Electric propulsion and other musings

[autogyro]

Mod - These posts were split from the Formula E thread http://www.f1technical.net/forum/viewto ... ead#unread
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The gear train in FE is subject to high torque over a wider rpm band than in comparable IC applications.
(I pointed this out in my original notes and presentation on FE to the FIA in 2010 along with the suggestion of using replaceable side pod batteries to be replaced in pit stops to give the required range.)
Because of this and the need to reduce load during gear shifts and to reduce gear side loads the gear teeth are cut closer to strait cut than would normally be the case in an IC road car lay shaft gearbox or even a racing IC gear train.
This is to give more area of tooth contact and hopefully better reliability with less gear tooth and bearing wear.
Over many years of development IC race car gear trains arrived at a reasonable angle of gear cut that satisfied the need for acceptable side loads, efficient torque transfer and acceptable noise levels. (full strait cut gears scream)
In IC race car gear trains there is still of course more gear noise than in road car gear trains, however the ear damaging engine noise usually covers up the problem and on media sound transmission the compression of the over all sound file will then result with the gear frequencies sent way back in the file mix. (you wont hear it over the engine noise distortion)

It is all a result of using an obsolete lay shaft gearbox for a 21st century power train application.
Almost all industrial and model electric motor applications where a reduced rpm is needed use a planetary reduction gear set.
These sets can be almost silent in operation.
All you need for FE is a modern concept gear train that uses planetary gear sets without the losses associated with hydraulic and mechanical shift systems.

[mzso]

Why on earth did they start using multi-gear boxes in the first place?

Almost all industrial and model electric motor applications where a reduced rpm is needed use a planetary reduction gear set.
These sets can be almost silent in operation.
All you need for FE is a modern concept gear train that uses planetary gear sets without the losses associated with hydraulic and mechanical shift systems.

Not my impression. All pikes peak prototypes did produce a fair amount ow whining noise.





I still think they should go direct drive. That would bring some efficiency gains and a bit of an engineering challenge.

[autogyro]

A 'proper' gear system would improve the efficiency by a decent amount.
The lay shaft gearbox makes little difference.
We will see where development goes.

Which of these cars you show has belt drive?
Belts whine as badly as offset gear sets.
The third car was pretty noiseless.

It is not much of an engineering challenge to go direct drive.
Most use pancake motors.
The Toyota record holder that sounds the least noisy is probably therefore more efficient.
So far electric motors used for cars are from other applications.
It is early days.

[machin]

I still think they should go direct drive. That would bring some efficiency gains and a bit of an engineering challenge.

Running direct drive will bring a slight increase in efficiency, but the direct drive motor will be heavier and larger, and therefore will lose out on overall vehicle economy. The gearbox arrangement will probably be more expensive though, but so what?

Throw in a multispeed gearbox and you will also gain additional performance or economy because even an electric motor doesn't have flat power or efficiency curves; multi-speed gearboxes allow you to run the motor in an rpm range which gives more power/efficiency for a greater range of road speeds.

[machin]

when I search boat rim drive with goggle, those look very similar to electric ducted fans, for boats obviously, but I can´t figure out what are you thinking about...

The difference is that the ducted fan arrangement has the motor situated in the air flow, whereas the rim drive option keeps the motor outside the flow. This is ideal in an application where you have additional space to house the motor (such as in a ship). It might not be ideal for other applications, although, maybe you could "hide" the motor in the wing of a model aircraft for example?

[Andres125sx]

when I search boat rim drive with goggle, those look very similar to electric ducted fans, for boats obviously, but I can´t figure out what are you thinking about...

The difference is that the ducted fan arrangement has the motor situated in the air flow, whereas the rim drive option keeps the motor outside the flow. This is ideal in an application where you have additional space to house the motor (such as in a ship). It might not be ideal for other applications, although, maybe you could "hide" the motor in the wing of a model aircraft for example?

That´s a possibility, but inside the wing there´s no cooling, and that´s a big advantage when in the air flow, you can push the motor a lot more

Anycase I posted that only because Autogyro said he was searching a motor for something similar to a rim drive because he was comparing high rpm model motors, so that was an example to see if it may be helpfull (small model motors, high rpm, some may spin up to 40k rpm or even more, there are from 40g/200W to 500g/5KW). But looks like he´s not interesested

[mzso]

I still think they should go direct drive. That would bring some efficiency gains and a bit of an engineering challenge.

Running direct drive will bring a slight increase in efficiency, but the direct drive motor will be heavier and larger, and therefore will lose out on overall vehicle economy. The gearbox arrangement will probably be more expensive though, but so what?

Throw in a multispeed gearbox and you will also gain additional performance or economy because even an electric motor doesn't have flat power or efficiency curves; multi-speed gearboxes allow you to run the motor in an rpm range which gives more power/efficiency for a greater range of road speeds.

You certainly won't get more efficiency. Because the gearbox constantly wastes a lot of it. Meanwhile with direct drive the lowest efficiency region is rarely used in racing because they go fast constantly.
It's probably be heavier but look at the Yasa motor for example. It's 200 kw peak for 33 kilos and it's not a racing design. (It has a big, heavy metal casing for example). It more than these measly FE engines have in race configuration...

[machin]

with direct drive the lowest efficiency region is rarely used in racing because they go fast constantly.

Except that with direct drive the motor must run at low rpm out of hairpins, and high rpm at the end of the straights.....

With a multispeed gearbox you can run in the high-speed high-power region, OR the low-speed high-efficiency region, over a greater range of road speeds. Throw in the economy (note, this is not the same as efficiency) gains from a smaller/lighter high speed motor-gearbox package and it is all looking less and less favourable for direct drive, despite the slight loss of efficiency from the gearbox.

Of course a multispeed gearbox adds complexity, but that just gives the engineers more of a challenge

[machin]

others have chosen direct drive (I think Drayson did with their Lola, as have other Formula Student teams).

According to the drayson website it used a single motor with single speed transmission (here).

I'm not surprised other (non winning!) formula student teams went direct drive; it is certainly simpler!

[mzso]

with direct drive the lowest efficiency region is rarely used in racing because they go fast constantly.

Except that with direct drive the motor must run at low rpm out of hairpins, and high rpm at the end of the straights.....

With a multispeed gearbox you can run in the high-speed high-power region, OR the low-speed high-efficiency region, over a greater range of road speeds. Throw in the economy (note, this is not the same as efficiency) gains from a smaller/lighter high speed motor-gearbox package and it is all looking less and less favourable for direct drive, despite the slight loss of efficiency from the gearbox.

Of course a multispeed gearbox adds complexity, but that just gives the engineers more of a challenge

As far as I know efficiency loss from a gearbox is anything but "slight". It negates anything efficiency wise and takes a bunch more.
The fact that you need an extra gearbox already compensates partially for the greater mass of the motor. Plus modern axial flux motors apparently can be made pretty light and powerful too. Good enough for wheel motors even:

http://www.electric-vehiclenews.com/201 ... firms.html
http://www.electric-vehiclenews.com/201 ... -make.html
http://green.autoblog.com/2013/07/29/ev ... own-under/

[Andres125sx]

Electromagnetic braking.....

I wonder how effective it is. If it works, that´s the future hands down.

Regenerative braking at the four wheels and get rid of brake disks, wich are the best way to waste tons of energy


But I´m not sure if electromagnetic braking is enough to stop a car similar to brake discs, or if it will be able to be similar some day wich is the important point.

OTOH, abs could be a lot more precise and effective with wheel motors, as the motor controller has perfect control of the wheel/bell

BTW, with this you get rid of gearbox, but also of differential, or as much as three differentials (for AWD), but with much better control of each wheel than any vehicle has ever had, both braking and accelerating.

Don´t know about efficiency, but with wheel motors dinamics would be miles away from any other configuration because of two reasons, light weight without gearbox and differential/s, and perfect control of each wheel at any situation

[autogyro]

Electromagnetic braking.....

I wonder how effective it is. If it works, that´s the future hands down.

Regenerative braking at the four wheels and get rid of brake disks, wich are the best way to waste tons of energy


But I´m not sure if electromagnetic braking is enough to stop a car similar to brake discs, or if it will be able to be similar some day wich is the important point.

OTOH, abs could be a lot more precise and effective with wheel motors, as the motor controller has perfect control of the wheel/bell

BTW, with this you get rid of gearbox, but also of differential, or as much as three differentials (for AWD), but with much better control of each wheel than any vehicle has ever had, both braking and accelerating.

Don´t know about efficiency, but with wheel motors dinamics would be miles away from any other configuration because of two reasons, light weight without gearbox and differential/s, and perfect control of each wheel at any situation

Electromagnetic braking is great if you can find somewhere to send all the electrical energy instantly.
You could feed the excess to an electric heat radiator but you might just as well use brake disks.
Wheel motors increase unsprung weight.

Sorry I did not reply earlier about rim motors, I am still looking.

[machin]

As far as I know efficiency loss from a gearbox is anything but "slight". It negates anything efficiency wise and takes a bunch more.

I disagree, an electric motor efficiency map is anything but flat (e.g. http://www.neweagle.net/support/wiki/do ... /PP150.pdf), which is where the multispeed gearbox comes in (by allowing the motor to run in the "highest efficiency zone" for more of the time, despite the fact that the gearbox introduces an additional inefficiency.

The fact that you need an extra gearbox already compensates partially for the greater mass of the motor. Plus modern axial flux motors apparently can be made pretty light and powerful too.

Whilst it is true that they are getting lighter, I've yet to see an application where it is not better ( in terms of weight and size) to use a higher speed motor and gearbox combination, (even for in-wheel applications):-

• RC planes (as per Andres125sx post)

• Starter Motors (one of my previous posts; look up Brise starter motors for info)

• Formula Student (AndyL's previous post)

• Formula E (Let's not forget that Williams and McLaren, who are responsible for the arrangement used on Formula E, are not stupid).

• Drayson-Lola (one of my previous posts)

[autogyro]

Electromagnetic braking is great if you can find somewhere to send all the electrical energy instantly

Capacitors?

I was going to say to heavy but I am unsure of the present level of development since I suggested them for use with batteries for the red bull F1 car.

Wheel motors increase unsprung weight.

They don´t need to be at the wheel, a drive shaft solve it, specially if you still need brake discs. If not a drive shaft would be problematic to apply too much braking torque, but if it´s not the case why not?

I dont consider shaft drive at each wheel as wheel motors. In fact my ideal would be a split motor or two driving shafts part time on the front primarily for energy recovery and a gearbox drive at the rear full time.

Sorry I did not reply earlier about rim motors, I am still looking.

No more clues about what are you looking for exactly?

I simply want to source a small 'rim drive' motor to make some packaging and power comparisons.
Not pancake or flat disk but 'rim drive'.

[machin]

. What I say is that gears, especially gearboxes waste a LOT of energy. I doubt it can be close to being less wasteful than a well designed, direct drive motor.

Where do you get this "gearboxes waste a LOT of energy" from? In my industry (Naval Marine) we use one or two ratio clutched boxes and they have 98.5% efficiency over a very wide RPM range. That is a often a contractual requirement and proven by dyno test. The efficiency drops as you run them below their optimum tooth face loading, but in a racing situation where a large majority of the time you're either running at high throttle openings, or, in the case of Electric cars, regenerating during braking, the gear tooth loading should be high most of the time.

Conversely, a typical electric motor, like the one I linked previously (http://www.neweagle.net/support/wiki/do ... /PP150.pdf), has efficiencies ranging from 65 to 95%across the RPM range at "full throttle".

If we overlay Andy's chart onto the above motor's power/efficirency chart:-



We see that at Clay Pigeon the majority of the time he would be running in the 88 to 90% motor efficiency region of the curve.

Now, If we had a two speed gearbox we could have one ratio for top speed and another ratio which allows him to run in the 95% efficiency region at Clay Pigeon:-



Not only would his overall efficiency be better (0.985x0.95= 93.7% efficiency, verses the previous 88 to 90%) at Clay Pigeon, but he would also have 50% more power in the 30 to 35mph region than with the direct drive arrangement....