well, the things you find out by accident - laser guns
Discussion
as you may or may not know I own a pro-laser speed gun, and have discovered something that really REALLY confuses the thing, this 'something' comes fitted as standard on a lot of cars.
Without revealing precicely what it is, thing along these lines..............
Hunt for Red October,
torpedos,
chaff,
Car,
laser gun,
water droplets.
Some cars have headlamp washers. Some of these washers are not adjusted and spray over the bonnet instead. Water droplets reflect light preferentially back in the direction in which it came.
2 + 2 ......??
Without revealing precicely what it is, thing along these lines..............
Hunt for Red October,
torpedos,
chaff,
Car,
laser gun,
water droplets.
Some cars have headlamp washers. Some of these washers are not adjusted and spray over the bonnet instead. Water droplets reflect light preferentially back in the direction in which it came.
2 + 2 ......??
Hmmmm, nice idea.
So does this mean readings taken in rain are pretty useless? Think of all the diffraction, refraction and absorbtion going on with respect to the entire beam being intersected by water droplets that were not perfectly spherical... Surely a rainbow proves what water droplets do to incident light!
Dave
So does this mean readings taken in rain are pretty useless? Think of all the diffraction, refraction and absorbtion going on with respect to the entire beam being intersected by water droplets that were not perfectly spherical... Surely a rainbow proves what water droplets do to incident light!
Dave
I've seen them testing these theories on tv, none of them worked. Not even wrapping the car in tin-foil. They even had a huge revolving mirror setup on the top of the car, nothing worked. They may have seen a difference of about 1 or 2 miles an hour with the revolving mirror.
It was probably mythbusters, but I can't be sure.
Edited so that I wasn't wrapping the car in cling-film.
>> Edited by dmitsi on Tuesday 28th March 13:54
It was probably mythbusters, but I can't be sure.
Edited so that I wasn't wrapping the car in cling-film.
>> Edited by dmitsi on Tuesday 28th March 13:54
dmitsi said:
I've seen them testing these theories on tv, none of them worked. Not even wrapping the car in tin-foil. They even had a huge revolving mirror setup on the top of the car, nothing worked. They may have seen a difference of about 1 or 2 miles an hour with the revolving mirror.
It was probably mythbusters, but I can't be sure.
Edited so that I wasn't wrapping the car in cling-film.
>> Edited by dmitsi on Tuesday 28th March 13:54
Mythbusters.
They also decided that anything that looked like it might begin to work was in itself illegal, and would probably get you pulled. (eg - the mirror ball)
madbadger said:
I've seen them testing these theories on tv, none of them worked. Not even wrapping the car in tin-foil. They even had a huge revolving mirror setup on the top of the car, nothing worked. They may have seen a difference of about 1 or 2 miles an hour with the revolving mirror.
It was probably mythbusters, but I can't be sure.
Edited so that I wasn't wrapping the car in cling-film.
>> Edited by dmitsi on Tuesday 28th March 13:54
Mythbusters.
They also decided that anything that looked like it might begin to work was in itself illegal, and would probably get you pulled. (eg - the mirror ball)
Odd, all those devices and ideas didn't do anything, yet slip error and user error of even the slightest amount can?
Surely if a big revolving mirror or a foil car generates no problems for the laser speed detectors, then how come so many people believe they are so easily made to be inaccurate and fallible?
Dave
well. I've had speed readings from a wet road. Also had 57MPH from the guttering on a house - again in the rain. by sweeping the beam.
Rain makes it harder to get a reading, especially with cars coming toward you for some reason.
Static range checks also change from one reading to the next when it rains, ie point at a car 710 feet, then 705 feet, then 712 feet, on a car that isn't moving. This is probably why the error detection doesn't give a speed.
Close up the highest speed reading from a parked car has been 7MPH, at a distance however I don't know, as the prolaser will only read down to 5MPH.
Rain makes it harder to get a reading, especially with cars coming toward you for some reason.
Static range checks also change from one reading to the next when it rains, ie point at a car 710 feet, then 705 feet, then 712 feet, on a car that isn't moving. This is probably why the error detection doesn't give a speed.
Close up the highest speed reading from a parked car has been 7MPH, at a distance however I don't know, as the prolaser will only read down to 5MPH.
The lidar gun will acquire the first significant reflection (the first decent reflected pulse edge); in almost all cases this will be from the retro-reflective VRM. Passive countermeasures installed behind the VRM will not affect the speed reading. Evenly distributed water droplets (a.k.a. rain) wont offer such a reflected edge so it will be ignored. According to the LTI manual, the unit will work just fine through rain although there may be some reduction in maximum operating range.
A possible method of lidar confusion would be to aim the spray of water significantly before the VRM, at varying distances during the 300mS duration to attempt to force a slip error. This would prove to be difficult when the vehicle is at a decent speed. However, I suspect the reflection from the VRM would still be the one detected.
A possible method of lidar confusion would be to aim the spray of water significantly before the VRM, at varying distances during the 300mS duration to attempt to force a slip error. This would prove to be difficult when the vehicle is at a decent speed. However, I suspect the reflection from the VRM would still be the one detected.
The only way to beat lidar is to remove reflection from the equation as much as possible.
This means losing the reflective plate on the front, headlights (ive got pop ups
) and foglights.
Anthing that gives a good reflection back in visible light will almost certainly work for ir, so the obvious way to give you an edge is to get rid of any reflectives.
Works for the front plate by increasing your effective range by approx 160 feet which aint to be sniffed at, and that dosent include dark/matted paint, whatever.
A rough guide to reflections is to eyeball the car from the front and see where bright spots are concentrated such as on edges, this will help you to get a grip on where to concentrate your efforts.
Passive diffusion they cant do sweet f/a about. :twofingersmiley:
This means losing the reflective plate on the front, headlights (ive got pop ups
) and foglights. Anthing that gives a good reflection back in visible light will almost certainly work for ir, so the obvious way to give you an edge is to get rid of any reflectives.
Works for the front plate by increasing your effective range by approx 160 feet which aint to be sniffed at, and that dosent include dark/matted paint, whatever.
A rough guide to reflections is to eyeball the car from the front and see where bright spots are concentrated such as on edges, this will help you to get a grip on where to concentrate your efforts.
Passive diffusion they cant do sweet f/a about. :twofingersmiley:
madbadger said:
Mythbusters.
Haven't seen that episode, but I'd be a bit wary of believing any of the results they come up with. Some of their experiments are fatally flawed from the outset, others fall apart during or in the interpretation of the results. Good entertainment, and sometimes scientifically accurate, but definitely not to be relied on as a source of definitive answers...
stu 9-5 said:
Seeing as motorbikes don't have a front VRM, what do the BiB aim at? Centre of mass? Helmet? Headlight?
Just interested......
I understand that it is difficult to get a reading from a Motorbike and especially difficult to get an accurate & consistent reading as motorbikes move around a lot, not only side to side but also backwards/forwards on the suspension as does the rider. But I don't suppose the Scammers are interested in physics - never let the truth get in the way of a good earner.......
paolow said:The rotational velocity of the tyre will not affect the speed measurement.
what if you catch an exposed front tyre such as on an ariel atom or 7esque car?
Lidar guns do not measure a target's velocity; they instead take a series of measurements each determining the distance to the target (whatever that target surface happened to be for each measurement - which is why they suffer from the slip effect) then calculate the rate of change of that distance over time. The rate of change of distance to the measured point of the tyre for each snapshot will not change relative to the rest of the vehicle. (I hope that made sense)
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