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Traffic Light Trigger (Neodymium magnet)

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"I'm no expert, but I don't think a magnet will work any better than any non-magnetic hunk of metal.

Most traffic light sensors are inductive loops in the road surface. You can sometimes you can see the cuts in the asphalt where the sensors are. An alternating current is sent through the loops, and if metal passes over it, the magnetic field from the loop causes eddy currents in the metal, which will alter the electrical characteristics of the loop. These altered characteristics can be detected. It makes no difference if the metal is magnetic or not, just that it is an electrical conductor. In a way, it's just a big metal detector.

I think most of the problem with motorcycles is width. A car is a larger and wider slab of metal as it rolls over the open loop. If you approach these triggers slowly and stop over the cuts in the asphalt, it may work better."
 

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I'm thinking we actually agree on this. The added hunk of metal you added, in your case a Neodymium magnet, probably increased the conductivity of your motorcycle. I'd bet that if you added an equal mass of silver or copper, it would have the same effect.
 

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"I'm no expert, but I don't think a magnet will work any better than any non-magnetic hunk of metal.

Most traffic light sensors are inductive loops in the road surface. You can sometimes you can see the cuts in the asphalt where the sensors are. An alternating current is sent through the loops, and if metal passes over it, the magnetic field from the loop causes eddy currents in the metal, which will alter the electrical characteristics of the loop. These altered characteristics can be detected. It makes no difference if the metal is magnetic or not, just that it is an electrical conductor. In a way, it's just a big metal detector.

I think most of the problem with motorcycles is width. A car is a larger and wider slab of metal as it rolls over the open loop. If you approach these triggers slowly and stop over the cuts in the asphalt, it may work better."
Enzo, not to quibble too much but... The physics that make a generator (or electric motor) work involve three main components: a conductor, a magnetic field, and relative motion between the two of them. moving a magnet and its associated magnetic field across the conductor will generate a current. The size of the current is directly related to the strength of the field. Now, if the conductor is already carrying some current, moving a magnetic field across it will either increase or impede existing current flow. Either way, same principles are at play in our street light sensing circuit. The combo of magnetic field, conductors, and relative motion result in current fluctuations. The fluctuation can be sensed and used as a signal to trip the light. Larger vehicles contain enough magnetic (mostly ferrous) material to influence the magnetic field and make the current in the wire fluctuate a detectable amount. I theorize that motorcycles are doubly disadvantaged in this process because of (1) their relatively small mass and (2) the fact that modern bikes are constructed of a larger proportion of non-magnetic material (aluminum, magnesium, unobtainium in the case of new-model-year Indian accessories). Bikes, especially new ones, simply don't have enough of the right material in them to provide the right kind of influence to the current carrying conductor buried in the ground below them. BUT.... When you add a powerful rare earth magnet in a location where it's associated magnetic filed has the least barriers in influencing the buried conductor, and then add the relative motion of the bike rolling up to the light, you have set up the conditions necessary to develop the fluctuation in current required to trip the light. It's elementary, really....
 

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Okay. I did a test early this morning before the traffic began at two different intersections with induction loops under the asphalt. I used an 8oz. N45 Neodymium magnet that has a holding power rating of 109 lbs. Five times the size and holding power of the magnets @ScotD is using. I made a few of passes without the 8oz. N45 Neodymium magnet in place each. The I made a few passes at each intersection with the magnet mounted to the bottom of the motor at the frame cross bar between the floorboards.

Conclusion: No perceptible difference in trigger time.


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Enzo - I don't think the purpose is to speed up the trigger time (that is built in to the stoplight electronics), but rather it is to trigger a sensor that normally doesn't trigger at all based on vehicle size. So the challenge would be to find a stoplight that normally never triggers for your bike and then see if it triggers after you add the magnet. It's not something I'd add because I've never had a problem getting stoplight sensors to read the presence of my Chieftain (bigger than a Scout).
 

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Enzo - I don't think the purpose is to speed up the trigger time (that is built in to the stoplight electronics), but rather it is to trigger a sensor that normally doesn't trigger at all based on vehicle size. So the challenge would be to find a stoplight that normally never triggers for your bike and then see if it triggers after you add the magnet. It's not something I'd add because I've never had a problem getting stoplight sensors to read the presence of my Chieftain (bigger than a Scout).
I guess I wasn't descriptive enough. Yup, I agree. The one intersection I tested never triggers if you're in the wrong spot and that didn't change with the addition of the magnet.

I'm not spending any more brain power on this one. If you think it works for you then go for it. Me, I'll use the magnet to play parlor tricks on my nieces and nephews.
 

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I don't think I've had the issue of light night changing more than a half dozen times EVER....if that many....in those cases it didn't change , I just pass through the red light...problem solved. Non issue....:)
 

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