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Has anyone had experience with any of the devices advertised in cycle magazines that supposedly enable a traffic light to sense the presence of a cycle? There are two lights in town here that won't change unless a car pulls up so a left turn is impossible unless one runs the light when it is safe. That is just inviting a meeting with an unseen patrolman.
 

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There was a review of this product some time ago in Wing World by Stu Oltman (WW's Tech Editor at the time). Believe it was then called "Stop light Trigger" a magnet about 6" Long that strapped to the Wing's center stand. Was found to be ineffective in triggering lights to change.

I've always had better luck coming to a stop over one of the embeded sensing lines in the pavement. Since a cycle doesn't have the mass of metal an auto has, it's best to get what you do have right over one of those lines.
 

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FYI

http://www.greenlightstuff.com/trigger.html


And by the way:

If we wait our turn at a stop light that won't trigger, and it's late a night, no cars, and just say a cop sees you *carefully* proceed through the light - if he does give you a ticket, wouldn't it be easy to beat in court? Sure, you might have gone through the light, but pardon us for not being a 3 ton SUV - don't we pay taxes too? Either fix the light to work for motorcycles (there are millions of us), or at least put common sense before protocol when we decide to inch through a red at night instead of taking 5 mile detours. My 2 cents.
 

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Ironshark,

I read some of the same stuff you have, being poor, I decided to order some small but very powerful rare earth magnets from a gent on eBay. I installed it under the bike & have been careful to always approach over the sensor loop line & thus far it has worked quite well for me.

Just a thought for you, & welcome to the ICOBO!
 

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Chuck, I have a Lee Valley Tools store in my neighborhood as well as one of those lights that won't change (two actually), for me at night.

Lee Valley sells those magnets too.

Can you tell me how many magnets you used and what size?

Think I'll try that.
 

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Traffic Light Sensors & Magnets

The traffic light sensors that you are talking about work by induction and
will be completely unaffected by a magnet, especially the small magnets
are sold for this purpose. By small I mean in terms of the mass of metal
making up the magnet. The magnetic field of the magnet will
have no effect whatever on the traffic light sensor.

Motorcycles dod not activate the sensors because they contain far less
metal than an auto, even a small one. Scooters such as the Burgman are
even worse, in that the body is almost entirely plastic.

A trick that some cyclists advocate is to fool the sensor by dismounting and placing a wheel of the bicycle immediately above the sensor, assuming you can identify the sensor site. By placing the wheel in very cloxe proximity to the sensor is apparently sufficient to (maybe) activate the sensor. I haven't tried it, so I have no idea if it works or not. though personally I am very skeptical and doubt it. And obviously, this is not practical with a motorcycle or scooter.

But one thing is certain : money spent on magnets for this purpose is
money wasted. A lot easier (and cheaper) to look right, left, front and back for traffic and police and if the road is clear, just scoot on through the red light. Which is what just about everyone does in these situations.
 

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Minnesota passed a law which allows a motorcyle rider to pass thru a red signal if they have given the lights adequate time to cycle and be sure that the bike won't trip the sensor. You may proceed only if the way is clear, of course.
 

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I purchased a 150#(pull) magnet at Harbor Freight for both our cruisers... it's about 10"X2"X1". Attached it under the bikes to some ferrous metal part and then put 2 zipties on it for extra security. Works great. Cost $7.50 at the time.
 

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tkw said:
The traffic light sensors that you are talking about work by induction and
will be completely unaffected by a magnet, especially the small magnets
are sold for this purpose. By small I mean in terms of the mass of metal
making up the magnet. The magnetic field of the magnet will
have no effect whatever on the traffic light sensor.

Motorcycles dod not activate the sensors because they contain far less
metal than an auto, even a small one. Scooters such as the Burgman are
even worse, in that the body is almost entirely plastic.

A trick that some cyclists advocate is to fool the sensor by dismounting and placing a wheel of the bicycle immediately above the sensor, assuming you can identify the sensor site. By placing the wheel in very cloxe proximity to the sensor is apparently sufficient to (maybe) activate the sensor. I haven't tried it, so I have no idea if it works or not. though personally I am very skeptical and doubt it. And obviously, this is not practical with a motorcycle or scooter.

But one thing is certain : money spent on magnets for this purpose is
money wasted. A lot easier (and cheaper) to look right, left, front and back for traffic and police and if the road is clear, just scoot on through the red light. Which is what just about everyone does in these situations.
Don't take this personally tkw, I don't mean to sound like a smartass but that is total B.S., Next to my Clearview XL vented windshield, my Greenlight trigger was the best thing I've purchased for my bike. It works likes a dream. No more having to run those red lights and never getting a left-turn arrow! There is one light my town that it won't change, all the others work like a charm. It is about 2.5 inchs long by 1 inch wide, mounts under the bike, you just roll slowly over the sensor and you'll get your green light 98% of the time.
I don't work for them, not affiliated in any way, but it's the best $15 I've spent on my bike!! You are completely mis-informed/wrong and I feel you are doing a real disservice to everyone who reads this.
You can keep running those red lights and take your chances with the law or buy a greenlight trigger (or an equally powered rare earth magnet) and be as happy as I am. As a relatively new rider (1.5 yrs) I've been shocked at how many people have been riding for years and don't even know that these devices are available.
 

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I recently bought a package of five 1" rare earth magnets.

I put 3 under my oil drain plug and two on the lower rad area.
So far, they have worked like a charm.

Within a few seconds of pulling up to what used to be a problem light in my neigbourhood, the "Don't Walk" light starts flashing for the cross street, and then it changes to green for my direction.

It helps to ride directly over a seam in the pavement where they have installed the sensors. :D
 

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We had a light in our neighborhood that would not trip with our cruisers. So I bought 150# pull magnets at Harbor Freight for $9 each and put them under my and my wifes cruisers... Works on almost all lights in our area.. Once in a while it takes the two of us to go into the sensing zone to trip a light but that's rare..

BIll...

PS I'm not sure if the magnet it's self has any effect, it just might be that little extra amount of iron that is doing the trick?
 

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As to the light sensors that work by induction, but won't sense a magnetic field - that's nonsense, electrically speaking.

Take a loop of wire. Put a sensitive voltmeter on it. Move a magnet past it. You'll see a small voltage. Now put a small current into the wire. Move a hunk of iron past it. You'll see a small voltage change. Put a current in the wire and move a magnet past it. You'll see a voltage change. Go see:

http://www.uark.edu/depts/aeedhp/course ... cument.htm

Either way it's the same principle. If it didn't work that way, neither electrical generators nor electrical motors would work at all.

Magnets will work, but they will work best if their field is not "short-circuited" through ferrous metals.

Glue a strong magnet on either side of where the fairing passes under your feet, but at least an inch away from frame members.

Don't put them in line with the rear tire, unless you like having that screw that was picked up by the magnet thrown under the tire at speed. And be sure and occasionally clean those screws and nails off the magnets!
 

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Triggering Traffic Light Sensors

I have been unable to find a single review of motorcycle magnets which shows that these things work in terms of triggering traffic light sensors.
If anyone knows of such a review, perhaps the site or review could be posted. If you think that the magents work, fine, but personal
opinion is not a review, at least not in my books. People believe what
they want to believe.

There is a discussion on triggering traffic light sensors at

http://bicycleuniverse.info/transpo/tri ... gnals.html

and parts of the discussin are excerpted here. Note comments
on Green Light Trigger mgnets for motorcycles.

Triggering Traffic Signals with a Bicycle
How to trigger Vehicle Loop Detectors

After we published our original article on this subject, we received the following from an engineer who seems to know what he's talking about:

"I read your article on triggering traffic signals with a bicycle and would like to tell you a few facts about vehicle detectors as I am a designer of these units. Firstly, magnets have no effect at all on loop detectors (unless of course the magnet is so big that it acts more like a big mass of metal.) If you want to trigger the traffic lights with 100% certainty, simply get off the bike and lay the front wheel of the cycle flat over the loop towards one corner for a second or two. The rim of a cycle wheel acts like a big short circuited turn of wire and used in this way will produce a bigger signal than most automobiles do. The reason for this is that you can place your wheel flat on the ground so that it is about 10 x closer to the loop than most automobiles can reach." -- Graham Lill, Dept. of Infrastructure, Energy, & Resources, Tasmania

Experimenting with ways to trigger traffic signal detectors

by Barry Stephens, Dec. 2002

Last month I began riding a bicycle regularly for exercise. I ride mainly at night and in the early morning when there are fewer cars on the streets. I was getting frustrated with traffic signals not changing for my bicycle so I made some attempts to solve this problem.

First I found out everything I could about traffic sensors. I found that many of the traffic signals in Austin have sensor loops placed in the pavement. Most, but not all are visible on the surface of the pavement as saw cuts, where a buzz saw was used to cut a groove in the pavement. Later a wire is put into the groove in the shape of a square or rectangular loop that is used as part of a big metal detector. The metal detector/sensor loop is supposed to "tell" the traffic signal when a vehicle is in the lane/over the loop and change the traffic signal to green. The loop cuts are sometimes covered over by later pavement and cannot be seen, but most of the ones I saw in Austin were not covered and were easily visible (see picture). Information obtained from the City of Austin indicated that the best way for a bicycle to be detected by a traffic signal sensor loop is to place both of the metal wheels directly on top of one of the sensor loop cuts. I tried this and it is true. Remember though that if the rider is busy looking for the loop cuts and attempting to place the bicycle wheels on one, (s)he's not watching traffic, either. Also, loop cuts covered by tar or paint will become very slick when wet.

I also attempted to trigger the signals with magnets. My first trial was with Radio Shack magnets on the bottom bracket of the frame, which did not work. While browsing the internet I came across the Green Light Trigger (GLT) which is a magnet made for motorcycles to make them more "visible" to traffic signals. I purchased a GLT at a local custom motorcycle shop for $10.80. I placed it on the bottom bracket of the frame and thought that it might be working. Later I moved the GLT to the bottom of the left pedal (see photos) where it seemed to work better.

After riding around for a few days it seemed like the magnet was working but I was not sure how well. So I did a test at 43 Austin traffic signal sensor loops. My results indicated that placing the wheels of the bicycle on a loop cut works just as well as a GLT. The magnet sometimes makes the traffic signal trigger a few seconds sooner but that was the only benefit noted. The bicycle used for the test was typical, Steel frame road bike with alloy wheels and plastic/resin ATB pedals. During the test I saw many other people out riding bicycles at night. Half of them had no lights and I did not see any that were thinking about triggering traffic signals.
 

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Traffic Light Sensors (cont'd)

A fairly lengthy discussion on the use of magents and their ability (or lack thereof) to activate traffic light sensors can be found at

http://www.mcnews.com/anforum/topic.asp?TOPIC_ID=86988

and portions are excerpted here. Not excerpted is the suggesion from one member of MCN news that the magnents are most effective when placed on the end of your kickstand. You then put your kickstand directly on top of the light sensor, then get off your bike and go and push the walk button for the light. Works every time.

----------------------------------------------

Anyone got any experience with the magnet type units that mount under the bike and are intended to trip the loop on traffic lights? Do they work or not? -RM

rnielsen
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98 Posts

Posted - 03/20/2005 : 15:39:49
I'm pretty sure MCN tried one out with mixed results. Sometimes it worked and other times it didn't.

The reason may be simple as to the discrepancy. Most modern lights use a coil under the pavement as part of an oscillator. The presence of ferrous metal (steel and iron) alters the inductance of the coil and changes the oscillator frequency. The change in frequency is detected and is the trigger for the signal to change.

Years ago the oscillator circuit could be "tuned" or adjusted for sensitivity. Nowdays the oscillator is a sealed module with no adjustability. The placement of the coil, the mass of ferrous metal above it, and the position of that mass determine whether the light will recognize the vehicle approaching.

You can maximize the effect by keeping your frame directly over the coil (if marks are visible on the street) or, when stopped you can help a bit by putting your sidestand down right over the coil. If your bike is in gear that can kill the motor -- put it in neutral. That doesn't always work, especially if the sensitivity is low, but it sometimes helps.

I got our city engineer (Minneapolis, MN) to replace the module on a nearby intersection when I couldn't get any of these tricks to work. It took three tries, but the third module did detect my bike (Suzuki Bandit) reliably even without putting the sidestand down. I called the city and asked for the engineers dept. and then asked them to try something -- they were quire accommodating and a technician met me at the intersection after rush hour was over to resolve it.

The magnets radiate a magnetic field that should affect the coils inductance according to the speed with which the field crosses the coil. Speed is the key here -- I suspect a slow, rolling stop wouldn't be effective. The key is speed as magnetic lines of force induce a voltage according to the speed of crossing.

Good luck and report back if you buy the magnet.
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A magnet is a magnet. There's nothing special about the magnet they sell just for bikes. You're paying a lot of money for fancy packaging. If you want a good magnet, then find a surplus hardware store and you'll find plenty of them for just a dollar or two. Use a hose clamp or zip ties to attach it to your lower frame, and you're all set.

'97 FXDWG: turbocharged
40,000+ miles

rnielsen
Junior Member

98 Posts
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Posted - 03/21/2005 : 15:00:03
The key is still speed of approach over the buried coils. A magnet is usually not ferrous material (iron or steel), rather it's often ALNICO an allow or Aluminum, Nickel and Cobalt.

The magnetic field must cut into the wires enough to induce a voltage that shifts oscillator frequency, which is then detected by a discriminator to trip the signal.

A really strong magnet attached to a steel frame will concentrate most of the field into the frame with the remainder extending outward toward the street.

The best place to put it would be under the aluminum engine and away from steel, but you'd have to ride with the magnet over the coil in the street to have the best effect.
 

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Since it hasn't been mentioned yet (no point in being redundant), one possible way to trigger a stubborn detector is to run your electric starter motor for a couple of seconds. The starter motor will generate a large magnetic field (okay, some people need to be impressed with terms like induced electromagnetic field), which may trip the detector. It won't hurt your starter motor or adversely affect your running Burg.
 
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