Impact detection sensor for car

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Hi all,
This is my first time posting, but I've been lurking around for a bit now. I want to find an appropriate sensor to detect small impacts at different places on a car's body (think door dings, parking lot bumps, etc.) I need a sensor that will help me sense an impact, so that I can then react to it by doing something else. At this point, I don't care to know where the impact occurred, just that the car has been hit. My preliminary research has me contemplating the following options:

- accelerometer(s) - don't know if the cheap hobby-style units have enough sensitivity to sense a very light impact. Don't even know the ballpark strength (g's) of such an impact.

- shock or vibration sensor (e.g. http://www.sparkfun.com/commerce...) - this would probably require more sensors and trickier installation. It seems like you would need one sensor/body panel.

Anyone thought about this before? Any suggestions appreciated. Thanks!

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Air bags fire upon detecting a couple of Gs decelleration. Needs to happen within some small 10s of ms. Parallax has a 3 axis accelerometer at radio shack for about $30. Parallax has a pic example, but I got mine working with imagecraft c. You could make a data logger out of it, tape it to your car and bang on it with a hammer and see if it detects. Great idea huh?

Imagecraft compiler user

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Welcome to the forum.

I think this would be a challenging project.

This Image shows the G forces on me driving around. Pretty low G range, and you should see me drive.

Tapping the car, given the energy of a "tap", and the mass of a typical car, would clearly be in the noise level for the sensor I was using, (data not in front of me, but IIRC a full scale < 5 G sensor).

JC

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Very interesting plot. 1G for a car accelerating is pretty high. Mind if I ask what you drive?
I'd love to experiment and take some measurements, like bobgardner suggests, with a high precision accelerometer. Any suggestions on which one I could use? Something very sensitive?

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Quote:

I need a sensor that will help me sense an impact, so that I can then react to it by doing something else.

So does Tiger Woods.

[What is the difference between a Cadillac and a golf ball? Tiger can drive a golf ball 300 yards without hitting a water hazard and a tree.]

Quote:

small impacts at different places on a car's body (think door dings, parking lot bumps, etc.)

Where do you think you could put a sensor to record >>any<< G-forces such as a door ding? Or even a good "tap" on any of today's energy-absorbing bumpers.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Quote:
Mind if I ask what you drive?

At the time I was driving a KIA Sorento SUV. (I have not had anything "sporty" in way too many years...).

(Semi OT: My first Pursuit and Emergnecy Vehicle driving course was in college, and I've taken multiple refreshers over the years. Knock on wood I've never rolled an SUV!)

This one was my Ford Explorer, which I drove before the Kia.

JC

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If all 4 wheels are locked, you are decellerating at 1G. 22mph per sec. Hit the brakes at 88: 66,44,22,0. 4 sec to stop. When the vomit comet pushes over, I guess his vertical velocity goes 22,44,66,88 etc till hes going down as fast as he can.

Imagecraft compiler user

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bobgardner, sorry, but you are wrong with 1g decel claim. The deceleration with 4 locked wheels is not necessarily 1g. It depends on the coefficient of friction, mass of the car, and tires (in real life), which can all vary. Imagine the same vehicle with 4 locked wheels on ice or a slippery road - it will decelerate at a different rate. Or change the tires - same thing.
But back to my original question.

Quote:

Where do you think you could put a sensor to record >>any<< G-forces such as a door ding? Or even a good "tap" on any of today's energy-absorbing bumpers.

Metal body panels transmit vibrations pretty well, so if you have a sensor mounted on the panel that's hit, I'm guessing it shouldn't be hard to detect, at least with a vibration sensor. If using an accelerometer, I don't know...
Now, if we just have one accelerometer mounted, say, on the roof, that light impact could be completely absorbed between the place of the hit and the sensor. That's why this is such a dilemma for me. :-)

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If the multi billion dollar car industry, with all it's combined research and development departments, has come to using accelerometers for air bag deployment (crash detection) - I would think it's probably the most suitable route to take. You can probably find some automotive engineering books on Amazon that will show you common ways to solve your dilema.

No point re-inventing the wheel is there?

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I'd argue here: (but what the hell, I'll argue anywhere!)

Accelerometers are all very well for detecting a 5-g stop, but as others have said, the effects of the door-ding-gnomes are a tiny fraction of that - and probably occur a lot more slowly.

I'd be tempted to glue a couple of crystal microphones to a panel and see what comes out when you ding it. An engine detects knock in the cylinder with essentially that mechanism (coil round a magnet) and some simple analog signal processing. It ought to produce some useful output.

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A design I worked on needed a sensor to tell if the equipment was moving. Look at this company's product. http://www.comus-intl.com/productpages/movement_vibration_switches_us.asp

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Thanks a lot for all the great suggestions. My next step will be to see what kind of signal I can get with an accelerometer placed at different places on the car. If that fails, I'll start experimenting with other sensors. I like the microphone idea, maybe I'll try that out too.

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Wow. It never occurred to me that locking all four wheels on ice wouldnt stop as fast. I claim coefficient of dry rubber tire on dry asphalt is sufficiently close to .99 that my 1G statement above is true within about .1G. Furthermore, I claim mass of car and type of tire variation in any combination will not give a reading off more than .1G than what I claimed. To convince me otherwise will take either an experiment with a stopwatch and tape measure or a text file with calcs and assumptions shown. I actually think a +-1.5G sensor running from 5V (better s/n ratio on a/d) will detect a shopping cart bump. If 512 counts is 1.5Gs, an LS bit is about 3 milliGs.

Imagecraft compiler user

Last Edited: Sat. Dec 19, 2009 - 03:59 PM
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Maybe the impacts you're going to detect really are so tiny that the force/vibration way is impractical. How about some kind of proximity/touch/field detection?

JHJ

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bobgardner wrote:
I claim coefficient of dry rubber tire on dry asphalt is sufficiently close to .99 that my 1G statement above is true within about .1G.

According to the Wikipedia article on friction: "Contrary to earlier explanations, kinetic friction is now understood not to be caused by surface roughness but by chemical bonding between the surfaces."

The usual equation for friction, namely, Ff <= μ Fn, holds only for friction caused by surface roughness. Friction caused by chemical bonding depends, instead, on the contact area.

If it were true that a car's deceleration is limited to 1 G, then acceleration would be similarly limited. This would imply that the fastest possible quarter-mile time is:

t = sqrt (2 * d / a) = sqrt (2 * (400 m) / (9.8 m / s^2)) = 9.03 s

The current record of 4.428 s is less than half of that.

Michael

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As technology goes advanced that’s why we can find additional features in our vehicles. Impact detection sensor is truly useful. There are different types of sensors are available in cars namely shock& impact sensors, vehicle crash sensor, collision avoidance sensors, vehicle detector sensor etc.

Up-to my understanding shock and impact sensors are designed to detect instances of sudden impact or severe vibration in order to output a value or, in the case of impact switches, activate or deactivate a circuit or device. As far as I know impact detectors are used for variety of applications i.e. tap detection, micro-drive protection, shipping and handling, automobile security system etc. To know details about sensors it’s better to contact your auto servicing center. I think to talk with an expert mechanic is the best idea.

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Impact/airbag sensors are in the front of car. The sensors, like in any other system, helps find any change in the standard values. When any collision occurs, an accelerometer records the change, above 20kmph to 30kmph speed, which in turn inform the sensor to inflate the bags. Check out the image: 

Airbag sensor process

To know more about the Airbags inflation process: https://autoportal.com/articles/safety-technology-in-car-airbags-2680.html​

Last Edited: Tue. Mar 27, 2018 - 05:00 AM
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Doing this with accellerometers does not seem like first choice to me.

Small dents and nicks are probably not enough to move the whole car and therefore register on your acellerometer.

Especially if the dent is made by high speed low mass objects such as flying pebbles.

 

You can also try "contact microphones", which are a piezo crystal with a weight, very similar to the vibration sensor from sparkfun mentioned earlier.

These are often used for tuning musical instruments. Imagine an orchestra of 100 people who all want to fine tune their instrument just before a performance...

In anti-burglar systems "glass break" sensors are pretty common. As far as I know these work with a microphone and a DSP which analyses the sound for specific characteristics of breaking glass to make them immune to other sounds.

 

@bobgardner:

You should really lubricate your rubbers and try it yourself if you can't imagine that road conditions have a significant influence on grip.

https://en.wikipedia.org/wiki/Formula_One wrote:
The cars underwent major changes in 2017,[4] allowing wider front and rear wings, and wider tyres, resulting in cornering forces closing in on 8g

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

Last Edited: Mon. Mar 26, 2018 - 02:03 PM
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@Paul: note that bobgardner last comment here was 2009.

 

The necromancer seems to be just spamming for publicity for her/his article

 

frown

 

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As this looks like spam to simply boost links to the article I have corrupted the link so the Google webbots won't find anything and therefore the page won't get a higher search score. If anyone is really interested in this (though the thread was clearly dead) replace XXX in the URL with "auto".

Last Edited: Mon. Mar 26, 2018 - 02:09 PM
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awneil wrote:
The necromancer seems to be just spamming for publicity for her/his article
Gosh, I didn't even read that last post, but didn't look at dates either. Auto locking old threads seems like a good idea, but has been mentioned before (multiple times).

 

Another idea which I have seen is to put a glaring read banner on old posts to alert new posters of such things.

And bob may still lubricate his rubbers if he wishes to do so.

But without this thread I would not have known that F1 does upto 8g in corners.

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

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clawson wrote:
I have corrupted the link

I think you've just edited the visible text - not the actual target URL ... ?

 

try now ;-)

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
Last Edited: Mon. Mar 26, 2018 - 02:32 PM