Hi, this is Wayne again with a topic “Make Inventions: The Air bag”.
We’Ve always pushed technology to make us go faster, but the inventions to keep us safe at those speeds haven’t always kept pace. For example, inventors tried using inflatable bags to blunt crashes as early as 1920, but it took another 50 years for a useful airbag to be developed, while the inflated bag is the most visible part of an airbag system. It’S only the final result of a complex chain of inventions that work together in a fraction of a second. The first link in this chain is a sensor that can reliably detect, collisions early sensors use magnetic marbles that would shake loose in a crash opening an electric circuit they worked but could be accidentally triggered instead of triggered in an accident. Modern airbags use solid-state accelerometers, similar to the ones in gain controllers and smartphones. The next link in the chain is the microprocessor. The decision to inflate the airbag needs to be made as quickly as possible.
Without microchips, it would be difficult to evaluate the crash sensor. Data and set off the airbag in time. The final link is the inflation mechanism safely and reliable, inflating a bag and five hundredths of a second is a major challenge. Early research tried using compressed air, but no one could make it work fast enough and the mechanisms were bulky and complex.
Eventually, someone figured out that explosives are a great way to produce lots of gas in a split second. Protecting someone by setting off explosives in their face might seem a little bizarre, but it’s the simplest and most reliable way to fill an airbag in time to be effective. The major drawback is that explosives create toxic gases, that is until the discovery of sodium acid, which, when detonated produces mostly harmless nitrogen gas. The explosive charge is encased in a metal assembly to contain the detonation and is screened, invented to cool and filter the gas before it inflates the bag once deployed. The bag should inflate to absorb the momentum of the passenger, but not so much. The passenger will bounce off the biggest open question for building this project is the explosive charge, i’m not a pyrotechnician, so i won’t be making custom explosives for this project, but there might be a commercial substitute.
My first choice is model rocket motors because they’re, pre-packaged and relatively safe. Unfortunately they don’t light quickly or reliably and even small motors burn a lot longer than i need next. I tried smokeless gunpowder, but it won’t burn explosively unless it’s under very high pressure. Finally, i try fine grain black powder, which gives very satisfying results. The next question is how to ignite it quickly and reliably. My first attempt with a spark gap generator is pretty but doesn’t create enough heat to ignite anything. The next option is nichrome wire. It’S what’s in your toaster and can reach over a thousand degrees when a current is run through it, but it’s the same method used to light model rockets that i found so slow and unreliable.
Regardless. I tested a bit of 40 gauge nichrome wire and found it got hot enough to melt in about 1 40 of a second which i hope is fast enough. Next is the container to channel and cool the explosion. I build a paper prototype to see how it will work before i start shaping metal. I didn’t account for the thickness of the material in the design, so the final result isn’t pretty, but it will contain the explosion. I line the inside with several layers of screen to help filter out the bigger particles and cool the expanding gases for the brains of the airbag.
I prototype a circuit with an arduino microcontroller. A green status light shows that it has power. Orange connects to a switch that arms, the explosive charge and red comes on when the charge is triggered to make it able to withstand crashes. I mount the components, so most of the force will push the electronics down into the board, making them less likely to flex or rip out. Finally, to really keep everything in place.
I bought the whole thing in hot glue. I originally tried to use ripstop nylon for the entire airbag since it’s light and strong. However, after testing, i found it melted when exposed directly to the gas vents. I reinforced the vent facing areas with duct cloth, which is much stiffer, but can absorb a lot more heat before burning.
A real airbag is encased in plastic that will break apart when the bag is triggered. I want to use mine for more than one test, so i make my case from wood and put hinge doors on the front to do the final assembly. I first place an igniter in the center of a piece of paper and cover it with a measure of black powder, then seal it with tape.
The charge goes in the bottom of the explosion chamber, which is then sealed and attached to the case. The airbag is attached over it with screws, then folded and sealed here’s the first full up test. Happily, it deploys in about six hundredths of a second, too much gas escapes from the rear, but i can fix that by sealing the back with tape, so it inflates, but will it protect someone in a crash for that? I need to build a test.
Rig gravity provides a free source of acceleration and pulleys can multiply and change its direction. I mock up a 12 scale model where dropping a weight accelerates, a toy cart to over 40 scale miles per hour. The full sized rig is made from pairs of two by sixes and is over 15 feet high.
I build a simple trigger from a couple of hinges. One hinge clamps the rope securely while the other holds the clamp in place. I also need a test vehicle.
I build a small cart out of lightweight materials so that there’s less energy to absorb in a crash. It’S mostly aluminum channel and insulating foam, but it turns out the foam isn’t up to the challenge. So i replace it with more aluminum, supports and add additional shock absorbers to the front.
And finally, i recruit a honeydew melon as a stunt driver here is a 22 mile per hour crash without the airbag. It’S a good thing. My stunt drivers are cheap and now for the first full test with an airbag in place.
It deploys in time but deflates too easily for the next run. I sew some of the deflation vents closed. I also add weight to the back of the cart to prevent the roll over the next several tests, either fire too early or too late.
This was a real problem with early airbags and can cause serious injury by firing at the wrong time. In fact, much of the recent effort in airbag deployment has been focused on improving the algorithms that decide when and how hard to trigger the airbags. The final test could have been the most successful, except the explosive charge burned through both the protective screen and the airbag itself, giving my stunt melon a face full of flames. Also, his head fell off. Unlike my contraption.
A modern airbag system is a split-second symphony of technology sensors throughout the car coordinate to select which of many airbags to deploy saving lives and reducing injuries which helps us travel faster, safer, i’m steve hofer for make inventions. You .