Traffic Light Trigger for Your Bike
Intro: Traffic Light Trigger for Your Bike
Not feeling ferrrous enough to trip the induction loops that trigger green lights? No problem - just epoxy a rare earth magnet to your shoe! Inspired by a product marketed to motorcyclists, which is basically a big neodymium magnet to stick under your ride. I thought it might be better to get a slightly smaller magnet closer to the road.
STEP 1: Dremel As Needed Between the Lugs of One Heel
I always put my right foot down, so I ground out a little extra space on my right heel. Luckily, my Sidis have tall, widely-spaced lugs, so I didn't have to remove much material.
STEP 2: Epoxy the Magnet, Backed With a Washer, to the Shoe
I used PC-7 heavy-duty epoxy paste and coated the entire magnet, both to protect it and to stick it firmly to the heel. Backing the magnet with a washer helps to focus the magnet field, aiming it down (and not up into your heel, not that it should do anything to you anyhow).
STEP 3: Using the Magnet to Trigger Lights
Look for the round or diamond-shaped cuts in the asphalt that show where induction loops are buried at intersections, and set your heel down near the tar lines. Here in Portland, some lights helpfully have a small bike between two hashmarks which you're supposed to line your wheels up with, which is a the perfect spot (and more sensitive, too).
82 Comments
TL22 5 years ago
unanw1 7 years ago
Will it work if I attach it on bottom of bike? I do not want to dig a whole in my shoe.
astral_mage 10 years ago
Advar 12 years ago
astral_mage 10 years ago
Advar 10 years ago
agustafson 10 years ago
more.mayhem 18 years ago
LesB 10 years ago
Advar 12 years ago
damagj 12 years ago
dinton 18 years ago
DrLex 17 years ago
storyhoc 15 years ago
DrLex 15 years ago
storyhoc 13 years ago
DrLex 13 years ago
When adding iron inside an empty coil, the current will align the spins inside the iron, increasing the magnetic field. This requires energy, hence if you would hook the coil to a Wattmeter, you would see a short bump in power consumption while the iron is added. This continues as long as the added iron is sufficiently near the coil to be influenced by it. At a certain point, the coil will be completely filled and surrounded by iron to such a degree that it's impossible to add extra iron that is influenced by the coil to any measurable degree.
The permanent magnet on the other hand behaves like such an electromagnet that already has the absolute maximum amount of iron added to it. Producing additional magnetic flux would require an energy source of some kind, and there is none inside a permanent magnet. Even the most ideal ferromagnetic material would still only be able to guide the magnetic field much like an electric wire can carry current from a battery, not increase it.
If your theory would be correct, it would be possible to keep on sticking iron coins indefinitely to a permanent magnet, or to build a perpetuum mobile of some kind.
storyhoc 13 years ago
DrLex 13 years ago
The energy release you're speaking of, is the kinetic energy of the iron being pulled towards the magnet because indeed the equilibrium state for molecules with aligned spins is as close together as possible. But that can only happen after the spins have already aligned. The pulling force of magnets is a consequence of the alignment, not a cause. The total magnetic energy of the combination magnet+iron cannot be higher than of the magnet itself (plus any stray magnetism that was already in the iron). With each piece of iron added to it, the magnet will have less energy to spare to magnetize additional iron. The coil on the other hand can draw current at leisure from its power source.
storyhoc 13 years ago