a compendium of tech stuff

Dec 4, 2010

On 7:53 AM by Lalith Varun   2 comments









A hubless wheel is a wheel lacking a central hub, first designed by an Italian mechanical engineer, Franco Sbarra especially for motor vehicles. but it is also been seen in the application of many bicycle prototypes over the years. The Orbital wheel, a type of hubless wheel was designed in 1990 by Dominique Mottas. Hubless wheels lack a central hub and an axle which form the major part of conventional wheels. The concept behind this is to reduce the number of rotating parts in the wheel to a bare minimum. Many scientists argue that the efficiency of the wheel is compromised by using hubless and spoke less wheels but others see its advantages as it claims to make the bike lighter and striking in appearance, not many prototypes have actually become commercially viable.
It consists of 3 parts, 1) a bearing with a thin section and a large diameter, 2) rotating part consisting of a tyre, a centre free rim and a brake ring all integrated with each other to form a rotating outer ring of the bearing and 3) fixed part consisting of the non rotating inner ring of the bearing on which the vehicle’s steering system is connected. With this arrangement we get an empty wheel that is free from midwheel structural constraints.
Due to the lack of a central hub this wheel is more advantageous than the conventional wheel. Steering becomes all the more easier due to the elimination of effects of deformation of stub axles and forks of the motorbikes and it is that kinda design that allows for more rational steering systems to be attached in the future. An automobiles stability is dependent on its roll angle, the greater the angle, the more stable the vehicle. But the manoeuvrability will be reduced on turns and tight bends. The hubless wheel comes with a roll angle variator. The greater the speed, the higher the roll angle and hence maximum stability is maintained at all times and when the speed is reduced, the roll angle is reduced thus increasing manoeuvrability. For any vehicle, be it an automobile or a railway car braking is a major source of concern. Conventionally braking occurs at the centre of the wheel which requires a complex braking system. As the hubless wheel has no central hub, braking power is applied close to the ground by using large diameter brake rings or discs and also the braking system has excellent ventilation.
In a traditional wheel, the dynamic forces acting on the wheel at the road-tyre interface passes through the midwheel causing damage to the forks of the wheel. But with the advent of hubless wheels, these forces are transmitted directly to the suspensions. As vibration and jarring are reduced by 50%, the driver is much more comfortable and can drive longer. Goods can be carried in better conditions as they undergo less vibration. There is less strain on the straps used for fastening the goods so road safety is also increased. As each tyre is subjected to the same load, the wear is evenly spread and is greatly reduced and hence its useful life is increased. Thus newer and cheaper tyres with an equal performance level can be used.
Although hubless wheels are striking in appearance and advantageous compared to the conventional wheel, their numerous practical disadvantages have impeded their widespread use as an alternative to conventional wheels. They are difficult and expensive to manufacture and require a great deal of precision while machining. And the design also leaves the bearings and other mechanical parts exposed, the drive system is also very difficult to design and is problematic hence conventional wheels are preferred to hubless ones though they are more efficient.

Oct 16, 2010

On 5:58 PM by Lalith Varun   No comments
An Inertial Navigation System (INS) is a navigational aid that makes use of a clock, accelerometers (sensors for measuring acceleration), gyroscopes (sensors for measuring rotation) and a computer to continuously calculate the position, orientation and velocity of an object on the move without any external references. Inertial navigation is a self-contained navigation technique in which measurements provided by accelerometers and gyroscopes are used to track the position and orientation of an object relative to a known starting point, orientation and velocity. Inertial measuring units (IMUs) typically contain 3 orthogonal rate-gyroscopes and 3 orthogonal accelerometers, measuring angular velocity and linear acceleration respectively. These signals are processed with the help of the on board computer and the position and orientation of the object can be tracked.
All the IMUs fall into 1 of the 2 categories outlined below. The difference between the 2 categories is the frame of reference in which the gyroscopes and accelerometers operate. The 2 categories are stable platform systems or gimballed platform systems and the strap down systems.
In stable platform type of systems, the inertial sensors are mounted on a platform which is isolated from any external rotational motion. This is achieved by using gimbals which allow the platform freedom to move in all the 3 axes. The gyroscopes on the platform detect rotations of the platform if any and the signals are fed back to the motors which rotate the gimbals in order to cancel out such rotations and hence keeping the platform aligned with the global frame. To track the position of the object, the angles between adjacent gimbals is calculated with the help of angle pick-offs and to calculate the position, the signals from the accelerometers mounted on the platform are double integrated. To get accurate results, we need to subtract acceleration due to gravity from the vertical channel before performing integration.
In strap down systems the sensors are mounted rigidly onto the device and hence the output is measured in the body frame and not global frame as in the case of stable platform systems. The orientation of the object can be determined by keeping track of the signals from the gyroscopes and integrating them while the position is determined from the accelerometer signals which are resolved into global co-ordinates and then integrated.
Both these types of systems are based on the same principles. Strap down systems are less complex and are physically smaller compared to stable platform systems. Due to this the strap down systems are the more dominant type of INS.
INS is autonomous and does not rely on external aids or visibility conditions and can operate in tunnels or underwater and anywhere. It is immune to jamming and inherently stealthy. It neither receives nor emits detectable radiation and requires no external antenna.
Errors increase with time as they are mean-squared. Cost of acquisition is high, the maintenance costs are also higher and so are the power requirements when compared to GPS receivers. With integration with GPS, these systems have become cheaper, maintenance costs have also gone down, the sensor errors have dropped to acceptable values and when there’s loss of GPS signals this integrated INS can be used.

Oct 7, 2010

On 10:08 PM by Lalith Varun   5 comments





The NAVSTAR-GPS (NAVigation System with Timing And Ranging Global Positioning System) commonly known as GPS, is a U.S. space based radio navigation system that provides reliable positioning, navigation and timing services to users on a continuous worldwide basis, freely available to all. GPS was originally intended for military applications, but in the 1980’s the government made the system available for civilian use. GPS works in all weather conditions, anywhere in the world, 24 hours a day. GPS was created by the U.S. Department of Defence (DOD) and was originally run with 24 satellites and there are currently 28 operational satellites orbiting the earth at a height of 20,180 km on 6 different orbital planes. Their orbits are inclined at an angle of 55° to the equator, ensuring that at least 4 satellites are in radio communication with any point on the planet. Each satellite orbits the earth in approximately 12 hrs and has 4 atomic clocks on board.

Before getting into the details of how the GPS works we should first know what signal transit time is and how it is measured. At some point or the other on a stormy night, you might have wondered how far away you are from a flash of lightning. This distance can be measured quite easily:
Distance = time the lightning flash was first perceived (start time) until the thunder is heard (stop time) multiplied by the speed of sound. The difference between the start and stop time is called transit time.
Hence distance = transit time * speed of sound
The GPS system exactly works under the same principle. In order to calculate one’s position, all that needs to be measured is the signal transit time between the point of observation and four different satellites whose positions are known.
Each satellite transmits its exact position and its precise on board time to earth at a frequency of 1575.42 Mhz. These signals are transmitted at the speed of light (3,00,000 km\s) and therefore require approx. 67.3 milli seconds to reach a position on the earth’s surface. The signals require a further 3.33 micro seconds for every extra km of travel.
Measuring the signal transit time and knowing the distance from a satellite isn’t enough to calculate one’s own position in 3-D space. To achieve this, 4 independent transit time measurements are required. It is for this reason that signal communication with 4 satellites is needed to calculate one’s exact position. All this time we have been assuming that the signal transit time that we measured was precise and highly accurate, but an error of 1 micro second can produce a positional error of 300m. As the clocks on all the satellites are synchronised, the transit time in all the measurements is inaccurate by the same amount. From the basic knowledge of mathematics we know that to solve a problem with n no. of unknowns, we need n no. of equations. To precisely determine the position of a person we need 4 equations i.e. one each for longitude, latitude, height and time error hence 4 satellites are required.
The most important applications of GPS are to determine one’s exact location and the precise time anywhere on the earth. The traditional fields of application for GPS are surveying, shipping and aviation. However with the increasing demand and popularity of the GPS, now it is being used in archaeology, geology, cartography, forestry and agricultural sciences, planning and managing of plantations, fleet management, navigation systems, trekking and sports activities and most importantly military services for which it was mainly developed for.

Oct 2, 2010

On 1:39 PM by Lalith Varun   3 comments







Ekranoplan is a Russian word which means 'screen craft' or 'skimmer'. It is not a plane nor is it a ship, moreover its a mixture of both. It is a transition between a hovercraft and an aircraft. It is a vehicle that attains level flight close to the surface of the earth which is possible by the cushion of high pressure air created by the aerodynamic interaction between the wings and the surface of the earth generated by its forward movement called as ground effect. It is also known as a flarecraft, sea skimmer, wing in surface effect ship etc.

In the 1970's when this vehicle was first photographed by the American satellite, it was believed to be a normal Jumbo jet sized aircraft under construction but when the vessel was later photographed sitting in water the American’s were puzzled! These crafts are big, fast and were kept secret from the west until the fall of communism in the early 1990's, when information about them was slowly revealed.

It can quite easily be envisaged that a hundred of such crafts zooming across the ocean, flying undetected by the radar as they fly underneath it and invading a country! By the time that country realized what was going on, it would have been too late. The front of the fuselage would have opened to allow soldiers, tanks, trucks, jeeps, and armoured cars to deploy and invade. You have to imagine several hundred of these craft, all flying at over 290 knots, all under radar in a mass invasion. We could then fully realise the element of surprise that they would have had.

It’s one hell of a ship, fast, manoeuvrable, and heavily armed but maybe not so well protected. Unlike a warship that has armor plating, the Ekranoplan would be susceptible to enemy firepower, a couple of rocket or bazooka hits could seriously damage or render the Ekranoplan inoperable. As the Ekranoplan picks up speed, the air is compressed under its short stabilizing wings until enough pressure produces lift and this supports the craft. Ekranoplan's as they are bigger, have more power and travel just a few feet over the water surface. Infinitely faster than any sea vessel ever designed the Ekranoplan is a marvel to behold. The terrific speed that these crafts can reach is mainly due to the fact that there is no friction between the hull of the craft and the water. This of course is a factor that keeps normal ships at such a comparatively slow speed, as they must push themselves through the water and not over it. They have better fuel efficiency than an equivalent aircraft flying at low level due to the close proximity of the ground, reducinglift-induced drag. There are also safety benefits for the people travelling in the craft in flying close to the water as an engine failure will not result in severe ditching. However, this particular configuration is difficult to fly even with computer assistance. Flying at very low altitudes, just above the sea, is dangerous if the craft banks too far to one side while making a small radius turn.

All Ekranoplan's are amphibious and will easily fly over land just as well as the sea, and at high speed, just as long as the surface is relatively flat. The last Ekranoplan from the former Soviet Union was the 400 ton LUN. It was built in 1987 with 100% military application in mind as a missile launcher and troop carrying ship. It was equipped with six large missiles on top of the fuselage, and could carry tanks and trucks in its large cargo hold. Also it must be reiterated here that it would not have been detected by radar as it would have travelled under the radar waves but the modern radar now has the ability to scan vessels on the surface of the sea so the surprise element of the Ekranoplan can be negated.

At the time when the Soviet Union fell apart, there was a second LUN under construction, it was about 90 percent finished when the military funding stopped. This was because of Russia's poor financial situation and also the end of the cold war. Later the eventual collapse of communism was enough to create further financial upheavals in much of Russia's economy. Most countries have now built prototypes of the Ekranoplan design as it has very useful application both in the military and commercial fields. As yet no commercial flights have been instigated but there are reports that a lot of private ventures are being developed, mostly in the USA.

Jan 19, 2010

On 8:29 PM by Lalith Varun   62 comments




The Segway PT also known as Segway Personal Transporter is the world's first self-balancing human transporter. The Segway PT only has two wheels, yet it manages to stay upright by itself. To move forward or backward on the Segway PT, the rider just leans slightly forward or backward. To turn left or right, the rider simply moves the LeanSteer frame left or right. You get the sense of power and speed, yet you also feel a sense of safety and absolute control. It all feels natural, safe, and instinctive. The Segway PT can take you places that a car or bicycle can't - including inside many stores, office buildings, businesses, airports, elevators, and trains. Although they're ideal for short jaunts, Segway PTs can travel as far as 24 miles/38 km on a single battery charge, depending on terrain, payload, and riding style and speeds upto 20.1 kmph (12.5 mph).

Now let us know the basic parts that make up the Segway. The Segway is a combination of a series of sensors, a control system and a motor system. The primary sensor system consists of an assemblage of gyroscopes. Gyroscopic sensors are used to detect tilting of the device which indicates a departure from perfect balance. Motors driving the wheels are commanded as needed to bring the PT back into balance. The Segway PT has five gyroscopic sensors, though it only needs three to detect forward and backward pitch as well as leaning to the left or right. The extra sensors add redundancy, to make the vehicle more reliable. Additionally, the Segway has two tilt sensors filled with electrolyte fluid. Like your inner ear, this system figures out its own position relative to the ground based on the tilt of the fluid surface.

All of the tilt information is passed on to the "brain" of the vehicle, two electronic controller circuit boards comprising a cluster of microprocessors. The Segway has a total of 10 onboard
microprocessors, which boast, in total, about three times the power of a typical PC. Normally, both boards work together, but if one board breaks down, the other will take over all functions so that the system can notify the rider of a failure and shut down gracefully. When the vehicle leans forward, the motors spin both wheels forward to keep from tilting over. When the vehicle leans backward, the motors spin both wheels backward. When the rider operates the handlebar control to turn left or right, the motors spin one wheel faster than the other, or spin the wheels in opposite directions, so that the vehicle rotates.

The Segway is only slightly larger than a person, so it does not cause as much congestion as a car or a bike. Once they get to their destination, riders can carry their Segways inside with them without worrying about parking. And there's no need to stop by the gas station, as the vehicle runs on ordinary household electricity. There is really no limit to how people might use the vehicle. The Segway can fit in most places you might walk, but it will get you there faster, and you won't exert much energy. So what are you waiting for? Go get yourself the worlds first self balancing electric vehicle.

Jan 18, 2010

On 7:44 PM by Lalith Varun   1 comment



NORTHROP SWITCHBLADE


BELL X-5

A variable-sweep wing is an aircraft wing that can be swept back or front and then returned to its original position during flight. It allows the aircraft's geometry to be modified in flight, and is an example of variable geometry. With different wing positions allowing for greater efficiency and performance in various flight modes, these aircraft are more versatile than aircraft with fixed wings. During the World War I and II, one would notice that most of the aircrafts had wings perpendicular to the fuselage and in very rare cases a couple of degrees swept back. But with the advent of jet engines after the World War II which gave a boost to the speed of the aircrafts, the traditional wing shapes weren't that efficient at such high speeds. So jet planes started using tapered wings, but this came at a cost of low efficiency at lower speeds.

And hence came the need for an aircraft which can alter its wing geometry in mid flight. This feature gives the airplane the best possible performance characteristics for any given speed. The German
Messerschmitt company first tested planes with variable wing geometry during World War II. The Messerschmitt P-1101's wings could be moved to different sweep angles, only while the plane was on the ground. Based on the Messerschmitt design, the U.S. developed a working test craft, the Bell X-5, which was slightly larger than the P-1101 and could change its wing-sweep angle while in flight.

Designers had to take into consideration many factors regarding sweep while designing a swing wing. Swept back wings make the aircraft more stable at high speeds while forward swept wings allows the aircraft to be agile. In the 1990s,
Northrop Grumman tested variable-geometry wings on another plane with the "Switchblade" nickname. The Northrop Bird of Prey had three wing configurations:
  • full-back position - The wings were perpendicular to the fuselage for low-speed flight.
  • intermediate position - The wings were swept forward for exceptional maneuverability.
  • full-forward position - The leading edge of the wings folded in against the fuselage, allowing the trailing edge to become the front of the wing for high speeds. This resulted in a triangular, or delta wing shape.
Lets now know how the wings position affects its performance, unswept wings are efficient at low speeds, providing a great amount of lift compared to the amount of induced drag exerted on the plane. Unswept wings are very bad at dealing with wave drag. Swept wings cut down on drag caused by turbulence at the wingtips. But the real advantage of swept wings comes in supersonic flight -- the configuration cuts down on wave drag by redistributing the shock waves along the plane's aerodynamic profile. They are ideal for these high-speed conditions. Unfortunately, they do not allow for heavy payloads at lower speeds. Swept wings are also inefficient and burn too much fuel to stay aloft, which reduces the range of the aircraft. Thus an aircraft with a variable sweep wing has become the need of the hour. The mechanisms required to make the wing movements function were complicated and heavy. They also took up a lot of space, cutting down on efficiency and payload. Swing wings were largely abandoned for more simplistic designs. Northrop Grumman plans a scaled-down test model with a 40-foot wingspan for 2010, with a full-size, fully-functional Switchblade ready for flight in 2020. As the project moves into the scale and full-sized phases, costs will likely escalate into the billions of dollars. Hopefully in the coming years we'll be having fully operational variable sweep wing aircrafts.