Formula E

[Tim.Wright]

I believe Newtonian physics was a bit before electric traction last time I read up on him.

Thats the great thing about newtonian mechanics, it doesn't care if the drivetrain is electric, combustion or nuclear it still determines how the vehicle will respond.

Well, as long as you are moving slower than the speed of light...

By the way, reversing the polarity of the electric motor would recover energy, not waste it right?

[autogyro]

I believe Newtonian physics was a bit before electric traction last time I read up on him.

Thats the great thing about newtonian mechanics, it doesn't care if the drivetrain is electric, combustion or nuclear it still determines how the vehicle will respond.

Well, as long as you are moving slower than the speed of light...

By the way, reversing the polarity of the electric motor would recover energy, not waste it right?

That would depend on whether you had to put energy in to slow the armature.
To capture energy the motor/generator would also have to be connected to the decelerating rear wheels.
You see unlike a reciprocating IC engine an electric motor/generator does not have a built in pump brake.
It does have a large amount of stored energy from rotation though.
Somehow you have to slow it down with your electronic control system to match the output rpm.
Any ideas?

[flynfrog]

sprag clutch next question

[Tim.Wright]

I believe Newtonian physics was a bit before electric traction last time I read up on him.

Thats the great thing about newtonian mechanics, it doesn't care if the drivetrain is electric, combustion or nuclear it still determines how the vehicle will respond.

Well, as long as you are moving slower than the speed of light...

By the way, reversing the polarity of the electric motor would recover energy, not waste it right?

That would depend on whether you had to put energy in to slow the armature.
To capture energy the motor/generator would also have to be connected to the decelerating rear wheels.
You see unlike a reciprocating IC engine an electric motor/generator does not have a built in pump brake.
It does have a large amount of stored energy from rotation though.
Somehow you have to slow it down with your electronic control system to match the output rpm.
Any ideas?

For a champion of EV's in general auto, I'm surprised that you seem not to understand how electric motors work. Electric motor/generators have something better than a built in pump brake - the generator part.

If you want to "brake" the motor you need only to put it in generator mode. Get it to dump its current to an energy store or ballast resistor and it will load the motor with a retarding torque.

It will slow the motor to match the rotational speed of the gearbox AND you recover energy.

Like I said, if there is a problem here its with the management of the motor torque, not the gearbox.

[Andres125sx]

Somehow you have to slow it down with your electronic control system to match the output rpm.
Any ideas?

All of my brushless controllers for my rc planes have a built in brake to stop the prop when you use a folding prop, so it can fold instead of freewheeling. I think even RC cars have brakes without phisical brakes or generator mode, just the controller, so I don´t think that must be a problem for automotive industry

[Andres125sx]

sprag clutch next question

[autogyro]

For a champion of EV's in general auto, I'm surprised that you seem not to understand how electric motors work. Electric motor/generators have something better than a built in pump brake - the generator part.

If you want to "brake" the motor you need only to put it in generator mode. Get it to dump its current to an energy store or ballast resistor and it will load the motor with a retarding torque.

It will slow the motor to match the rotational speed of the gearbox AND you recover energy.

Like I said, if there is a problem here its with the management of the motor torque, not the gearbox.

To harvest energy effectively you have to place the motor/generator up against a mechanical load.
You cannot do this during the shift overlap of the gear change which is exactly where you need to decelerate the motor/generator to match the input rpm to the output rpm
Applying electrical resistance will slow the armature far to rapidly, usually to stationary.
So I agree with you partly, it is also a control problem.
The end result is still 'BANG'.
It is the gearbox that is unsuitable for the job.

[autogyro]

Somehow you have to slow it down with your electronic control system to match the output rpm.
Any ideas?

All of my brushless controllers for my rc planes have a built in brake to stop the prop when you use a folding prop, so it can fold instead of freewheeling. I think even RC cars have brakes without phisical brakes or generator mode, just the controller, so I don´t think that must be a problem for automotive industry

Brilliant if you want to stop the electric motor rotating.
No use at all if you want to accurately control the armature rpm just by using a variable electrical resistance.
Even a slight electrical load will stop the armature almost instantly.
If you do that to the input of a lay shaft or a epicyclic gearbox, when you connect the output it stands a very good chance of blowing the gearbox casing in half.

[autogyro]

sprag clutch next question

Munchkin next question

[Tim.Wright]

To harvest energy effectively you have to place the motor/generator up against a mechanical load.
You cannot do this during the shift overlap of the gear change which is exactly where you need to decelerate the motor/generator to match the input rpm to the output rpm
Applying electrical resistance will slow the armature far to rapidly, usually to stationary.
So I agree with you partly, it is also a control problem.
The end result is still 'BANG'.
It is the gearbox that is unsuitable for the job.

The inertial reaction of the motor rotor is a mechanical load. Torque = AngularAccel x PolarInertia.

Also, nicely, in BLDC motors torque is more or less proportional to stator current. So you choose what current you want to get which torque you require to slow the rotor.

Doing it in a nice gradual way which "mimics" a spring loaded friction clutch is obviously still an open control issue.

Still... I don't see any reason why an e-motor is any worse with a traditional gearbox then an IC motor....

[Tim.Wright]

Even a slight electrical load will stop the armature almost instantly.

Come on man, thats crap. The electrical resistance will have associated power which it can absorb which for a fixed resistence is V^2/ R.

This power will impose a torque on the motor which is torque = power / speed which is V^2 / R / RPM

The torque is inversely proportional to the resistence.

If you harvest to an energy store that current (therefore the motor load) is more or less infinately variable.

In other words, any electrical load will slow the motor by an amount related to the current that it draws.

[autogyro]

You could of course add a flywheel to the motor/generator or even a clutch for the same purpose, after all F1 cars have them.
But that would be going backwards and would not be 21st century progress.

[autogyro]

Even a slight electrical load will stop the armature almost instantly.

Come on man, thats crap. The electrical resistance will have associated power which it can absorb which for a fixed resistence is V^2/ R.

This power will impose a torque on the motor which is torque = power / speed which is V^2 / R / RPM

The torque is inversely proportional to the resistence.

If you harvest to an energy store that current (therefore the motor load) is more or less infinately variable.

In other words, any electrical load will slow the motor by an amount related to the current that it draws.

But Tim the armature has to be in freewheel before you place an electrical load on it, it is probably already close to stationary the moment you disengage the input from the mechanical load.
Its rpm would have dropped way below the match up point for the gear shift before you even start control.
All you do by adding electrical load then is to make things worse.

[Tim.Wright]

, it is probably already close to stationary the moment you disengage the input from the mechanical load.

Newton's second law would beg to differ... Rotor inertias are not insignificant.

[NTS]

Ok, I've found something, it's obviously a press-release inspired article so it only mentions the good parts. But I think it may help if Autogyro would point out the problems in this thing so we get the point a bit better:

The transmission has a "fairly conventional" twin shaft layout and uses two lubrication pumps - one mechanical, one electric - and a dual clutch for seamless gear changing. It could also be modified to become a 4-speed.


[..]

So why haven't we seen three (or more) speed transmissions in electric vehicles before? The idea goes against conventional thinking regarding electric drive systems and Paul believes that engineers engaged in EV development have thus far kept a narrow focus. Perhaps no-one realized the significant difference a multi-speed transmission can make ...

Source: http://www.gizmag.com/antonov-3-speed-t ... -ev/19088/

So they claim that a dual clutch setup allows them to do seamless gear changing.