If traffic lights' or garage door's Inductive-Loop Traffic Detector doesn't detect you, here's a solution

Of course, for our electric scoots, the magnetic signature is already enormous. The guy was putting only two eraser-sized magnets up on the frame, at least 5" from the ground at the best.

In fact, traffic departments fiddle with he sensitivity of the loops all the time. There was one light I used to frequent that would change to green before I even came to a stop. Very gratifying. Unfortunately, that got changed...

I got one of those eraser sized magnets on eBay and it seem to work on some lights. Placement is very critical. I poured epoxy over mine and mounted it with plywood strip to my scooter. I have taken apart my old microwave tubes to get out all of the magnets and I am going to see if round stronger magnets work any better to generate a larger signature on my other bikes. Most of the time if it doesn't work I just go right on red and make a u-turn. Still it is a royal PITA

Rusty

Hi there. I took apart an old hard drive and zip tied the two shielded magnets under the frame. I make every light see me here in Oregon. Works awesome and the price is right.

Happy scooting. Scott

Well I don't know how it could affect the Nimh batteries. Or any other chemistry since I am not a scientist. But I believe I had an issue the other day. I was coming home from work and after rounding a right turn my power cut out. All of it. Just like before when I had Xtreme replace my whole pack. At any rate after looking the scoot over I found one of my magnets hanging by one zip tie. This led me to believe that when I made that turn I bounced the magnet on the road and directed the magnetic force upwards towards my pack and its circuit board, thereby triggering an LVC episode. I reattached the magnet and haven't had any more problems. Go figure.

Good luck and happy scooting. Scott

I just talked with an engineer at a company that manufactures the road loop sensors. I am an EE, and the discussion was rather technical and enlightening. Here is what I learned from him.

The loop senors are more sensitive to aluminum than steel, and magnets will not help.

The sensors are typically rectangular, and the best way for a bike to trigger them is with one wheel centered over either of the short legs of the rectangle. For a bit more input, the bike should be leaned 30 degrees towards the center of the loop. Sitting still is best, but it should not take more than a couple of seconds to register, if it is going to sense you.

-- Alan

These sensors have a sensitivity adjustment. The one I was having problem was set on 3 (on a scale of 0 - 7). Moving it to 4 made it go from almost complete unresponsive to my bike, to easy triggering on my bike without having to stop on it. However, if the loop is too close to the garage door you are having problems with, too high of sensitivity setting can cause the door itself to interfere with the loop.

-- Alan

Loop sensors are only affected by ferrous metals. Aluminum has no affect on them. They work on the same principal as all "metal" detectors.
A very strong magnet on the bottom of the bike will work if it is close enough to the surface, ie; on the lower edge of a mudflap. (You will be surprised how many nails and screws you catch) Best trick is small strong magnet epoxied to the edge of a boot. Place the boot directly over the cut in the pavement.

Reid250 says: "Loop sensors are only affected by ferrous metals. Aluminum has no affect on them."

Any source for your information that contradicts what the manufacturer of the loop sensor told me?

The loop is detecting interference with the RF field it is generating (sub-MHz range), and is not sensing magnetic fields.

-- Alan

Alan;
I sent an email to an EE traffic engineer I know and he sent me a short note and a reference:

An RF field is very similar to a "magnetic" field. The Radio Frequency field as you point out is 20 KHz to 170 KHz. Ferrous metal cause a change in the frequency in the loop. This change is what is detected and used to trigger the light.

http://www.tfhrc.gov/its/pubs/06139/chapt5b.htm

Caltrans tests their loops as follows;

"Measurement of the change in frequency created when a vehicle model (such as that for a small motorcycle) is placed in the center of the loop under test. The small motorcycle (100 cc Honda) model consists of a 2- x 2-ft (0.6- x 0.6-m), 1/2-inch- (1.3-cm-) thick plywood board, containing one turn of #14 AWG solid wire laid into a 1/8-inch- (4-mm-) wide by 1/4-inch- (7-mm-) deep groove cut into its perimeter. The wire is spliced and soldered to form a shorted turn."

My experience with the magnets was gained over many years of riding with GWRRA and GWTA. I did not believe the magnet on the front mud flat worked until riding with a fellow who had installed it. At some lights that we were unable to trigger, he was always able to trigger them.

Take magnet, walk to loop, test it (don't wear your iron underpants though, or the aluminum cap!) ;-)

Mik;
I'm going to also take a one square foot piece of aluminum and place it over the wire, right on the pavement.

I found a good, not-too-technical article of loop sensing titled "Detection of Bicycles by Quadrupole Loops at Demand-Actuated Traffic Signals". It does explain why aluminum is easier to detect, but does not address magnets. Here is a quote from the article:
"Most quality adult bicycles feature aluminum rims, which are excellent conductors. Lower quality bicycles and some older bicycles feature steel rims. Steel rims have lower conductivity than aluminum rims, per pound, but perform adequately for detection over a properly adjusted quadrupole loop sensor."

From other papers I've read, it looks like a magnet properly oriented and moving at an appropriate speed would easily be sensed (by reducing the loop inductance as needed), perhaps better than aluminum at rest. I found the equations to solve for the delta-H with a moving magnet, but don't feel up to solving them now. It is not obvious to me what the orientation of the magnet needs to be, and I think the optimum velocity is a function of the loop frequency.

-- Alan

I found a good, not-too-technical article of loop sensing titled "Detection of Bicycles by Quadrupole Loops at Demand-Actuated Traffic Signals".

One thing I wondered as I read this thread is - does everyone use the same loop detection method? Is it possible that not everyone uses "quadrapole loops"? Hence, more than one solution? Hence the fact that some swear X works and others claim Y?

Just wondering...

One thing I wondered as I read this thread is - does everyone use the same loop detection method?

I believe the answer is basically, yes, but with variation in design. Different loop shapes, ranging from circles, to narrow rectangles, to "hatched" diagonals sub-loops within the loop are used. Different frequencies are used. Different types of circuitry for the delta-Henry detection. Most of the differences are to control for things like adjacent lane interference, controlled gate feedback, high-ground clearance vehicle sensing, etc.

There are other very different vehicle detection methods as well, such as optical, pneumatic tube, in-vehicle transponder, etc. However, the loop detection systems are all fundamentally using the same method: creating a resonant electro-magnetic field whose resonance is changed due to a change in the loop inductance caused by an object interfering with the field.

-- Alan

Alan;
I expected the best orientation of the magnet to be inline with the cut, but this is incorrect. 90* to the cut is preferable. My background in VHF electronics provides me with no understanding on what the conductivity of aluminum vs steel rims has to do with interrupting the the field around the embedded wire loop. Delta-H is simply the change in inductance. A given volume of steel has a much greater ability to change the inductance than aluminum. The inductance of the vehicle changes the resonant frequency of the loop. It is this frequency shift that the receiver detects. Try making an electromagnet out of an aluminum bar, if you doubt this. All tuned inductors use an iron or ferrite core for this reason. The loop detectors are primarily designed to sense the steel in a vehicle and as I sited the California Transportation has fine tuned their loops to detect a 100cc Honda Scooter, not a bicycle. Locally, our traffic lights use a microwave beam to detect a bicycle. The position the bicycle must be in, is painted on the road.

Please read this reference. It proves that my thinking is totally wrong;

http://www.humantransport.org/bicycledriving/library/signals/detection.htm

It is a good day when you learn something. I have learned a lot from this discussion.
Thanks;
Reid