neodymium magnet

"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."

enzo5000 said:

"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."

Click to expand...

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....