Mechanical Engineer Answers Car Questions From Twitter

I'm Chris Gerdy, Professor Emeritus

of Mechanical Engineering at Stanford University.

Let's answer some questions from the internet.

This is Automotive Support.

[upbeat rock music]

@DonkeyDelph asks, Should I buy an EV now

or wait a couple years whilst they're still improving

technology and prices come down?

One thing you may wanna think about

is Ford has recently announced that they're going

to use Tesla's charging system

on their future electric vehicles.

Tesla built the supercharger network specifically

for their own cars, but other manufacturers have decided

that that's actually a really good engineering option,

and so they are engineering in the Tesla charging system

into their cars.

So if what's out there today meets your needs,

go ahead and buy, but if not, you probably don't have long

to wait until something comes out that does.

@Punicist wonders, I wonder why solar powered cars

aren't a thing yet.

So if I take the Mercedes behind me,

that's a really large car.

I could fit maybe four solar panels.

Each of those under peak conditions

would produce about 400 watts.

Put it together, and I have 1600 watts,

almost enough to power this hair dryer,

somewhere on the order of about two horsepower.

All right, but maybe I could use this

as an alternative to charging.

That same amount of power would actually be less effective

than plugging your electric car

into a standard 120 volt wall outlet.

It would really take forever to charge.

So if you want a solar powered car,

simply put solar panels on your roof, generate electricity,

and use it to charge your electric car.

@alanbuxley asks, Why isn't there a huge market

to retrofit most popular petrol cars with battery packs

and electric motors?

So you can take a petrol car

and turn it into an electric vehicle.

My team and I did that with this DeLorean.

In order to fit everything in, we actually had to design

and fabricate our own subframe for the car

to hold these new components,

but this is not the easiest way

to go about getting an electric car.

You're gonna spend a lot more time and money

than you would simply buying an electric vehicle.

The challenge is that your car was designed

to have an engine and a gas tank.

If you start to pull in electric vehicle components,

there is a lot of things you have to ask,

like how safe is that going to be in a crash?

What have you done to the weight distribution of the car?

So this is why you don't really see many electric vehicle

retrofits out there.

@theulteriorkid writes, How do self-driving cars see?

Self-driving cars can use a range of different sensors.

Radars can be very helpful sensing metallic objects

that are near the car, but sometimes,

it's hard to tell exactly what that radar

is bouncing off of.

Cameras give a picture of the world that's not unlike

what we see with our eyes,

but it doesn't really give you distance information.

Finally, Lidar, or laser scanners, this is a series of beams

of light that tells very precisely how far away an object is

from the Lidar.

You'll see that the Lidar is spinning on top

of our X1 vehicle behind me right now,

and it's painting a picture of me sitting here

at this table.

So if I move my arms, you can see the image move.

Each one of these lines represents one

of the spinning lasers.

The color tells how intense

of a reflection the laser is getting.

So autonomous cars see by using a variety of sensors

and AI to turn all of these sensor signals into a picture

of the environment.

@kindman72672657 asks,

Why do autonomous vehicles have steering wheels?

Our federal motor vehicle safety standards

are generally interpreted to mean that all cars have

to have driver controls.

It's easier for manufacturers

to simply leave the steering wheels

and driver controls in the cars.

Engineers like to talk about levels of automation.

A level one vehicle is a system

with an adaptive cruise control,

something that uses a radar to follow another vehicle safely

or a lane-keeping system.

A level two combines these two systems,

but the driver needs to remain

with their hands on the wheel.

A level three autonomous vehicle,

that's this Mercedes EQS here,

that car will actually drive itself

in limited conditions in traffic jams.

The driver can take their hands off the wheel

and their eyes off the road.

A level four automated vehicle is a vehicle

that can drive itself within a specified area.

These driverless robotaxis that you see,

companies like Waymo, Cruze.

Level five autonomous vehicle is really the highest level.

That's a car that can drive from one point

to any other point that you want.

That car obviously won't need a steering wheel,

but that's a long ways off in the future.

@Koecheruiyot wonders, How will flying cars operate?

There are several manufacturers out there looking

at very light aircraft that could take off

and land vertically and might travel electrically over 50

to 60 miles, looking a lot like bigger versions

of the drones you may be flying.

These aircraft could in fact operate autonomously.

In some ways, that's an easier problem than trying

to make a robotaxi.

You don't have to worry about pedestrians

or many other vehicles if you're flying fairly low

over the ground.

@heyzell asks, Can anyone explain to me

why Miatas are cool now?

It's a [beep] Miata.

They have a 50-50 weight distribution.

When you turn your steering wheel,

what you're trying to control is the yaw rate of the car

or how fast it's turning.

In many cars, what you'll see is a yaw rate response

that tends to oscillate.

The car kind of wiggles as it's getting

into its turning rate, but with a 50-50 weight balance,

like the Miata has,

the car has a neutral steering characteristic.

When you turn your steering wheel,

you get a nice, smooth response.

So if you wanna learn to race,

you're gonna find that this neutral steering characteristic

in the Miata is the perfect way to learn racing.

@ywen8698 writes, Drove down I-40 earlier and hit a long

and indistinguishable object falling from the car

in front of me.

My car drifted at high speed for about five seconds.

Wonder how autonomous vehicles will react to this.

Autonomous vehicles need to react to unexpected situations

on the road with skills that are

as good as the very best human drivers.

That was the reasoning behind building

our autonomous drifting DeLorean, Marty.

Marty is able to drift intentionally,

putting the car sideways, so that it's very,

very controllable, and it can track exactly the path

that it wants even in emergency situations.

@ChorizoFan420 writes, You built a drift machine

out of a DeLorean?

Yes, so in the hands of an inexperienced driver,

you're likely to over rotate and spin out,

but a skilled drifter can keep the car sideways

and maneuver the car with pinpoint accuracy.

This is what we were trying to do with our software.

We've now largely achieved the ability

to control the vehicle's path

within a few centimeters while sideways.

@weenz0 asks, Why were cars back then more boxy

and more curvy now?

Older cars were certainly more boxy.

They came from carriages, in the early days,

would often be built upon a frame,

and somebody else would build a body that went on top of it.

At that time, there wasn't a lot of attention paid

to aerodynamics or how lightweight a car body could be.

In fact, if you went a little bit further,

there still wasn't a lot of attention paid to aerodynamics,

but more towards tail fins and what the car looked like.

The size of the tail fins became an important marketing

feature with new cars.

So in the 1970s, there was a severe energy crisis,

and that made manufacturers want to develop cars

that were lighter weight and more fuel efficient.

The way to make them lighter weight was

to use unibody construction,

design the car really as one unit.

The way to save fuel was to make cars more aerodynamic,

and that really changed the shape to the sleeker shapes

that we associate with modern cars.

In the future, one area that manufacturers

are really looking at is removing the side mirrors,

which create a fair amount of drag

and replacing these with cameras.

@CupacGeorge asks, Why are vehicles from the seventies

outlasting vehicles from 2022?

Cars in the 1970s had very few computers.

With a reasonable set of tools, you could maintain that car

then and continue to maintain that car today.

The price that we pay for cars that are more fuel efficient

and more environmentally friendly

is that they've become more computerized.

Cars increasingly have over-the-air software updates.

Will you be able to continually update your software

in the future?

It's become impossible to do all of the work yourself

on a modern vehicle.

@planetaryjim asks, Why, you put spoilers on race cars?

To make sure that they can grip the ground better.

So if you think about an airplane,

they generate so much lift that they can overcome the force

of gravity and fly through the air.

We can put something like an upside down airplane wing

on the car, which is a spoiler.

You can generate so much down force with aerodynamics

that you can overcome gravity.

Imagine that I create a Formula one track upside down.

If I can get my car to run that way,

my downforce becomes upforce.

It can actually stay stuck to this upside down track.

Some people just attach something to the back

of their Honda Civic to look cool.

That's not an engineering thing, more of a styling choice.

@Luminrio1 asks, So you're telling me that if someone puts

up a sign with the image of a green traffic light,

it will confuse autonomous cars?

Maybe, if it's using cameras to try to make sense

of its current environment, it may very well be looking

for traffic signals.

If it finds one on the back of a semi

and not actually signaling an intersection,

it could get confused by that.

One of the difficult things about programming autonomous

cars is you have to think in advance about things

that might confuse them.

News reports from San Francisco show

that people have been able to confuse Waymo cars

by putting a cone on the hood of the car.

That's something I doubt any engineer would've thought about

when they were designing the automated vehicle.

@LitterPickerPro wonders, Will cars of the future have

wooden wheels?

Can't get much greener than that.

Are we going that direction in the future?

No, but on the other hand, you may have tires

that are coming from shrubbery.

Bridgestone has been working with Quayule,

which is a shrub that produces hypoallergenic latex.

Tires could be biodegradable.

We've paid a lot of attention to pollution

from the tailpipe of cars.

As tires wear out, they produce little bits of rubber

and petroleum products

that can actually cause health issues.

@MrXavierM writes, Get at me!

Ferrari versus Porsche?

Both of these marks have tremendous racing history.

On the Ferrari side, you've got that Italian styling,

but I'm gonna have to actually come down on the side

of the German precision.

If you want handling designed precisely to go

where you're commanding with your steering

and your throttle, it's hard to beat a Porsche.

@real_griddyboy0 asks, Why does people get in crash

when they have on Tesla autopilot?

So psychologists know that if we don't have enough to do,

our mind wanders, and it's hard to keep our attention

on being ready to take control if we need to.

Tesla's autopilot are level two automation systems.

They require the human driver to be engaged

and in control all the time.

This is a challenge that the whole industry faces,

and they're working on different solutions to warn

or reengage the driver.

@emvdn, Self-driving cars running

with AI present a new version of the trolley problem.

How does the car make an ethical decision about who to kill

by running over?

So in one classic version of the trolley car problem,

you're a bystander, and you see a trolley headed

towards five people on the track.

You could switch to another track where only one is killed.

Do you pull that switch?

Automated vehicles have to consider situations

where there may be loss of life,

but they're not really using this sort of moral calculus.

Part of my work with a safety advisor for Ford,

I actually helped develop a set of rules

that autonomous vehicles could use,

and this just simply involves following the duty of care

that the law outlines.

Now, if other people violate their duty of care to the car

by jumping in front of it, when it doesn't have enough time

to avoid a crash, you can program the autonomous vehicle

to do the best it can to do everything under its power

to avoid that crash.

Autonomous vehicles are out there protecting people

who follow the rules and not making determinations

about who's more worthy to live or die.

@theaoti asks, If my self-driving car gets

into an accident, why wouldn't whomever made the car

be at fault?

I wasn't driving.

If a car is driving itself, the manufacturers will,

in general, be liable for that.

Mercedes has already made a very strong statement

with their level three drive pilot that if it has a crash,

the company is responsible and not the human driver.

So we're shifting really into an entirely different world.

In fact, in San Francisco,

they've already run into the problem

of how does a police officer give a ticket

to an autonomous vehicle?

That doesn't make sense when there's not a driver.

@Mbj2042, Why would I buy a hydrogen car

when I could charge my electric vehicle at home?

Think, for a moment, about over-the-road heavy trucks.

In order to recharge them,

they would actually need vast amounts

of electrical charging capability if they wanted to do that

in a reasonable period of time.

They'd also have to carry massive amounts of batteries.

Hydrogen may actually make sense for buses,

over-the-road heavy trucks,

probably not gonna replace your electric vehicle

and your charger at home.

@digitalbladeca wonders, If you had

to solve real world driving, would you go down the path

of programming the rules of the road and expect the car

to obey or let a neural network learn to drive

like an experienced Uber driver?

You really want a combination of these techniques.

So Tesla, they use neural networks to learn

from their camera system and what the cars are likely

to do around them.

In contrast, Mercedes' level three system tends

to rely on rules.

Engineers can program specific behaviors into the car

to ensure that it follows the traffic laws

or follows a vehicle at an appropriate distance.

@ChiuMeister asks, I'm really concerned about security

when autonomous cars take over.

What if they're hacked?

Hacking is a real concern with automated vehicles,

particularly those systems that can receive

over-the-air software updates.

There's also a threat as we move towards AI systems

that hackers could get involved with the data stream.

AI in an autonomous vehicle is trained by feeding it lots

of data, which could be, for instance,

a series of camera images.

If you could hack that set of images,

you could make it so that the vehicle failed

to recognize certain objects in the environment,

and that could create some serious safety risks.

@RAVerBruggen asks, Why do cars have four wheels?

Because we found out that is a really great combination

to design vehicles that are stable, comfortable,

and high-performing.

Motorcycles have two wheels,

and it's up to the rider to balance.

With a car, the suspension handles all of the balance.

As my car goes around a corner,

my tire forces increase on the outside

and decrease on the inside to keep the car upright.

If you have a three wheel car, you actually have only two

of those wheels helping to keep the car upright,

and what this means is that the weight can shift very

dramatically from one wheel to the other.

These cars have a much greater tendency to roll over.

@MtnDewMlg asks, Why aren't we all driving electric cars

by now?

It's not a technology that makes sense for everybody.

Range remains a limitation.

If you wanna take a long road trip,

it is gonna take you some time to stop

and recharge your car, more time than it would take you

to fill up a gasoline tank.

So for many people, an electric vehicle is cheaper,

because they can plug it in at their home

and use their own electricity,

but if you have to charge your vehicle all the time

at a commercial charging facility,

you're likely not gonna save that much money.

@DubaiFuture asks, Will autonomous vehicles reduce the

number of accidents?

So autonomous vehicles will certainly eliminate some forms

of human error.

Autonomous vehicles don't text while driving.

They don't drive impaired.

They're never distracted,

because they can see 360 degrees around the vehicle.

Autonomous vehicles won't eliminate all errors,

but they will shift from the human driving errors

to the programming errors.

Over time, that should be a shift towards safer cars.

So those are all the questions for today.

Thanks for watching Automotive Support.