Red Light Changer

Kingfish

100 MW
Joined
Feb 3, 2010
Messages
4,064
Location
Redmond, WA-USA, Earth, Sol, Orion–Cygnus Arm, Mil
I was lurking for something else and ran across this novelty on Amazon; never heard if it before, but I suppose it makes sense. The problem however is that my frame is aluminum, so I doubt this would help unless I mounted a steel plate or rod. But then why spend money on this when a strong magnet might do?

Anyone have experience with this auguring witchery? :)

Senseless, KF
 
I guess it just trips the inductive loop sensor in the road, so demand driven lights know that there's a vehicle at the red light. Maybe something as simple as a big magnet.

Having a vehicle that hasn't got enough steel to trigger lights is a pain. Years ago I drive a composite monocoque car with an alloy engine ( a Clan Crusader for geeks who are interested in lightweight 70s sports cars). Because it only had small amounts of steel it would never trigger lights or lift up barriers at car parks. I had to choose routes to drive and places to park where I wouldn't need to trigger any inductive loops, which was a bit of a pain.

Jeremy
 
First time I realized this was a problem, I read about magnet devices for motorcycles to trip the loops. Then I realized, how strong a magnet is this? After all, the ones in my hubmotor are pretty dang strong. Why don't they trip the light?

Early in the morning, no cars will come along to do it for me, so the choices are run the light, or go push the crosswalk button, if the button works on that light that is. Some intersections won't trip as fast untill a second car arrives and parks on another loop.
 
The hub motors do leak flux; I discovered this by accident during the FEMM studies for AF when considering the effects of a flux ring. The magnet used in the images below is the same used for the Magnetic Reed Switch deployed as an eBrake on my previous bike. The field is not strong enough to retain a paperclip, and yet – quite strong to retain a simple magnet in any direction. Note that the tiny magnet is round, yet does not roll.

HubFluxLeakage.jpg


I suspect that the iron core of the hub motor acts as a sink to the flux leakage, thus preventing it from being useful in triggering the inductance loop.

Demagnetized, KF
 
I don't think a permanent magnet will work any better than a piece of iron for triggering a light sensor.
The coil in the road is part of an oscillator circuit that runs at some frequency. Metal in the field will cause the frequency to shift, which triggers the detector. Getting the metal closer to the coil will help.

If we knew the frequency of oscillation (probably varies by manufacturer), it might be possible to build a passive coil/capacitor tuned circuit that would interact more strongly with the road sensor.
 
In California (and maybe other areas) the emergency vehicles turn the light green using a strobe light. We used to do it sometimes for fun, but I imagine it's illegal.

If you look at some stoplights, you'll see the strobe detector on top. It's relatively small, but hit with a strobe it will cause the other light to turn yellow and then red. Obviously it won't immediately turn your light green because the cross traffic needs time to adjust.

But strobes definitely work on the traffic lights equiped with detectors.
 
MikeFairbanks said:
In California (and maybe other areas) the emergency vehicles turn the light green using a strobe light.
<snip>
But strobes definitely work on the traffic lights equiped with detectors.
Hmmm, exclusive to visible light? :idea: :twisted:

Given to frequency... KF
 
Kingfish said:
The hub motors do leak flux; I discovered this by accident during the FEMM studies for AF when considering the effects of a flux ring. The magnet used in the images below is the same used for the Magnetic Reed Switch deployed as an eBrake on my previous bike. The field is not strong enough to retain a paperclip, and yet – quite strong to retain a simple magnet in any direction. Note that the tiny magnet is round, yet does not roll.


I suspect that the iron core of the hub motor acts as a sink to the flux leakage, thus preventing it from being useful in triggering the inductance loop.

Demagnetized, KF


Bro, the magnet sticks to the motors back-iron, not because it's leaking flux.
 
I've seen a few homebrew electronic devices to solve this problem. IIRC, some of them were just big (well, maybe 6"x12" or so), flat electromagnet coils that they would pulse while sitting at the light. I'll look around later and see if I can find any links.
 
Sounds like a perfect excuse to just proceed when traffic permits. If the light doesn't function properly, then treating it as a stop sign is appropriate.

I thought the thread was about the IR transmitters that emergency vehicles have in some areas to enable them to override the timing and give the emergency vehicles all green lights.
 
Luke, I haven’t removed magnets from the hub periphery so I cannot confirm or deny the presence of a flux ring (back-iron).

  • The hub flange et al where the spokes attach is aluminum.
  • I performed multiple scratch tests on a clean unpainted hub (front) with the exact same configuration and the material is soft across the entire flange face.
  • I found the original hub in the pictures (magnets still attached) and moved the magnets over the stainless steel spokes: The magnet sticks to the butted face passing through the flange, but the magnetic forces are weaker, and unable to hold the magnet on the actual spokes.
  • The screwdriver used in the scratch test is a Sears Craftsman vintage 1980s hard carbon steel. It is not attracted to the aluminum, however is strongly attracted to the magnets.
  • It is remotely possible that the aluminum is of an alloy having properties of permeance – however the screwdriver is unaffected. Still, weak magnetic flux appears to be directed through it, and it profoundly affects the tiny magnet-faces; the orientation of the tiny magnet is very much overtly directed & aligned; this can only happen with magnetic polarized fields/flux.
  • If there is back-iron present then it is buried below the ring of magnets. But I am circumspect without further proof. A flux ring, if properly designed, should not allow for this behavior. Then again it could be in saturation without the iron core.
Luke, do you have inside knowledge on the 9C construction? :)

MikeFairbanks, we are missing the link :)

BTW – I found this article scanning the web for “motorcycle running lights red green”: Running red lights or waiting for green lights
Gist: Proposes that motorcycles can run a red light after 120 seconds of waiting for a green. I have done that a number of times but only after being cheated for my light twice or more cycles – and then proceding after traffic is clear.

Truly amused by the thread direction; potential solutions for both waiting motorcycles & initiating green lights! :lol:
"What song is it you want to hear?" KF
 
Kingfish said:
Luke, I haven’t removed magnets from the hub periphery so I cannot confirm or deny the presence of a flux ring (back-iron).
On the black E-Bikekit 9C front hub that I have, the spoke flange and ring is indeed steel. Magnets stick to it so well that I just left one stuck on the flange to use for the CA speed sensor, and even at 34MPH no-load off-ground it doesn't budge, nor has it moved with all the road bumps and stuff, either.

But on the silver one from Icecube57 is aluminum, and a magnet won't stick to it at all, although I can feel the pull from the internal magnets and flux ring pretty strongly.

Both of them do have a separate flux ring within the spoke flange, presumably bonded to each other in some way, or interference-fit.


Regarding the triggering of lights, I have found that *some* of the sensors are sensitive enough to be affected by me sticking a couple of harddisk magnets on the lowest points of the frame (bottom of front forks and kickstand base) on my alloy-framed DayGlo Avenger. So far, neither the Fusin nor the 9C will change the light triggering behavior at these lights, but the magnets do, on a very few lights.

On the much bigger steel-framed CrazyBike2, which will occasionally trigger some of those same lights itself, the 9C does make some of them trigger more consistently. But again, the magnets (placed on the fork) make some difference at other lights that didn't trigger before.

The thing that makes the most difference is the speed and position at which I approach and cross the first threshold of the sensor; if I manage around 1/2 of the speed limit for that road and I stay on the centerline of the sensor, then I will usually trigger more lights than any other method I've tried.

FWIW, I have less trouble triggering them than several motorcycles I've seen, some of which cannot trigger them at all, apparently. Kinda P/Od one guy, when the light went green as I rode up in the lane next to him, when he'd been sitting there at least a couple of minutes (I could see him the whole time I was approaching, a mile or more away).
 
There is another solution. If you have problems with particular lights you can call the city and ask them to adjust them. I did, and they adjusted. I can now set most of them off with the bicycle.
 
Kingfish said:
Luke, I haven’t removed magnets from the hub periphery so I cannot confirm or deny the presence of a flux ring (back-iron).

  • The hub flange et al where the spokes attach is aluminum.
  • I performed multiple scratch tests on a clean unpainted hub (front) with the exact same configuration and the material is soft across the entire flange face.
  • I found the original hub in the pictures (magnets still attached) and moved the magnets over the stainless steel spokes: The magnet sticks to the butted face passing through the flange, but the magnetic forces are weaker, and unable to hold the magnet on the actual spokes.
  • The screwdriver used in the scratch test is a Sears Craftsman vintage 1980s hard carbon steel. It is not attracted to the aluminum, however is strongly attracted to the magnets.
  • It is remotely possible that the aluminum is of an alloy having properties of permeance – however the screwdriver is unaffected. Still, weak magnetic flux appears to be directed through it, and it profoundly affects the tiny magnet-faces; the orientation of the tiny magnet is very much overtly directed & aligned; this can only happen with magnetic polarized fields/flux.
  • If there is back-iron present then it is buried below the ring of magnets. But I am circumspect without further proof. A flux ring, if properly designed, should not allow for this behavior. Then again it could be in saturation without the iron core.
Luke, do you have inside knowledge on the 9C construction? :)

KF,

I didn't pull out a magnet and check mine, but I can tell from your pics that spoke flange isn't AL. Your scratch test just proved how cheap the steel/iron is on 9C's, which doesn't surprise me at all given the manufacturing flaws in the one I have. Plus soft and pliable is probably better than hard and brittle on a spoke flange anyway.

Placing the extra magnets on it changes things enough for the flux pattern from the motor magnets to leak and affect the orientation of the added magnets.
 
drewjet said:
There is another solution. If you have problems with particular lights you can call the city and ask them to adjust them. I did, and they adjusted. I can now set most of them off with the bicycle.
That'd be nice, but here in Phoenix (and in supposedly-bike-friendly Glendale), their opinion is that it's not their problem. :evil:
 
John, Luke, AW:
I stand corrected. After switching coffee, I went back and examined both hub flanges (sans iron core) and we are both correct. Front Hub Flange is aluminum; Rear Hub Flange is mild steel which is why it gets painted. The weight difference gives it away. I was lame and missed this. <slurp more coffee; make it stronger…> :roll: :)

Tracing the little magnet around on BOTH models yields these slight differences:
  • No magnetic attraction on the aluminum rims (sanity-checking & presumed as much) even though the physical shape is slightly different between front and rear.
  • Spokes do show minor attraction; they are alloys of SST though not of the same manufacture (butting is different). That said the rear spokes have weak attraction whilst the front spokes exert nearly double the force (though still much less than steel frame, iron, or hub magnets). Not much else to glean here other than quality observation.
  • Hub Flanges are aluminum in front and iron alloy in the rear; a side-by-side scrutiny makes this comparison obvious without a scratch test (not done on the rear). The little magnet has profound attraction and orientation on the rear hub flange. The front however varies from insignificant to mild attraction depending on proximity to embedded magnets – probably inversely proportional to the square…
Humbled; old dog – new tricks… <woof! Happy pant> :)

Back to the germane issue, I rather like the idea of having a momentarily-energized coil loop rather than a magnet to trigger the sensor. The question remains whether it passively pulses or is on-demand/linked to the eBrake. I will try and follow up locally and see what can be learned about the sensors.

~KF
 
All hubmotors have back iron for the magnets. Most have it as something press-fit or glued into the aluminum outer shell that has the spoke flanges etc.

The reason you know ALL hubmotors will have back iron is simple. An iron ring is cheaper than paying for magnets of twice the thickness.
 
Also, to get on-topic, the magnet trick has been used for many years on motorcycles to trigger the inductive loop red-light sensors.

The trick is getting it close enough to the ground. Just a hard drive magnet hanging from the lowest reasonable mounting point you can find does a fine job. A hubmotor would have minimal effect. To create the same inductive disruption with steel/iron, you would need a chunk a few hundred times larger than you could get with a good magnet.
 
I was riding in a car this Christmas with an ex-Ontario firefighter and he told me the light changing systems here are (were?) triggered by high powered headlights... that a x-million candlepower hand-held light otta do it.
tks
LocK
 
Lock said:
I was riding in a car this Christmas with an ex-Ontario firefighter and he told me the light changing systems here are (were?) triggered by high powered headlights... that a x-million candlepower hand-held light otta do it.
tks
LocK


For emergency services, the standard is a strobe of a certain frequency to cause the light to change. Easily spoofed by anyone with an adjustable freq strobe.


What we are talking about in this thread is nothing illegal or improper. This is about simply getting the inductive intersection vehicle present sensor to activate, as it's tuned to sense a giant chunk of iron above it, and our bicycles and/or exotic cars don't have this.
 
Its a problem for the 4X4 crowd too. My Jeep used to have problems tripping lights. My solution was patience. Another car always comes along eventualy. ... or no one was looking, so no crime was commited. :D
I had a friend who had a couple of piston rods on a rope. he'd toss it under his truck at stop lights if they wouldn't change, then haul them back in when it changed. But his was a vehicle with ground clerarance measured in feet, not inches.
 
A friend of mine had this problem with his motorcycle too...his solution was a big metal toolbox that he kept on the back and put on the ground at stoplights. :D
 
liveforphysics said:
Also, to get on-topic, the magnet trick has been used for many years on motorcycles to trigger the inductive loop red-light sensors.

The trick is getting it close enough to the ground. Just a hard drive magnet hanging from the lowest reasonable mounting point you can find does a fine job. A hubmotor would have minimal effect. To create the same inductive disruption with steel/iron, you would need a chunk a few hundred times larger than you could get with a good magnet.

I'll have to play with one sometime, though there may be different models out there. My understanding is they are basically like a metal detector. A permanent magnet does not really have any more effect than a chunk of steel on a typical metal detector. Perhaps the trick is to drag the magnet over the coil to induce a voltage in the coil. Most metal detectors run at a fairly high frequency and have filters to take out the low frequency stuff like somebody dragging a magnet across them.

I suppose if that works, then you could stick a magnet on the end of your kick stand and lower it in the event of getting stuck at a light.

The strobe light thing works for sure around here, but the local law enforcement officials will take a dim view of anyone using that method. Somewhere I have a strobe with an infrared filter over it (used for some kind of remote photography flash). The IR filter will make it invisible to humans but still able to trigger the light changer. I should try that one. :wink:

Actually it could be just as much fun if you could trigger a light to go red. Some jerk tries to run you off the road in a hurry to beat the light and it just turns red on him, like forever.
 
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