Hacker News Reader

Comment by londons_explore | Hacker News Reader

One day, I believe car design regulations will be amended to allow fully electric braking (ie. no hydraulics, drums, rotors, or pads). At that point, the motor can be moved into the wheel (unsprung mass = bad, but weight savings from not needing an axle or gearbox will outweigh this). Suspension and steering design is then far easier, because there is no axle to need to keep straight.

Braking redundancy will be achieved by having motors/brakes on all four wheels, and within each motor 3 independant phase coils with independant controllers, such that there are effectively 12 brakes on a car. Normally the controllers work together for smooth braking, traction control, software differential, etc. But even after 3+ failures braking performance should still be satisfactory for an emergency stop.

Obviously braking energy needs to go somewhere. In the happy case, it's regen'ed into a battery. If the battery can't accept it, it gets dumped into dump resistors. If the dump resistors fail, it gets dumped into motor coils (of which there are 12 remember). Obviously the motor coils will heat up very fast, so this is probably a one-use-only failsafe, like airbags.

So the whole system (except the pedal itself) is 12 way redundant.

View on HN

So a big reason why this probably wouldn't fly is that it has a common mode failure which is loss of power. Most EVs don't use permanent magnetic motors so it needs power to be able to use the motors for regen. So lets say the relay fails from the main battery pack suddenly you have no power, and no way to energize the coils in the motors to use them to regen. This could be mitigated by using permanent magnet motors but you still have the issue if control power is lost the vehicle cannot stop. The beauty of hydraulic brakes is that they work really well with power, but still function without it.

Interesting. Is there no way to design the circuitry so that when given no input, it defaults to a fully brakes-engaged mode? I’ve only worked with PM motors, so I know how that sort of h-bridge could be designed, but my knowledge of non-PM motors is fuzzy at best.

If you're driving 75 mph and one or more motors suddenly lose power and it fully brakes, that's a certain death in my opinion.

Well, it is certainly a very shaky proposition, and the car will probably be a total loss.

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

are people under the impression that when you're driving down the highway at 75mph, there isn't already a hundred ways you could die?

I mean, now we have 101 ways, and not all those ways are equally likely...

I'd imagine this was introduce adverse failure modes like - slamming to a stop without warning within seconds on the highway if power is lost, rather than coasting to a halt... and then being untowwable as the car can't be put into neutral.

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

So looking into it a bit there are what is called Eddy current brakes. In the section of disk eddy current brakes it talks about the power tool implementation where there is just a metal disk and the magnetics are pulled away from the disk when the device is powered on and passively return to the disk when power is removed. Something like that could work, but I am unsure of the size of magnets or disks necessary to adequately stop a vehicle. Most likely you could also add a normally closed relay hooking the motor to a resistor load. So when power is applied the resistor load is disconnected, and in a loss of power event the motor is directly tied to the resistor load.

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

Eddy currents develop in proportion to the speed of the moving magnetic field. So if you used eddy currents for braking, it would be most effective at high speed and gradually have no stopping power at low speed.

That is mostly true about regenerative braking as well. Once you hit a certain speed the vehicle has to use some energy to get the motors to actually stop the vehicle. Usually EVs and such will just rely on the friction brakes for the last bit but some cars like the Bolt will automatically use some energy to slow the car to a stop so you can use do one pedal driving.

Good point, and a good reason to have friction brakes also installed.

Hmmm. So you're travelling along the interstate at night, you lose power and your car screeches to a stop in the middle of high-speed traffic and your lights are off.

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

Maybe dedicated capacitors it’s enough power for one stop? Or a mechanical fail safe? Just a big pad that drops down on top of your tires.

Hold up capacitors definitely could extend the length of time the brakes would work but it would depend on what the power failure was and how long you need to brake. A mechanical fail safe just seems like a worse version of hydraulic brakes.

Maybe the capacitors could store enough energy to start braking, and then the braking energy could recharge the capacitors.

That is easy to accommodate as you can design the electronics such that when there is no power they cause maximum braking force and dump energy into the braking resistors. This can be done completely with power taken from the motor itself and if it’s not turning to generate power, then I would expect the parking brake system to engage, eg: a spring defaults it to “On” and power is used to keep it disengaged.

This can only be done with permanent magnetic motors which is not the norm for EVs for many reasons. In a non permanent magnetic motor on loss of power there is no energy to dump into braking resistors since the motor is not causing any resistance because the coils have been de-energized.

Most EVs have permanent magnet motors of some flavor right now (some have both a PM motor and a pure induction). I would assume that if you were having the motor be the primary braking system, and it was induction, there would be a tiny cheap magnet installed in it to generate bootstrap power to prevent exactly this scenario.

An even simpler design is to assume that the car can only start moving when there is power. If there is a loss of power while moving, then you can use the energy in the HV capacitors in the inverters to make a bootstrap field. That can be maintained till the car stops (and the user still has control of when/how much to brake). When the car comes to a halt, the parking brake is applied, and it won't move again till repaired.

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

Parking brakes are pretty useless to slow down a car from any decent speed.

This is entirely dependent on how your vehicle is designed. Pulling the electronic parking brake in my car (Audi S4) at a decent speed applies maximum braking effort to all 4 wheels simultaneously. It'll practically pop your eyeballs out.

Interesting. Although if that brake is electronic you can't really use it as backup in case something goes wrong with the car's computer systems.

Define "decent." I lost all hydraulic brakes on my 87 Toyota pickup due to a hole in a brake line and I had to drive it to the repair shop using only the cable-operated handbrake. Granted, I didn't go on the interstate, but at some point I was still doing 35-40mph.

Having a stick shift definitely helped, though.

Letting the driver decide whether to coast or brake is far safer than making the decision for them.

Slamming on the breaks is not a solution. Part of what makes hydraulic breaks safe without power is you can still control the breaking force.

That would be the default of this system if the brakes are still able to communicate with and provide power for the brake pedal. Basically if the brake system lost external power, it would get the power needed to run via scavenging it from the motors. Once the vehicle came to a stop, it would then loose power and the parking brake would then engage.

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.

I think you've lost sight of the initial concern that was raised. There's still a common-mode failure of loss of control power.

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.

To lose local regen braking derived power requires a failure of the cars systems similar in nature to one that would cause loss of hydraulic fluid or air in a traditional braking system.

Edit: made more concise.

I see what you're saying now

It is trivial to derive control power from actuation power - at least enough for a few can-busses that run from each wheel to up-to-12 independent sensors on the brake pedal.

It's trivial if you're doing an opportunistic design, but it's challenging to match the safety and reliability of a hydraulic system while beating the cost.

So rather than coasting to the shoulder when you run out of gas your tires immediately slam full on coming to a screeching, uncontrolled stop in the middle of the highway?

hah. I didn't see this before I wrote my comment. Really makes you wonder about this common SWE fantasy of mew ways to turn cars into big electronic touch screen devices, whether the people dreaming these ideas up have ever actually driven a car.

Nope. If your car lost power for whatever reason, the system would scavenge power from the inertia of the car and the brakes would still operate as they do when the car is operating nominally. The 1-10w needed to run the braking system is a rounding error in comparison to the 4-10kW of wind/rolling resistance at freeway speeds.

1-10W will run the entire braking system, from foot pedal through computer systems to activating the breaking resistance?

It is possible. Some embedded systems can work in the milliwatts to microwatts region.

>That is easy to accommodate as you can design the electronics such that when there is no power they cause maximum braking force and dump energy into the braking resistors

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 no power would be hard as the brake system can easily generate power to operate itself if the vehicle is moving (and if its not moving that is what the parking brake is for). This is more of a scenario that occurs when there is a catastrophic failure in the braking system, such as the motor control electronics getting damaged.

So fallback in the case of power loss is you don't come coasting to a stop, your car just suddenly and unexpectedly slams on the brakes? What's it do for recovery, accelerate into the car in front of you?

Good point. Feels a little like airplanes where at some point it was decided that mechanical backup is not needed for fly by wire.

So a fly by wire aircraft might not have physical cable moving surfaces, but most of them have a backup mode that relies basically entirely off of physical switches and direct communication with the surfaces. Those modes are only used in extreme emergencies but they are still designed into the system. Also what works in airplanes doesn't always translate to cars. Aircraft have rigorous maintenance requirements, while cars leave the manufacturer and might not have any sort of inspection or maintenance done for 20 years.

Interestingly enough, I've had hydraulic brakes fail on me for two different cars (thankfully it was 20 years apart, but still I would have preferred that the first time was the last time).

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.

I don't deny that there can be physical failures to the systems. And I also drive a hybrid currently that most of the time only uses the electric motor for slowing down, I don't find using the motor for braking scary. I personally see having both regen and hydraulic brakes on a vehicle a great step forward in redundancy and safety.

Electrical slowdown in hybrids does not provide redundancy for emergency braking. The battery has to absorb like 500kWt during 1s, this is well outside what a small battery can do.

Redundancy doesn't mean it will bring the car to a stop as quickly as hydraulic brakes, it is just another means to bring the car to a stop safely. From personal experience I could safely get my car to a stop in many situations without using the friction brakes at all.

I've also had two cars lose brake pressure. I'm very thankful that the cable-operated parking/emergency brake was functional on both cars; it saved one of them from going through the back wall of the garage.

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.)

I've never had my breaks fail on me. I also don't use the parking break that often. I would be so proud of myself if I realized what was going on, remembered that the e break exists, and used it before hitting the back wall of my garage.

Good on you.

When the hydraulics failed (brake line exploded) on my old vehicle I discovered that the cable is also attached to the brake pedal, so I didn't have to play games with the parking brake mechanism. There is a world of difference in braking force though, it's like pushing on the side of a brick building to gently encourage the vehicle to stop. I was lucky that I was driving a manual so I could also downshift to kill the speed.

I had the engine fail (timing belt broke) and that also killed the hydraulics in that car, very different behaviour of the brakes compared to normal and you need a hell of a lot of pressure to stop but it still works. Downshifting was not an option since the engine didn't work anymore.

> that also killed the hydraulics in that ca

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.

> I've never had my breaks fail on me.

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

I had _a_ brake caliper jam on my tundra. Completely frozen sliders on the caliper. The good news about hydraulic brakes is that the other circuits on the brakes still worked fine! I actually didn't realize the caliper was dead for (likely) a few months. With modern cars, each wheel is independent, so leaks and failures are more failsafe.

“It still kind of works without power” was an idea that kept hydraulic actuators in planes for a long time. But now most new planes are fly-by-wire (fully electric). Reliably stopping an electric car in an emergency should be a solvable problem.

So the fly by wire just means it is digital control to the hydraulic actuator instead of a physical cable running from the yoke or something to the actuator. They have not gotten rid of hydraulic actuators yet, they are working do that in the future but that is still a long ways out. Aircraft power systems also have significantly more redundancy so loss of control power is not a common mode failure due to have multiple dissimilar power sources.

It could be solved but it might not be worth it.

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.

They already have an auxiliary power unit of sorts: the 12V battery.

The air brakes used on heavy vehicles (semi trucks, etc) have a very simple fail-safe. You need power to not brake. I.E. Air pressure is used to disengage the brakes. If you lose power/air pressure, the brakes engage and are stuck engaged.

I see a lot of good ideas for how to get around this failure mode, I'll throw one more in the ring: "giant spring loaded spike to jab into the road"

I actually don't think that's a bad idea... Specifically, most cars can only brake at about 1 G, and if that's insufficient, they use crumple zones and airbags which brake at far more than 1 G.

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.

I don't claim any physical engineering skills, but don't you need a mechanical (non electrical) system for parking breaks?

I would think so too. Any parking brake has to be a fail-safe type brake which has to function in the absence of electricity. Hence, as you mentioned, purely mechanical.

It only has to remain engaged, engaging it in cars with push button parking brakes requires electricity to drive a small electric motor at each wheel.

They need to be able to remain applied without power, but the application can require power.

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

You do, yes. But that can be a metal pin the size of your pinky finger. It's a super easy engineering challenge compared to the regular brakes that slow down the car, which, when emergency braking a 2 ton car from 100 mph, needs to briefly absorb nearly 1 megawatt. Thats the power used by 1000 houses, which is a lot to absorb in a lightweight system that needs to still work if part of the system fails.

The parking brake is the emergency brake, cant be a pin

You don't, many modern cars have electronic parking brakes with small electric motors mounted on the rear calipers which push the brake pads against the discs when activated.

I am very glad you commented here as my initial skepticism of your claim lead me to do a spot of research that answered several unresolved questions I'd had about one of the most obnoxious features I've ever seen in a new car. My mother in law has a car with (apparently) electronic parking brake and I have loathed everything about it from the moment I first sat down in the car. This at least explains why an utterly unintuitive double toggle button replaced the "standard" mechanical lever on the center console and what notional benefits (hill holding) come with this system. I'd hate this a lot less if the manufacturer had included a tell-tale of some kind to visually indicate if/when the ECM thinks the P-brake is engaged.

If it's using brake pads, then it's still a partially mechanical suggestion. The comment at the top of the thread was suggesting doing away with brake pads entirely!

Nope. Many modern vehicles have push button electric parking brakes.

>, but don't you need a mechanical (non electrical) system for parking breaks?

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)."

Hub motors will be common on scooters and other small electric vehicles, but it will never make sense on full sized cars. The size of motor required to move a car with the acceleration and speed modern traffic demands just won't work in a hub. Reduction gearboxes and axle-shafts already represent a pretty tiny fraction of the total mass of drive units on EVs and there are no mass savings coming on motors that will somehow get them into the range of acceptable unsprung weight, even axial flux motors.

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.

Hub motors are in development for cars too, e.g.:

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

I love when people make broad sweeping assertions of impossibility, they are often proven wrong.

This is interesting because it also potentially solves the problem of particulate pollution from brake dust. There’d still be pollution from tire wear so it’s not a perfect fix but it gets partway there!

I could not find anything that would prevent this in my brief skim of FVMSS 105 (US car brake regulations). The regulations are mainly about the performance of the braking system (eg: needs to stop car 10x from 60mph in under a specific distance) and only care a little about the specific technique.

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...

> S5.1 Service brake systems. Each vehicle must be equipped with a service brake system acting on all wheels.

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...

> Suspension and steering design is then far easier, because there is no axle to need to keep straight.

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).

There are no up-down movements in full size cars and trucks, some kids toys maybe. Everything bigger moves an arm along a radius, which is "close" to up and down but not up and down.

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.

You should take into account that regen braking (even with resistors) only works at high rpm. The final phase of the braking you need to put even more energy into the coils on top of what the they already must dissipate for braking the car. Electrically, you would need to run the engine in reverse to come to a full stop.

> You should take into account that regen braking (even with resistors) only works at high rpm.

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.

That's an awesome idea!

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.

The government will turn off the MASERs on hot days though …

It probably makes more sense then a huge infrastructure build of giant maser units that would have to be able to simultaneously track hundreds of vehicles on every dense street corner and then you would have to put up mitigation for all the reflective power losses going through windows into peoples houses.

Most importantly it would also allow to go away with the steering wheel and make cars with Tank Controls* as god intended.

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

With no axle it'd also be a lot easier to allow them to turn 90 degrees (or 360(+), I'm just not sure there's any point), and have all-wheel turning, for optimal (and stupidly easy) parallel parking.

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.

> Obviously the motor coils will heat up very fast, so this is probably a one-use-only failsafe, like airbags.

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

This could vastly improve ABS too. Right? We wouldn’t have to deal with pulsating pads and could adjust force in milliseconds.

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

Not a mechanical engineer. This design is interesting. Do you think regulation is the only reason this did not happen yet? Why is nobody building this otherwise?

The main reasons against this are:

* 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.

What about potholes? Wouldn't they lead to the premature death of the motors if not the wheels themselves?

Also, more exposed to salt spray than inboard motors.

Drum brakes are in the same spot and can last for the life of the vehicle.

You've not maintained drum brakes in New England, I guess. Not as finicky as calipers, but the cylinders do rust and fail.

That's how they will make money after their current golden goose, automatic transmissions with "lifetime oil changes," is exhausted.

2 main reasons I can think of (tl;dr: cost):

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.

I suspect vibration, and the need for 4 motors instead of 1. I'll bet it'll be a long time before motors are cheaper than brakes. Also, braking involves a lot more torque than accelerating or cruising.

I think having one motor per wheel is very useful in terms of all-wheel drive (and braking) -- being able to selectively apply varied amounts of power to each wheel depending on conditions.

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.

I'm thinking in terms of f=ma, or the equivalent in terms of torque. I can live with my car getting up to highway speed within a much longer time duration than how quickly it needs to slow down if I hit the brakes. So the brakes need to exert more torque on the wheels than the motor does.

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.

Modern brake systems are so good though, they're cheap, powerful, reliable, and easy to service. I am not sure that the juice would be worth the squeeze

Is the Aptera doing this? I remember them talking about having the motors in the wheels but I'm not sure if it's what you're proposing.

Most higher end electric stand-up scooters are actually setup this way.

and tend to weigh a lot less than cars and also travel a lot slower, where e = mv^2

In the same vein, they tend to have much smaller motors, and the weight of the occupant is 10x the weight of the vehicle.

Gearbox serves more purpose than just getting the power to the wheel, it also improves the efficiency of the motor and\or expands and optimizes the usable speed range of the motor.

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

Reply on news.ycombinator.com