RE: McLaren P1: Driven

[Mr Whippy]

fatbutt said:

Oh for crying out loud.

See the previous pages for exactly the same discussion.

ETA: starts about page 16, ends page 22.

Sorry, some of us don't have time to read 22 pages of thread. I came here from the PH front page article posted earlier, which oddly linked back to an existing thread on the subject!?


You'd have thunk that the contents of this thread if they discussed things in such detail would have found their way into the latest article but nope. Still Chris Goodwin tells Chris Harris that the car has an open differential, and Chris talks as if the P1 has some other kind of diff to a mechanical locking one, with computer control, which is apparently what it DOES have?


This is a mechanical infinitely variable locking differential then? Or not?


Dave

[Dr JonboyG]

Mr Whippy said:

Analogue and digital? Another complete bunch of junk written by cretinous journalists who have no idea what they are talking about at the best of times.

Braking is will probably be completely electronic, with the brake pedal working on a potentiometer that the car then interprets to decide how much regen and how much brake to apply.

Mr Whippy said:

The only reason they put electrics on is to widen the appeal to less capable drivers.

I think you might find McLaren wanted access to the US car market and traction and stability control are both mandatory over here now.

[Mr Whippy]

I think braking is still completely hydraulic with the ABS units intercepting signals and altering as necessary.

Imagine if the electronics failed hehe


Ah I didn't realise the stability systems etc were all mandatory over in the US. I suppose it makes sense in the end.


In the end though all these systems have been around a long time, but it's only the last few years people say digital vs analogue etc. It's always been a combo of the two since computers found their way into cars.

[anonymous-user]

A few points:

I have explained in some detail why the "brake steer" system possess a fundamentally higher yaw authority that a conventional limited slip differential, and pointed out that the LSD is unable to provide Positive yaw control.

Mclaren Automotive would have fitted an LSD if it were required. It isn't. Endless road and track miles, driven by some of the best drivers in the world have proven this. The on-cost of an LSD, even an electrohydraulic one, is in the region of $500 at those volumes. It's >$1M car, so i think it's safe to say, if it had needed one, it would have got one.


Endless PH armchair 'engineers' have now endlessly stated "this car should have a mech diff" or "It would be much better with an Ediff" and they have all failed to understand the basic dynamics at work. Luckily, the P1 has been designed, developed and calibrated by actual, real, engineers, and some bl**dy good ones at that, so the car drives and performs incredibly well (anyone think the performance is somehow lacking??)

Mr Whippy said:

Really I don't get why McLaren didn't just use an open diff and a motor on each output shaft that could apply positive and negative torques. Then they could brake and regenerate, bias and regenerate, trim torque to control traction to a point and so on.

Having the electric motor simply adding to an open differential and then having to trim it back with braking at the wheels seems a bit crude... well that is my opinion given their blank sheet of paper opportunity.

Dave

You need to understand that that would also require either two multispeed gearboxes, or a very large and complicated cross axle epicyclic driven by a very large and complicated Emachine. (Have a think about the relationship between the torque and speed of a driven wheel necessary to control vehicle yaw)
And yes, it would be able to "save" some energy (compared to brake steer) but this isn't a Prius. In Race mode, fuel economy is irrelevant.

And i will say it one final time: If you think you can do better, please be my guest. There is nothing stopping you from building your own P1 you know.

So, if you think you have a better solution to systems fitted to the P1, i suggest you call Mclaren and let them know. I'm sure they'll be very understanding..............

[Mr Whippy]

With all due respect Max Torque, it doesn't help when everyone from the two guys on the linked video, to the article contents, to armchair engineers on here, are all telling everyone different information.

I don't even know what systems the P1 has for certain, there is no full technical specification available anywhere for those interested to look at to draw conclusions from.
So in the end we make assumptions based on what is available.


In the end I appreciate (and said this earlier) that an engineering requirement is chosen and the engineering solution is made to fit that requirement. The P1 is thus set up with that in mind and it'll perform optimally given that option.

But my argument is that no system is better or worse if the performance it offers fits within the desired brief of the requirements to begin with. A locked diff has it's place, just as a completely open one does. Requirements and the overall package determine which one you use.



Good point on speed vs torque, I'm still confused with the finer elements of differentials, simply understanding that people choose specific ones to fit their needs, and that is good enough reason for me.

I don't think I can do better by any means, my points were all based upon an open differential and wheel braking which is clearly completely wrong. Cheers Chris Harris hehe

Dave

[isaldiri]

Max_Torque said:

A few points:

I have explained in some detail why the "brake steer" system possess a fundamentally higher yaw authority that a conventional limited slip differential, and pointed out that the LSD is unable to provide Positive yaw control.

Mclaren Automotive would have fitted an LSD if it were required. It isn't. Endless road and track miles, driven by some of the best drivers in the world have proven this. The on-cost of an LSD, even an electrohydraulic one, is in the region of $500 at those volumes. It's >$1M car, so i think it's safe to say, if it had needed one, it would have got one.


Endless PH armchair 'engineers' have now endlessly stated "this car should have a mech diff" or "It would be much better with an Ediff" and they have all failed to understand the basic dynamics at work. Luckily, the P1 has been designed, developed and calibrated by actual, real, engineers, and some bl**dy good ones at that, so the car drives and performs incredibly well (anyone think the performance is somehow lacking??)

You need to understand that that would also require either two multispeed gearboxes, or a very large and complicated cross axle epicyclic driven by a very large and complicated Emachine. (Have a think about the relationship between the torque and speed of a driven wheel necessary to control vehicle yaw)
And yes, it would be able to "save" some energy (compared to brake steer) but this isn't a Prius. In Race mode, fuel economy is irrelevant.

And i will say it one final time: If you think you can do better, please be my guest. There is nothing stopping you from building your own P1 you know.

So, if you think you have a better solution to systems fitted to the P1, i suggest you call Mclaren and let them know. I'm sure they'll be very understanding..............

Asked this earlier but don't think there was a reply.... The thing that does strike me though, if brake steer alone is such a superior system why have Ferrari/Porsche who one would I think hesitate to say have any less good engineers than Mclaren persisted in including BOTH the electrohydraulic diff and brake steer type systems in their latest cars the 458 Speciale and the 991 GT3? And indeed the Laferrari/918 as well....

[E65Ross]

isaldiri said:

Asked this earlier but don't think there was a reply.... The thing that does strike me though, if brake steer alone is such a superior system why have Ferrari/Porsche who one would I think hesitate to say have any less good engineers than Mclaren persisted in including BOTH the electrohydraulic diff and brake steer type systems in their latest cars the 458 Speciale and the 991 GT3? And indeed the Laferrari/918 as well....

No idea, but CH has driven all those cars except the LaFerrari and says there is no questions that the McLaren system is better....

[isaldiri]

E65Ross said:

No idea, but CH has driven all those cars except the LaFerrari and says there is no questions that the McLaren system is better....

My take on what CH said on his comments earlier was that he felt that the calibration of brake steer on the P1 had advanced from that on the 12C (which as much as I like the car, would be improved with superior calibration or a proper diff IMO) to the point that it now equaled the feel of the LSD equipped cars, which is pretty impressive but not quite the same as saying that he thought it was better...

[AlexS]

Dr JonboyG said:

Braking is will probably be completely electronic, with the brake pedal working on a potentiometer that the car then interprets to decide how much regen and how much brake to apply.

The McLaren doesn't use brake regen. I think you are getting confused with the current F1 cars.

[Dr JonboyG]

Mr Whippy said:

I think braking is still completely hydraulic with the ABS units intercepting signals and altering as necessary.

Maybe the P1 is set up differently, but that's not how the brakes work on the 918, or the Audi R18 or Toyota TS030, for what it's worth.

AlexS said:

The McLaren doesn't use brake regen. I think you are getting confused with the current F1 cars.

Ah, so they do. McLaren make a point of saying they don't use regen specifically to improve pedal feel, in fact: http://media.mclarenautomotive.com/model/7/EN/doc/...

Edited by Dr JonboyG on Thursday 20th February 19:04

[anonymous-user]

AlexS said:

Dr JonboyG said:

Braking is will probably be completely electronic, with the brake pedal working on a potentiometer that the car then interprets to decide how much regen and how much brake to apply.

The McLaren doesn't use brake regen. I think you are getting confused with the current F1 cars.

Actually it does. it's just:

1) it doesn't only use Electrical Regen, and "lock out" the driver from the brake pedal (the bit that is tricky for brake feel) The Emachine negative torque is simply commmanded from a brake pressure signal. So when you are braking, the system IS recovering energy from the vehicles mass, but that augments rather than replaces the service brake retardation

2) the absolute negative torque is relatively low because the Emachine is only coupled to the rear wheels, and as such, weight transfer under braking limits the maximum retardation before the rear tyre slip is at a maximum. The 918 can regen a lot harder using it's front Emachine without a loss of control.

[adz2001]

Well done Chris, you've done a great job of reporting on a seminal moment in automotive history. Cheers Adam

Edited by adz2001 on Thursday 20th February 19:49

[Mr Whippy]

Dr JonboyG said:

Mr Whippy said:

I think braking is still completely hydraulic with the ABS units intercepting signals and altering as necessary.

Maybe the P1 is set up differently, but that's not how the brakes work on the 918, or the Audi R18 or Toyota TS030, for what it's worth.

AlexS said:

The McLaren doesn't use brake regen. I think you are getting confused with the current F1 cars.

Ah, so they do. McLaren make a point of saying they don't use regen specifically to improve pedal feel, in fact: http://media.mclarenautomotive.com/model/7/EN/doc/...

I'm fairly certain a road car has to have two hydraulic braking circuits so there is some redundancy in the event of failure of the hydraulic lines.

Having electric brakes is probably possible, but I've not heard of any other road cars that have them!?

[Mr Whippy]

E65Ross said:

isaldiri said:

Asked this earlier but don't think there was a reply.... The thing that does strike me though, if brake steer alone is such a superior system why have Ferrari/Porsche who one would I think hesitate to say have any less good engineers than Mclaren persisted in including BOTH the electrohydraulic diff and brake steer type systems in their latest cars the 458 Speciale and the 991 GT3? And indeed the Laferrari/918 as well....

No idea, but CH has driven all those cars except the LaFerrari and says there is no questions that the McLaren system is better....

But Chris Harris said this car has an open diff and uses brakes to control slip, but it doesn't.

I really enjoy what Chris Harris has to say about cars and he's a great entertaining guy, but can he really isolate his experiences so clearly and say anything like that with any authority?

Things like brake steer effectiveness will be intertwined with things like the presence of a super fancy differential that the P1 has, along with numerous other systems too no doubt.

Clearly a LOT of systems are all overlaid and calibrated to work together elegantly in this car, so to tie down brake-steer as a feature for the P1's great turn-in is somewhat missing the point.
It's the entire combination of all the systems *working together* by fine-tuned calibrations that give the end result.


I've no doubt the P1 is amazing, but every time journos drive the latest cars in controlled isolation they are always amazing and better than anything else ever!11!!!

Nothing wrong with that, but it's when you read reviews years later with a few cars side by side that you get the real comparisons and honest views from several reviewers.

I just think it's exciting that we have three uber-cars that are all so different in approach yet so terrifically well engineered.

Dave

[Monty Zoomer]

Mr Whippy said:

But Chris Harris said this car has an open diff and uses brakes to control slip, but it doesn't.

Things like brake steer effectiveness will be intertwined with things like the presence of a super fancy differential that the P1 has

Well, what sort of diff is it then?

[RoverP6B]

Mr Whippy said:

I'm still wondering why no one has made a car like this but with 4 leccy motors, but NOT just battery powered only. Ie, petrol-electric 4wd with absolute per-wheel torque control.

That's what the original twin-jet Jag CX-75 concept was - two little 60,000rpm hairdriers burning anything you can pour and purely electric drive. I think it'll see the light of day yet...

[DP33]

I've just read Monkey's intervention on the LSD vrs open diff debate. Got to say it made me feel a bit slow and ignorant...

[kikiturbo]

Max_Torque said:

A few points:

I have explained in some detail why the "brake steer" system possess a fundamentally higher yaw authority that a conventional limited slip differential, and pointed out that the LSD is unable to provide Positive yaw control.

But an Active yaw control electro hydraulic diff can provide positive yaw control in a way that even brake steer can't..

[Peloton25]

Man what a mess this became. Let me help...

iloveboost said:

I think the reason they use an E-LSD instead of a mechanical limited slip differential is that... <snip>

Who is this "they" you are referring to? If in our minds we were supposed to assume "McLaren" then...

iloveboost said:

All of the above could be wrong but that's the way I understand it.

...that final statement of yours is no longer 'could be' but is in fact 'is'. There is no E-LSD or E-Diff in the McLaren P1.

Now look what you have done:

Mr Whippy said:

So I have a new appreciation for the P1's diff.

Revert to your earlier appreciation (though still flawed) as what he wrote was not an accurate description of what the P1 uses.

Mr Whippy said:

You'd have thunk that the contents of this thread if they discussed things in such detail would have found their way into the latest article but nope. Still Chris Goodwin tells Chris Harris that the car has an open differential, and Chris talks as if the P1 has some other kind of diff to a mechanical locking one, with computer control, which is apparently what it DOES have?

This is a mechanical infinitely variable locking differential then? Or not?

Or not! The differential where torque is passed from the transmission to the driveshafts in the McLaren P1 is open, not mechanically nor electronically controlled in any form or fashion to balance torque output directly inside the diff itself. All the magic to replicate what a limited slip differential would do is provided by McLaren's Brake Steer technology to put it in the simplest of terms.

Mr Whippy said:

...my points were all based upon an open differential and wheel braking which is clearly completely wrong.

...and yet it is working so well for McLaren with the P1. Hmmmm...

isaldiri said:

E65Ross said:

No idea, but CH has driven all those cars except the LaFerrari and says there is no questions that the McLaren system is better....

My take on what CH said on his comments earlier was that he felt that the calibration of brake steer on the P1 had advanced from that on the 12C (which as much as I like the car, would be improved with superior calibration or a proper diff IMO) to the point that it now equaled the feel of the LSD equipped cars, which is pretty impressive but not quite the same as saying that he thought it was better...

Should not a system be considered 'better' if it can perform a highly similar function without the weight penalty or cost penalty of another system? Perhaps the end result from a functional standpoint is equal, but one has to look at all factors when determining which system is 'better' as function is hardly the only variable. This is what McLaren have done to arrive at their preferred choice of solutions.

Mr Whippy said:

But Chris Harris said this car has an open diff and uses brakes to control slip, but it doesn't.

I really enjoy what Chris Harris has to say about cars and he's a great entertaining guy, but can he really isolate his experiences so clearly and say anything like that with any authority?

In case it is still not clear, Mr Harris was always correct. Make it habit of listening to the people in the discussion who don't end their posts (or their statements to their millions of viewers in the case of Chris) with "All of the above could be wrong..." and you'll do much better.

>8^)
ER

Edited by Peloton25 on Friday 21st February 00:14

[Justices]

Less than 10 minutes into this video. I very much want this car. I mean, really, really want this car.

What a fantastic job they've done.