Traffic light changer for motorcycles

[cvrefugee]

What's the best device to get or best place to purchase one of those magnet things that helps the traffic light sense your presence? I'm asking because my friend recently purchased a Honda Ruckus and for his upcoming birthday I wanted to get him one. I searched on Google but I have no idea about the quality of what I found. I know a lot of you have bikes so I figured this would be a good place to ask. Thanks.

[Jon]

I had this problem the other day, sometimes it's just ridiculous.

[Viper007Bond]

How would a magnet get it to work? I thought only metal in general would do it (I can trigger them with my bicycle for example if I lay it on it's side over the censor).

[Spectre]

The sensors work on magnetic principles. How do you think it "detects" metal?

See: http://auto.howstuffworks.com/question234.htm

How does a traffic light detect that a car has pulled up and is waiting for the light to change?

There is something exotic about the traffic lights that "know" you are there -- the instant you pull up, they change! How do they detect your presence?

Some lights don't have any sort of detectors. For example, in a large city, the traffic lights may simply operate on timers -- no matter what time of day it is, there is going to be a lot of traffic. In the suburbs and on country roads, however, detectors are common. They may detect when a car arrives at an intersection, when too many cars are stacked up at an intersection (to control the length of the light), or when cars have entered a turn lane (in order to activate the arrow light).

There are all sorts of technologies for detecting cars -- everything from lasers to rubber hoses filled with air! By far the most common technique is the inductive loop. An inductive loop is simply a coil of wire embedded in the road's surface. To install the loop, they lay the asphalt and then come back and cut a groove in the asphalt with a saw. The wire is placed in the groove and sealed with a rubbery compound. You can often see these big rectangular loops cut in the pavement because the compound is obvious.

Inductive loops work by detecting a change of inductance. To understand the process, let's first look at what inductance is. This figure is helpful:



What you see here is a battery, a light bulb, a coil of wire around a piece of iron (yellow), and a switch. The coil of wire is an inductor. If you have read How Electromagnets Work, you will also recognize that the inductor is an electromagnet.

If you were to take the inductor out of this circuit, then what you have is a normal flashlight. You close the switch and the bulb lights up. With the inductor in the circuit as shown, the behavior is completely different. The light bulb is a resistor (the resistance creates heat to make the filament in the bulb glow). The wire in the coil has much lower resistance (it's just wire), so what you would expect when you turn on the switch is for the bulb to glow very dimly. Most of the current should follow the low-resistance path through the loop. What happens instead is that when you close the switch, the bulb burns brightly and then gets dimmer. When you open the switch, the bulb burns very brightly and then quickly goes out.

The reason for this strange behavior is the inductor. When current first starts flowing in the coil, the coil wants to build up a magnetic field. While the field is building, the coil inhibits the flow of current. Once the field is built, then current can flow normally through the wire. When the switch gets opened, the magnetic field around the coil keeps current flowing in the coil until the field collapses. This current keeps the bulb lit for a period of time even though the switch is open.

The capacity of an inductor is controlled by two factors:

* The number of coils
* The material that the coils are wrapped around (the core)

Putting iron in the core of an inductor gives it much more inductance than air or any other non-magnetic core would. There are devices that can measure the inductance of a coil, and the standard unit of measure is the henry.

So... Let's say you take a coil of wire perhaps 5 feet in diameter, containing five or six loops of wire. You cut some grooves in a road and place the coil in the grooves. You attach an inductance meter to the coil and see what the inductance of the coil is. Now you park a car over the coil and check the inductance again. The inductance will be much larger because of the large steel object positioned in the loop's magnetic field. The car parked over the coil is acting like the core of the inductor, and its presence changes the inductance of the coil.

A traffic light sensor uses the loop in that same way. It constantly tests the inductance of the loop in the road, and when the inductance rises, it knows there is a car waiting!

Often the loops' control circuitry is set to a high detection threshold to keep from falsing. However, often it's too high and there isn't enough ferrous metal in a motorcycle to get the loop above the detection threshold. Using a powerful magnet takes the place of the large ferrous mass of the car's engine block and subframe so a motorcycle can trip the sensor instead. Otherwise, you can sit there for hours and nothing will happen - a particular problem at lights that have red light cameras.

I have an intersection near my home that routinely ignores bikes, and the local street department won't do anything about it. Adding a magnet to the underside of my CB700 solves the problem quite nicely. It doesn't have to be a special magnet, you can get powerful enough ones from local scientific supply shops.

[NecroJoe]

I believe in Wisconsin you are only obligated to wait, on a motorcycle, 60 seconds at a red before you can run it.

[Jon]

I've ran red several times. Just plain had to.

[Spectre]

About a month ago I got one of the magnets, stuck it to the bottom of the bike and don't have to wait at badly adjusted lights any longer than I do with my truck or one of the Jags. I got tired of having to sit at the light one block from my house.... which has the police station on the corner, so I can forget about running it.

Yes, the magnets do work.

[NecroJoe]

How large/heavy are these magnets?

[Spectre]

Mine's about the size of a Snicker's bar, weighs a few ounces.

[petarkb]

Originally Posted by NecroJoe

How large/heavy are these magnets?

Heavy enough to KILL A MAN WITH!!!

[Night_Hawk]

I have a few of these in my town away from where Its busiest.

They must be fucked from the cold though because sometimes you wait 5 seconds and sometimes you wait 5 minutes, I've ran them many times in my buick

Ill have to keep an eye out for motorcycles not going anywhere.

[Nabster]

Wouldn't say, one of the neodymium magnets from an old hard drive be plenty? The old iron ferrite magnets have nothing on the NIB magnets.

[Spectre]

People have tried those with no result. Go figure.

[Nabster]

Hmm... probably a field issue, while those NIB magnets are powerful, they have a relatively small magnetic field, so you need a big one to get a big field, but then you run into the trouble of having a hugely powerful magnet on the underside of your motorcycle.

[Spectre]

Yeah, that's probably it.

You don't want TOO powerful a magnet on the underside of your bike, as you've noted, because there can be problems - not least of which is because the *magnetic* ignition pickup is located close to the bottom.

A friend of mine has one on his low-rider H-D, and he has to clean off the nails, screws, bolts and other metal road debris the thing picks up on a regular basis.

[Jon]

I can see why that would be a problem.. But it's that or waiting.. and i'm impatient so i'm sold!