Difference Between Gyroscope and Gymbal

GYROSCOPE

A gyroscope (from Greek γῦρος gûros, “circle” and σκοπέω skopéō, “to look”) is a spinning wheel or disc in which the axis of rotation is free to assume any orientation by itself. When rotating, the orientation of this axis is unaffected by tilting or rotation of the mounting, according to theconservation of angular momentum. Because of this, gyroscopes are useful for measuring or maintaining orientation.

Image Source : wikipedia

Gyroscopes based on other operating principles also exist, such as the electronic, microchip-packaged MEMS gyroscopes found in consumer electronics devices, solid-state ring lasers, fibre optic gyroscopes, and the extremely sensitive quantum gyroscope.[citation needed]

Applications of gyroscopes include inertial navigation systems where magnetic compasses would not work (as in the Hubble telescope) or would not be precise enough (as in intercontinental ballistic missiles), or for the stabilization of flying vehicles like radio-controlled helicopters orunmanned aerial vehicles, and recreational boats and commercial ships. Due to their precision, gyroscopes are also used in gyrotheodolites to maintain direction in tunnel mining. Gyroscopes can be used to construct gyrocompasses, which complement or replace magnetic compasses (in ships, aircraft and spacecraft, vehicles in general), to assist in stability (Hubble Space Telescope, bicycles, motorcycles, and ships) or be used as part of an inertial guidance system.

GYMBAL

Gimbal lock is the loss of one degree of freedom in a three-dimensional, three-gimbal mechanism that occurs when the axes of two of the three gimbals are driven into a parallel configuration, “locking” the system into rotation in a degenerate two-dimensional space.

The word lock is misleading: no gimbal is restrained. All three gimbals can still rotate freely about their respective axes of suspension. Nevertheless, because of the parallel orientation of two of the gimbals axes there is no gimbal available to accommodate rotation along one axis.

A gimbal is a ring that is suspended so it can rotate about an axis. Gimbals are typically nested one within another to accommodate rotation about multiple axes.

They appear in gyroscopes and in inertial measurement units to allow the inner gimbal’s orientation to remain fixed while the outer gimbal suspension assumes any orientation. In compasses and flywheel energy storage mechanisms they allow objects to remain upright. They are used to orientthrusters on rockets.[1]

Some coordinate systems in mathematics behave as if there were real gimbals used to measure the angles, notably Euler angles.

For cases of three or fewer nested gimbals, gimbal lock inevitably occurs at some point in the system due to properties of covering spaces (described below).

Difference Between Gyroscope and Gimbal

While there is a connection between a gyroscope and a gimbal, the fact is that the two devices are not identical. In fact, the gimbal is an integral part of the gyroscope. Without the use of the gimbal, the gyroscope would be much less effective.

The best way to understand the difference between a gimbal and a gyroscope is to define the nature and structure of both devices. Essentially, a gimbal is some type or base or ring that is mounted on an axis. The gimbal allows an object that is mounted on the base to move freely in any direction, so that the object remains in a horizontal position regardless of the angle of the base. This freedom of movement makes the gimbal an essential element in many devices that are used to measure momentum and directional orientation.

 

A gyroscope is one of the objects that makes efficient usage of the gimbal. Gyroscopes are composed of a rotor that is configured to spin around a single axis. Surrounding the rotor are one or more gimbals that help the device to maintain proper pitch and thus help to maintain inertia. This means that the gyroscope will often employ the use of both an inner and an outer gimbal in order to function properly. The outer ring of the gimbal configuration pivots around the axis and helps to maintain the level of force. The inner gimbal is mounted within the outer gimbal and pivots on an axis that maintains a consistent perpendicular relationship with the axis of the outer gimbal.

The function of the gyroscope would not be possible without the presence of a gimbal. One excellent example is with aviation. Because the gyroscopes are used to monitor or adjust the roll, pitch, and yaw of angles during flight, the devices are essential to maintaining the force and directional control needed to successfully fly from one location to another. Without the balance created by the gimbal, the gyroscope would not provide this type of data and would serve no useful purpose.

SOURCE :WIKIPEDIA,  WISEGEEK ,

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Composite – Prepreg Basics

Take some composite reinforcement, such as carbon fiber mat, lay it out and saturate it with a thermoset resin. What you have then, in the uncured state, is prepreg. Sounds simple? Well, just think about the practical problems – for example shelf life. Resins cure once they have the catalyst or hardener has been added, so how is curing of a prepreg prevented?

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Image Source : EASYCOMPOSITE

There are two approaches, both aspects of the same solution – thermal control.

Prepreg resins are specially formulated so that they cure very slowly or not at all at room temperature. If they are then stored in refrigerated conditions then curing can be halted completely.

The length of time the prepreg can spend at room temperature before partial curing prevents practical use is known as the material’s ‘out life’.

The freezer storage time of a prepreg without affecting practical use when thawed-out is known as its ‘freezer life’ or ‘shelf-life’.

Complex Curing

The second approach is to cure the shaped prepreg product (say a rowing scull) at a high temperature – in a pressurized oven. These special ovens are called autoclaves. Clearly there is a practical limit to the size of oven that can be economically built. The largest of autoclaves can cure massive sections of airplanes.

The curing process can be complex. Here are the instructions for curing a specialized commercial prepreg used for tooling:

30 minutes at 300°F/150°C, then 4 hours 350°F/177°C followed by 6 hours at 383°F/195°C

This kind of process is hardly practical for the average DIY person building a skateboard, but nevertheless prepregs can be used in the home workshop – and the kitchen too as a domestic cooking oven can be used for some home projects.

Voids

When multiple layers of prepreg are required in a structure, then there is a risk of voids being introduced between the layers. For example, aerospace requirements dictate less than 1% void content in composite structures and components.

Vacuum bagging is used during manufacture of the prepreg, but to minmize inter-layer voids then then lamination should also be vacuum bagged if void content is a concern.

Why Use Prepreg?

The convenience of using prepreg is considerable. Prepreg is easy to handle and depending on its ‘tackiness’ it is to place in a mold and sticks in place.

It can be bought ready to use, so there is no resin mixing and no ‘wetting-out’ to be done. This improves the quality and consistency of the finished product (saturating the mat with resin – ‘wetting-out’ – is usually done using a vacuum bag by the manufacturer). For example, aerospace requirements dictate less than 1% void content in composite structures and components. The result is that in the finished product surface blemishes are almost entirely eliminated and weak spots due to resin voids are likewise minimized.

Why People don’t use Prepreg

The key reason is practicality. This can be because the structure is too large for an autoclave, or simply than it is impractical to keep the material in a freezer and on-site mixing is necessary.

Also cost, prepregs generally cost more then the same dry fiber and a similar liquid resin.

In some applications – for example in satellites – any void at all can cause cavitation damage when the structure is itself used in a vacuum and the pressure in the void blows out into space.

The Future of Prepreg

The key problem with prepreg has been the need for the autoclave, making it uneconomic for large structures. However, research into Out-of-Autoclave (‘OOA’) techniques is now starting to change the picture. Using Vacuum-Bag-Only (‘VBO’) curing processes at near-ambient temperatures, we should soon have the technology to make prepreg economic and practical for building airplanes (as opposed to building components).

SOURCE : COMPOSITEABOUT.COM

Using CFD to predict flow-generated noise and other Aeroacoustic effects

Environmental noise can have significantly adverse effects on our everyday lives, including interference with communication, sleep disturbance, learning acquisition, annoyance responses, performance effects as well as our health through cardiovascular and psycho-physiological effects.  Product designers and engineers at the world’s most innovative and successful companies have recognised this fact, and incorporate effective noise mitigation elements into their product design process.

 

When we mostly think of noise harshness, we tend to think “loud and up-close”. Doubling the distance between yourself and the source of a noise will effectively cut the intensity of the sound by 6 dB; i.e. the noise will only sound about 25% as loud. However, annoyance is the most widespread problem caused by environmental noise and occurs when we are constantly exposed to a noise source, regardless of the intensity. Annoyance reflects the way that noise affects daily activities. People’s social circumstances, their culture and the environment in which they live can all determine the degree of perceived annoyance for a given noise level.

acoustics-intro2

Aeroacoustics techniques in engineering were pioneered by engineers investigating noise generation and acoustic signatures in military and defence applications, particularly for detection and survivability. In civil industries, aeroacoustic noise is increasingly a hot topic for engineers working in ground and air transport, industrial machinery, concert hall acoustics, environmental conditions, as well as complex fluid-structure interactions (i.e. vibrations). Our increased awareness of the adverse effects of noise annoyance has led to aero-acoustically generated noise (aka flow generated noise) being identified as a critical design variable in modern engineering design. This in turn has led to an increase in the research efforts aimed at numerical prediction of aerodynamic noise, often dubbed Computational Aero-Acoustics (CAA).

 

Computational Aeroacoustics (CAA)

 

CAA is capable, in principle, of modelling both the aerodynamic sound source and the propagation to the far field. Fluid flow at the source and sound wave propagation both fall under fluid phenomena, thus they are solved using the CFD governing equations. The principle constraint in direct CAA is that the computing resources required to model the entire flow domain (i.e. from the source to the receiver) often makes this approach impractical. Thus, practical problems solved using CAA are therefore more likely to be when:

 

  • Frequency range is between 20 to 20000 Hz. Acoustic timescales are often orders of magnitude greater than turbulence time scales. Hence, simulation needs to be run for an extended period of time, i.e. large number of time steps.
  • Domain can extend from sound source to the receiver. Therefore, this approach is currently not practical for far-field sound prediction such as aircraft noise being heard on the ground.
  • Magnitude of acoustic pressure is much less than the hydrodynamic pressure. Therefore, CAA requires the use of very high order discretization schemes to propagate sound over large distances.

acoustics-intro

You can see that the advantage of CAA is that it is simple to implement, however it does require large meshes and extensive transient simulations. Proper resolution of the tonal and broadband noise sources also dictates the use of advanced scale-resolving simulations for turbulence effects. CAA can also account for flow-sound coupling, i.e. cases where the sound has a backward effect on the flow.

 

For these reasons, direct CAA is generally not applied to most industrial engineering problems. Fortunately, there are alternative methods by which a reasonable solution of the sound propagation may be obtained with today’s modern hardware:

 

Broadband noise models

 

We all know that unsteady CFD simulations are time consuming, but many do not know that steady RANS results can still provide a great deal of useful & acoustically-relevant information (including mean velocity components/pressure, turbulent kinetic energy, turbulent dissipation, etc.). This information can be used to estimate turbulent or broadband sound, which can in turn be used to identify the primary sources of noise in our CFD domain (such as an automotive A-pillar and wing mirrors).  ANSYS CFD tools offer a number of broadband sound models which only require steady RANS results to provide a useful quantification of the noise source levels, allowing designers and engineers to quickly rank their designs (by acoustics performance) and eliminate geometry that acts as large potential sources of noise.acoustics-intro21-300x164.png

Sound Source-Propagation Methods (SSPM)

 

Remember that sound generation and propagation are independent phenomena in most cases. They happen at vastly different scales, i.e. Flow pressure ~ kPa; acoustic pressure ~ mPa. Turbulence length scales ~ µm; acoustic wavelengths ~ m. Turbulence time scales ~ µs; acoustic time scales ~ ms.

 

Therefore, we can consider the problem domain in two distinct layers: The flow field (governs sound source and generation through Navier-Stokes equations) and the acoustic field (governs sound propagation through the wave equation). This provides us with the opportunity to reduce our computational efforts significantly which opens up a wider variety of applications. Connection of the two segregated components (i.e. source and propagation) is achieved using an acoustic analogy. Generally the tensor term in the acoustic analogy represents the sound source calculated by the CFD simulation. Once CFD provides sound source information, the problem reduces to solving for sound propagation.

acoustics-analogy

ANSYS Fluent provides features to compute sound propagation using the Ffowcks-Williams and Hawkins (FHW) boundary element method (BEM), meaning it relies solely on unsteady pressure information at the domain boundary. Since this approach is much less computationally expensive, it provides considerable benefits to aerodynamic and hydrodynamic far-field noise scenarios as the CFD domain is only required to encompass the object generating the noise source (to calculate unsteady pressure fluctuations). ANSYS Fluent additionally offers coupling to other BEM/FEM acoustics tools, if real geometry effects, acoustic impedance or vibrating structures are to be considered.

 

 

 

Acoustics and Aeroacoustics training – Melbourne, August 10-11, 2015

 

acoustics-fea3

This advanced training will provide you with everything you need to confidently tackle acoustics and aeroacoustics problems, including:

  • A background on the theory of acoustics and aeroacoustics
  • Details on other important physics such as transient turbulence modelling
  • Details of the different types of FEA based acoustic simulations, including modal, harmonic, transient and vibro-acoustic analysis
  • Examine noise sources, perforated material and far field processing
  • Details of CFD-based aeroacoustics simulation techniques including direct CAA methods, FWH (segregated source/propagation methods, boundary element methods) and stochastic noise generation / broadband noise models
  • Overview of coupling Mechanical with CFD tools for aero-vibro-acoustics

SOURCE : COMPUTATIONALFLUIDDYNAMICS.COM

GLASS FIBERS AND FIBERGLASS

Selecting Composite Materials

Fiber reinforced composites are common, but do you know how to select the different types of fiber and resin used?rte

Comparing and Choosing Composite Materials

Composite materials are broadly defined as those in which a binder is reinforced with a strengthening material. Here we take a look at the pros and cons of the components: the resins and the fibers used to strengthen them.

Resins

Most modern composites share a common bond – almost literally. The binding resins – the chemical matrix in which the reinforcing fibers are embedded – are relatively few in number.

There are three main recipes: polyester, vinylester and epoxy. Various flavours of each are available, depending on whether they are strengthened with glass, carbon or aramid fibers, and the particular application. For example, high UV (sunlight) tolerance may be chemically engineered using additives.

Common Issues

The presence of volatile organic compounds(‘VOC’) is of concern both for health reasons and ‘greenhouse effect’ impact. Modern epoxies are VOC free, but polyester and vinylester compounds have high concentrations of VOC in the form of styrene. This means that fabrication using esters should take place in well ventilated space.

Curing

The epoxy compound is formed by mixing two different chemicals which react to form a ‘copolymer’. The curing rate is sensitive to temperature and the ratio of the two components, but curing is almost always assured. Some epoxy paste formulations will even cure underwater.

 

Polyester and vinylester by comparison, cure with the use of a peroxide catalyst (usually known as MEKP).

Vinylester is sensitive to temperature, and may not cure at all under certain conditions.

Water resistance

Epoxies are highly water resistant, with vinylesters also showing a high resistance.Polyester composites absorb water to a significant degree, and when used – say, in boat hulls – osmotic blistering occurs due to a reaction with water (hydrolysis) which results in chemical breakdown.

Insoluble pthallic acid crystals damage the GRP laminate and acetic acid is a by-product.

Chemical resistance

Epoxies are very stable chemically, and offer excellent resistance to chemical attack. Polyesters are moderately resistant at room temperatures to most common chemicals, but vinylesters offer much higher resistance, though falling short of the protection that epoxies afford. The resistance of polyesters and vinylesters falls quickly at higher temperatures. Vinylesters may be used to provide a barrier coating to protect polyester, particularly in the marine environment.

Shrinkage, Strength and Stiffness

Polyesters and vinylesters typically shrink by 7% on curing, but epoxies shrink less than 2% and where dimensional stability is important, then epoxies are much to be preferred.

Shrinkage can introduce stress into a structure, and designers much factor this in. Both for tensile strength and stiffness, polyester is lowest on the scale, with epoxy highest and vinylester just superior to polyester.

Adhesion

This is an important property when using composites. Adhesion has to be strong between the resin and the fiber strengthener. Vinylester is not the best in this respect.

Cost

Polyester is by far the cheapest of the three resin systems, much cheaper even than vinylester, weight for weight. Polyester is preferred for boats and bathtubs, but where strength/weight is important and budget less of an issue, then epoxies win – for example in motorsport and aerospace.

Fiber Types

There are three main families in use at present: glass fiber, carbon fiber and aramid fiber (more commonly known as Kevlar, a trademark of the DuPont Corporation).

Glass fiber is by far the cheapest and most widely used, and works well with all three resin types, but it is relatively heavy. Carbon fiber is much lighter, as are aramid fibers.

Glass fibers (either in chopped strand or woven cloth form) are most commonly used with a polyester resin, whereas carbon fiber, as a relatively high cost strengthener, is most usually combined with epoxy resins.

Adhesion

A resin has to ‘stick’ to the fiber strengthener, and it is important to select a resin/fiber combination (particularly with carbon and aramid fibers) so that there is good adhesion and the fibers are properly bonded within the resin.

Composite Comparisons

In general terms, Kevlar mechanical properties are good in strength (double that of glass fibers) but very poor in stiffness, whilst the glass composite is ten times as stiff and half the strength.

Kevlar is very expensive compared to glass, so it is used where higher strength and elongation is needed.

Both aramid composites and GRP are good at handling repeated flexing cycles (such as in a boat hull), but carbon fiber has an unpredictable life when subject to repeated flexing.

GRP requires a considerably ‘heavier’ construction to achieve the strength of carbon fiber. Aramid fibers offer equivalent strength to fiberglass at a much lower weight, although abrasion resistance is lower.

Summary

When choosing a composite, there are many factors to take into account. Many users of advanced composites – for example in the premium boat building industry – will combine all three composites to tailor engineering properties and weight distribution. In fact, we now have structures which are composites of composites.

SOURCE : COMPOSITE ABOUT.COM

QUAD COPTER CONTROLS

Quadcopter Controls

When learning how to fly a quadcopter, the controls will become your bread and butter.

They will become second nature once you know how they act individually and how they interact together to form a complete flying experience.

With any of these controls, the harder you push the stick, the stronger your quadcopter will move in either direction.

When you first start out, push the sticks very gently so the quadcopter performs slight movements.

As you get more comfortable, you can make sharper movements.

There are four main quadcopter controls:

  • Roll
  • Pitch
  • Yaw
  • Throttle
How-to-Fly-a-Quadcopter-Transmitter-Image.jpg
Simple Sketch of Roll, Pitch, Yaw and throttle on a transmitter (left image) and Quad copter (right image)

(Image source: Quadcopters Are Fun)

Let’s go through each of them.

Roll

Roll moves your quadcopter left or right. It’s done by pushing the right stick on your transmitter to the left or to the right.

It’s called “roll” because it literally rolls the quadcopter.

For example, as you push the right stick to the right, the quadcopter will angle diagonally downwards to the right.

How-to-Fly-a-Quadcopter-Image-Roll.png
Example of a Quad copter rolling left and right . Notice the tilt of the quad copter and the angle of the parameters.

(Image source: Best Quadcopter Spot)

Here, the bottom of the propellers will be facing to the left. This pushes air to the left, forcing the quadcopter to fly to the right.

The same thing happens when you push the stick to the left, except now the propellers will be pushing air to the right, forcing the copter to fly to the left.

Pitch

Pitch is done by pushing the right stick on your transmitter forwards or backwards. This will tilt the quadcopter, resulting in forwards or backwards movement.

How-to-Fly-a-Quadcopter-Image-Pitch.png
Example of a Quad copter pitching forwards and backwards. Note that this view is from the left side.

Yaw

Yaw was a little bit confusing for me in the beginning. Essentially, it rotates the quadcopter clockwise or counterclockwise.

This is done by pushing the left stick to the left or to the right.

Check out the video (Watch from 3:00 to 3:40 and pay attention to how he adjusts the sticks.)

Yaw is typically used at the same time as throttle during continuous flight. This allows the pilot to make circles and patterns. It also allows videographers and photographers to follow objects that might be changing directions.

Throttle

Throttle gives the propellers on your quadcopter enough power to get airborne. When flying, you will have the throttle engaged constantly.

Related: See the top 100 drone news sites of 2015

To engage the throttle, push the left stick forwards. To disengage, pull it backwards.

Make sure not to disengage completely until you’re a couple inches away from the ground. Otherwise, you might damage the quadcopter, and your training will be cut short.

Important note:

When the quadcopter is facing you (instead of facing away from you) the controls are all switched.

This makes intuitive sense…

  • Pushing the right stick to the right moves the quadcopter to the right (roll)
  • Pushing the right stick forward moves the quadcopter forward (pitch)
  • Pushing the right stick backward moves the quadcopter backward (pitch)
  • And so on.

So pay attention to that as you start changing directions. Always be thinking in terms of how the quadcopter will move, rather than how the copter is oriented towards you.

SOURCE : UAVCOACH.COM