Friday, November 23, 2012

A Study of Air Bags in Automobiles


Definition for airbag
An airbag is a vehicle safety device. It is an occupant restraint system consisting of a flexible envelope designed to inflate rapidly during an automobile collision. Its purpose is to cushion occupants during a crash and provide protection to their bodies when they strike interior objects such as the steering wheel or a window.

Modern vehicles may contain multiple airbags in various side and frontal locations of the passenger seating positions, and sensors may deploy one or more airbags in an impact zone at variable rates based on the type and severity of impact; the airbag is designed to only inflate in moderate to severe frontal crashes. Airbags are normally designed with the intention of supplementing the protection of an occupant who is correctly restrained with a seatbelt. Most designs are inflated through pyrotechnic means and can only be operated once.

Various manufacturers have over time used different terms for airbags. General Motors first bags, in the 1970s, were marketed as the Air Cushion Restraint System (ACRS). Common terms in North America include Supplemental Restraint System (SRS) and Supplemental Inflatable Restraint (SIR). These terms reflect the airbag system's nominal role as a supplement to active restraints, i.e., seat belts. Because no action by the vehicle occupant is required to activate or use the airbag, it is considered a passive device. This is in contrast to seat belts, which are considered active devices because the vehicle occupant must act to enable them

v In 1951 a German Walter Linderer designed an airbag. It was based on compressed air system. But later research found that it was not efficient.
v In Japan Yasuzaburou Kobori made an airbag in 1963, in which technology current airbags are based.
v In 1967, a breakthrough occurred in the development of airbags when Allen K. Breed invented a practical component for crash detection.
v In 1971 Ford introduced air bag in their vehicle as an experimental fleet followed by GM.
v In 1981 Mercedes-Benz introduced airbags in its S-class
v The first car in the world to have driver and passenger airbag was Porsche 944 turbo in 1987.
v The first airbag in motorcycles was in 2006 on Honda Gold wing.
v In 2009, Toyota developed the first production rear-seat center airbag designed to reduce the severity of secondary injuries to rear passengers in a side collision.

Typical components used
w  Front crash/safing sensors.
w  Airbag control module
w  Airbag assembly
w  Clock springs
w  Airbag circuit harness and connectors.

Ø Frond crash/safing sensor: These devices are usually located in the front grill area. They are designed to complete a circuit back to the air bag module when a hard enough crash is measured.  Most Safing sensors will be located inside the air bag control module.
Ø Airbag control module: The air bag control module is almost always located inside the passenger compartment.  There are at least 1 and sometimes 2 more safing sensors located inside this unit that must also close for deployment to occur.  This unit is responsible for sending the deploy command to the air bag.
Ø Airbag assembly: There could be as many as 14 of these air bags located throughout the vehicle.  The main assembly is located in the steering wheel.  This unit’s main purpose is to protect the passengers and driver in the event of a crash.  These could be inflated at different speeds depending on size and weight of occupants.
Ø Clock springs: Located inside the steering wheel.  This device is used to connect the hard wired air bag harness to the systems harness while allowing the steering wheel to maintain a full range of motion.
Ø Airbag harness & connecters: harness and connecters are yellow in colour

How airbags work
The design is conceptually simple; a central "Airbag control unit" (ACU) (a specific type of ECU) monitors a number of related sensors within the vehicle, including accelerometers, impact sensors, side (door) pressure sensors  wheel speed sensors, gyroscopes, brake pressure sensors, and seat occupancy sensors. When the requisite 'threshold' has been reached or exceeded, the airbag control unit will trigger the ignition of a gas generator propellant to rapidly inflate a fabric bag. As the vehicle occupant collides with and squeezes the bag, the gas escapes in a controlled manner through small vent holes. The airbag's volume and the size of the vents in the bag are tailored to each vehicle type, to spread out the deceleration of (and thus force experienced by) the occupant over time and over the occupant's body, compared to a seat belt alone.
The signals from the various sensors are fed into the Airbag control unit, which determines from them the angle of impact, the severity, or force of the crash, along with other variables. Depending on the result of these calculations, the ACU may also deploy various additional restraint devices, such asset pre-tensioners, and/or airbags (including frontal bags for driver and front passenger, along with seat-mounted side bags, and "curtain" airbags which cover the side glass). Each restraint device is typically activated with one or more pyrotechnic devices, commonly called an initiator or electric match. The electric match, which consists of an electrical conductor wrapped in a combustible material, activates with a current pulse between 1 to 3 amperes in less than 2 milliseconds. When the conductor becomes hot enough, it ignites the combustible material, which initiates the gas generator. In a seat belt pre-tensioner, this hot gas is used to drive a piston that pulls the slack out of the seat belt. In an airbag, the initiator is used to ignite solid propellant inside the airbag inflator. The burning propellant generates inert gas which rapidly inflates the airbag in approximately 20 to 30 milliseconds. An airbag must inflate quickly in order to be fully inflated by the time the forward-travelling occupant reaches its outer surface. Typically, the decision to deploy an airbag in a frontal crash is made within 15 to 30 milliseconds after the onset of the crash, and both the driver and passenger airbags are fully inflated within approximately 60-80 milliseconds after the first moment of vehicle contact. If an airbag deploys too late or too slowly, the risk of occupant injury from contact with the inflating airbag may increase. Since more distance typically exists between the passenger and the instrument panel, the passenger airbag is larger and requires more gas to fill it.
An air bag contains a mixture of sodium azide (NaN3), KNO3, and SiO2. A typical driver-side airbag contains approximately 50-80 g of NaN3, with the larger passenger-side airbag containing about 250 g. Within about 40 milliseconds of impact, all these components react in three separate reactions that produce nitrogen gas. The reactions, in order, are as follows.
(1) 2 NaN3 → 2 Na + 3 N2 (g)
(2) 10 Na + 2 KNO3 → K2O + 5 Na2O + N2 (g)
(3) K2O + Na2O + 2 SiO2 → K2O3Si + Na2O3Si (silicate glass)
          The first reaction is the decomposition of NaN3 under high temperature conditions using an electric impulse. This impulse generates to 300°C temperatures required for the decomposition of the NaN3 which produces Na metal and N2 gas. Since Na metal is highly reactive, the KNO3 and SiO2 react and remove it, in turn producing more N2 gas. The second reaction shows just that. The reason that KNO3 is used rather than something like NaNO3 is because it is less hygroscopic. It is very important that the materials used in this reaction are not hygroscopic because absorbed moisture can de-sensitize the system and cause the reaction to fail. The final reaction is used to eliminate the K2O and Na2O produced in the previous reactions because the first-period metal oxides are highly reactive. These products react with SiO2 to produce a silicate glass which is a harmless and stable compound.
According to a patent, the particle size of the sodium azide, potassium nitrate, and silicon dioxide are important. The NaN3 and KNO3 must be between 10 and 20 microns, while the SiO2 must be between 5 and 10 microns.

Triggering conditions
Airbags are designed to deploy in frontal and near-frontal collisions more severe than a threshold defined by the regulations governing vehicle construction in whatever particular market the vehicle is intended for: U.S. regulations require deployment in crashes at least equivalent in deceleration to a 23 km/h (14 mph) barrier collision, or similarly, striking a parked car of similar size across the full front of each vehicle at about twice the speed. International regulations are performance based, rather than technology-based, so airbag deployment threshold is a function of overall vehicle design.
Today, airbag triggering algorithms are becoming much more complex. They try to reduce unnecessary deployments and to adapt the deployment speed to the crash conditions. The algorithms are considered valuable intellectual property. Experimental algorithms may take into account such factors as the weight of the occupant, the seat location, seatbelt use, and even attempt to determine if a baby seat is present.

Types of airbags
v frontal airbag: the normal airbags in the steering wheel and dash board meant to protect the passenger and driver from head injuries
v side airbag: there are mainly two types
w  Side torso airbag: these airbags locate between the occupant and the door. These are designed to avoid the risk of injury of pelvic and lower abdomen regions.
w  Side tubular or curtain airbags: this airbag was designed to offer head protection in side impact collisions.
v Knee airbag: this type of airbags are meant for the protection of  knee of the occupants on collision.
v Rear curtain airbag: this is to protect the head of the rear occupants on collision
v Center airbag: this is meant to avoid the second injuries of the rear occupants on side collisions.
v Seat belt airbag: these are seen at the seat belts to protect the body on collisions.

Airbag replacement
If you have been through an accident and you are safe just because of the airbags been deployed, along with the car repair, you will also have to consider replacing the airbags. Replacing airbags is the only alternative left if they have already been used for driving safety. Considering the benefits that you get from airbags in your car, the replacement cost seems very low in comparison with the protection and road safety offered. Unlike repairs to the other car parts after an accident, airbag replacement will not cost you a lot out of your pocket. The airbag replacement cost depends on many different factors such as the make and model of your car, the location of the airbag, and the kind of product used.

Future updates
Ø Smart Systems
v Seat Sensors
ü Determine size and weight of individual.
v Optical Sensors
ü Determines how close and size of occupant/car seat.
ü Determines which way the car seat is facing.
v Child-Car Seat Sensors
ü Determines direction of car seat.
v Occupant Sensors
ü Determines if someone is present by measuring for body heat.
v Air Bag Curtains
                        Designed to protect the entire passenger compartment.

Friday, November 2, 2012

Single stretch board wiper

            Here i am giving a small mini project idea, which can be done so easily. The main objective of this project is to reduce the time of wiping the board while taking classes. We can see that we are loosing much time while the faculties are wiping the boards. (Meanwhile many may be relaxing while this extra time!!.)

            So by doing this project we can save a lot of time. The construction is simple, and we can erase the board very easily. The board wiper is a hand operated mechanism. The operation of wiping in a single stretch is done by using a clad roller and a duster holder. This mechanism is simple, compact and concise.


  • Two guideways are fixed, one at the top and other at the bottom of the board with respect to the board size.
  • One end of the duster bar is connected to the roller which rolls inside the guideway.
  •  Other end of duster bar is also fixed to roller which rolls at the body of guideway.
  • Duster is fixed at one side of the rod.
  • When the rod is moved with force it wipes out the entire board at one stretch.
  • The above figure shows the demonstration of the single stretch board...try it.

Monday, October 8, 2012

How to build a Quadcopter

Maybe you want to build your own? Maybe you want to take this design and mod it for agility, weight, or style. Awesome. First, here’s the base pattern:
Getting Started
First off, you’ll need some tools:
·         CNC laser cutter. In theory, you could cut these parts out with an x-acto knife, which is madness. You’ll want to borrow a laser cutter. Honestly, you should just buy one. They’re the absolute best thing in the world, and the prices are dropping very fast. Check out Hurricane Laser, for example. Or TechShop.
·         Scissors, for cutting tape.
·         Soldering iron, and solder.
·         A can of Super77 spray glue.
·         60degree hole chamfer. Handheld is fine.
You’ll need the following build materials. For my examples, I use cardboard sheeting from ULINE.
·         Several sheets of 4mm cardboard. The thickness matters, if you change the thickness, make sure you update the tab cutouts to match. They’re 3x the thickness, or 12mm.
·         Brown paper packing tape for sealing the edges. The clear stuff doesn’t stick very well. You can also use fiber reinforced tape.
·         4×4″x1/8″ black ABS plastic sheet. You can also use heavy card stock, sheet metal, acrylic, or aluminum bar stock.
·         No. 127 Black ESD or similar. 7”x1/8″
·         One 14oz ZipLock plastic container, or other lightweight 5″ diameter bowl.
·         Double sided copper clad PCB board, you’ll need about a 0.5×0.5″ square piece.
·         4 paperclips.

For electronic components, you’ll need the following:
·         4ea 22mm brushless outrunner motors. I’ve used both Cobra 1300kV and DiyDrones 850kV motors.
·         4ea matching prop adapters for your motors and propellers.
·         4ea regular propellers. GWS 8×3, GemFan 10×45, etc. Yes, 4ea. You’ll want extras, lots of extras. You’ll break a lot of props at first.
·         4ea reverse propellers.
·         4ea ESC controllers for your motors, with an on board BEC. I use 20A NextLevel controllers.
·         20mm heatshrink, for the covering the copper clad power board. Electrical tape works too.
·         6mm heatshink for covering connectors and wires.
·         0.1″ spacing jumper wires, female socket. For the battery power sense line.
·         Controller board. I use the Quadrino Zoom.
·         Cable assembly for Quadrino Zoom.
·         Spread spectrum 2.4ghz transmitter and receiver. 6 channel or better. Spektrum DX6i, etc. There are 4 control channels, and 2 mode channels. You’ll need another two channels if you want to add head tracking later.
·         2-4ea, 2000-1300mAh 3S LiPo battery. Trust me, you’ll want more than one. Your motors must match the battery voltage. I use Turnigy batteries.
·         Lipo battery charger.
·         Battery connector plug and wires. I use XT60 plugs.
·         Sparkfun Blutooth module, if you want wireless telemetry. Totally optional.
·         Nylon mesh wire sleeve. I use this to protect the motor leads from prop strikes. Also optional.
It’s a lot of parts and pieces, it’s true. Depending on where you source things from, and how fast your shipping times are, it can take up to a month for all the parts and pieces to arrive. HobbyKing has notoriously long wait times, for example. If you care about customer service and speed, order domestic. I recommend Innov8tive Designs.
Got all your parts and pieces? Great! Let’s get started…
Step One – Cut The Pieces Out
The major consideration when cutting out the corrugated paper parts is to make sure the corrugation pattern runs it different directions for the different layers. This helps to create an internal truss structure and makes the beam considerably stronger once assembled. Note also, that how evenly the layers are glued together will affect the strength of the beam dramatically.

 This generally makes for a less-than-efficient usage of cardboard unless one is cutting out a dozen or so quadcopters. Cardboard is cheap though, so it shouldn’t hit your wallet too hard.

The corrugation patterns should look like so when they’re all stacked up. Sometimes, as is in the case of parts from ponoko, you may not be able to get the corrugation pattern to line the way you want it to. This is okay. The order and direction of the layers isn’t that crucial, just that they change angle between layers.
For the motor mounts, which are just little tabs that screw into the back side of the motor, I used ABS. It cuts great on a laser, usually in a couple passes. ABS is extremely impact resistant, but it does have two undesirable properties: it smells really bad when cut, and it’s susceptible to long term UV damage. Use proper ventilation, and wait a few minutes after your done cutting before opening the laser bed door. It will smell for a few days, but eventually will be tolerable.

The motor mounts can be made out of pretty much anything, you could use aluminum bar stock from the hardware store, and drill out the motor mount screw holes. You could laser cut heavy tag board, or acrylic. Anything that is reasonably stiff will work. You could even use 1/8″ plywood, but ABS or aluminum will last the longest.
Step Two – Glue It Together
Next up we glue the pieces together. I use Super77 spray adhesive, which Joachim points out in the previous Tricopter build post, is expensive. It’s also not as strong as paper glue, but in practice, it really doesn’t matter all that much. In the 15 or so frames I’ve built so far, none has ever failed.

As the arm layers are symmetric, it’s possible to have all the exterior faces show the white side of the cardboard outward. Start by labeling the two middle arm layers, they’re the ones with the horizontal or vertical corrugation pattern. Placing them down, brown side up, along with two of the four outside layers, on a sheet of newsprint. Set the other two outside layers aside, we won’t be spraying them with glue. Spray the four total arm pieces with Super77.
To give myself a little wiggling room, I don’t wait until it’s dry before I carefully pick up the middle piece and place them each on their matching outside layer. Alignment is important, if the arms are misaligned it will be harder to mount the motors vertically later. If one of the motors is tilted slightly, it will cause minor yaw drift. You can usually trim this out in the controller though. Make sure you check the alignment of the notch corners.
Remember, it’s an accuracy test, not a speed test 

Then we spray one side of the bottom plate layers, and the underside of the upper top plate layer with glue. Again, alignment is important. While the orientation of the bottom plate doesn’t matter too much, make sure that the quadrino wire holes are oriented down, and that the label for motor A is in the upper left corner. Otherwise the labels will be wrong.

 Now you should have 4 parts. The top plate, bottom plate, upper arm, and lower arm. Before we put them together though, we need to…
Step Three – Tape The Edges
This is an important step. The edges of cardboard aren’t particularly strong. To keep them from getting crushed and damaged over time, we need to place tape across them. The type of tape we use is also important. A paper gum tape is the best. This is the kind where you wet one side with a sponge to make it sticky, like a stamp. As an added bonus feature, it comes in white. You’ll want to use a gum tape if you’re going to coat the frame in polyurethane or resin later. Coatings will dramatically increase the stiffness and strength of the frame, at the expense of a little bit more weight. You can also use a craft paper and glue in lieu of tape.
If you’re not going to coat the frame, use brown paper boxing tape. Avoid clear boxing tape, it’s terrible and comes undone easily. The brown paper boxing tape is very strong.

Start by taping the top edges, and on the undersides. For the motor mount area I wrap an extra layer of tape around the arm. I also cover the feet, as they take a lot of impact.

Put a tiny little piece of tape over each tab, and re-cut the paperclip slit with a knife. This will make the tabs easier to insert without them getting damaged.

Once all the tabs and edges ares taped, we’re ready to assemble the frame. Slot the arms together, and push them gently into the upper plate. Add a pair of paper clips, and set the bottom plate aside. To make the paper clips easier to remove later, I bend them up at 90 degrees on one side, and then slot them in.
Step Four – Solder The ESCs
I use a tiny copper board to solder all the ESCs together. You can also strip the wires a little more, and solder them all together. If you do this, wrap the bundle together with some thin, bare copper wire. It will make soldering the mess together much, much easier. The most important thing, is to have two of the ESCs pointed in one direction, and two pointed in the other.
I then solder on the battery connector whip, and add two motor controllers. After it cools, I slide a piece of the large heatshrink down over the wires, and out of the way. Then I solder the remaining two motor controllers and a small 22AWG red wire to the positive rail.
The little red wire will be used for on-board voltage sensing by the controller. If you bought female 0.1″ spacing jumper wires, use one of these. After that cools, I slide the heatshrink over the whole mess and shrink it down. Viola! A nice little power distribution board 
I put nylon mesh jackets on the motor lead wires. This helps keep them neat and tidy, and protects the leads from prop strikes and other mishaps.

Step Five – Attach The Motors

I put nylon mesh jackets on the motor lead wires. This helps keep them neat and tidy, and protects the leads from prop strikes and other mishaps.
As your motors probably didn’t come with the 3mm bullet connectors, you’ll want to solder them on now. I use a little piece of cardboard with holes punched in it to keep them stead while soldering. Drilling into a block of wood also works well too. Careful, if you put them in a metal vice it will make it very difficult to heat the connector and wire up.
Unlike most multi-rotor designs, the thing this one lacks is screws. Except for the motor mounts, pretty much no way out of that. This is important because screws, bolts and standoffs can add a lot to the cost of a frame. There are a lot of different ways to construct the motor mounts, but what’s most important is that there be two flat tabs sticking out from under the motor that are about 0.5″ or 12mm wide which we can use to tape the motor onto the arm. I can hear you now: “tape?” If you use the right tape, it works amazingly well.
The first step is to use the hole chamfer to but a bevel in the the motor screw holes one one side. The next step is also important: on the other side, taper the center hole slightly. This is important as otherwise the shaft snap collar on the motor will brush against the motor mount and you’ll see a lot of yaw drift in flight.
Attach the motor mounts to the underside of the motors, and put a little Lock-Tight in the screw holes. Without it, they’re pretty much guaranteed to vibrate out in flight, sending you on a quick trip to the hardware store for a somewhat rare 3mm machine screw

Place them at the end of each arm and tape them down tight. If they’re taped on loosely the extra play will get larger over time from vibration. If they’re tight they’ll stay put for a very long time.
Step Six – Finishing
The remainder of the build involves rubber bands. Lots of rubber bands. I use 7″x1/8″ No. 127 Platinum Crepe brand black rubber bands to attach components, hold on batteries, and keep things put. They’re very fast to add and remove, and unlike zip-ties, they’re reusable.

I use four rubber bands to secure the motor lead wires to the arm. Hook it onto the landing leg, wrap it around twice, and loop it over the same leg.
Another two to hold the ESCs in place. It goes from one side, to the other.
One to hold the battery pack on. This one has to be attached while the plate is removed, after that you just pull on the middle section and slide a battery in. If you have a particularly heavy battery add two rubber bands. One will probably be enough.

One more to hold the controller in place. Be careful to avoid resting the rubber band on the pins, it’s under enough tension to either bend the pins, or snap the rubber band due to vibration. Notice those four little holes in the top plate? They’re for nylon screws, you can optionally add them to help keep the controller board on axis. In practice though, the rubber band should be enough.

Step Seven – Software Setup
I chose the Quadrino Zoom, which is about mid-range price-wise, because it has a full 10DOF sensor platform, and is very well laid out. Flying with mag-lock is great for beginners and lets you fly without having to worry about craft orientation. I wish it had a built in buzzer, and an on-board current sensor, but it’s a very nice out of box experience as far as controllers go.
Once you download the multiwii software and open it up in Arduino, head on over to the config.h file and change a few important things.
·         #define QUADX // our flight configuration
·         #define QUADRINO_ZOOM // our controller
·         #define MOTOR_STOP // this will keep the props spun down when throttle is at a minimum. Useful for throttle cut when you’re first crashing^H^Hlearning to fly.
You’ll also need to set the minimum ESC engage threshold. Again, see the MultiWii site for that howto.
Go Fly!