Red Light Changer

I used to go to work early in the morning for a few years on a motorcycle. There are (as you know) many lights that stay green for the main highway at night, until something comes along on a side street to trip the sensor. Many a time, I made a right turn, U-turn, and then another Right turn to get through those lights...wish I had known back then...
 
FWIW, in AZ it's considered a "nonfunctioning traffic control light" if it doesn't change when you are on the sensor, after a "reasonable period", and as long as there is no opposing traffic there's nothing wrong with simply crossing anyway, regardless of the kind of vehicle you're in. I suspect the same is true in most places, but I don't know the laws in any other state.
 
Regmeister, thanks muchly for the insights; quite illuminating :)

<sigh> For the latter, it appears that the Frame must be steel or have permeance attributes to take advantage of the effect. I rather like the former - being that the gismo is at the bottom, though not the fin-antenna.

Measuring for a fitting, KF
 
It is interesting that they state flatly that the magnet cannot work, but I have empirically tested that they do, in at least some cases. Probably it depends on the sensor's threshold setting, as if it was very close already, then riding directly down the centerline of the sensor loop (or sometimes the left or right edge cut, depending on the intersection, possibly having to do with depth the loop is buried at), and passing over it at specific speed ranges. Too slow, and it may not work at all, too fast and it won't have time to change the light before I'm in the intersection running a red. :lol:

It doesn't work if I just add iron mass to a bike, in any position lengthwise or heightwise, but it does work with the harddisk magnets.

It also works with some speaker magnets; for some reason it works better if I have a broken ring magnet than a whole one (tested using identical magnets from a pair of blown speakers, one of which I broke in pieces getting it out). :?
 
The oscillator gizmo is interesting. He's right about the sensing coil needs to shift in frequency in order for the sensor to trigger. I susupect the gizmo works by creating a frequency that's slightly off from the sensor's. With enough power, it should overpower the oscillator's natural frequency. The bike frame transformer looks like a torroidal core over the frame and uses the frame as a large, single turn coil. That should work with either steel or aluminum, but the self-resonant frequency will vary widely between bikes.

My experience with metal detectors is they are most sensitive at the center of the loop, and not so much at the edge, depending on distance. They are also affected by capacitance, but being burried and probably shielded should eliminate that pretty much.

Here's some interesting data:
Finding the sensor's sensitive spot:
http://www.humantransport.org/bicycledriving/library/signals/green.htm
Sensor principle of operation:
http://www.humantransport.org/bicycledriving/library/signals/detection.htm

Sounds like most of them operate 20 - 30kHz.
They also mention marking the pavement with lines to indicate the sensitive spot for bikes. That sounds like a good idea.

Now if there was a way to blast the thing with a few hundred watts from a motor controller at 20kHz you might have a way to trigger it from a distance. That's right in the PWM frequency range of many controllers. Perhaps a coil in series with a phase wire with a switch to bypass it during normal riding might do something. Then just hold the brake and give some throttle to generate a disturbance.
 
fechter said:
They also mention marking the pavement with lines to indicate the sensitive spot for bikes. That sounds like a good idea.
Click to expand...
Yes, it does. Too bad the only way it would happen is if cyclists were to do it guerilla-style. :(

BTW, I forgot to mention that in Glendale, there are separate sensors in some of the bike lanes, but they are not sensitive enough to actually pickup many bicycles. They work on CrazyBike2, but not on DayGlo Avenger or even on a couple of other steel-framed regular bikes of mine, nor on many, maybe even most, of the bikes I see riding thru there. Lots of regular cyclists I see on the same paths all the time don't even bother, and either just stop and then ride thru when it's safe to, or ride up onto the sidewalk to press the walk button.

With the magnet trick, more of the bike-lane sensors work than the car-lane sensors, but even then not all of them do.
 
"
A popular myth is that a strong permanent magnet will do the trick. This is complete nonsense, since a magnet produces a constant (D.C.) field and can not change the inductance of the sensor loop, nor can it in any way pull the frequency of the sensor's oscillator. One must inject a signal at or near the operating frequency of the loop in order to cause the sensor to notice a change.
"


Holy chit. What does this guy think happens when you put something in the loop of an inductor that increases or decrease the core permability. Does he think when a car sits on top of it that it injects a signal at near the operating frequency? lol Clueless. It's unrelated to the magnets magnetic field, it would work equally well in a relaxed state with no field, it's just being used as high permeability core material for the inductor.

Straight from the inductor article on wikipedia:

" For example, the magnetic flux linking these turns can be increased by coiling the conductor around a material with a high permeability such as iron. This can increase the inductance by 2000 times."


You pick the material with the highest permeability you can find, and you put it as low, and ideally as centered in the loop as possible, though it doesn't make a lot of difference as long as you're inside the loop.

What material has the highest permeability?
Mu-metal.

And using Mu-Metal rather than a magnet (which also has good permeability) avoids having a bunch of things stick to it.
10grams of Mu-Metal can have the same inductive effect as a 200Kg of steel sitting over the sensor.

Your goal is to alter the resonate point of the coil. That's how it knows something is there. Coil some wire up, measure the inductance, slip in a chunk of magnet or a kitchen fork or mu-metal, or whatever the hell you want with permeability, re-measure inductance, it changes, this makes the resonate point change and it knows a car is there. I've done these tests before with my motorcycle, and anyone else here can duplicate it in 10mins. Find a light with no traffic. Set a hard drive magnet in the coil. Watch it change.
 
One of the main factors here is the size of the object shunting the field relative to the size of the coil. A small object, no matter its permeability, will have a small effect. A larger object (even thin sheet steel) that is a good fraction of the size of the coil will have great effect.

Unfortunately this is not good for a bicycle.

Another approach is to use a passive coupled tuned circuit near resonant to the frequency they are detecting. That will pull their oscillator. Unfortunately they are not likely all the same frequency. But one could build something that would sweep, and I suppose it could be coordinated with a GPS so it would tune the proper frequency depending on which signal you were waiting for...
 
Alan B said:
One of the main factors here is the size of the object shunting the field relative to the size of the coil. A small object, no matter its permeability, will have a small effect. A larger object (even thin sheet steel) that is a good fraction of the size of the coil will have great effect.

Unfortunately this is not good for a bicycle.

Another approach is to use a passive coupled tuned circuit near resonant to the frequency they are detecting. That will pull their oscillator. Unfortunately they are not likely all the same frequency. But one could build something that would sweep, and I suppose it could be coordinated with a GPS so it would tune the proper frequency depending on which signal you were waiting for...
Click to expand...

I agree the limited size makes it's tough, that's why getting it close to the ground, as the highest permeability material you can find becomes more critical.

But a magnet all ready works. This stuff has been tried and proven on every motorcycle forum I've ever been a part of. Some traffic lights seem to be very unresponsive to anything, even light cars. Most traffic lights trip fine off a hard drive magnet alone.
 
I should add, my Honda Insight, which features an entirely aluminum chassis and aluminum suspension often struggles with traffic lights that my GSX-R 1000 fitted with a couple HD magnets glued into the inside lip of the lowest part of the fairing can easily trigger. I guess I need to fit magnets (or a Mu-Metal foil strip) to my insight as well. lol.
 
mumetal-roll.jpg

Mu-metal on ebay

Makes yer eyes water just thinking' about it, huh :twisted:
<Dr. Evil laugh> KF
 
Mu metal is the stuff to give the maximum change in inductance. If you wound a coil around some Mu metal or possibly ferrite, and put it in parallel with a capacitor to make it near resonant at the sensor frequency, it might be able to pull the oscillator from a good distance. I think this is how some of those anti-shoplifting sensors work. The problem there would be possibly different frequencies at different intersections.

How about some thin Mu metal shoe liners? They would stop thorns too. :wink: You could stick your foot right over the crack where the coil is to get the distance as close as possible.

I still wonder about the hard drive magnets. They're usually mounted on a chunk of high saturation kind of Mu metal. Maybe the backing does more than the magnet? Maybe the magnet material itself has a high permeability. The fact that it's magnetized might not have much to do with it.
 
Shoe liners: Brilliant Richard! Up till now I was thinking along the lines of plating the down tube and bottom of the rear suspension. But the shoes – that’s the ticket! :idea: :wink:

Touché, KF
 
Say, how thick would that MuMetal need to be for insoles?

BTW – I found some magnetic insoles here:

Worshiping crystals next, KF :lol:
 
I'm not sure what thickness is needed. Obviously thicker is better, but I suspect there won't be much change beyond a certain thickness. I have some Mu metal at work. I'll have to try this out, as there is one signal that frequently won't change for me. If the stiffness of the metal is a problem, I think you could cut it into segments and tile them together with tape and it would have the same effect as a solid piece.

The field strength at the shoe will be way below the saturation point, so that won't be a limitation.

If Mu metal is too exotic, just plain old low carbon steel might do the job but the permeability is quite a bit lower.
 
I used to commute in OKC on an XR600 and it wouldn't set off any lights. I saw the ads for the different devices and thought I'd stick a big neo magnet on the frame and try it. It was a round one the size of a golf ball. It triggered every light I came up on. I thought it was a pretty slick solution and felt dumb for waiting through so many lights and getting two tickets for proceeding safely after 120 seconds. Cops in Oklahoma are awesome.
 
mdd0127 said:
I used to commute in OKC on an XR600 and it wouldn't set off any lights. I saw the ads for the different devices and thought I'd stick a big neo magnet on the frame and try it. It was a round one the size of a golf ball. It triggered every light I came up on. I thought it was a pretty slick solution and felt dumb for waiting through so many lights and getting two tickets for proceeding safely after 120 seconds. Cops in Oklahoma are awesome.
Click to expand...

Sounds interesting, although the idea of an infra-red strobe attached to my helmet visor just sounds so kewl!! :twisted: :twisted:

How much did your giant neo magnet cost ya?
 
I have absolutely no idea where that magnet even came from. It was stuck to my crimping tool in my toolbox one day and pulled every tool out of the box when I went for the crimpers. I used to install car audio and alarms so my best guess is that it was on someone's floor and I didn't notice that it had stuck to the crimpers. Either that or my boss or one of my co-workers was playing a practical joke on me. I did look pretty confused when I reached into the box for crimpers and a magic string of tools came out. I've never seen one like it and accidentally sold it with the bike. It was a very serious magnet though. If you stuck it to an iron I-beam, the only way to get it off was to roll it off. The day I found it, I had it in my pocket and walked a little too close to my car door. It made a nice dent.

They may have changed sensor types in the last few years or something but I know for sure that 5 years ago in OKC, a strong magnet on the lower front or your frame was your friend.
 
This company sells round Nd magnets, as well as "Neodymium Motorcycle Traffic Light Magnets" (where the link leads)>

Cameron
 
You can get ridiculously large magnets like that several places around the interwebs. :D These two 2" spheres, for example:
http://www.kjmagnetics.com/proddetail.asp?prod=SY0
http://unitednuclear.com/index.php?main_page=product_info&cPath=70_71&products_id=281

K&J Magnetics is usually cheaper, but if you want something truly absurd...like this 2"x3"x2" block...United Nuclear is one of the few places I've seen them actually for sale.
http://unitednuclear.com/index.php?main_page=product_info&cPath=70_71&products_id=289

Honestly though, I wouldn't want one as powerful as that 2" sphere on a vehicle that I was planning on driving around. :p

EDIT:
Whoops, nvm, turns out K&J has expanded their inventory of absurdly huge magnets since I last checked. ..like this 4"x4"x2" N52 block! 1,226.5lb of pull force! :shock:
http://www.kjmagnetics.com/proddetail.asp?prod=BZX0ZX0Y0-N52&cat=168
 
Yeah, who needs tow-chains, anyway. Just pull up close to the vehicle, latch on, and drive away with the both of you. :lol:


Realistically, if you have old dead harddrives laying around, you could just pull the arm magnets out of it, stick them on your frame, and it'd probably work for many lights. I'm not sure if more separate ones in different places on the frame works better than sticking them all into one physically large block, as I haven't tried that experiment yet.
 
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