Unfair traffic lights.

On 14 May 2009 16:38:14 +0100 (BST)
David Damerell wrote:

Quoting Simon Mason :
On my commute, I encounter no fewer than 27 sets of traffic lights,
the vast majority of which do not sense my bike, probably as it is
nearly all carbon.

Instructables suggests you can fix a rare-earth magnet to the BB to
improve matters. No idea if it works.

I don't think so. The detection system works because the loop is part
of a tuned circuit whose resonant frequency (all other things being
equal[1]) depends on the reluctance of the space above the loop - an
increase in the frequency indicates the presence of a vehicle.
Introducing a strong magnetic flux wouldn't actually change the
reluctance, except the little bit caused by the material of the magnet.
What you want is a low-reluctance material close to and in the same
plane as the loop, to have an effect like a car (that's why laying your
bike on the loop often works if it's not normally detected) - a piece of
sheet steel laid on the ground will probably be as effective as
anything.


[1] Of course they're not, which is probably why some lights which have
been recalibrated to detect bikes drift out of adjustment again after a
few weeks.

In ,
David Damerell tweaked the Babbage-Engine
to tell us:
Quoting Simon Mason :
On my commute, I encounter no fewer than 27 sets of traffic lights,
the vast majority of which do not sense my bike, probably as it is
nearly all carbon.

Instructables suggests you can fix a rare-earth magnet to the BB to
improve matters. No idea if it works.

If a sensor can't detect a couple of 2" diameter steel tubes 3" off the
ground[1], I suspect a small magnet is unlikley to have much effect.

1 - June 18th 2006, junction of B6135 and A61, Pat Hurt's Trice Monster and
my Tice XXL

--
Dave Larrington
http://www.legslarry.beerdrinkers.co.uk
I thought I saw his name on a jar of marmalade the other day,
but when I looked more closely, I saw it read 'thick cut'.

On 2009-05-11, Simon Mason wrote:
On my commute, I encounter no fewer than 27 sets of traffic lights, the vast
majority of which do not sense my bike, probably as it is nearly all carbon.
Because of this, I find myself waiting at many sets of lights as they show
red, whereas if I was in a car, there would be enough metal to trip the
lights.

In this case, I have to lay my bike down on the sensors to show enough
chainring metal to the sensors and get them to change.

And you reckon doing that is safer than just riding through the red
light?!