Why do electric powered automobiles need to be so complicated?

[[email protected]]

Seems like the right place to ask this question which has been on my
mind for a long time. I'm no engineer, but this one almost seems like
common since to me (unless some of my facts are wrong).

The basic question is, why do you need a clutch and/or transmission, or
brakes, on an automobile with an electric motor? It can't just be
because that is what people are used to driving, and what mechanics are
used to working on, can it?

Don't electric motors have the same amount of torque at any RPM? I
understand this is why they use them to power trains.

If they do, then why would you need to change "gears" (shift)?
--Unless you couldn't build a motor with a finite enough control over
the RPMs?

You don't need reverse, since an electric motor can turn both ways.

You don't need brakes because the motor can be used to stop the
vehicle. I bet someone could design it so the battery gets recharged
(a tiny bit) as you stop -- afterall, a motor and a generator have a
lot in common.

I think back to R/C cars, which I had as a child, which never had any
of those things. Sure, some of them were pretty rough at startup, or
slow down, but I've also seen some that were smooth and it seems like a
computer control system could fix that problem. It also seemed like
they would travel pretty far without a recharge, for the scale. My
cousin had a 1/10 scale car that would do 60 MPH, and it would run for
30+ minutes. Probably 20 of those minutes were top speed... It seems
like a full-size version of the same thing could travel 200+ miles,
probably more, without a recharge.

 

[Genome]

Seems like the right place to ask this question which has been on my
mind for a long time.

Google was not invented for you to ask wordy twat questions of us demigodz

OK, I'm speaking for the others.

As the son of my Dad I can guarantee that you are wasting your time.

Kindly **** off until you have figured out how to do fusion the simple way
like what I have. No one will pay bugger all interest anyway.

Footnote, Dad said Whoops and then rolled around larfing.

These things I understand.

DNA

 

[Jim Thompson]

Google was not invented for you to ask wordy twat questions of us demigodz

OK, I'm speaking for the others.

As the son of my Dad I can guarantee that you are wasting your time.

Kindly **** off until you have figured out how to do fusion the simple way
like what I have. No one will pay bugger all interest anyway.

Footnote, Dad said Whoops and then rolled around larfing.

These things I understand.

DNA

Sno-o-o-o-ort !-)

...Jim Thompson

 

[[email protected]]

There are much information on DIY electric cars on the net. Use Google
and search for "electric car +DIY", without the quotation marks.

It is a real education.

Have fun!

Rolf

 

[[email protected]]

Here is one of the better explained conversions, that explains why it
is rather complicated and expensive. Link:
http://www.metricmind.com/ac_honda/main2.htm

Rolf

 

[Pooh Bear]

Seems like the right place to ask this question which has been on my
mind for a long time. I'm no engineer, but this one almost seems like
common since to me (unless some of my facts are wrong).

The basic question is, why do you need a clutch and/or transmission, or
brakes, on an automobile with an electric motor?

As far as I know you don't. You will need them on a hybrid though which may be
what you're thinking of.

It can't just be
because that is what people are used to driving, and what mechanics are
used to working on, can it?
No.

Don't electric motors have the same amount of torque at any RPM? I
understand this is why they use them to power trains.

Not sure if it's the *same* but they can do this very well.

If they do, then why would you need to change "gears" (shift)?
--Unless you couldn't build a motor with a finite enough control over
the RPMs?

You don't need reverse, since an electric motor can turn both ways.

You don't need brakes because the motor can be used to stop the
vehicle.

It can certainly slow it.

In any event would you feel safe in a car without brakes ?

I bet someone could design it so the battery gets recharged
(a tiny bit) as you stop -- afterall, a motor and a generator have a
lot in common.

This is already done. See 'regenerative braking'.

I think back to R/C cars, which I had as a child, which never had any
of those things. Sure, some of them were pretty rough at startup, or
slow down, but I've also seen some that were smooth and it seems like a
computer control system could fix that problem. It also seemed like
they would travel pretty far without a recharge, for the scale. My
cousin had a 1/10 scale car that would do 60 MPH, and it would run for
30+ minutes. Probably 20 of those minutes were top speed... It seems
like a full-size version of the same thing could travel 200+ miles,
probably more, without a recharge.

Toys aren't the same.

Graham

 

[Gareth]

Seems like the right place to ask this question which has been on my
mind for a long time. I'm no engineer, but this one almost seems like
common since to me (unless some of my facts are wrong).

The basic question is, why do you need a clutch and/or transmission, or
brakes, on an automobile with an electric motor? It can't just be
because that is what people are used to driving, and what mechanics are
used to working on, can it?

Don't electric motors have the same amount of torque at any RPM? I
understand this is why they use them to power trains.

Actually, an electric motor will have its greatest torque when it is
stalled. You know that a motor is the same as a generator, well when
the motor is running it generates an EMF which opposes the applied EMF.
In other words, the generated voltage is subtracted from the applied
voltage, this will reduce the current flowing in the coils of the motor
and therefore the torque.

If they do, then why would you need to change "gears" (shift)?
--Unless you couldn't build a motor with a finite enough control over
the RPMs?

I don't see why electronic speed control would be a problem

You don't need reverse, since an electric motor can turn both ways.

You don't need brakes because the motor can be used to stop the
vehicle. I bet someone could design it so the battery gets recharged
(a tiny bit) as you stop -- afterall, a motor and a generator have a
lot in common.

Regenerative braking is certainly be possible. However, it may be wise
to include some additional system for safety.

I doubt regenerative braking could stop a car as quickly as a
conventional braking system. Also remember that the regenerative
braking would only act on the driving wheels, which may not be all four.

You would still want a brake pedal even if the actual braking was done
via the motor as you would need some way for the driver to tell the car
to break and how hard. You probably wouldn't want the car to do
emergency stop every time you took your foot off the accelerator.

I think back to R/C cars, which I had as a child, which never had any
of those things. Sure, some of them were pretty rough at startup, or
slow down, but I've also seen some that were smooth and it seems like a
computer control system could fix that problem. It also seemed like
they would travel pretty far without a recharge, for the scale. My
cousin had a 1/10 scale car that would do 60 MPH, and it would run for
30+ minutes. Probably 20 of those minutes were top speed... It seems
like a full-size version of the same thing could travel 200+ miles,
probably more, without a recharge.

Petrol (gasoline) has energy of about 33 MJ (Mega Joules) per litre, or
about 125 MJ per gallon. So a 10 gallon fuel tank will hold
approximately 1250 MJ of energy. Now internal combustion engines are
not very efficient, lets assume 20% of this energy is usable, we then
have ~250MJ of usable energy in a car fuel tank.

1 Watt Hour = 3600 J

Therefore:

250MJ = 250 000 000 / 3600 Wh

= 70 000 Wh

The energy density of NiMH batteries is ~70Wh/Kg so we would need ~1000
kg = 1 tonne of batteries to hold as much usable energy as 10 gallons of
gasoline. Even taking into account the poor efficiency of an internal
combustion engine.

I think this is the real problem with electric vehicles.


--

 

[Paul Burke]

Gareth wrote:

I doubt regenerative braking could stop a car as quickly as a
conventional braking system. Also remember that the regenerative
braking would only act on the driving wheels, which may not be all four.

Regenerative braking would make the braking asymptotic, which isn't much
good when a kid is in the road in front of you. Four wheel braking could
be accomplished by four wheel motors, but now we start to get
complicated. First, the braking characteristics have to be right when
cornering as much as when stopping. Also, when cornering, the wheels
have to go at different speeds (thats what the diff is for on an IC car).

So the drive has got to be coordinated with conventional brakes. And
it's got to be coordinated with the steering. That's why electric
powered automobiles need to be so complicated.

Paul Burke

 

[Pooh Bear]

I doubt regenerative braking could stop a car as quickly as a
conventional braking system.

Good point. The braking effect would be limited by motor power. Just compare
acceleration with much the more rapid braking and it becomes obvious why it's
not practical to use this alone.

Graham

 

[John Perry]

Clutch/transmission, because accelerating requires much greater force
than does overcoming aerodynamic and other losses at cruise. You either
start moving very slowly (which most people don't like to wait for), or
you shift gears as you get to higher speeds.

Mostly true. But trains don't have to accelerate quickly.

Actually, an electric motor will have its greatest torque when it is
stalled. You know that a motor is the same as a generator, well when
the motor is running it generates an EMF which opposes the applied EMF.
In other words, the generated voltage is subtracted from the applied
voltage, this will reduce the current flowing in the coils of the motor
and therefore the torque.

Which is easily handled by varying the applied voltage with the drive
frequency, and is already done in many variable speed motor drive
applications.

You don't need as many gears, but without them, you either install a
gigantic motor to handle accelerating torque (and then is grossly
overpowered for its use), or you accept very slow acceleration.

I don't see why electronic speed control would be a problem

It isn't, and is in fact required for practical use.

John Perry

 

[[email protected]]

Thanks to all who replied! Other than the a-hole who thinks too much
of himself. Nice to know that he/she only represents a small part of
this group.

 

[Ken Muldrew]

It isn't, and is in fact required for practical use.

But let's not forget that the controller is switching hundreds of amps
so while not a problem, it's not trivial either (mentioned since the
op was asking why ev's are so complicated).

Ken Muldrew
[email protected]
(remove all letters after y in the alphabet)

 

[Richard Henry]

Thanks to all who replied! Other than the a-hole who thinks too much
of himself. Nice to know that he/she only represents a small part of
this group.

A little research will tell who to ignore on which topics. Mr. Thompson,
for example, (and I know he's not the a-hole you had in mind) is a whiz of
an engineer but is, er, "old-fashioned" on social issues.

A little further research will convince you that this is actually a
social/pilitical issues discussion group among engineers.

 

[Jim Thompson]

A little research will tell who to ignore on which topics. Mr. Thompson,
for example, (and I know he's not the a-hole you had in mind) is a whiz of
an engineer but is, er, "old-fashioned" on social issues.

"old-fashioned"? Am I now? I'm probably as liberal as they come on
"personal" choice issues. I'm even for freedom FROM religion. But I
AM a HAWK... kill or be killed.

Illegal immigration? Nothing that a few gunship helicopters couldn't
cure in a few hours.

A little further research will convince you that this is actually a
social/political issues discussion group among engineers.

Indeed ;-)

...Jim Thompson

 

[Luhan]

"old-fashioned"? Am I now? I'm probably as liberal as they come on
"personal" choice issues. I'm even for freedom FROM religion. But I
AM a HAWK... kill or be killed.

Illegal immigration? Nothing that a few gunship helicopters couldn't
cure in a few hours.

Lets make all immigration illegal. But if you are shrewd enough to
come here and land a job for a year, you get instant citizenship. That
way we skim the best from other countries, and leave them with the bad
end of the gene pool.

Luhan

 

[John Larkin]

Lets make all immigration illegal. But if you are shrewd enough to
come here and land a job for a year, you get instant citizenship. That
way we skim the best from other countries, and leave them with the bad
end of the gene pool.

Too easily scammed.

John

 

[Luhan]

Too easily scammed.

Thats the point, we want the ones who show initiative. We want the
scammers, schemers, and others who just dont go allong with the status
que - exactly the type of people who started this country in the first
place. Or do you suggest going back to British rule?

Luhan

 

[Phil Hobbs]

Thats the point, we want the ones who show initiative. We want the
scammers, schemers, and others who just dont go allong with the status
que - exactly the type of people who started this country in the first
place. Or do you suggest going back to British rule?

Luhan

Nah, you can be honest and still show initiative--most of the crooks I've
known (several to many) were crooked because they were lazy or greedy, not
because they were smart. Of course, if the scammers and schemers all promise
to live in your neighbourhood, I'll be less worried about it.

Cheers,

Phil Hobbs

 

[Luhan]

Nah, you can be honest and still show initiative--most of the crooks I've
known (several to many) were crooked because they were lazy or greedy, not
because they were smart. Of course, if the scammers and schemers all promise
to live in your neighbourhood, I'll be less worried about it.

Scan back yourself and you'll see I specified holding a job here - not
being a crook.

This is really my commentary on the issue of 'illegal' aliens. I just
have no problem with anyone who comes here to work. Friends of mine
often hire guys right off the local street corner here when they need
some heavy work done. Far as I have seen, they are really good
workers.

Luhan

 

[Jim Thompson]

[snip]

Scan back yourself and you'll see I specified holding a job here - not
being a crook.

This is really my commentary on the issue of 'illegal' aliens. I just
have no problem with anyone who comes here to work. Friends of mine
often hire guys right off the local street corner here when they need
some heavy work done. Far as I have seen, they are really good
workers.

Luhan

But they're sinking the health care systems in places like Yuma, AZ.

...Jim Thompson