Emergency Braking Technology for Automobiles

[DonRocks]

I was pondering Newton's Three Laws of Motion (particularly the second), and an idea popped into my head.

In an emergency automotive braking situation, why can't a car shoot out grappling hooks - from the front of the car, or the back, or even both - which will dig like wedges into the road ahead, and come as close as possible to being a direct counter-force to the auto's forward motion? Disk brakes are fine, too, but they only stop the wheels from turning; I'm talking about a life-threatening situation where the entire vehicle needs to stop ASAP.

Even if they don't go into the road, front-shooting, 45-degree-angle, non-jointed "rods" (resistant to snapping) would perhaps apply the maximum stopping pressure.

Picture a car extending rods forward-and-down like this: oo^oo\\\

It does sound like Batman, and admittedly, I can visualize this causing the car to flip over the rods, but has anyone at least thought about this? If you're about to ski off a cliff, wouldn't you stick your poles out, forward, into the snow, even if it meant breaking your elbows?

Or maybe there's some sort of "tire-retraction" mechanism, that would make all four tires retract into the chassis, allowing the entire bottom of the car to make contact with the ground and skid, maximizing friction?

Expensive, but in certain situations, worth it. Think about an airplane landing, and about to roll off the end of the runway - better to have the wheels instantly retract and have the entire plane slide along the ground on its belly, no?

Back to the skiing analogy: If you're about to ride a bicycle off a cliff, wouldn't you hit the deck, and take your chances with a few broken bones, rather than continue to roll forward?

[zgast]

20 minutes ago, DonRocks said:

I was pondering Newton's Three Laws of Motion (particularly the second), and an idea popped into my head.

In an emergency automotive braking situation, why can't a car shoot out grappling hooks - from the front of the car, or the back, or even both - which will dig like wedges into the road ahead, and come as close as possible to being a direct counter-force to the auto's forward motion? Disk brakes are fine, too, but they only stop the wheels from turning; I'm talking about a life-threatening situation where the entire vehicle needs to stop ASAP.

Even if they don't go into the road, front-shooting, 45-degree-angle, non-jointed "rods" (resistant to snapping) would perhaps apply the maximum stopping pressure.

Picture a car extending rods forward-and-down like this: oo^oo\\\

It does sound like Batman, and admittedly, I can visualize this causing the car to flip over the rods, but has anyone at least thought about this? If you're about to ski off a cliff, wouldn't you stick your poles out, forward, into the snow, even if it meant breaking your elbows?

Or maybe there's some sort of "tire-retraction" mechanism, that would make all four tires retract into the chassis, allowing the entire bottom of the car to make contact with the ground and skid, maximizing friction?

Expensive, but in certain situations, worth it. Think about an airplane landing, and about to roll off the end of the runway - better to have the wheels instantly retract and have the entire plane slide along the ground on its belly, no?

Back to the skiing analogy: If you're about to ride a bicycle off a cliff, wouldn't you hit the deck, and take your chances with a few broken bones, rather than continue to roll forward?

I don't know. Kind of sounds like pole vaulting to me.  But with a car.

[DonRocks]

37 minutes ago, zgast said:

I don't know. Kind of sounds like pole vaulting to me.  But with a car.

That's why the counter-force needs to be "opposite" (i.e., as close to directly in front as possible); if it's too low, it would produce car-vaulting (if nothing more than a speed bump). They could also come out the sides - as much friction as possible. The angle needs to be optimized,.

Front-wheel-only brakes could theoretically create a similar car-vaulting effect.

[TedE]

You aren't taking into consideration possible human damage due to sudden deceleration from your spikes. When it comes to car accidents, the goal is to protect the fragile bags of flesh inside. In an emergency a modern car itself functions as a disposable force absorption device; people irrationally don't like to think of it that way, but that's really the choice automotive engineers are paid to make when designing crumple zones, etc.  A sudden stop like you are describing would invariably be more likely to cause major harm or death than a relatively controlled deceleration with ABS and, yes, massive deformation of the car frame at collision.  And the pop-off-the-wheels solution is missing one huge factor: the coefficient of friction of bare metal vs. tires.  Think of it the other way around.  Let's say you have two square foot slabs of asphalt, kind of like curling stones.  You slide one as hard as you can down one of two surfaces: one sheet metal, the other vulcanized rubber.  Which slab is going to stop in the shortest distance?

We recently got a MY2019 car with most of the enhanced safety features common these days: lane guidance, blind spot warnings and automatic braking.  I'm tempted to turn that last one off.  It functions in three basic modes as it constantly scans ahead for objects, closing speed and trajectories relative to the car.  First is an audible beep and a flashing "BRAKE" on the dash when it detects something that it deems too close for comfort.  The second is the same warning with an automatic brake pulse to scrub speed when it determines something is in the way and collision may be imminent.  Third is full on automatic application of the brakes to a full stop when it determines that you are actually going to hit something directly in your path.  Like any system it isn't perfect and we get things like Stage 1 warnings on gentle curves when an oncoming car in it's proper lane is read briefly as something in our path.  Those are annoyances. I've only had it apply brakes like Stage 2 once when a car cut us off on the highway trying to make an exit.  It was a situation that I didn't think warranted the braking; I didn't feel in actual danger as a driver, and reacted the way I would have normally while the car exited out in front of us.  Had it been a different situation I think that automatic braking could have made things *worse*, and here's why.

In my few decades of driving I've only been in one situation where I really felt I was in imminent danger, and had things gone even slightly differently would have been in a collision with potential for serious injury (*knocks vigorously on wood*).  Back before the turn of the century I was driving south on 95 through DE with light rain.  Road was crowded, but not backed up or congested, and traffic was moving at speed.  I was in the middle lane with a steady line of cars in the passing lane.  A jacka** had passed me, tailgating the car in front, and was weaving in an out trying to get around cars in any lane.  During one sudden change from behind a box truck he obviously didn't see a car in front also changing into his path on the right.  They clipped bumpers and he started to spin, his car now rotating into my lane directly in front of me.  All of this happened in a split second.  There was a car on my left about even with my rear quarter panel.  I hit the gas hard and pulled left, barely pulling ahead of that car and around the jacka** who miraculously didn't hit anybody else.  Had I mashed the brakes, I'm 100% sure my non-ABS equipped 1990s car would have skidded on the wet pavement and slammed into him, sending one or both of us off into other lanes and possibly other cars.  Even if I'd had ABS the collision was probably unavoidable.  In my current car I don't think it would have allowed me to avoid it by accelerating into the only opening around that car; the collision avoidance system would have applied full brakes.  And that scares me.

Look, I get that these things save lives from the countless terrible, inattentive drivers they rescue on a daily basis.  But they are also a dangerous crutch to exactly the idiots they protect the most.  Witness the handful of Tesla drivers who have lost their lives by thinking the car tech was good enough that they could nap or read a book on the highway (let me re-phrase: they didn't lose their lives, they handed their life over to a fucking collection of metal and circuit boards)