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Discussion Starter #1
Any Elise owners care to comment on how easy/difficult it is to trigger traffic signals with your Elise?

The vast majority of traffic signals use an induction trigger buried in the tarmac (loop). This requires some ferro-magnetic metal (read steel or iron) to pass or stop above it. Clearly the Elise lacks significant steel/iron. Elise steel/iron parts would include brake rotors, engine bits (crank, rods, flywheel), tranny parts and not much else!

With the lack of steel/iron some signals with high sensitivity could potentially ignore the Elise and you'd be parked at the light for the ages... Comments?
 

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The brake rotors should be enough to trigger the light, especially if you can position one side or the other directly over an edge of the loop. If not, call the local DOT and ask them to recalibrate.

Or you can do what I did at a light near my apartment when I was commuting by motorcycle. No matter what the traffic guys did, I could never trigger the light. I think a repaving job put the loop too far down to ever sense a motorcycle. I'd pull up to the line, put down my sidestand and walk over to the sidewalk and kick the crosswalk button as hard as I could. (note: the extra force did nothing other than vent frustration) I'd have just enough time to walk back and get on my bike before I'd get the green.
 

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Interesting. I always assumed it was a 'weight' thing. My bike never/rarely triggers the light, but I guess that could be a 'quantity' issue RE iron/steel.
 

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The inductive pickups on traffic signals work just fine sensing aluminum, maybe better. No ferric metals are required, just something conductive. It would pick up carbon fiber or copper too.

They can be made as sensitive as needed. The ones on my gate will sense a motorcycle, bicycle, or Segway scooter..

I don't advocate it, but some motorcycle riders plagued by lame/insensitive/damaged pickup coils will take a knife to the coil, breaking it entirely. Then after a cop figures out that it doesn't work at all for anyone, they will have it repaired. 'Broken' is fixed faster than 'insensitive'.
 

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Ground Loop said:
The inductive pickups on traffic signals work just fine sensing aluminum, maybe better. No ferric metals are required, just something conductive. It would pick up carbon fiber or copper too.
Well, poop. So much for what I thought I knew.
 

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FYI, moving parts from the car's drivetrain create a magnetic flux which induces a current in the wires buried in the road. The current travels to the intersection's control box. It has nothing to do with weight or composition of the body of the car.

That's also the reason bikes don't trigger these lights.
 

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Ahhhhhhh, I see, its the flux capacitor...............
 

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Discussion Starter #9
Are these snake oil products?

http://www.cruisercustomizing.com/d...ory_ID=0&manufacturer_ID=336&product_ID=11580

http://www.greenlightstuff.com/trigger.html

Here's a good article...
http://www.utexas.edu/research/cem/programs/vehicleloop.html

A quote from it...
<i>"Technology for bicycle detection

Bicycles cause two very different types of inductive effects, depending on the type of their wheel rims:

Steel rims
Ferromagnetic steel rims cause a noticeable increase in flux and inductance due to their close proximity to the loop, which is greater than the minute inductance drop caused by induced currents. The net effect is an inductance rise.

Aluminum (or other non-ferromagnetic) rims
The ferromagnetic effect is absent in this case. The surface offered by these rims for eddy-current induction is not large enough to cause any appreciable inductance change.
By directly detecting the inductance shift, both these behaviors were measured. Short (in the direction of travel) loops enhance selectivity."</i>

And finally...
http://auto.howstuffworks.com/question234.htm
 

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Are these snake oil products?
I'm a bit far removed from my studies in electomagnetism to have a definite answer, but here's my best edumacated guess. :)

I suspect these products are simply magnets. I have no clue if they could induce a strong enough current to be recognized, but I suspect not. They'd have to be either very strong magnets or mounted to be very near the street wires. Probably both. I can't see a small magnet mounted to the bottom bracket matching the magnetic field generated by a crankshaft idling, say, at 800 rpm.

As a cyclist myself, I'd rather not carry the extra wieght - especially since I don't think it'd work.
 

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Discussion Starter #11
One suggestion comes from these articles... induction loops sense "stuff" moving through their magnetic fields. So, if you're stopped and the signal fails to be triggered, move the car a couple of feet or so to trigger the loop.

I also get from these pieces that ferro-mag metal is better than non-ferro (aluminum, mag, copper etc) at triggering the loop.
 

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Jeeze, i just learned something on this post. Thanks. By the way, there's a light up the road from me that is notorious for being a pain in the bullocks. My Elise has triggered it without problem.
Dan
 

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Signal Sorcerer is junk for the misinformed

khamai said:
Are these snake oil products?
Resoundingly, YES.

There is so much misinformation out there about the simple inductive loop sensor. How can these companies continue to publish such outright lies and falacies? such as:
Inductive loops detect iron (ferrite [Fe]) not aluminum, rubber, plastic, weight, titanium, etc.
BS. Iron, and (lesser) aluminum, and titanium will all conduct current and trip the inductive sensors. Look up "Lenz's Law" for the physics details.

Motorcycles, particularly the newer models, rarely have enough iron to cause the inductive loop to detect their presence at the intersection – ergo, the light does not change.
Wrong again. The metal wheels alone will trip the light if they're in the right place and the sensor is working correctly. The metal engine is bonus, and the frame too. Because a motorcycle is smaller than a car, a borderline sensor might fail.

Signal SorcererTM generates a very powerful field that substantially increases the inductance in these loops, therefore causing the traffic signal to detect the vehicle it's attached to, and initiate a cycle change.
Total and utter BS. The best way they could "increase your inductance" is to give you a nice big flat piece of metal to strap flat across the bottom of your bike. Or a big hoop of wire about the size of... a bicycle wheel.

Furthermore, a static permanent magnet will do nothing for your inductive reactance unless it's big enough to do the same thing a nonmagnetized piece of metal would do.

Nothing. These are EASY experiments to do.. get your biggest most powerful burly subwoofer magnet and go for a walk.. see if you can trip the traffic coils.

Here's the thing.. they're not looking for magnet. Know many magnetized cars? No?

They're looking for something to 'push back' on their alternating field. It alternates at 10KHz or higher, so unless your magnet passes through their coil at about Mach1, it's not going to make much of a blip on the magnetic radar.

Inductive loop technology has been employed in this capacity since the early 1960's.
I don't know for certain, but I suspect it's been in use for even longer than this. Any time you pull up to a gate and it opens, you're probably driving over a coil.


Think of the traffic coils as metal detectors.. because that's exactly what they are. Ever play with a metal detector in the sand? Did it sense aluminum? Sure did! Did it go crazy over magnets? Not unless they were big hunks of metal.


Those products are a tax on the people who don't do basic science.

Read this article and you will know more about traffic loops than anyone selling this junk:
http://www.humantransport.org/bicycledriving/library/signals/detection.htm
 

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Discussion Starter #14
Thanks Ground! Well explained. I echo what eliseowner2b said about getting some useful info from this thread.

From what Chris & eliseowner2b shared, they've had no problems with triggering inductive loops.

Hey, there's one signal near my home that even my Exploder won't trigger!!!
 

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True fact: The Elise will trigger inductive sensors more easily than your Explorer.

Why? Because it sits lower to the ground, closer to the pickup coil where it has a more significant inductive reactance.

Your Explorer, if it's lifted, has about the same inductive footprint as a motorcycle.
 

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swimbikerun said:
FYI, moving parts from the car's drivetrain create a magnetic flux which induces a current in the wires buried in the road. The current travels to the intersection's control box. It has nothing to do with weight or composition of the body of the car.

That's also the reason bikes don't trigger these lights.
A) Moving metal pieces do not generate magnetic flux unless they have a net electric charge. That is unlikely to be true of drivetrain components.

B) Bicycles do trigger the sensors if the sensors have a low enough threshold.
 

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John Stimson said:
A) Moving metal pieces do not generate magnetic flux unless they have a net electric charge. That is unlikely to be true of drivetrain components.
Preach on.. And to be a significant magnetic flux anyway, it would have to be at a frequency at least in the ballpark of 10-30kHz. Got anything moving that fast in your idling car?


B) Bicycles do trigger the sensors if the sensors have a low enough threshold.
Position is also very important. It's best to ride up on the 'groove' to one side or the other. This orients the vertical wheel right above the loop edge for maximum reactance.

If it's a figure-8, ride to the middle.
 
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