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[Specter]

Ok, how many times have we all sat at a red light because our bikes didn't trip the sensor properly?

What if we could put a coil under the bike, it wouldn't have to be huge, but just pulse some current through it, to pop pop out a magnetic field under the bike to trip the sensor so it sees the bike and sets off the lights.  We got electric bikes, the battle's mostly done.  You pull up to a stop light, press a button and it fires for say 10 seconds to trigger the light activation.

I wonder if that could work?

Aaron

[TheRan]

Never. I think it's just an American thing to have poorly calibrated induction sensors. Also I don't know if a magnetic field would actually work. A permanent magnet at least apparently wouldn't help, nor a DC electromagnet, but maybe if it was pulsed AC.

[flynnstig82r]

A low-tech version of your idea already exists: https://www.jpcycles.com/product/green-light-trigger?sku_id=10262965

There’s some debate about whether they are effective. I had one on my FZ6R and I was convinced that it worked until a speed bump liberated it from the bike’s underbelly. Always thought about getting another one but never did.

[Richard230]

The public workers at the city that I used to work for used a shovel to calibrate the signal sensors. They would throw a shovel on top of the loops and if the signal was triggered, they would go on to another signal. If the shovel didn't trigger the signal, they would adjust the sensitivity so that it would finally work. So that tells you something about the loop detectors. They can be made quite sensitive if you adjust them correctly. I was told that the magnets that some companies sell to trigger the signals don't work.

The other day I was at a signal while on my bicycle and no one else was around. I was quite surprised when the signal turned green for me.

Most jurisdictions are now replacing detector loops with TV cameras that will trigger the signal when they observe a vehicle at the intersection. They work quite well. Plus, you don't need to replace the loops when you repave the street.

[DonTom]

Most jurisdictions are now replacing detector loops with TV cameras that will trigger the signal when they observe a vehicle at the intersection. They work quite well. Plus, you don't need to replace the loops when you repave the street.

When I came home from work in a car in the morning when I worked nights in SSF, the stoplight at where Sister Cities Blvd met with Hillside had (has?) such a camera. The sun would shine on it during certain months of the year so it would NEVER change with a line of cars and trucks waiting. The only way to go for an hour or two was to blow the red light. That was a big problem when there was a car in front of me who didn't know they had to blow the red light.


-Don-  Reno, NV

[Grauteufel]

Yeah, also never had a sensor not trigger. If anything, electric bikes induce a greater current than a standard bike (the emf from the motor is huge)....are you riding over the sensor? I know yanks often use round induction loops rather than rectangles, this would leave greater gaps between the loop and the edge of the lane.

[DonTom]

Yeah, also never had a sensor not trigger. If anything, electric bikes induce a greater current than a standard bike (the emf from the motor is huge)....are you riding over the sensor? I know yanks often use round induction loops rather than rectangles, this would leave greater gaps between the loop and the edge of the lane.

There is one about a mile down the hill from me here that I don't think has ever triggered for me when I am on a bike, but I am usually on an ICE bike when going that direction. I hate to be the first one at that red light. I want a car in front of me there as then there is no problem.


-Don-  Reno, NV

[Specter]

Yeah, also never had a sensor not trigger. If anything, electric bikes induce a greater current than a standard bike (the emf from the motor is huge)....are you riding over the sensor? I know yanks often use round induction loops rather than rectangles, this would leave greater gaps between the loop and the edge of the lane.

If you were driving over it under power then possibly but when you are coming to a stop light, you are pretty much coasting at that point, so no power being applied to the motor to make that 'huge' field.

Unfortunately out here I know of at least 3 lights that flat out won't work with a bike, mine or other riders ive been with, and others that are a coin toss.  The iffy ones, Ive tried driving over the left, right center, seeing if there is a sweet spot... nope.  I think most of them it's the sensitivity on the things that needs to be adjusted, but yah it's annoying sitting there waiting for a light to fully cycle so you can run thru at the next, what was supposed to be your turn.

Aaron

[TheRan]

So from a little bit of research it would seem the the loops don't detect EMF (which would be passive, the magnetic field inducing a current in the loop), it's the presence of ferrous material that changes the inductance in the loop. As bikes are both small and mostly constructed of non-ferrous materials (especially electric ones) they of course affect the loop less. So it would seem that strapping a steel plate to the bottom of the bike may be the best thing to increase the chance of detection. Also the effect should vary based on the location, but I've read that both being over the wire in the loop and in the centre of the loop is best. The car park to my brother's apartment has a loop to exit it and my bike will trigger it, but to get in without a fob people use a paint can and place it over the wire.

[Specter]

Maybe we could get solid steel tires, like a mini steam roller.  Once you got them things rolling you'd go and go and go !! 

So it's acting like a proximitor then.  I would think having another electric field interfere with it, would change it's value enough as well.  It's running at a resonant freq most likely and ferrous metal, like an iron tuning slug in a coil, would change that resonance.  Inducing a diff frequency into that wire should switch it too.  Well shit, time to get the Wobulator out and play around and see !!  We use something similar for vibration and rpm detectors on the generators.  Maybe something like a degaussing coil, that hits hard and winds down over a few seconds.  Hmm

Aaron

[SwampNut]

I used to work in traffic management technology, and my best friend leads a team of ITS construction/installation state-wide.  I'm very familiar with this problem.  They test the loops using simple loops of heavy copper.  Nothing premade, they coil up this heavy "wire" and wave it over the coil.  Over time, calibration can drift, and as they add pavement for repairs, the loops get farther away from the vehicle.  But I don't think you could possibly add more copper to a bike with a huge magnet and coil already under it.  I asked him.

A lot of US intersections are moving to video detection, as that tech has become cheaper and cheaper, and more reliable.  It can count cars, which inductive loops do poorly (they sorta can, roughly).  Signal timing to clear a lane is very precise with video.  It's also excellent at detecting pedestrians, bicycles, and motorcycles.

[Specter]

Basically you just have to change the impedance / resonance, ie current flow thru that coil's circuit to trip the sensor to make you seen.  the magnetic field is happy, you want to make it unhappy. Ferrous metal intrusion can do that, or another field can do that.
If you pulsed a magnetic field, solid magnet, electromagnet, black hole or otherwise, it should interrupt that resonant circuit enough to cause it to say, "Ooh something changed my field, it must be a vehicle" and set off the light sequence.  Even a piece of magnetic metal, which would cause a change in the existing field when it entered it would work, but be clunky on the bike.

Maybe we can get a beer can sized nuclear reactor and just EMP it every time we drive by and not have to worry about it !!

Aaron

[TheRan]

It's not just a change in the inductance, it's a reduction. I don't know enough to know whether an electromagnet would have that effect like a big chuck of steel would. And it's also constantly pulsed at many kilohertz so perhaps just a quick pulse from an electromagnet wouldn't be enough.

[DonTom]

It's not just a change in the inductance, it's a reduction. I don't know enough to know whether an electromagnet would have that effect like a big chuck of steel would. And it's also constantly pulsed at many kilohertz so perhaps just a quick pulse from an electromagnet wouldn't be enough.

Metal next to a coil will increase the inductive reactance, which will reduce the AC current through it. It's much like adding resistance to an AC circuit.


-Don-  Reno, NV

[TheRan]

Well the wiki article says there's a reduction due to eddy currents. Whichever it is my point is it's looking for something specific, not just any change.

When a vehicle passes over the loop or is stopped within the loop, some of the vehicle's ferrous body material increases the loop's inductance, in the same principle as including a metal core within a solenoid coil. However, the peripheral metal of the vehicle has an opposite effect on the inductance due to eddy currents that are produced. The decrease in inductance from the eddy currents more than offsets the increase from the ferrous mass of the engine, and the net effect is an overall reduction in the inductance of the wire loop.

https://en.wikipedia.org/wiki/Induction_loop