h a l f b a k e r yI didn't say you were on to something, I said you were on something.
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i dunno, I see some problems. |
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Isn't rubber solution (the stuff you use to mend bike punctures) just rubber dissolved in petrol? |
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So, simply divert petrol from the engine to a spray system in the wheel arches, and dissolve the tyres. |
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Explosive bolts on the wheels instead? |
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I'm not confident that the idea's solution would necessarily stop things all that faster.[] |
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Just wack a parachute on it... maybe external airbags would be more fun. |
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This would work better if you used it for getting going, eg, for those difficult traction exercises, such as driving up the face of skyscrapers. |
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Some locomotives use a sand spray when they need more traction. The racing slicks of drag racers are made of soft rubber that gets sticky when you spin them aginst the track, thus getting more grip. |
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Increasing the friction between the tires an the road will not, I think, stop the car faster, and this would just make the car undriveable afterwards. |
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How about an emergency plate under the car that can be pressed against the road for emergency stops? Much larger surface area, hence much higher friction. |
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Dr Curry needs to familiarize himself with physics. |
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ldischler-I know about sand spray for locomotives,
but sand actually decreases grip on asphalt. |
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DrCurry- Larger surface area does not mean greater
friction. |
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I came up with the idea when working on a
project.
I have been working on a mechanical ABS system
for a while. For testing the system I use a
test patch of road with different friction changing
material on the road at intervals (sand, gravel, a
layer of smooth steel with detergent on it, and
thin layer of silicone rubber). If the Silicone does
not rip off from the road on braking (it happens
sometimes) it actually does wonders. It never
activated the ABS system and but the force is too
much for the disc brakes on my test rig. It slips. I
will put an accelerometer on the system once
school starts, but I know from the feel of the
system that the braking force is amazing. |
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I am not saying silicone rubber is a practical
solution. Don't know what but someone can
probably find some substance that has a higher
coefficient of friction than rubber-asphalt, and
that can bond with the asphalt immediately. May
be even someone can find some adhesive that
activates on pressure (like duct tape). |
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The forces on the suspension components, tires
will be enormous but that is another issue. |
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[DrCurry] // Much larger surface area, hence much higher friction // One would think so, except not. Friction depends on how much force is being applied at the area in question. If you press another thing down onto the ground, that takes part of the car's weight off of the tires, so you're not getting as much friction from the tires. |
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But [kneeslider], this could still be helpful if the emergency plate's surface has a much higher frictional coefficient than the tires - i.e. it's already covered with whatever you were planning to spray on the tires. And if it's a big plate under the chassis, attached to the frame throughout the length of the car, then maybe the braking force is distributed more evenly, so you don't tear out your suspension as you might do if the whole force of stopping the car was applied through your 4 wheels. |
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Got it - Big rake spikes along the underside of the vehicle, and pyro tyre bursters. |
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The plate will have to slide unlike the wheel. As
far as I know kinetic friction is always smaller than
static friction (thats why people invented ABS).
More over when the plate will slide you will lose
directional control (thats another reason people
invented ABS).
Lastly the plate will need a elaborate mechanical
system for it to work and it will need a strong
support on the chassis. It's not easy to find strong
supports on modern day monoque chassis. |
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Lastly, another idea- if you want to stop even
faster (and if you can find a strong areas on the
chassis) explosively drive an anchor into the road
and use a elastic cable to stop the car (similar to
stopping a jet on the carrier- it produces several g
deceleration). |
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In the UK it is an offense to damage the road surface, which spikes or anchors would I believe tend to do. |
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I have posted a rocket-based idea inspired by this one though. |
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//In the UK it is an offense //
No, in the UK, it is an offence. |
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// The plate will have to slide unlike the wheel. As far as I know kinetic friction is always smaller than static friction //
True. So instead of a plate, how about a big conveyor belt - in effect a giant flat tire. Still preserves your suspension from abrupt forces a suspension isn't meant to stand... plus, if the wheels don't have to do as much of the braking, doesn't that increase steerability? |
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Pocmloc- its illegal to damage the road surface. But I will prefer to do it instead of crashing my car. The system is supposed to only activate during panic stops (the car computer detects there is a barrier 10m ahead and the brake pedal is fully depressed- it activates the system). |
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The rocket seems to be a good idea. Don't know how you will produce significant thrust though (i will add the details in your post) |
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hob- conveyor belt may be theoretically possible but probably not mechanically feasible. Secondly, deploying the belt will not increase friction until the belt has a higher coefficient (area of contact is not important). |
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Well as a cyclist I am offended by potholes and grooves in the road. |
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Has anyone said "hello" to our newbie here? Hi, kneeslider,
and welcome to the HB. |
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[kneeslider] But I already said that surface area wasn't the important thing. The point of the plate was to be able to put the stickier-than-a-tire material on something other than your tires, and also to save the suspension. And then I changed the plate to a belt because as you pointed out, rolly things make more efficient use of friction than skiddy things. |
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Oh yeah! Hi [kneeslider]! Welcome to the land where surreal nitpicking is applied to practical ideas, and vice versa. :) |
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[hob] My bad- didn't realize you wrote area was
not important. But why use a conveyor belt then?
If you want to put something stickier then why
not use extra wheels? After all conveyors need
rollers. |
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I am not convinced about the mechanical
feasibility of the system. Will anyone really add
extra wheels or conveyor to a already superfluous
heavy modern car? But I still love the surreal
nitpicking :D |
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Hello [hob], [MaxwellBuchanan] and everyone.
Love this place already. |
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ever noticed that some areas are smeared with ABS marks? These areas would be thick with tire goo.
The idea fails on any loose top surface.
The idea fails in wet conditions.
The idea fails because it destroys perfectly good tires when drivers over react.
It messes up the road. |
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Mercedes just showed a concept that exploded an airbag under the vehicle for such circumstance, with a high friction surface, to reduce impact speed of accidents the vehicle's CPU deems inevitable.
To have any effect on routine braking performance, even at moderate speeds, any device attempting to increase friction would have to operate very quickly - hence, expensive, heavy and energy-consumptive. Espescially for variable road surfaces.
I guess we're stuck with putting the dollars into better tyres, faster-reacting brakes (google 'electronic wedge brakes'), lower unsprung weight, and a lower centre of gravity. There might be ways to dynamically increase available friction on wet & icy surfaces; any ideas?? |
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I recently came across a spray-on product to increase traction in the winter... next time I'm in the store I'll investigate further; not sure if the product itself is the contact material or if the product makes the existing rubber gooier. |
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[ssvtp] my "Torquing Tweel" concept (posted) increases the contact patch under deceleration: effectively "deflates" the tyre when braked. |
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Flying Toaster....GOOD NAME!!!! |
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Those spray cans have been around for a while, and they do seem to have some effect - but only after a delay of a minute or so. The resins in them are derived from fir tree sap and bark, and over in their original Norway, they were originally deployed by a system remarkably like a windshield washer, mounted in the wheelarch. I don't think it worked any faster, though. |
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There is an emergency brake system for Semi trucks that consists of 20 foot conveyor belt like strips a foot and a half wide that are released with explosive bolts and sucked under the wheels and attached to the chassis, esentially increasing the brake area 10 fold. |
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why not have all cars airbagged with long rubber strips on the bottom, in a panic the car deflates and drops. |
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I'm not certain why I'm posting this irrelevant formula, but for interested parties, rolling resistance for legal highway speeds, (not tire friction, mind you), is approximated by the following equation: |
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rolling resistance =~= u(1 + V/100), where u is a coefficient of rolling resistance specific to the tire and V is the vehicle speed. |
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In generating friction, larger surface area does help by allowing softer rubber in the tire compound and thus affecting the friction coefficient. Larger surface area also helps by increasing the probability that the highest friction coefficient in the contact patch makes contact with the ground. |
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Tires are complex to analyze, because during harder stops or starts material shears or tears instead of sliding. See the link. |
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[Wcw] The system does not necessarily have to fail
in the rain. The idea behind Coefficient of friction
is fairly complex. The imperfections on the roads
are a major factor. You wouldn't have produced
much grip with your car tire if the roads were
smooth . The rubber compounds in the tire
actually digs a little in to the road imperfection
and allows more grip. One of the reasons softer
formula one tires produce more grip is because
they can dig more into the road imperfections
(they also have a higher coefficient of static
friction to start with). It should also act the same
on wet asphalt but probably not as good because
it may be trap water between the tire and the
asphalt and not allowing the compound to dig in as
much. We can discharge the rubbery substance in
several streams with some distance between each
and thus allow to have channels for water to
escape as there are in rain tires. |
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It's hard to predict how the
system will behave on a loose top surface, but I
don't see any obvious reason why it should fail. |
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Hang on. Isn't something that can be sprayed, inevitably going to act as a lubricant?? |
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<already ignorant, now also confused, sorry>
In [RayfordSteele]'s link, it says |
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"The maximum coefficient of friction can occur anywhere in the contact area, so that the greater the area, the greater the likelihood of maximum traction." |
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So, should we imagine the coefficient of friction of a 5 sq. cm. contact patch as the maximum of the various coefficients of friction of, say, five 1 sq. cm. areas?
</ainacs> |
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Thanks for any clarification of this. |
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makes sense I think... the larger the contact area the better chance that a portion will be in full contact. Regarding tires, all weight does is squish more rubber into the road's nooks and crannies, ie: if you had a tire that just happened to be the exact mirror image of the road, then it (more or less) wouldn't matter how much weight you put onto it. |
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[sstvp] Does spray on adhesives act as lubricants? |
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I did not say it has to be sprayed on. I suppose our
imaginary friction increasing material is going to
quite viscous. It can be pressurized to flow
through small pipes. |
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[pertinax] and [everyone else], To prevent any
confusion, I will try to explain
the theory of tyre traction as much as possible in
short. |
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Contrary to popular belief, for a particular tyre
pressure and weight of the vehicle, the contact
patch of a narrow tyre is (almost(1)) the same as
contact patch of a wide tyre. The size of the
contact patch depends on the tyre pressure and
the weight of the vehicle. In an ideal world (1), at
any
instant, tyre pressue= weight on the wheel/area
of the contact patch. |
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For a narrow tyre, the contact patch is longer
along the length of the tyre. Therefore the side
walls have to deflect a lot. The side wall deflection
produces heat by hysteresis loss (one of the
reasons behind rolling resistance). Harder tyre
compounds produces less heat, and can withstand
more heat. Therefore narrower tyre has to be
made from less grippy harder material (see my
previous post for explanation of why harder rubber
is less grippy) whereas a wider
tyre can be easily made from soft rubber. (In
practice there is a limit to how soft a tyre can be
made. Softer tyres wears more and are more prone
to tears and leaks. That is why I want to pour soft
rubber like substance on the wheels only during
panic stops) |
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(1) The thick sidewalls of a narrow tyre, takes
some of
the weight of the vehicle, making the contact
patch of a narrow tyre marginally smaller compared
to a wider tyre for the same tyre pressure and
weight. |
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A wider tyre can run with a slightly lower tyre
pressure with little ill effect because the side walls
have to deflect less compared to a narrow tyre.
Therefore the contact patch can be a bit larger. |
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Now, think of Total Friction=F= Summation of
[coefficient of friction for unit area * weight on
unit area] over the total area of contact. |
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The coefficient of friction for unit area is not
homogeneous. They can vary at different positions
on the contact patch (think of what happens
when half of a tyres contact patch is on ice). A
wider contact patch has more summation terms
than a narrow tyre. Therefore, there is a greater
chance of having a higher total friction. |
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Well... if the material is heated or pressurized to move through an applicator, then yes it is acting as a lubricant in that condition. Adhesives typically don't adhere until they're exposed to chemical, temperature, or pressure changes. At 50km per hour a vehicle travels 14 metres per second, its wheels are rotating about 11 times per second, and I don't think that allows a lot of time for anything to move from a fluid to adhesive state. The best shot might be applying multiple resins that rapidly become adhesive - only when combined. |
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Could something not be devised which, in an emergency,
deploys a succession of cyclists in front of the vehicle,
thereby bleeding off the speed in a series of small
increments and preventing a serious collision? |
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"deploys a succession of cyclists in front of the vehicle" ________ This has been devised. It's called the cellphone. The problem is that it generates its own emergencies by deploying cyclists in front of vehicles at random intervals. Works on pedestrians and vehicles too. |
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Best explanation I've seen on Benz's under-car airbag is on popularmechanics.com.
Apparently, it can get you braking at 2G, while the tyres can only make 1G - but like all airbags it can fire only once, expensively. |
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For evryday panics, I still think evolution of better brakes & tyres is the way to go for dry & wet asphalt, and something mechanical for ice & snow. |
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[Ian] You don't need time travel for that. You just need an
ASHPD and a pair of deployable walls. |
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