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IMHO
Strut suspension is easy to design and make - and is easy to set to achieve the suspension results
The fact that the angles are set by the position of the strut top means that you can get precise angles

The only issue that I can see is that it prevents some body shapes - but only at the front - the back is almost always high enough to mean that you can fit your struts

Edit
I used Strut suspension on the front and rear of my "Device" - and decades ago I used Strut suspension on the front of my Twin Cam Mini
 

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Strut suspension is easy to design and make - and is easy to set to achieve the suspension results
The fact that the angles are set by the position of the strut top means that you can get precise angles

The only issue that I can see is that it prevents some body shapes - but only at the front - the back is almost always high enough to mean that you can fit your struts
It's no worse to design than other non-trivial (not single arm) suspensions, but Duncan wisely chose not to design or make one, but instead to incorporate a production Subaru suspension to the Device.

True, there's lots of height in most bodies, including the XJ6. Of course, there's that little detail of an existing body structure... :rolleyes:

I used Strut suspension on the front and rear of my "Device"...
The Device is a tube-framed vehicle designed to fit the components, including the suspension. That's a substantially different situation from the XJ6.
 

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Brian
You are completely WRONG in this
A twin wishbone setup is very sensitive to the positions of all of the pivot points - and it feeds large loads into all of those joints

For my mini I designed the suspension with my own bottom wishbones

I did use complete Subaru subframes for my device as it was easy - and made certification a lot easier

But designing a strut type rear suspension for something like the jag would be relatively easy - you just need the two pivot points for the lower wishbone and a single high mounting point for the strut top - you could cut the turret off another car (like a Subaru - or almost any car with struts) and weld it into position a trivial task compared to any of the other types of suspension

Almost all current production vehicles use Strut suspension - because it is easy to design and make AND works very well
 

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Brian
You are completely WRONG in this...
That's strange... because I didn't disagree with any of the points which followed this, except...
Almost all current production vehicles use Strut suspension...
No. A large fraction (probably the majority by sales volume) of current production cars (not light trucks) do use MacPherson strut front suspension, but few have used it at the rear in the last decade or two.

We're supposed to be discussing a suspension to make a Tesla drive unit work in the back of the Jaguar XJ6. In the current Jaguar lineup only the E-Pace (the smallest and least expensive model) uses a MacPherson strut front suspension, and none uses a MacPherson strut rear suspension. The rest of the front suspensions are all extended hub carrier double A-arms, while the rears are all multi-link (generally Jag's Integral Link design) or double A-arm.
 

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We're supposed to be discussing a suspension to make a Tesla drive unit work in the back of the Jaguar XJ6

YES
And in that situation I would be designing and making a Strut type rear suspension

It is easier to design
Easier to make
There are a LOT more parts available
And - importantly - it requires lower level of precision to make it work

Finally - if at all sensibly designed it works very well indeed
 

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Discussion Starter · #26 ·
I stopped getting updates for some reason and regret not being up to date with the conversation. I had looked at McPherson Struts (the difference between them and Chapman struts is not immediately obvious, perhaps how they mount to the wheel hub?, i'll look into it further). Holding all the wiggliness of a 400kw car with a single control arm and strut seemed like a lot to ask so I had perhaps incorrectly, dismissed the idea early on for lack of understanding. There us heaps and heaps of space for struts and a lower control arm is easy to find space for so I should reconsider this option.

After our conversations so far, I had another look at the rear suspension today. The front upper control arm is about 20cm long, the lower, 30cm long, not as long as I thought. I had dismissed the idea double wishbone suspension would be possible in the rear. With some clever positioning, perhaps I could get something similarly long into the rear, I had expected it would need to be much longer to get reasonable wheel travel. The current rear lower control arm is about 45cm long and may need to be shortened, I imagine there is a sweet spot for the length of upper vs lower control arm. All that said, this train of thought has just landed me in the poo pile that is lining up u-joints and suspension pivots and I can feel a cold sweat coming on :)

As I said I had not put much thought to suspension design and now i'm suffering some errors as a result. For now I should put all options back on the table and educate myself for all options their strengths and weaknesses. Regrettably there is no perfect, easy and cheap option for my handling/ performance goals.
 

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The strut design on the back of my device is (each side)

Two in/out links - one with length adjustment - both effectively simple tubes with eyes for the rubber bushes

One fore/aft link - in the Subaru it goes forwards but I swapped the rear hubs right to left so that it went backwards

These three nicely constrain the bottom of the strut - then all you need is the top of the strut

As a general rule the more that you can move the top of the strut towards the center of the car the more the suspension compensates for vehicle roll to keep the tyres square to the road

On the Subaru the strut ends in a bracket that goes either side of a bit sticking up out of the hub

These two parts are clamped by friction so you can enlarge the holes to get more adjustment if you want
 

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I had looked at McPherson Struts (the difference between them and Chapman struts is not immediately obvious, perhaps how they mount to the wheel hub?, i'll look into it further).
The difference is that a Chapman struts use the axle shaft as a suspension link (so cornering force is carried through the differential bearings), while MacPherson struts have normal shafts with CV joints and separate suspension links. Few cars ever had Chapman struts, and none have had them for decades; they're a historical curiosity.

Holding all the wiggliness of a 400kw car with a single control arm and strut seemed like a lot to ask so I had perhaps incorrectly, dismissed the idea early on for lack of understanding.
There's no problem with strength at all. The strut does take bending stress (unlike the shock in other designs), but they have a larger rod diameter and this isn't a problem. Where MacPherson struts are currently used (at the front of unibody cars, particularly those with transverse engines), they're usually supporting the heavier end of the vehicle and they are often controlling the drive axle. The current 6- and 8-wheeled vehicles armoured vehicles used by the Canadian army have strut suspensions for the forward axle(s)... and they weigh 16 tons or more.

After our conversations so far, I had another look at the rear suspension today. The front upper control arm is about 20cm long, the lower, 30cm long, not as long as I thought. I had dismissed the idea double wishbone suspension would be possible in the rear. With some clever positioning, perhaps I could get something similarly long into the rear, I had expected it would need to be much longer to get reasonable wheel travel. The current rear lower control arm is about 45cm long and may need to be shortened, I imagine there is a sweet spot for the length of upper vs lower control arm. All that said, this train of thought has just landed me in the poo pile that is lining up u-joints and suspension pivots and I can feel a cold sweat coming on :)

As I said I had not put much thought to suspension design and now i'm suffering some errors as a result. For now I should put all options back on the table and educate myself for all options their strengths and weaknesses. Regrettably there is no perfect, easy and cheap option for my handling/ performance goals.
There are a lot of factors in suspension design. I wouldn't consider playing with arm lengths without a substantial understanding of the geometry, which is a good reason to use a production design. For instance, there is no ideal ratio of upper to lower control arm length.

The strut design on the back of my device is (each side)

Two in/out links - one with length adjustment - both effectively simple tubes with eyes for the rubber bushes

One fore/aft link - in the Subaru it goes forwards but I swapped the rear hubs right to left so that it went backwards

These three nicely constrain the bottom of the strut - then all you need is the top of the strut...
This is a common design of the 1980's; I had a 1984 Toyota Tercel with the same design. The "in/out" links are usually called lateral links; the fore/aft link is usually called a longitudinal link.
 

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You should reconsider using a motor in the transmission tunnel and keeping the Jag IRS. You see why I ended up taking the route I did with mine, the rear suspension problem is quite difficult to solve!

Good news is that four Tesla modules fit in the spare tire well and probably 12 under the hood (I have ten)
 

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Discussion Starter · #30 ·
Thanks Bry5on, I agree it is a shame to get rid of the original IRS. It appears difficult, but we have at our finger tips all of human knowledge in the internet. I am confident i can come up with something 95% what i want.

The transmission tunnel will be housing four modules, plus another two stacks of four on the front suspension. Plus four on the shelf above the IRS. Could probably fit a few more in the front but im trying to even out weight distribution and having four identical boxes minimises engineering design and certificate work/ costs. The spare tyre well is shrinking to fit the motor but is probably enough room left for a charger.
 

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Have you measured out the space on the shelf already? I thought about doing this as well but because the seat back is reclined and not vertical, it looks like stacking four modules is not possible without eating into the trunk space a bit more.

Very curious to see how it ask pans out! Wish it were easier for us to get together and share musings
 

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The biggest challenge of using a strut suspension at the rear is that - completely unlike the original Jag IRS which is obviously designed to be low and flat across the top - it fundamentally requires two towers to accommodate the struts.
...- you could cut the turret off another car (like a Subaru - or almost any car with struts) and weld it into position...
This is true, but those towers (or turrets) would go through the existing structure, and into the interior.

I'm not clear on the rules yet but am working on the assumption I cant cut and move the chassis rails.
This could be one problem with fitting in strut towers, depending on frame rail spacing and strut spacing.

The other problem is what strut towers would run into in the interior, but I noticed these comments:
The transmission tunnel will be housing four modules, plus another two stacks of four on the front suspension. Plus four on the shelf above the IRS...
There us heaps and heaps of space for struts...
I've driven an XJ6 (I think a Series III, rather than this Series I), but I didn't look behind the rear seat and I don't recall the details of the trunk. It sounded at first like this body had a feature which was common in the 1960's, in which the trunk is behind base of the rear window, the rear seat back near the leading edge of the rear window, and in between them is a wasteland of awkward "parcel shelf" over the rear axle and suspension, within the passenger compartment volume. Looking at online images of bare XJ body shells, it seems more likely that these are references to the forward section of the trunk, where the floor is stepped up over the rear axle and suspension, ahead of the trunk opening and below the rear window.
(an old bodyshell image is attached to the end of this post)

In either case, that's a great battery location for some cars (as long as you package the modules safely), and if strut towers (for MacPherson struts or just springs and shocks of another IRS design) were to poke into there it wouldn't interfere with seating space or the main trunk space (although of course now battery and suspension are competing for space). There are just those structural issues to consider... struts outboard of those frame rails (visible in the bodyshell image) would require a very wide track.

While looking for information on the XJ body, I discovered that if you have buckets of money Jaguar Classic might still produce a complete new bodyshell for you (although only for the Series III, not earlier). :D
 

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If you look at the picture Brian attached you will see that there is plenty of room for the struts

IMHO you do NOT want your batteries high up at strut level - the best place for all the heavy bits like batteries is down on the floor - as low as possible
 

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IMHO you do NOT want your batteries high up at strut level - the best place for all the heavy bits like batteries is down on the floor - as low as possible
Ideally, yes. Unfortunately the reality of a car body not designed for an under-floor battery box is that low locations are not likely available. The engine compartment and transmission tunnel go to the bottom of the car, and are planned locations; even the top of the engine area stack will be higher than that over-axle shelf. For the rest, there is the portion of the spare tire well behind the Tesla drive unit, but that's well behind the axle and so it is undesirable as well. Stacking them on the floor in the rear seat space might not be popular with the rear seat passengers... ;)

The stock "saddlebag" fuel tank locations are not very low, either... and not shaped to accommodate big flat modules.
 

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Discussion Starter · #35 ·
If i'm ever in the US bry5on i'll look you up, would be great to shoot the breeze with a fellow jag lover.
I believe a strut tower would fit. The fuel tanks sit above the wheels so without them leave plenty of height. The bulge locates under the filler cap but there is still space forward of that.

Battery location has been a compromise. I'm trying to get it as low as possible. however the cells are quite long. one method I have designed is mounting them lengthwise which means they fit closer to the middle of the car. however fitting a stack in the transmission is taking up some dash and theyre just a little too long to make that work without altering th cabin appearance which i dont want to do.

Another option is Perpendicular, as Bry5on has done, leaves more engine bay room, better space for radiators if you need one. However one mounts almost entirely forward of the front axle, the other must be mounted 10cm higher than my original design to clear the chassis rails, as is visible in Bry5ons photos.

In the rear, i am losing most of the spare wheel well to fit the motor might check space again though. The 4 module stack is 34cm high (14'). i think i'll put a coolant motor or something behind the stack so i dont lose the space because of the sloped seat. There is very nearly enough room to mount two modules in the original fuel tank location. but mounting vertically and in such a position prone to collisions, i thought better of it.
 

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Fuel tank spaces

I believe a strut tower would fit. The fuel tanks sit above the wheels so without them leave plenty of height. The bulge locates under the filler cap but there is still space forward of that.
Just to be clear, with or without fuel tanks doesn't matter to struts, because the front of the tank is still well behind the axle line, and so behind even a large spring on a strut. The tanks are also behind the tires, and so mostly outboard of a strut location.

The tank locations look like good places for components such as chargers or coolant pumps, or even just storage bins. And one of the fill cap locations is just begging to become the charge port. :D
 

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Spare tire well

In the rear, i am losing most of the spare wheel well to fit the motor might check space again though. The 4 module stack is 34cm high...
It appears that a 1969 XJ6 came with E70-15 tires, which are 26" or 660 mm in diameter. The spare tire well appears to be entirely behind the differential housing, so it must extend at least 26" or 660 mm past the diff. The front side of the Tesla motor will sit further forward that the back of the Jag diff, so the rear mount of the drive unit should end up about mid-way back in the spare tire well.

Does that leave enough space for modules (only stack of two due to height) in the spare well behind the motor? Is the spare well width (which looks like it is barely enough for the tire) enough for the length of a module? Both dimensions look tight, but especially the width, so I wouldn't be surprised if a module won't fit there.

This could be another space for various ancillary components (electronics, coolant pumps...), or just a storage cubby for the air compressor and tire puncture-repair stuff that one needs when one doesn't have a spare tire.
 

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There is not enough space in the trunk for a module to fit width-wise, it is about 1" shy of being doable without cutting into the old muffler compartment (which is not the end of the world if this much fabrication work is already happening).

The old tank locations are indeed great spots for chargers and yes the gas door makes a great charge port 😉
 

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There is not enough space in the trunk for a module to fit width-wise, it is about 1" shy of being doable without cutting into the old muffler compartment (which is not the end of the world if this much fabrication work is already happening).
The mufflers flank the spare tire well, so I can see how cutting out one or both sides of the spare well would allow the use of the muffler space, but isn't there a structural ("frame") rail between them? The structure has to be somewhere, and forward around the axle it is in two rails essentially lined up with the sides of the spare tire well. Does the structure run outboard of the mufflers, or above them? The mufflers look like they might be under the fuel tanks.
 
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