above.


texts: What is required to implement Positive Train Control on railroads in the US?

texts:
Background

On May 12, 2015, an Amtrak train derailed in Philadelphia, PA, killing 8 and injuring 200 people. I saw a story on the incident where multiple NTSB spokespeople have said at this and other train derailments that Positive Train Control (PTC), had it been installed,
could have prevented the derailments from happening, particularly in incidents where human error is the key factor, rather than technical failures or track obstructions. PTC uses GPS and transponder technology to avoid collisions and derailments by ensuring that trains operate within speed limits and do not cross improperly-switched tracks.

As the first link points out, the Rail Safety Improvement Act of 2008 (passed in the wake of the Chatsworth train collision) mandates that much of the nation's rail system have PTC installed by Dec. 31, 2015. However, the rail industry has been lobbying to extend the deadline, claiming that they will be unable to have PTC installed and operational on all required lines, and be forced to either cease operations, or operate illegally.

Questions

What is required to implement Positive Train Control on existing rail lines in the United States? Does implementation require track improvements, engine/car improvements, or both?
Are the systems that are currently used or in development inter-compatible? For instance, a commuter rail system near me uses existing BNSF and Union Pacific lines (among others) in addition to lines that it owns itself, and Amtrak operates on some of these lines as well. Do all trains operating on these lines need identical PTC systems, or can the commuter rail develop a different but compatible system than the freight rail?
How long have complete rollouts of PTC taken, and what have they cost? (This is a fact-based way of answering the more debatable question 'Is 7 years a reasonable period of time to allow for PTC development and implementation?' and to examine what kind of budgetary strain the unfunded mandate places on smaller rail systems.)


texts:
Assuming, I've got a machine, that runs with pressurized air and provides the following measurements:

$\dot m$ - mass-flow through the machine (same for input and output)
$p_{1}$ - input pressure
$T_1$ - input temperature
$p_{2}$ - output pressure
$T_2$ - output temperature
$P_{mech}$ - mechanical output power

How can I calculate the power $P_{fluid}$ the air gives to the machine?
In a first step, the heat-flow through the housing of the machine can be neglected, yet its influence to the process is interesting to me.


texts: Why are bird flight diverters shaped like a spiral?

texts:
I was out walking and saw these strange looking spirals on some power lines.

When I got home I did some research and discovered that they are to prevent birds form hitting the power lines, mainly used in conservation areas. I found this interesting study about which types of flight diverter are the most effective at preventing bird collisions. It mentions a few other types of diverter (plate, swivel, sphere), but the spiral seems to be the preferred shape to experiment with (big vs small) and the reason for this is not explained.

I can understand that a spiral wire has a good visibility to weight ratio, but is this the only reason for the shape? Would there be any current transmitted through (or induced in) the spiral, and would this shape help in any way to prevent any negative effects this might have? Or am I just thinking that there is an electrical reason because the spirals remind me of magnetic field lines, when really that's nothing to do with it?


texts: I would like to know the algorithm of switching between 4g/3g/2g. When will the phone switch from 4G to 3G or from 3G to 2G, when we select for corresponding option in the mobile phone. Is it based on dBm/RSCP etc? I am looking for some technical document. TY


texts: O-Ring Selection for a round rectangle groove

texts: I'm designing a water proof case for a power bank to be used in an occasional underwater condition. The input and out put port components already have a gasket or sealing ring. Now to close the case I am planning to mill a metal with all walls and floor and then screw the top along with and O-ring. I haven't used an O-Ring before and wanted to know how to select an O-ring for a rounded rectangle groove (Does the circumference being equal to the grove length , enough). Is there any handbook for the same?


texts: Why resolution of photolithography evolved gradually?

texts: Moore's law states that no of transistors on a given area doubles every 18 months. Electronic components are typically made by photolithography. So,  Moores law basically limits the resolution of photolithography. Why resolution of photolithography evolved gradually and not abruptly?


texts: How to simulate the contact between two distant parts in Ansys workbench？

texts: I made a test in Ansys but the result doesn't seem to be the final steady state. The two bodies didn't touch each other. How can I get the right result?


texts: What kind of pump to choose for a weight-based rain gauge?

texts:
I'm designing a rain gauge which uses accurate electronic scales to measure weight of water (and therefore volume) that has entered the sump. Ideally the system will not require any manual intervention.
When the water level exceeds some suitable value I switch on a pump (I'm using a low voltage submersible centrifugal pump) for a fixed time. That time is long enough for the water level to drop so that the pump is now "empty". I then reset the scales to get my new zero weight level.
So far so good - but the outflow tube now has air in it. Some of the water in the tube may flow back down into the sump. This will create an error in the weight measurement.
A solution would be to stop pumping when the weight reaches some lower value, but which is enough to stop air entering the pump. Now, the outflow tube should not have any air in it so the water in it will stay there. But in a dry spell the water in the sump could evaporate, so we are back to the original problem.
I suspect (but don't know) that some kind of lift pump might get over the problems. Is such a pump available at low voltage and low cost? Or some other kind of pump perhaps?


texts: I need to send out some PRT files for tooling that have been made using Creo. I do not have a windows PC or mac available at the moment, only linux. Does anyone have some advice how to go from here?


texts: How to control an underactuated platform with a single servo

texts:
What's the best way to control the following type of platform so that it remains balanced and upright?

It's a box supported by a single leg that can pivot at the foot (F) and at the hip (H). The foot and hip joints are designed so that they can only rotate in the xz plane (where x goes left-to-right and z goes up-and-down). It's similar in concept to the inverted pendulum, except the base (F) is fixed, and the actuation is done by shifting the mass at the "top" of the pendulum. I've seen some academic papers refer to this as the "cart-table model".

The hip joint is powered by a servo motor which can report its angle of deflection relative to the box (ϴⱼ).

At the center-of-mass (COM), there's an accelerometer that reports the box's angle of deflection relative to gravity (ϴᵢ).

I've constructed this platform and I'm now trying to program a microcontroller to actuate the servo so that the platform remains both upright and level.

The figure depicts the four basic states that the platform will experience. At t₀, it's perfectly level, but in an unstable leg configuration so that its center-of-mass is off-center and will cause it to begin toppling over.

At t₁, the platform has tipped forward slightly. I've been able to program my controller to detect this and start actuating the servo to rotate the box counter to the angle of deflection so that the center-of-mass shifts to the other side of the leg, taking me to state t₂.

However, this is where I run into problems. I'm using a simple PID controller that's being told the target value of ϴᵢ, while being fed the current value of ϴᵢ, and it's attempting to output a servo control signal to achieve this correction. After some testing, I realized this doesn't work because ϴᵢ isn't the only angle that needs to be controlled. By only looking at ϴᵢ, I was seeing massive oscillations of the servo all while the box topples over, because as soon as the servo tilted the box over the foot, ϴᵢ was then horribly unbalanced in the opposite direction, causing the PID controller to again correct it by shifting the box back over the foot...in the direction that the platform is falling, which only hastens the fall. I'm not sure how to tell the controller to "ignore" the unbalanced ϴᵢ once the center-of-mass has been shifted.

So I think the solution is that I need to either directly measure ϴₖ, or infer it by using ϴᵢ and ϴⱼ, and then feed both ϴₖ and ϴᵢ into my controller. However, I'm only familiar with simple PID controllers that take a single input. What type of controller would I use to take two inputs and output a servo signal?

If I input ϴₖ into my PID controller, I could probably get my platform to stop toppling over, but the box wouldn't be level. It would achieve a state close to that shown at t₂, where the box is skewed but its center-of-mass is balanced.

Would another solution be to re-locate the accelerometer to point H? If it were there, I could use the raw acceleration readings to get a reliable sense of when the platform has stopped shifting in the wrong direction, and use that period to temporarily disable the PID controller so it doesn't erroneously un-shift itself.

My goal is to get the platform to the state depicted in tₙ, where the box is level and the leg is angled so that the center-of-mass is evenly distributed so that the platform can remain upright. What type of controller would I use to accomplish this? Is there anything else I'm missing?

Edit: Updated the figure to depict the state described by @fibonatic.


texts:
For an assignment, I was given:

  Calculate the heat loss per linear ft from $2$ $in$ nominal pipe. ($2.375$ $in$ outside diameter covered with $1$ $in$ of an insulating material having an average thermal conductivity of $0.0375$ $Btu/hrft^oF$. Assume that the inner and outer surface temperatures of the insulation are $380^oF$ and $80^oF$ respectively.

The correct answer is $116$ $Btu/lb^oF$

I used the formula from conduction through pipes:

$${ Q = \frac{\triangle t}{R_{total}} = \frac{\triangle t}{ \frac{ln \frac{r_2}{r_1} }{2 \times \pi \times k \times L} }  = \frac{\triangle t}{ \frac{ln \frac{d_2}{d_1} }{2 \times \pi \times k \times L} } }$$

Where:

$${ \triangle t = 380-80= 300^oF }$$
$${ d_2 = 3.375 }$$
$${ d_1 = 2 }$$
$${ k = 0.0375 }$$

And I get close, but not correct.  I calculated it to be: $135.090464$ $Btu$

What am I doing wrong?


texts: Determination of delivery pressure from pump in my Parts Washer

texts:
We want to know how can we determine the pressure of the liquid at the delivery end of the pump. We have a centrifugal pump and a 2" pipeline at the delivery end. Pump delivery performance as per catalog is 510LPM @20 mtr head to 348LPM @36mtr head.

The delivery pipe is connected to a manifold on which spray nozzles are connected around 70 Nos.

The total length of pipe from the pump outlet to the spray manifold will be approx 5 metres of which 1.5mtr is vertical & remaining horizontal.

We have mounted a pressure gauge on the line which gives a constant reading of 0.6-0.8 Kg/cm2 which is lower is lower than our expectations from a 5HP pump.

When we block the line just before the manifold, the gauge shows a reading of 3.5-4 kg/cm2.

Kindly help us determine the process of finding out the pressure in the line.

Also, If I have to select a pump that constantly delivers liquid at 3 Kg/Cm2, how do I go about the selection?


texts: Parameter Estimation for First Order System

texts:
I would like to get a simple estimation of the parameters for a humidity chamber system. The humidity chamber has one constant inflow ($k_1$) and and outflow which depends on the humidity of a neighbor humidity chamber (diffusion, modeled as $k_2(RH_{ext} - RH)$. $RH$ is the humidity of the chamber, $RH_{ext}$ is the humidity of the external chamber. I have the following system description (first order):
$$
\frac{dRH}{dt} = k_1 + k_2(RH_{ext} - RH)
$$

Now, I have measurement data for $RH$ (output) and $RH_{ext}$ (input). $k_1$ could be seen as a second (constant) input. I would like to estimate the parameters $k_1$ and $k_2$ in a simple manner (maybe least-square based) using my (discrete) measurement data in Matlab, but I don't know how I could proceed. Use the system identification toolbox? Other ways?


texts:
I am trying to understand what the drawing states for a transmission tower.

Specifically, the underlined portion. Any help would be greatly appreciated.

BC65X31 + CO45
CT41X38
CO45


texts: What is the Difference between ASCE and IBC Code?

texts:
What is the fundamental difference between the ASCE Code and IBC Code and what is the objective of each one?

Thank you in Advance.


texts: How to calculate the interface shear of UHPC girder to a concrete deck slab without intentional roughening. Is mu = 0.6, c = 0?

texts: Uhpc girder interface shear capacity without intentional roughening is quite low, suggesting impractical rebar spacing.


texts: When To Ignore Changes In Pressure When Computing Flow Energy For Gases?

texts: In reference to this example problem (only partially shown), I need to understand why for $\Delta h$ the change in enthalpy, which is $\Delta P/\rho + \Delta u$, the change in pressure is ignored in the solution even though it is considerably large. Could somebody please explain this to me?


texts: What is the meaning of “load case consistent” in stress analysis terms?

texts:
I’m a (junior) stress engineer and have been tasked with sizing a lug. Various loadcases have been run through FEM and loads have been distributed into the lug bolt for each. In other words, each loadcase has its own set of x, y, and z loads at the bolt.
An initial analysis (spreadsheet) was run, where the lug was sized using the max x, y, and z loads across all loadcases. My understanding is that this is conservative.
Now I’m being asked to take out conservatism by applying case consistent loads. Would I go about that just by doing an analysis for each loadcase with a max value? Am I understanding the meaning of “case consistent”?
As an example:
Loadcase 1 has no maxes, so I don’t even look at it
Loadcase 2 has the max x, so I analyze the lug using all values from this loadcase
Loadcase 3 has no maxes, so I don’t even look at it
Loadcase 4 has the max y, so I analyze the lug using all values from this loadcase
Loadcase 5 has the max z, so I analyze the lug using all values from this loadcase
Sorry for the long post, but any help is appreciated.


texts: How can we prevent/detect hydrogen embrittlement?

texts:
There has recently been a series of high profile bolt failures on 'The Cheesegrater' in London, which have been attributed to hydrogen embrittlement.

What can engineers do to ensure that hydrogen embrittlement doesn't effect their structures?


texts: House construction using concrete panels

texts:
Background Information

Currently looking to buy a house in the Southampton area in the UK and have noted there are quite a few houses which use a concrete panelling construction technique see example image below:

Some are advertised as Reema construction which can be difficult / impossible to obtain a mortgage on.  I have read up on Reema construction and this has currently put me off any type of concrete panel type buildings currently.

The Questions

What are the major pros and cons of concrete panelling construction, other than the obvious it's cheap and quick to build?

Is there a register in the UK to obtain information about the building type and construction which is accessible to the general public?

Thanks inadvance,
Suze


texts: Strongest brazing materials for titanium?

texts:
What are the strongest brazing materials for titanium?

The main materials I would like to use would be copper or silver, in which case I would like to ask which would form a stronger bond with titanium.  Otherwise what are the strongest bond forming materials for brazing nickel titanium wire to titanium?


texts: Is consumption of car (engine+gearbox) monotonic with (steady) speed?

texts:
I try to understand the interaction of (real) engine + gearbox on the consumption. So I purposely don't want to account for friction on air and floor for now.

For the engine alone, the optimal efficiency is obtained for some given rotation speed ( about 2000 RPM, I guess ), then the consumption per turn increases above as well as below this optimal.

Now if we couple a gear box, as the wheels velocity slowly increase (slowly for quasi-stationarity) we have to change gear. During this slow process the engine thus cycles between under-rev, optimal, over-rev several times.

→ at the end, might it be that the consumption per km/h varies non monotonically with the wheels velocity ? (again, not accounting for air and floor friction. Could be tested on rolls.)


texts: How to lift a roof using no electricity?

texts:
I constructed a small building to protect irrigation valves from freezing. The roof is hinged and rests at a 110 degree angle. The goal is to lift it up to about 20 degrees. The roof is 4'x 8', and weighs 100#. I want counter balance the lid to assist in lifting. The hard part is the lift mechanism needs to be hidden inside.

My idea for lift is to mount a bar to lid and mount a bar to the building base, then connect the two rods, and have all 3 connection points hinged. Then use pulley's and a counter weight to pull the bars to near vertical alignment. So the bars will be in a tight v position when lid is closed. As lid opens the v would get larger until bars are almost I vertical alignment.

How could I improve this design?


texts:
I wish to rotate a short cylinder (thick disc) by 150 degrees. I chosed to use a double torsion spring for this (as the picture below). The picture shows only one side.

I wonder if the above design (cylinder and spring) would actually work. I have no knowledge in springs..
Do you have alternative suggestions for the design of cylinder and spring?


texts:
I have a design for a gasoline engine cylinder that is open at the top, closed at the bottom (a single pipe cylinder) that operates on opposed force (the pistons move lateral to the up-down direction of the pipe.  I believe it's an extremely efficient engine design that would produce -no disorganized cloud of vapor explosion-, absolutely none, but a single diamond shaped concentrated vapor burst between the two pistons, and at the top the flame profile turns into a string before disintegrating.  The description is, it says top torus, actually those are the pistons, and they're both half hemispheres.  The ring around the base of the pistons are repeated metallic X's that control the flame profile, and the cylinders move in a horizontal position laterally, not up and down as this is an opposed force design.  Here is a youtube video of an open pipe explosion: Open Pipe Explosion #2

My question is, since this a nonlinear explosion in an engine that should be the most efficient, how would somebody go about making the engine, or convincing an automaker to build one.  I don't have a patent on it, but I designed it.


texts: Why is minimum pressure specified on a PSU water cooling circuit?

texts:
I work in consultancy and I am designing a product for a customer. The customer has requested a specific PSU. I have contacted this PSU manufacturer and they request 6 L/min of coolant flow and minimum 3 Bar. I now have to specify a suitable pump to deliver these fluid characteristics to the PSU.

I have confirmed this is not a typo for "maximum pressure," but no reasoning for specifying a minimum pressure is forthcoming.

My confusion is why the flow rate AND minimum pressure are specified. The manufacturer does not know what pressure differential I require to generate the specified flow around my bespoke circuit - so why specify a minimum pressure AND a flow rate?


texts: What is the focal distance of an optical mouse?

texts:
I am trying to build an optical sensor for my old school, state property, standard french watt-o-meter. EDF ( Electricité de France ) has a gig which turns a wheel depending on watt consumption. The higher the wattage, the faster a tiny disk turns.

Now the disk can be read by eye, so here is my question: why not use a hacked optical mouse to gather data ?

The contraints are:

can't open the gig
the wheel is 1.5 cm away from a protective glass
I have an optical mouse

The CMOS has a half milimeter opening, and a 2mm lens from the standard casing.

What optical system do I need to read half milimeters from 15 milimeter distance using a classic optical mouse?

Can anybody help me calculate the correct lenses for this, or point me in the right direction?


texts:
I studied a thesis about a axial turbine and but i didn't understood the bold part of following sentences. What is the exact meaning of "dot product of the pressure and viscous force coefficients on each face with the specified force vector"? This thesis is performed by using Fluent.

*The forces coefficients  (CA and CT) on blade surface were calculated by summing the dot product of the pressure and viscous force coefficients on each face with the specified force vector.


texts: What motor torque specs that is suited for a horizontal to vertical 90 degree lift?

texts:
I have this simple design to lift an access door, but I am looking for the motor specs to do this heavy duty job. This is a simple design, I have added some information of the time, length of the part and weight that I am looking to move.

the time factor that I am looking for this is, 3sec to 6 sec speed for the lift.
the door weight is 250lbs
The door length is 7’6”
Door access will move in 90 degree in a horizontal to vertical motion.

Everything is made of steel (frame and access door).
Looking for a motor and gear box that can handle that work in a daily basis.

If any more info is needed to help me out to find a motor that handle this work, i am available to provide it.


texts: Looking for a formula that states the stiffness of a composite

texts: I am looking for a formula that states the breaking point of a composite - How much pressure it can withstand before it 'snaps'. Specifically I am looking for a formula that states the materials stiffness.


texts: Why is the tension on mass m1 not 2T here?

texts:
I have named the strings as S1,S2 and S3 on diagram. T is the tension in the string.
If I draw the Free body diagram for m1, I think it should be 2T force on it but on internet  , it is just T. So , why do I think it is 2T?
Just imagine that when m2 is pulled , the pulley connecting mass m1 also gets pulled with 2T tension. Then , We have a fixed wall. So , the fixed wall can’t and would never move. So , it applies a T force on the string which travel to mass m1 and pulls it towards m2 direction. Now , till here the force is applied by string S1.
Then , when the pulley gets pulled. The string S2 also applied another T on the mass m1 which pulls it too. So , in conclusion . Total tension on the mass m1 is 2T.
So , where is it that I am going wrong ?
EDIT: Example of double tension or 2T .

So ,here. There is a 2T force applied on 6kg mass.


texts: If a system is globally asymptotically stable AND locally exponentially stable, can we say claim that it is globally exponentially stable?

texts:
I am taking a nonlinear control class. As we were discussing stability, we came across 'weaker' and 'stronger' stability conditions. For example asymptotic stability (AS) is stronger than stability in the sense of lyapunov (SISL), and exponential stability (ES) is stronger than AS. Then we across local and global definitions of stability.

The question then arises, if for some system we have a global form of some stability, say AS, and a local form of another 'stronger' stability for the same system, say ES, then which statement is actually stronger. Or does it so happen that global AS + local ES => global ES?


texts: ASCE 7-10 Wind Loading with roof overhangs

texts:
A textbook is attempting to convince me that the following figure:

Represents the generic zones for a Case B wind loading including roof overhangs based on the ASCE 7-10 Chapter 28, Part 2 (Enclosed Simple Diaphragm Low-Rise Buildings) procedure. This procedure addresses roof overhangs via footnote 8 on Figure 28.6-1:

"Where zone E or G falls on a roof overhang on the windward side of the building, use EOH and GOH f`or the pressure on the horizontal projection of the overhang.  Overhangs on the leeward and side edges shall have the basic zone pressure applied."

I absolutely do not agree that the figure is a correct application of the Chapter 28, Part 2 wind loading provisions for Case B wind direction. Please see below for ASCE 7-10 Figure 28.6-1 Case B zoning. You may observe that zones H, E , A and C correspond, while zones G and F have been flipped.

I would like to know if the textbook is not applying the wind provisions properly, or if I am missing something in the code? Thanks.

Assuming ASCE 7-10 Figure 28.6-1 is correct and footnote 8 applies, I believe the following (edited) figure shows the correct distribution.


texts: What is meant by the terms "low pass sensor" and "band pass sensor" in a course syllabus?

texts:
I am doing B.E. in Mechatronics Engineering. I am due to take a subject called 'Sensors and instrumentation'. So far I only have the syllabus for the course. I decided to do some reading in advance of the course starting.

The syllabus refers to "low pass sensors" and "band pass sensors".
When I web search for these terms I find many mentions of low pass filters and band pass filters, but nowhere on the Net are "low pass sensors" and "band pass sensors" mentioned.

Do the terms "low pass sensors" and "band pass sensors" have their own meanings and, if so, what are they?

I have been googling for the past five days for these two words but none of the results satisfactorily explained the meaning of 'low pass sensor' or 'band pass sensor'.


texts: can someone explain me what 1/8" or 1/16" means in the image below?


texts: Heating an uninsulated campground building with high ceiling and radiant floor in New England

texts:
We have a beautiful dining hall designed for summer camp use, which we want to keep warm enough for group activities in the winter.   The chosen heat is radiant floor, hoping to keep temperatures within a few feet of the floor comfortable.
How can we estimate whether we can accomplish this with a given number of BTUS per square foot from the floor?  The standard online calculators suggest 60 to 80 btus per square foot required for "poor insulation" and the high ceiling.  We want to use Warm Board for which I see no btu designation except a comparison around 16 btus per hour within 2 hours.  Thanks in advance for anyone with either the engineering or the practical expertise doing something like this.
Charlie


texts: How can I increase my processor's ADC resolution?

texts:
I have an Atmel SAM4S MCU with a 12-bit internal ADC.  I would like to achieve 16-bit resolution at a sample rate of 500 Hz.  The input to the ADC is fairly low-frequency (about 20 Hz max frequency content), and low noise (less than one 12-bit lsb RMS).

How can I achieve 16-bit resolution with this processor's ADC?


texts: Shortest recommended length of stainless steel tubing between fittings

texts:
Just a quick poll to anybody with experience putting together stainless steel tubing.  I have two swagelok fittings for 1/16" stainless steel tubing (0.02" thick), and just wanted to know what the minimum length of tube between fittings is (NOT including the length of tube inside the compression sleeves of the fittings themselves).  My guesstimate is that somewhere around half an inch of metal tube showing between the fittings is probably as short as you'd want to go.
Any best practices or recommendations based upon experience?
Thanks!


texts: Fluid mechanics - how to calculate flow distribution in piping network?

texts:
I am trying to build flexible, visual tool to calculate flow distribution through the piping network (mobile hydraulics).

I have root node of the network which has defined flow and pressure inputs.
Each node (of course including root one) can have multiple children - lines, connectors or outputs. Each branch ends up with outlet to atmospheric pressure.

So far I know that I have to calculate losses at each node going from the bottom of the tree, but losses are flow dependent... When I would have losses at each node, I could somehow (how?) calculate flow distribution going from the root node I would get flow to each child, then for each child flow to each of its children etc. Not sure if it helps, but I know the target flow for each output.

The main issue is probably the fact that there is no particular example as it suppose to be generic tool.

Any help?

I though it is pretty simple (I still believe it is) but I got stuck and cannot find the way out.


texts: Does good electrical conductivity imply good thermal conductivity?

texts: Typically materials which are good conductor of electricity are also good conductor of heat, and vice versa. Are there notable exceptions?


texts: I have made a CNC machine from CD drive and want it to use for engraving purpose. which laser would be best for this job?


texts:
I thought of an injector nozzle for a diesel engine with an alternate combustion chamber format (somewhat like a Heron combustion chamber), and would now like to get an estimate of the size of the opening for it.

The injector nozzle is basically a tube with a pintle inside it; the pintle has a flange at its end, outside of the tube and in the combustion chamber, which extends past the radius of the tube. When the injector is spraying, the fuel flows between the tube wall and pintle and is deflected outwards by the flange into the combustion chamber, forming a planar 'disk' of fuel between the piston and the top of the cylinder. The problem is to calculate an estimate of the opening $l$ between the flange and the butt end of the tube from a simplified description of the intended spray front.

I'll be using cylindrical coordinates $r,\theta,z$.

Design parameters:

$Q_0$, the mass flow rate in the tube
$r_0$, the flange radius (and thus of the nozzle)
$r_c$, the radius of the combustion chamber
$t_c$, the time allotted for fuel injection at max RPM.

Problem domain:

$S(r)=2\pi(r-r_0) l$ (spray front)
$V(r)=\pi(r^2-r_0^2) l$ (volume occupied)

Assumptions:

The fuel occupies the whole opening of the nozzle, doesn't diverge vertically and distributes itself uniformly ($\frac{\partial\rho}{\partial r} = \frac{\partial\rho}{\partial\theta} =\frac{\partial\rho}{\partial z} = 0$)
$Q_0$ is the flow not just in the nozzle, but also at the spray front ($Q_0=\iint_S \mathbf j\cdot d\mathbf S$)

So,

$$m(t_c)=\pi\rho(r_c^2-r_0^2) l=Q_0 t_c\\
\implies l=\frac{Q_0 t_c}{\pi\rho(r_c^2-r_0^2)}$$

I get $l$ = 1.34×10-5 cm = 134 nm for an application in a high-speed two-stroke ($r_c$ = 2.2cm, $r_0$ = 1mm, $t_c$ = 2×10-4s (more or less the time taken to traverse 10°, my estimate of the injection duration, at 8000 rpm), $Q_0$ = .8 g/s), which is absurdly tiny.

Even though the order of magnitude of the result comes mainly from the injection duration, I don't trust my results and think that it comes from the assumptions I made. On top of that, I don't know how to take into account the end of injection prior to combustion, so I assumed the injector stops injecting at combustion.

Is there anything wrong with the analysis or calculation that I did?


texts: How do I interpret this DC motor datasheet?

texts:
Problem summary:
I need to produce about 0.289 Nm with a rack and pinion system and compress 24 mm of a 110 mm x 21.6 mm, 0.99 N/mm steel spring.
I thought about using with a 10mm pitch diameter gear with ten 1mm gear modules at an angular velocity of about 15rpm (or 1.571 rad/s).
Ignoring the efficiency losses, and the friction of the gear system a 12 V DC motor consuming 37.8 mA would do the job:
$$E \cdot w=0.454 W$$
$$ V=12 V \quad I =\frac{(E \cdot w)}{V}=37.837 \mathrm{~mA}$$
(I assumed the torque on the gear to be the same as the work done by compressing the spring and set this to be the electrical power consumed.)
However, in the real world, things are more complicated and I have been oriented here. To choose a motor expecting a final efficiency of 25% and, thus, expect using about 4 times more current.
Motor specs:
After some research I found a DC motor with the following specifications:
Supply Voltage                  12 V dc
DC Motor Type                   Geared
Output Speed                    14 rpm
Shaft Diameter                  6mm
Maximum Output Torque           59 Ncm
Gear Ratio                      300:1
Dimensions                      39 (Dia.) x 83.2 mm
Current Rating                  180 mA

My questions:
Because the output speed is about the same as my rack and pinion uses, I imagine my operating conditions will be the same as the graph Gear ratio 1/300. Is that correct?
Thinking back now, I assumed the torque on the gear to be the same as the work done by compressing the spring and set this to be the electrical power consumed.That's wrong, isn't it?
$$Tangential force \cdot \frac{( pitch diameter)}{2} = torque$$
so if I need about 24N of linear force on my rack, the torque will actually be about 13 Ncm instead of 29 Ncm like I first thought.
In that case, is this motor I found still a good choice?
Any corrections, comments and/or suggestions are welcome!
For a more thorough description of my problem go to here


texts: Is there an upper limit to how fast a self balancing one wheeled vehicle can become while also being able to safely stop?

texts:
I've recently come across pictures of segway/hoverboard like self balancing motorcycle type vehicles that were supposedly able to become as fast as a street legal scooter. I kept wondering how they would do an emergency brake from top speed.
If the wheel just blocked you would slam face down into the ground. So of course the vehicle had to try to lean the driver as far back as possible to use their weight for braking. But even then with enough speed and a subsequent brake my intuition tells me the driver would still just be lifted and slammed into the ground.
I really just wondered if my intuition is right and the top speed these things can go is reached quite early or if I am mistaken because I'm missing the insights in how these things work physically.


texts:
I am trying to understand the meaning of 'Trip force' of keypad dome on these pages, and this, and this.
Example: Trip Force: 14.1 oz. [400g]
Does it mean that when I put a mass of 400g on this dome then it will be depressed?
On another website this parameter has a different name 'operating force' and is given in units of gram-force (gf).
Does these 2 websites show same parameter with different names and units or these are different?


texts: Connect Redis which is installed on same network's different machine's VMWare's ubuntu

texts:
I have a laptop (windows OS) which is connected to a wifi network.
On same wifi network, there is another PC (Windows OS). In that PC, I have ubuntu installed inside VMWare. And in that ubuntu, I have installed Redis.
How do I access that PC's VMware's Ubuntu's Redis from my laptop?


texts: Calculating optimal angle on a rolling pulley wheel, which holds weight, on a horizontal cable

texts:
The 40 kg load on the rope accelerates from 0 to 50km / h in 6 seconds.

The rope is tightened with a force of 500kg while the whole assembly is on it.
The middle pulley is driven by a dc motor.

I want to calculate the optimum angle between the middle (drive) pulley and the end pulley (pulley 2 on the picture) for driving without slipping or without too much load on the motor.

An angle between two pulleys that is too small would cause slippage on the rope, while too big angle would cause a higher load on the motor, and a higher power consumption.

The pulleys are made of aluminum and the rope has a coefficient of friction of 0.1

The current angle between the two pulleys is 15 degrees, as seen in the picture.

Motor spec are: 24V, 3560 oz/in stall torque, 4.3 HP

If you need more information, please ask.


texts: Flow Simulation for Laminar Flow in Annular Gap?

texts:
Would anyone be able to run an air flow simulation through the following geometry at 100 cc/min? I'm curious if any dead spots occur and if the geometry of the annular gap will produce laminar flow.

Dimensions are in inches.

Reynold's number analysis:

Hydraulic Diameter* = 0.003 in = 7.62E-5 m
Absolute Viscosity of Air at 20.2C = 1.983E-5 N-s/m^2
Density of Air at 20C = 1.293 kg/m^3
Mean Velocity =
   => A_cs = 0.004089 cm^2
   => Q = 100 cc/min
   => V = 24455.9 cm/min = 4.076 m/s

Therefore,

Re = (rhoVD)/nu
   = (1.293 kg/m^3 * 4.076 m/s * 7.62E-5 m) / 1.983E-5 N-s/m^2
Re = 20.25


texts: How can I implement S-curve motion profile on mobile robotic platform / wheeled robot?

texts:
I want to plan a robot's motion according to an S curve profile. I am following the article mention below, which contains basics related to S curve motion profiles in robotic platforms.
https://www.pmdcorp.com/resources/type/articles/get/mathematics-of-motion-control-profiles-article
For this purpose I am using one sigmoidal function,
https://en.wikipedia.org/wiki/Sigmoid_function
Is there any other equation or any other method available to achieve this type of S curve profile.
I use python programming language, are there methods available in python other than the  Boltzmann sigmoid function?
Also, what are the basic steps which I have to follow in order to implement S-curve motion profile on a robot?


texts: Mechanical Engineering- Modeling contact in Abaqus

texts: I have simulated a 2D model in Abaqus which indicates 2 main part, first a sector that represent as wheel and, second a rectangular that represent rail. the wheel and rail are in contact and wheel should rotate and move from left to right. there is a vertical small crack in middle of the rail to studying the result of contact on fracture mechanics. my model has been completed, and in the 1/10 of total time good result has been achieved but after that the stress distribution is completely wrong and although the contact seems to exist, the stress is almost zero. Any guide, comment or advice would be appreciated. thank you


texts: Angular Velocity of motor shaft as function of Angular Position

texts:
I have a set of shafts that need to be rotated at a high frequency (~1000 RPM) but not at a constant speed. That is to say, the angular velocity of the shaft needs to be a periodic function of the shaft's angular position.

This bizarre predicament has arisen in the context of operating an unsteady, transonic wind tunnel. We have a set of vanes whose angular positions determine the Mach number of the flow through the tunnel's test section. For the research we hope to conduct, the test section Mach number will have to oscillate in a specific pattern as a function of time. Technically, there are several ways we could modify the tunnel's design to accomplish this. We are looking into all of them, but in theory, having a motor whose angular velocity is precisely controlled as a function of its angular position would be the most ideal solution to our problem.

I'm no expert in electrical engineering. I understand that some motors, like servomotors, are made to rotate at any desired speed within their operating range, and that their speed can be precisely controlled by a closed-loop feedback system. Does this mean that I might be able to program a servomotor to rotate in such a way that its angular velocity is constantly changing as it rotates, even at average rotation speeds of up to 1000 RPM?

If so, what type of equipment might I need to do this? Is this what a Variable-Frequency Drive (VDF) is for?

If a servomotor is not appropriate for this task, what type of motor might I need?


texts:
At the end of the James Bond movie View to a kill, the aeroplane runs out of fuel - both the propellers stop and the plane glides.  There are holes at the bottom of the tank so all the fuel has drained out.  The plane then glides into the mountain and blows up in a typical movie spectacular fireball.
Aeroplane fuel is typically kerosene.  Kerosene is one of those liquids that needs a fine spray for it to be combustible.  If I drop a lighted match in liquid kerosene, the match will go out.
As a kid, I've dropped a match in an empty kerosene can and nothing happened.  I know now that it was a silly thing to do but I was a 10 year old who didn't know any better.  If it was petrol, it might have blown up in my face.
If it was a pressurised system, then the pressure would be neutral because of the holes in the tank.  If the tank is empty, would kerosene exist in vapour form within the tank?
Is it still possible for the plane to blow up or would it just crash and fall to the bottom of the hill?


texts: I am working on a project using springs. What is the maximum load per deflection of springs available in market?


texts: We know that time varying magnetic field produces voltage in a coil. But what if the wire forms a semicircle or an arc instead of a complete loop,  will such magnetic field produce voltage between the ends of the wire?  If yes,  what is the formula to calculate the induced voltage?


texts: How to let a "screw" leave and reenter a thread

texts:
The setup

Consider a cylinder inside another cylinder (placed with their symmetry axis horizontal).

The inner cylinder is about Ø100 mm in diameter and a centimeter or two in lenght/thickness. On the perimeter there is a thread. This cylinder is fixed in rotational motion, and cannot rotate.

The outer cylinder is much longer. It has a thread on the inside through half of its' lenght or so and this thread fits with the inner cylinder thread.

The question

Now, when rotating the outer cylinder, the inner cylinder will move back and forth (the inner cannot rotate but can move translationally).

My issue is that the outer cylinder might rotate many revolutions (it follows a bicycle wheel), and therefor at some point the inner cylinder will move out of the thread of the outer cylinder.

Is there a mechanical and smart method to let such a cylinder leave and reenter the thread of the outer cylinder? E.g. the outer cylinder would rotate in one direction untill the inner cylinder leaves the thread. Then when the outer cylinder is reversed in rotational direction, I want the inner cylinder to reenter the thread and start moving the opposite way.


texts: Compression members with moment to BS 5950-1:2000

texts:
According to clause 4.8.3.2 the cross-section capacity for non-slender section is:
$$\frac{F_c}{A_g p_y}+\frac{M_x}{M_{cx}}+\frac{M_y}{M_{cy}}\leq 1 \qquad (1)$$

According to clause 4.8.3.3.1 simplified method of member buckling resistance, the following relationship should be satisfied:
$$\frac{F_c}{P_c}+\frac{m_x M_x}{p_y Z_x}+\frac{m_y M_y}{p_y Z_y}\leq 1\quad (2)$$

Let's consider a beam-column with class 1 section (doubly-symmetric) under uniform moment (so that the equivalent moment factor $m_x = m_y =1$ according to Table 26) and axial compression, and ignore lateral-torsional buckling. In this case, equation (2) is always critical than equation (1), because $P_c \leq A_g p_y$ and $p_y Z_x \leq M_{cx}$, $p_y Z_y \leq M_{cy}$.

My questions are:

What is the use of equation (1), or clause 4.8.3.2, if buckling resistance is always more critical? Is there any case that equation (1) is more critical?
If the member is under biaxial bending but without axial force, i.e. $F_c=0, M_x>0, M_y>0$, is checking equation (2), or clause 4.8.3.3 still required?

I understand that the simplified method is at the cost of conservatism, but making one criterion obsolete seems too much to me.

Thank you for your time.

Edit 1:

I am aware of that the equivalent moment factor can be taken as minimum as $m_x = m_y =0.4$ for double curvature member, which should make equation (2) less critical if the axial compression is not large. However, I would like to confine the discussion in the case of single curvature and uniform moment.
I welcome any example that a non-doubly-symmetric class 1 section has $p_y Z_x \geq M_{cx}$, $p_y Z_y \geq M_{cy}$.


texts: What is the unbraced length of the compression portion of an X brace?

texts:
In the diagram below, the compression member is $AC$. What is its unbraced length for determining buckling capacity? This also matters because certain codes put limits on the maximum value of $\frac{KL}{r}$ for bracing members.

I know that the conservative answer is to consider the entire length, AC. This can be too conservative when lots of braces are used (total weight of steel increases). It can also be conservative if the actual compressive force is low enough that a member size is increased solely to meet the $\frac{KL}{r}$ requirements.

I can justify to myself that the tension member braces the compression member in one direction (in the plane of the page), but can the tension member be considered to provide bracing in the orthogonal direction (in and out of the page)?

There are two reasons why I think this might be possible:

The tension brace provides resistance solely from being present. (i.e. something is better than nothing)
The other brace is in tension so it will provide additional restraint similar to a bow string.

Note: Some codes have requirements that a brace be able to withstand 5% of the axial force in the member being braced. I would think that this would be the lower limit for restraint coming from the tension member.


texts: multidimensional function for object description

texts:
I want to simulate a bow tie antenna and build it up with a function. so far i have managed to create a piece of cake with sin and cos.
Now I would like to expand the function and round off the corners, but I don't know how to do it mathematically. does anyone know how to create such a function?
I have attached a picture of the current state.


texts:
I was wondering, basicly every radio-transsmission works with electromagnetic waves which travels at the same speed whether I modulate the information with a low frequency or high frequency such as done with LI-FI.
What makes Li-fi faster? what makes any wireless transmission faster/slower if eventually I send my information with electromagnetic wave which travels at the same speed?
What makes lifi special?


texts: How to resolve file space issue on CDAQ Controller with Labview Test System?

texts:
Question: I am currently encountering Hard Drive Memory space issue to store file on a National Instruments based CDAQ Tester. I am using Labview  2013 SP1 and have to all the software load in the CDAQ Controller.  Some of the basic specifications for the CDAQ are as follows

Processor: Intel Atom 1.33GHz Dual Core
Controller OS: Windows Embedded Standard 7
Hard Drive Memory Size: 16 GB
Number of Slots: 8

Background: I am trying to control and acquire electrical measurement data from a Keysight 34461A digital multimeter via GBIP using Labview and CDAQ.


texts: What lining design holds better for a tunnel? Spiral lining or cylindrical lining?

texts:
Hy everyone :) I don't know much about structural engineering, maybe spiral lining and cylindrical lining are not the proper terms - but take a look at the pictures below to understand what i mean.

I need help to form some intuition about which one of this 2 is better for lining a tunnel. I want to know specifically about earthquake resistance  And also other important factors which play a role in choosing between this 2 designs - factors i'm not aware of right now.

I couldn't find a proper spiral lining image - this just gives you an idea - but let say it was a proper lining with joints and such - like the cylindrical one has.

Assuming that the spiral components will be connected in the most practical way possible - and assuming they have the same wall thickness, same concrete composition, etc..  which one is better?

Will they behave the same under stress ? Or the cylindrical one is better ? But why?

And also i want to understand how a cylinder compares with this shape in terms or resistance..

Which one of 2 geometries ( cylinder or arch ) is most effective for preventing damage in case of earthquakes, or just in general ?

Explanation: - why i'm interested in this?

I want to find the drawbacks of spiral lining. I think that from a construction perspective spiral lining is better - because can be constructed continuously.

By contrast, if your TBM moves fast enough - the cylindrical lining requires stopping of the hole machine - to insert each segment all at once. And then another cycle begins. This takes valuable time. Time that can be used for drilling.

For increasing tunneling speed - i think spiral lining has this amazing advantage - will not require stopping.. you build as you go, smooth and continuous.

But i don't want to trade safety for tunneling speed. I want to understand if spiral lining is actually viable.

Maybe i'm wrong about this stopping, but that's another topic :) Let's keep this discussion  only about geometry for now.

Thank you, and have a nice day!

Disclaimer:
With input from Solar Mike, i will add this disclamer: neither of this images are mine,
Tunnel image is taken from here: http://www.sciencedirect.com/science/article/pii/S1674775515001195
Spiral image is taken from here: http://www.sunshinecoastformatubesupplies.com.au/spiraltube-steel/


texts: what is the role of potentiometer in this circuit?

texts: Below is the circuit for a shadow alarm. Please tell me the role of potentiometer(VR1) used in the circuit.


texts: For building something like a big building or a parking garage, there is a need for a large flat surface of concrete. Wondering how they make the dirt and the concrete flat. It's hard to make a tiny flat surface at the beach in sand let along thousands of square feet. Wondering what sorts of machines tools or techniques are used at a high level.


texts: Figuring out how much torque dc motor will need to run at a certain speed. (E-skateboard project)

texts:
Suppose I want to purchase a DC motor online, how can i determine how much torque my motor will need to run at a certain speed? I.e. 15mph

This is for my electric skateboard project and the load on top of the board will be 140 lbs.

Really having a hard time figuring this out and was hoping someone can share their knowledge.


texts:
Curious as to what extent a shaft/pin will will follow a bore when being pressed in.
Considering fixturing for a project to hold a shaft straight, but most of what I have seen, the shaft will self align to an extent(as long as the angle is not too much).
Is there anything out there that says you can expect a shaft to align with the bore as long as the pressing angle is not more than x?


texts: Cutting flattened out "threads" to prevent small-scale slipping

texts:
I have a product where we transmit quite a lot of shear force through a small bolted join. On our current design the contact area is about 10mm², the bolt is M2, and the force is 45N, and it works quite well. But now we want more, the requirements are:

We want to go up to 300N, in either direction along one axis.
No sliding between the parts, even at the micron level.  Elastic deformation of a few microns is OK though.
Both parts are grade 4 (pure) titanium.
The top of the lower part must be flat, nothing sticking up when the second part is removed. Shallow holes are OK.
Ideally, the position of the top part in the direction of the force should be adjustable. Preferably continuously, but failing that then in about 0.5mm steps.
The join can be made and un-made about 100-1000 times over the life of the product. By a competent and careful operator.

As is, at 300N the joint as is slides around all over the place.  I could go up to a M2.5 machine screw, or maybe M3 at a pinch, but some back-of-the-envelope scribbling suggests that won't be enough. I could specify a removable epoxy, but can't find one strong enough. So I thought about mechanically keying the two parts so that they cannot slide.

I could cut both surfaces with a zig-zag profile, like a screw thread.  In fact I guess it might be possible for a machine shop to do that with an M3 thread cutting mill (if I pick the right profile) or the corner of an end mill (for a 45 degree profile).

I've not seen such a thing before, at least not at this scale.  Does it sound like a good plan? What should I watch out for?  Is there an easier option I have missed?

Here's a rough sketch of what I mean:

Left: as we have it now, for 45N. Right: What I mean by zig-zag profile.  I've sketched it as if it were an M3 that's been "unrolled" onto the yellow part.


texts: What are the technical obstacles for using flywheel-based regenerative braking on bicycles?

texts:
Is it possible to convert the energy you would normally lose when braking your bicycle to rotational energy by attaching an extra wheel which would start to rotate once you use your brakes? E.g., when facing a red light after riding down a hill.

If you could restore that energy, you could regain part of your velocity without as much effort after stopping at the light.

I am quite sure I'm not the first one who had this idea (as I heard about some projects trying to achieve the same thing but then with cars) so I wonder what the technical difficulties are and why I have not seen bicycles like this on the road?


texts: How do I configure g-simple so it does not use G81 code?

texts: I have a CNC that does not understand the G81 code for drilling. G-Simple looks to be configurable but I am finding it difficult to find information on it. It looks to have a "USE" command with a "G81" parameter but no idea how to make it not use this command and just drill a hole by constructing the movements itself. Just a simple CNC so not too bothered about the timing etc.


texts: Valve/Filter allowing through gas only, no liquid

texts:
I need to devise a way to ensure only NG passes through a pipe, and no condensates or other liquids. It is ok to shut down the pipeline if liquids would be detected. The dimensions involved are small and space limited.

Is there a valve which shuts if liquid starts passing through but stays open for gas? Aside from a involved solution with a trap with a sensor attached, is there any other way to solve this?


texts: I can roughly understand the working of an axial flow gas turbine i.e. the fluid moves over the blade and gets redirected, its whirl velocity component changes and the blade is pushed in the opposite direction.But I couldnt understand the working of a table fan or an aircraft propeller.I know that its the opposite of an axial flow gas turbine but couldnt really imagine it.Please explain the principle?


texts: Building bed out of 8020 aluminium extrusion

texts:
I want to build a rock and roll bed out of 8020 aluminium extrusion, in order to avoid the bother of welding steel pipe. However, I don't have much of a 'feel' for how strong this stuff is. Will 20x20mm T-Slot extrusion be strong enough to support the weight of two people (in a simple frame like the one in the link) or would I need to go for a thicker strength?

Many thanks!


texts: I want to design a leakage detection system along the pipeline that will use differences in pressure of flowing liquid (change in pressure between two points). Which sensor I should use?


texts: How to choose type of output from a water level switch?

texts:
I need to buy a level switch for a quench tower water drainage system. I intend to use its output directly to open a solenoid valve to drain the tank when the switch detects water and close it afterward when the water recedes. I have identified make and model of a level switch I think is good. But the manufacturer provides multiple types of electrical outputs. It would be great if someone could advise on which of the following type is best for a simple level switch - solenoid valve circuit.

Relay
NAMUR
Transistor
2-wire

P.S: I am a newbie regarding electrical stuff. I'll consult a friend who will help me to design the circuit, but I just need to place the order for the level switch.


texts:
I recently bought two 12 V DC motors from Amazon. After I received them today, I tried testing them. One of the two motors run fine but the other motor shows erratic behaviour. It gets very hot within 10-15 seconds of running, and then stops. It also doesn't run as fast as the other motor.

During testing I directly connected a 8.6 V LiPo battery to the motor and it had sparks coming out of it. I then soldered wires to the motor's contacts and added another cell to the pack making it 11.98 V. The sparking stopped, and the motor started working, but I noticed this behaviour. There's also very high resistance when I try to rotate the motor shaft by hand, while on the other motor, it turns very easily.

I'm not sure if I damaged my motor, or if it was already damaged when I received it. How can I determine the cause of the problem?


texts: Not a good idea to rub two of the same material against each other?

texts:
I've read that it's not a good idea to rub two surfaces of the same material against each other, e.g., plastic against plastic, metal against metal. Plastic against metal is preferred. Why is this the case? Is it because that the coefficient of friction is higher for same materials?

According to this site, steel-steel gives 0.5, plastic-plastic gives 0.3, but plastic-metal gives 0.25.

Suppose two rollers rotate and rub against each other. Will it be better for one to be made of metal and one of plastic?


texts: How are earthfills not eroded before they are overgrown with grass?

texts:
Almost every railroad and vehicle road landfill has its slopes overgrown with grass which is quite good at preventing erosion. However it takes some time (a year or more) for the grass to grow and emit enough roots to form a reliable mesh that would hold the earthfill surface and rains can cause enough damage to the earthfills before grass grows and becomes efficient against erosion.

How are earthfills not eroded by rainfall before they are overgrown with grass?


texts: Transfer Function of Spring-Damper System

texts: Given the spring-damper system below where $x_i$, $x_i$, and $y_i$ are position values, how do I find the transfer function $\frac{X_o(s)}{X_i(s)}$? Wouldn't it require mass? I tried neglecting the masses in the equation but it zeros out the acceleration term and does not work. Any diea?


texts: How to calculate bearing loads in a two stage helical gear box?

texts:
Here P, Q, R, S are the bearings and G1, G2, G3, G4 are four helical gears.
The gear forces tangential(Kp), Axial(Ka), Radial(Kn) are known.
All the distances are known. The forces acting on bearing are radial on non locating bearing and both radial and axial on locating bearing.  P, R are non locating bearings. Q, S are locating bearings.. Fh and Fv are components of radial force on bearings and Fa is the axial force... How to calculate Fh, Fv and Fa for each bearing shown??

I have calculated all the gear forces but i am confused about the calculation of the forces. will be solved using moment equations?

Thanks in advance..


texts: What happens to the sedimentation collected in water treatment plants?

texts:
The Washington DC water treatment plant appears to use sedimentation tanks for both treating water before consumption and for treating sewage that is then discharged.

My question: What happens to the sedimentation after it is collects? None of the articles that I have read discuss this.

It seems to me that the sediment in the water source won't necessarily be toxic, but I suspect that the sediment in the sewage contains a brew of toxic metals and organics. So does that need to be treated as toxic waste? Is the source sediment used for fertilizer, or is it just sent to a landfill? Is there an issue with dust?