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Old 10-25-13, 10:48 PM   #26
dougmc
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Here's such a system (on a truck, not a bike, and aimed forward) in action: http://www.youtube.com/watch?v=ridS396W2BY

Quite impressive.
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Old 10-26-13, 07:31 AM   #27
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You simply can't aim ultrasonic that tightly. ...
Seams to me, it'd be coupling and attenuation limiting the range at high acoustic frequencies in air that would be the problem using ultrasonic sensors. Consider medical ultrasound at 2MHz with a 4 cm wide sensor. Using the Rayleigh criterion, you could get an angular resolution ~0.3 degrees. Unfortunately, at that frequency and at reasonable powers, the range would be limited to a few cm in air. Frequencies 10 times lower would have one tenth the resolution with the same "antenna" width, but have much greater range...still likely not enough range to be useful in this application though.

Whatever is used and works, I still have trouble with seeing the utility. I car traveling at 40 mph is moving ~60 ft/sec and a bike at 15 mph is moving 22 ft/sec. Assuming it's coming at you with the intention of starting to move over to make at safe pass when 150' behind you, that's only 4 seconds. Lets say you'd only want a warning if the approaching car was within that, so less the 4 seconds warning. In that time you have to perceive and then react to the threat in some useful way. I don't see that as reasonable.
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Old 10-28-13, 08:30 AM   #28
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Use your ears and a $15.00 bar end mirror, YRMV.
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Old 06-06-14, 12:43 AM   #29
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Use your ears and a $15.00 bar end mirror, YRMV.
Ears don't do much. The car that's going to hit you from behind will sound pretty much the same as the thousands that won't hit you.
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Old 06-06-14, 12:56 AM   #30
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I think the fallacy in this approach is assuming you can get out of the way of a car that's going to hit you. You can't, not with a mirror, not with an early warning (because of too many false positives). It's an objective danger of being on the road at all (cars get hit from behind too). Stop trying to change objective dangers and focus on changing subjective dangers. Make yourself more visible, stay off busy roads etc..
Only if the bridge pylons are tilting...
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Old 06-06-14, 11:30 AM   #31
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Ears don't do much. The car that's going to hit you from behind will sound pretty much the same as the thousands that won't hit you.
Disagree, brake squeal, squealing tires and Bubba trucks all get my attention. ( Bubba trucks have loud exhasts, lift kits, and bad drivers, imho). Revving engines as well.
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Old 06-06-14, 11:34 AM   #32
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I think the fallacy in this approach is assuming you can get out of the way of a car that's going to hit you. You can't, not with a mirror, not with an early warning (because of too many false positives). It's an objective danger of being on the road at all (cars get hit from behind too). Stop trying to change objective dangers and focus on changing subjective dangers. Make yourself more visible, stay off busy roads etc..
Twice , using my mirror, I have avoided drivers drifting in my lane .One was on the phone, the other texting and looking down. I use my mirror constantly.
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Old 06-06-14, 11:39 AM   #33
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Sneak Peek: Radar Powered Vehicle Avoidance from Backtracker
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Old 06-06-14, 11:54 AM   #34
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The sensing and processing technology need not weigh more than a few ounces using laser radar, IR pattern triangulation (think XBox Kinect) or stereo vision and purpose-built ASICS with embedded processor cores. I work with very small digital video cameras that perform computer vision on an embedded processor the size of my fingernail. Power consumption would be less than or equal to that consumed by a bike light, mostly for those solutions involving an active emitter; the imaging and processing would require only a couple of Watts. For instance, any of the triangulation based solutions could be implemented by leveraging the block matching components already built into the motion vector estimators of commercial video compression SOCs used in low power digital video cameras and IP cameras.

I agree that the main problem is deciding what to do with such information with so little time. By the time one knows that a collision is imminent, there might not be time for more than deploying an airbag, which may or may not be practical - airbags involve technologies I know much less about.
Thank you for pointing out some of the practical technical information.

As I recall, IR and acoustic currently don't really have the necessary range, at least not with what's reasonably affordable for something like this. The technology for laser ranging devices however is doable IMO (although I'm not 100% certain that you could have enough parallax for a direction). Honestly I think that image processing is where we'll eventually see this, combined with laser ranging or radar to provide scale. Given some sophistication you could determine an object's motion, even better if you had two or more video sources. The processing power is nearly there generally, if not already there with specialized processors.

This type of device could be put to good use (not simply an automated collision avoidance feature). We like mirrors after all, and mirrors at best show us what's approaching and just an idea of how fast. This device could do the same, but with more information having better precision and more consistently, and displayed (or otherwise interfaced) more conveniently. It just takes a little imagination.
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Old 06-07-14, 02:43 PM   #35
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If ever a thread deserved to come around again, I think this one was a good candidate. Personally, I'm interested in an affordable rear view camera that could accurately show what's coming with enough resolution to determine what lane they're in and how close to the fog line they are as they approach. If it worked with a smartphone or tiny tablet, that would be reasonable. I've seen one offered (I forget which webstore), but the reviews were horrible.

Another reason why this discussion could be made current is because Google just demonstrated their little self-driving pod-car, and it looks for pedestrians and, according to their blog, understands bicycle hand signals. Whether it understands the more common "point to where you want to go," I didn't gleam.

By the way, I have been buzzed (on US 1, a four-lane in FL), but I don't have a morbid fear about being hit from behind and understand it's the least likely cause to actually happen. It is, however, the aspect that I think my actions have the least effect on. I can minimize the risk of the other common scenarios by exercising common sense.
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Old 06-07-14, 06:40 PM   #36
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I just use a mirror. I'm reminded of the apocryphal story of how the US space program developed a special pen for zero gravity at a cost of millions of dollars and the Soviet program used pencils in space. Sometimes, old tech is best.
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Old 06-07-14, 09:31 PM   #37
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sorry if someone posted it already.. I didn't feel like reading all the post.

Sneak Peek: Radar Powered Vehicle Avoidance from Backtracker
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Old 06-08-14, 05:57 AM   #38
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You guys are working the problem wrong... put the detector on the automobile and make them avoid cyclists. This is already being done in some expensive luxury cars that have mm wave radar systems to help them avoid things like deer.

Don't complicate the bicycle, it is near perfect as it is. Not to mention that avoidance of objects in front of the vehicle is the responsibility of the driver of that vehicle (be it computer or human). This is even written into law.
Not to mention, a cyclist may react by shifting one direction or another and wind up placing himself/herself right in the newly adjusted path of the motorist trying to avoid a collision.
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Old 06-08-14, 08:21 AM   #39
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I'm not a fan of mirrors (and feel I can't judge a car's side-to-side position very well with them)...
Like anything else, it takes a little practice. Hat/eye-glass mounted mirrors shake less and can survey the entire scene behind you without turning the handlebars. These small mirrors are FLAT so reflection is actual size as opposed to those convex mirrors made for handlebars which make things look tiny AND are not positioned at eye level.

Mirrors are light, waterproof, cheap, have no moving parts, do not require batteries, and never need winding. Most motor vehicles have at least 3 mirrors with most large trucks needing at least 4. You just need one itty-bitty one.

Sorry, I know this was not the answer you were looking for. But a mirror is THE answer for most cyclists with your concerns.

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Old 06-08-14, 07:02 PM   #40
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Like anything else, it takes a little practice. Hat/eye-glass mounted mirrors shake less and can survey the entire scene behind you without turning the handlebars. These small mirrors are FLAT so reflection is actual size as opposed to those convex mirrors made for handlebars which make things look tiny AND are not positioned at eye level.

Mirrors are light, waterproof, cheap, have no moving parts, do not require batteries, and never need winding. Most motor vehicles have at least 3 mirrors with most large trucks needing at least 4. You just need one itty-bitty one.

Sorry, I know this was not the answer you were looking for. But a mirror is THE answer for most cyclists with your concerns.
+1 for cyclist worn mirrors

The company I drive for has VORAD or one of the equivalent on all the new tractors and I find it to be fairly useless. Mirrors are the way to go, warning devices are still too random and redundant for all but the very worst drivers who probably won't react correctly anyway.
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Old 06-08-14, 07:30 PM   #41
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Just to tinker, I was / am going to fabricate a rear sensor out of a radar unit that blind people attach to their canes that emits different tones when they are approaching stuff. My company makes them and I got hold of an out-of-date unit so just for fun, I was going to experiment with it.
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