iirc both times it was some sort of brake fluid leak.

So, while I totally agree that having motorized breaks is really scary, hydraulic brakes can fail as well.

The cable-operated E-brake definitely doesn't stop the car anywhere near as well as the power-assisted hydraulic brakes, but having two different braking methods can be a literal lifesaver when one system fails. (And all systems fail! I'd previously had two other cars where the E-brake didn't work.)

Good on you.

You are probably referring to the brake assist mechanism in all cars after the 90's. It uses vacuum pressure from the engine to help you push the pedal down. Without the engine running, the brakes will work ~3 times, and then they'll get super hard to press - but they will still function if you have leg muscles strong enough to work them.

Just a friendly reminder that your car has brakes. When they break, then they will fail.

Planes have a whole different set of expectations on their reliability and upkeep.

For example I don’t think people would be excited about an electric car with an aux power unit.

All of that can be done with software-only - no hardware changes needed.

The slam on brakes case would only trigger if there was gross damage to the braking system, where you might have bigger things to worry about.

Control power is different from actuation power, the latter of which is what you're addressing. And it's not "gross damage" because it's a common-mode failure, so you can't just ignore it like that.

Edit: made more concise.

This is still uncontrollable failure. What if the car is in the third lane doing enough speed and there's some cars behind? I assume no ABS, because ABS can't work with locked up brakes. This means no steering, just skidding whatever way.

Having a stick shift definitely helped, though.

But there are ways you could walk away from this.

You see some pretty crazy crash survivals in race driving, for example.

And I remember stories from a few years ago, when Ford had a recall on F150 tires because they tended to blow out at highway speeds, with an effect similar to full wheel lockup-- yes, people died, but others didn't.

life == hope

https://en.wikipedia.org/wiki/Eddy_current_brake

Tesla's that lose battery are already a challenge to tow as the parking brake cannot be disengaged without power.

I would love to be present at the DFMEA (Design Failure Modes Effects Analysis) meeting when this came up!

If emergency braking could use an explosive-spike-in-ground deceleration at say 5 G, then far more crashes would be survivable.

I think the reason it hasn't been done are human reasons - users don't like the idea that jabbing the brake pedal hard will mean they have to pay tens of thousands of dollars to repave the road and replace their spike.

To some of the replies... I think some clarification needed because the wording caused folks to think of something else such as electronically _controlled_ physical brake pads: https://en.wikipedia.org/wiki/Electronic_parking_brake

I think the gp was trying to ask about feasibility of electric _powered_ magnetic field resistance braking ... similar to an exercise bike ... which would require constant electrical power source. (Similar to : https://www.google.com/search?q=magnetic+resistant+braking+o...)

Magnetic field resistance brakes is practical for regenerative braking but not safe for parking brakes on an incline if the batteries run out of juice. The context is the gp's premise of no physical friction brake components via "(ie. no hydraulics, drums, rotors, or pads)."

In my Tesla, I push a button and I can hear an electric motor engaging the brake.

The whole industry is working on tighter integration of the drive unit components to reduce things like cooling circuits, length of high voltage cable runs, and the total mass of the components required to move the car. No one is working on splitting the motors out into the hubs.

As you point out, unsprung mass is bad. Especially for something like a motor it's beyond bad, it's a complete killer of ride quality and reliability. As sprung mass the entire drive system can be isolated from all the knocks and oscillations that happen from driving around. A hub motor will get crashed and bashed around and have a miserable MTBF. The occupants will hate the car since it will have awful handling and hitting even moderate-sized bumps will be terribly unpleasant. Lighter stuff like scooters can get away with hub motors since there just isn't that much mass to begin with, but cars are huge now.

Aptera is planning to use hub motors, but their car is the vapourist of wares and relies on being counted as a motorcycle under regulations. Their basic engineering just doesn't work when scaled to a 3500 pound car and beyond.

https://lightyear.one/articles/lightyear-and-elaphe-develop-...

You should see what you propose on cheap cars if motor pricing becomes less than the cost of regular hydraulic brakes.

FVMSS 105: https://www.govinfo.gov/content/pkg/CFR-2011-title49-vol6/pd...

What is a "service brake"? Notice that the regulation you linked to includes requirements for EVs that have braking regeneration as a component of their "service brake".

It turns out that the top-level of FVMSS [1] says that "service brake means the primary mechanism designed to stop a motor vehicle."

So I think you are exactly right. There is nothing in the law that says you can't use a 100% brake regen system in an EV. It just has to work and meet the performance standards (and perform regen on all wheels). But I'd guess that you aren't going to see the traditional brake system disappear unless it starts getting in the way. They don't cost a lot (relative to the price of the car), don't weigh a lot, are really reliable, and work really well.

[1] https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/p...

I don't understand what you mean by this. Isn't independent suspension already a thing? Each wheel has independent up/down movement because there is no axle that remains straight (driveshafts are independent from each other in both FWD and RWD).

Tire friction usually works on a vector-like system so being able to move more up-down rather than along a radius means maybe you'd get a couple percent more friction forward and back if not moving a little side to side when moving up and down. Which sounds useless, but 5% more usable tire friction means an improvement in braking and cornering performance which either makes the car safer or could theoretically make it cheaper/lighter to compensate.

It's note even with resistors it's only with resistive braking that this applies.

If this is an electric car then the inverter can be programmed to give pretty much any braking force you desire just by altering the phase of the driving waveform. This can be done at any rotational speed.

My Model S can dump 50 kW back into the battery so long as the battery is not fully charged. At 60 km/h the kinetic energy of the car is about 300kJ so the car can be brought to a stop in about six seconds purely by regenerative braking.

In the final phase of braking the car has hardly any kinetic energy left so the huge 250 kW motors can easily bring the car to a halt and hold the car still just by balancing the magnetic forces in the motor against the motion of the car or gravity. In fact this is exactly what it does when running on traffic aware cruise control in stop go traffic, whether on level ground or on steep slopes.

I'm looking forward to the day where beamed power (e.g., MASER) will allow us to ditch most of the batteries too, with a tow trailer battery pack for trips into the deep country. It makes no sense to me to accelerate and decelerate over a ton of battery pack and have to deal with so much regeneration loss when we could just have overhead beamers optically track vehicles and cut power whenever a stray bird enters the picture.

I jest, of course, but I would kind of like to drive a car with steampunk levers more in theme with the giant spider in Wild Wild West.

* https://en.wikipedia.org/wiki/Tank_controls

I used to make Lego vehicles like that (well before I could drive), because it felt so silly as a passenger being parallel parked I suppose.

Replacing airbags (at least individually) is cheap enough. Having your entire engine-equivalent need a replacement just to reduce the sprung weight?

And maintenance would be way cheaper. Just remove the wheel and put a new one on.

* Regulation. Plenty of countries are very specific about the exact mechanicals of brakes, in laws that are 100+ years old from when runaway cars killed people.

* Unsprung mass. Cars handle better if the wheels are very light and all heavy bits are in the body of the car.

* Large diameter motors are harder to design - there is no opportunity for a gearbox, so you lose one design parameter, and need the motor magnetics to be right around the rim of the wheel to make up for it.

* Difficulty of making the air gap within the motor very thin at such large diameters - you end up needing super large diameter roller bearings.

However, I think despite those downsides, the benefits outweigh them.

1. Braking generates a LOT of energy which needs to be sent somewhere very quickly. Each wheel might need to dissipate hundreds of kW of power, simultaneously, on-demand, at any time in normal situations where mechanical brakes function fine today. This is not inexpensive.

2. Today, most EVs do not have 1 motor per wheel, which would be almost surely required to implement this type of system effectively. That's also not inexpensive and unless you can actually put the motor in the wheel-area you still need an axle to connect the motor to the wheel due to the suspension and steering movement, and then that axle would need to be able to sustain these braking forces.

It surely could be done from an engineering point of view today, it's just going to add tremendous cost over using conventional mechanical brakes regardless of if those brakes are a traditional hydraulic type or if they're a brake by wire system.

Not sure I'm convinced by the torque claim -- we've seen cars skidding / losing traction in both scenarios (accelerating and braking). ABS brakes were developed specifically to prevent that (and so was Traction Control).

My experience with electric vehicles is limited to a Boosted longboard, so take this with a grain of sand -- but it seems to me that electric motors are as effective at braking as they are at accelerating.

Putting a motor on each wheel could have some performance benefits, but I'm not sure I'd pay for it if I could get a single-motor car for cheaper. I'm talking about "econo box" performance, which is all I want anyway.

Also cars can stop way harder than any regen can, massive amounts of energy will be at play and likely any solution is more complex than just grabbing a rotor, which is a more direct way to heat dump