Triggering traffic lights with a magnet - does it work?

[Steam]

I read you can trigger the traffic lights with a big loudspeaker-magnet glued to the underside of your bike, because the induction loop sensor under the road picks you up as a sodding great truck with a huge magnetic field.
Or something.

Will this really work? Someone with some electrickery knowledge...?

How big does the magnet need to be, and how close to the ground?

[Mikkel]

I read you can trigger the traffic lights with a big loudspeaker-magnet glued to the underside of your bike, because the induction loop sensor under the road picks you up as a sodding great truck with a huge magnetic field.
Or something.

Will this really work? Someone with some electrickery knowledge...?

How big does the magnet need to be, and how close to the ground?

Hmmm, I thought they were just regular pressure sensors...

That, with the common kiwi flair for premonition, have been placed where you stop to wait for the lights. No, not a distance before the intersection so they'd actually allow you to cruise through - you have to stop! :no:

[Steam]

Hmmm, I thought they were just regular pressure sensors..

No, they are induction loops, they have a magnetic field. Metal passing over them /through their magnetic field induces an electric current in the sensors, which triggers the lights.
Will a big magnet do the same? Or does it have to be metal passing through the magnetic field? I need to raise the "inductance", which metal does, but I don't know if a magnet will do the same.

[Mikkel]

No, they are induction loops, they have a magnetic field. Metal passing over them /through their magnetic field induces an electric current in the sensors, which triggers the lights.
Will a big magnet do the same? Or does it have to be metal passing through the magnetic field?

Most magnets are metal...

Are you positive that's how it works? Seems a bit odd to me...

Especially since if you move metal through a magnetic field then a current can be induced in the metal (i.e. the vehicle - not to worry we're talking small currents here).

On the other hand a car shouldn't have a large magnetic field - but if they did they would be able to induce an induction current in a coil hidden beneath the tarmac, yes.

Edit: I recall some advice somewhere about leaning your bike on the stand onto the road surface if you got caught behind a light that is unwilling to change... Would indicate a pressure sensor me thinks...

[twotyred]

It may work,I believe most of the commercial traffic light triggers are basicly a high flux magnet... have thought about getting one a few times but your idea is certainly worth a punt in the name of science!

[gijoe1313]

My RZ Daisy has no probs with the lights, but my little ol'hornet does ... I have to flick my kickstand down and then just flick it back up and no probs after that!

[Steam]

Are you positive that's how it works?

Yes.

Edit: I recall some advice somewhere about leaning your bike on the stand onto the road surface if you got caught behind a light that is unwilling to change... Would indicate a pressure sensor me thinks...
That's because leaning it on the stand brings that lump of metal (the stand) to the road surface, hopefully triggering the sensor.


Oh, here's a thing I found by an electrician dude, that shows a magnet will not work any better than a similar weight of steel:

Will not work, at least not better than any non-magnetic metal lump.

Traffic light sensors are inductive loops in the road surface (sometimes you can see the cuts in the asphalt where it is). 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 a magnet or not, just that it is an electrical conductor. In a way, it's just a big metal detector. So a magnet will make no difference.
So maybe I have started and ended my own thread.

[twotyred]

How big does the magnet need to be, and how close to the ground?

commercial units are usually only a 100mm in size or so and are just attached to the bottom of the fairing or frame although they may be gruntier than a speaker magnet... with magnets,size is no guarantee of power

[Steam]

commercial units are usually only a 100mm in size or so and are just attached to the bottom of the fairing or frame although they may be gruntier than a speaker magnet... with magnets,size is no guarantee of power

WOnder how that works? Are they powered by the bike's electrics itself? I suppose an alternating-current electromagnet would do the trick to induce a current in the loop...

[mowgli]

No, they are induction loops, they have a magnetic field. Metal passing over them /through their magnetic field induces an electric current in the sensors, which triggers the lights.
Will a big magnet do the same? Or does it have to be metal passing through the magnetic field? I need to raise the "inductance", which metal does, but I don't know if a magnet will do the same.

Yes, a large speaker magnet will increase the chances of triggering the lights. For best results you'll need to orient the magnet with the poles in the vertical sense so that you get the greatest number of flux lines cutting the induction loop. Being closer to the road will increase the induced signal as will moving over the sensor quicker. I make a point of stopping smartly over the sensor rather than creeping up to the lights.

Edit: See post #7. I stand corrected.

[davereid]

Yep, my scooter won't trigger them - BUT its OK to apply right hand rule if they don't work. ie you don't need to sit there stuck.

Thats because you are allowed to use right hand rule at faulty lights... and if they don't detect a vehicle but are supposed to they are faulty.

(I got a ticket for it years ago).

[McJim]

This is the reason the congestion is so bad in NZ cities. In the UK the lights are generally phased so you stand a fair chance of getting a green light as you approach but in NZ you have to stop at every fucken light. Daft. Proper phasing is cheaper and more efficient than embedding induction loops.

Moron planners.

[No FX]

with a big loudspeaker-magnet glued to the underside of your bike

You need to "glue" a big magnet to the metal underside of your bike?:lol: p/t

[Mikkel]

YSo maybe I have started and ended my own thread.

It would appear so! :)

[MIXONE]

Fuck it just ride through the red light.

[homer]

i agre ride throught it .if youve been waiting a fair while and nothing going through the other direction

no waiting for nothing

[Steam]

You need to "glue" a big magnet to the metal underside of your bike?:lol: p/t

I didn't understand what you were on about for a good half hour. But now... DOH!

[Jiminy]

This is the reason the congestion is so bad in NZ cities. In the UK the lights are generally phased so you stand a fair chance of getting a green light as you approach but in NZ you have to stop at every fucken light. Daft. Proper phasing is cheaper and more efficient than embedding induction loops.

Moron planners.

I think they're starting to change that, at least they did for the Wellington city bypass. I think it didn't come cheap though (the light phasing).

[Waylander]

Get the magnet, walk up yo a light at night sometime, pass the magnet over, if it changes it may have worked. Wait for light to go red again then repeat.

If the light changes a small amount of time after each time you pass the magnet over the loop, guess what, it works.

[Steam]

Get the magnet, walk up yo a light at night sometime, pass the magnet over, if it changes it may have worked. Wait for light to go red again then repeat.

If the light changes a small amount of time after each time you pass the magnet over the loop, guess what, it works.

You sir, are a fucking genius.
PLUS, I get to have hours of fun at the pub watching people having their eftpos cards declined after I degaussed them with the wacking great speaker magnet,. then stumbling home drunk and testing all the traffic lights, while running down the middle of the road with my magnet, screaming "Yeeeharr! I'm riding an invisible bike, look, the traffic lights say I am!"

[All]

Yep, my scooter won't trigger them - BUT its OK to apply right hand rule if they don't work. ie you don't need to sit there stuck.

Thats because you are allowed to use right hand rule at faulty lights... and if they don't detect a vehicle but are supposed to they are faulty.

(I got a ticket for it years ago).Why is Hitler in your avatar?

[All]

Traffic lights are just guidelines for the inexperienced anyway. A real biker just ignores them.

[Mikkel]

That's because leaning it on the stand brings that lump of metal (the stand) to the road surface, hopefully triggering the sensor.


Actually... that would make next to no sense. Induction requires that the coil and the metal is moved relative to each other. I guess it's fair to assume that you are stationary while putting your stand down (and yes, I am aware that the stand moves when you put it down... but compared to the bike rolling on to the coil that is nothing!).


Fuck it just ride through the red light.


Traffic lights are just guidelines for the inexperienced anyway. A real biker just ignores them.

You have given out too much Reputation in the last 24 hours, try again later.

Just don't come whinging next time you or one of your mates get throttled by a delivery truck running slightly late... :nono:

[Disco Dan]

I read you can trigger the traffic lights with a big loudspeaker-magnet glued to the underside of your bike, because the induction loop sensor under the road picks you up as a sodding great truck with a huge magnetic field.
Or something.

Will this really work? Someone with some electrickery knowledge...?

How big does the magnet need to be, and how close to the ground?

There is a big silver button for making the lights change... :cool:

[DIN PELENDA]

my st1100 ex police is got magnet sistem that police put it in and it triger trafik ligts much bater than my R1.

[All]

Just don't come whinging next time you or one of your mates get throttled by a delivery truck running slightly late... :nono:My policy is to have no mates.

[bungbung]

This is the reason the congestion is so bad in NZ cities. In the UK the lights are generally phased so you stand a fair chance of getting a green light as you approach but in NZ you have to stop at every fucken light. Daft. Proper phasing is cheaper and more efficient than embedding induction loops.

Moron planners.

Invercargill has traffic lights?

[xwhatsit]

My RZ Daisy has no probs with the lights, but my little ol'hornet does ... I have to flick my kickstand down and then just flick it back up and no probs after that!

No, you just forget to park right on top of the sensor.

That, my friends, is the key. Right in the middle of the road at the head of the lights, there are marks in the tarmac wot look like this:
+-+-+
| | |
| | |
+-+-+

Park right on the middle vertical line. Yes, it's in the middle of the intersection where there's oil and diesel and shit, but it will trigger the lights every time.

[No FX]

Just saw these on tardme


http://www.trademe.co.nz/Trade-Me-Motors/Motorbikes/Parts-accessories/Other/auction-143235555.htm

[Radar]

Just saw these on tardme


http://www.trademe.co.nz/Trade-Me-Motors/Motorbikes/Parts-accessories/Other/auction-143235555.htm

:no: $45 for what must just be a magnet. Anyway, if the blurb is correct, it would seem that any strong magnet would work, such as from a speaker.

OK, this may be a stupid question but here it is: Are bike wheels made of steel, i.e. will they affect the induction coil in the road, or are they made of an alloy which would not be magnetic and therefore would not affect the road induction wires?

[Steam]

:no: [B]... if the blurb is correct, it would seem that any strong magnet would work, such as from a speaker.
From what the physics guy said in a quote on page one, magnets don't work.
They have no effect on the sensor, and he gave reasons:


{A Magnet} Will not work, at least not better than any non-magnetic metal lump.

Traffic light sensors are inductive loops in the road surface (sometimes you can see the cuts in the asphalt where it is). 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 a magnet or not, just that it is an electrical conductor. In a way, it's just a big metal detector. So a magnet will make no difference.


or are they made of an alloy which would not be magnetic and therefore would not affect the road induction wires?
Yeah, my wheels are alloy. I think most are.