Sacli Suspension

[Lemon Lime]

Hey colleagues ; I was just wondering if we are permitted to use Sacli type suspension in FSAE UK or not ?! Note on that : Sacli suspension is great for handling rolling motion and also in bump and rebound motion , But I was wondering if it is any good in handling bump steer ... Here is a pic ---> http://www.saclisuspension.com/siteImages/fullImages/OVERVIEW-REAL.jpg ... And here is a link Sacli Suspension (http://www.saclisuspension.com/HowItWorks.php)

[Tim.Wright]

wow thats mental

[Tim.Wright]

I'd suggest reading up on a few more suspension fundamentals before you go for such a complicated solution.

You do realise all that extra crap is going to just weigh the car down and make it slower right?

[Lemon Lime]

Dear Mr. Wright , Hahahaha http://fsae.com/groupee_common/emoticons/icon_biggrin.gif ... Yes that's mental , but I like the idea although it is crazy , Ofcourse I'll read TONS before getting into these , But allow me to emphasis my question again ... Is it allowed though ?! And yes I know the car will weigh about 10 KG more ( I THINK SO !! ) http://fsae.com/groupee_common/emoticons/icon_smile.gif HEY I'M 18 YEARS OLD I KNOW THAT WILL SLOW THE CAR OFCOURSE .. The main problem is that it will increase the unsprung mass more relatively to the sprung mass ... Finally thank you sir for your attention and valuable time ... And thank you for your guidance http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Claude Rouelle]

Why not?

But

- Major issue suspension load in braking. Try a FBD of the top front wishbone reaction to braking torque (m for braking and acceleration torque at the rear)

- One of my best teacher in mechanical engineering always said "The less you do, the fewer mistake you make". Here you have EIGHT springs and dampers, more possible compliance, more weight... More parts, more cost, more complication, more tuning, more causes for failure are the reasons why it probably has not been used in passenger cars design. One motto of the OptimumG seminar is "Why don't you try to make it useful before you make it complicate?"

- Can you use it? Patent...

- The concept makes sense .... in 2 D. 3D ...Braking, acceleration....I have some doubts.

- The whole concept (Sacli website) is about camber control in heave (also in pitch) and roll but my experience is that with a good understanding and experience in efficient use of tire model and tire data as well and some freedom in suspension kinematics design, there is need to go to this level of complication to get efficient use of tire and car performances.


Still, I would like to see a Formula Student car built this way. I bet it won't be quick (too complicated to setup and tune even for most good FS teams) but would be nice to see on track for the sake of innovation.

The Sacli website is interesting and the author has the honesty and openness to write the equations. I like innovations and I would like to take the time to go through the calculation my self but I am not sure I like innovations. The engineering community needs more of this outside the box thinking.

[Lemon Lime]

WOOOOOW ... Mr. Rouelle himself .. That's a great honor Sir , Thanks for your reply and motivation , Allow me to carry after your speech sir ; Yes I want to make this for the sake of innovation ... It will cost a lot ... weighs a lot ... in short it needs study a lot ( AS A WHOLE NOT AS AN IDEA ) After all Sir I don't want to make it then come up in the late 40s positions !!! Doesn't make any sense ... Anyway Thank you a lot Sir for your valuable time and attention .

[Claude Rouelle]

Lemon LIme,

My name is Claude, not sir. I am just one the guys in this forum. Because of my international consulting travels, our seminars and software, the design judging in several countries and maybe my "confrontational" style with students http://fsae.com/groupee_common/emoticons/icon_smile.gif and simply my passion for FSAE, I am pretty well known in the FS/ FSAE community.... But believe me, there are many contributors, young and old, in this forum and in the FSAE / FS jugging who know more than I do and who deserve more credit than I do. No "sir", please. Each of us is just one of the 7.1 billions, trying the best we can.

[TurboTom]

Perhaps you might also want to consider how having a damper in such close proximity to your brake disc will have an impact on it's performance. I know FSAE doesn't see super high brake temps, but I'd imagine plus or minus 50 deg C might make a big difference on your damping characteristics.

[Warpspeed]

Packaging all the "stuff" correctly inside a normal size front wheel is always an interesting challenge.

Putting a spring and shock inside there as well, along with sufficient travel and steering lock, would require either running enormous wheels, or the design effort of a Super Hero.

Innovative suspension theory is one thing, converting it into useful practical and durable hardware can be far more difficult.

[ben]

This looks like a textbook example of setting a very narrow design goal rather than a vehicle system level target.

The camber control might be a good thing, but in the negative column is the extra weight, complexity, cost, compliance, etc...

Ben

[Luniz]

I can imagine tuning this system could be a bit complicated though!. It is nice to have a set of springs and dampers for controlling pitch/heave exclusively, so this setup could be very straightforward. But in Roll or one sided obstacles, you have two systems controlling the movement. The "dive suspension" in the upright is also contributing to roll movement. So you have two springrates and four damper (rebound and compression) settings to adjust, and maybe also an additional ARB... Not impossible but very complicated

By the way... which FSAE team are those guys from? ;-)

[Tim.Wright]

Originally posted by ben:
This looks like a textbook example of setting a very narrow design goal rather than a vehicle system level target.

To me its something else. Its a mix up I see a lot where people choose a system (based on nothing really), and then later work out what problems it solves.

You should be working in the other direction. First you define your problem then you decide which system will solve it best.

E.g consider thinking this way:
Can't get correct roll/ride rates with traditional suspension > Use Sacli suspension
Instead of like this
Use Sacli suspension > ZZOMMGGG so many links how can it not work!!

If you are just picking ideas randomly out of the air, why wouldn't you choose this (http://www.walker-partnership.com/) system? Or why bother trying to control the rates using the links? Why not use an interconnected suspension? F1 are doing it now so it must be ace!

[Lemon Lime]

Thank you all Seniors , And a special thanks to Mr.Ben & Mr.Rouelle , First this might ( WILL !! ) sound funny ofcourse ... Here is the story ; I was thinking of a suspension type to control camber change during rolling , Then few days later , I dreamt ( DREAMING WHILE SLEEPING ) of the Sacli wishbones setup ; I woke up and started to draw like an insane TONS of drawings about that wishbones setup , Then 2 days after ; I was surfing the internet for some good references , And I found a picture of Lancaster Uni. FSAE team , I was shocked because it had the same idea which I dreamt of days ago !!! ( Google " Lancaster Links " ) ... I started to look for similar pictures and some information about that sort of links ... And by the mere coincidence I found a link about Sacli Suspension and I was completely taken over by the idea !!! I know this seems crazy and stupid to dream about something and to wake up wanting to do it not knowing the consequences !!!! But I'm still 18 years old and the road is ahead to me very long and bumpy and what I might need is guidance or ( ADOPTION ) , I know there is a lot of people who are a lot smarter than me and better than me , But all I want is one chance ; And I don't want anyone to give me this chance ; After all God gave me the chance now ; ALL I HAVE TO DO IS STUDY WITHOUT MERCY TO MYSELF ; HOURS WITHOUT SLEEPING BECAUSE I AM DETERMINANT TO BE SOMEONE AND SOMETHING IN THE FUTURE ... By the way My real name is Marwan Alabassiry , I'm an engineering student ( First year ) And I decided to join the HFS Racing Team ( Helwan Uni. Formula Student ) this year , And I am willing to make a difference in FSAE community in 2014 . Once again I loved the soul of this community and Thank you all who guided me through this discussion , REALLY THANKS ALOT http://fsae.com/groupee_common/emoticons/icon_smile.gif And a special message to you Mr.Rouelle ... IT WAS HONOR TO SPEAK WITH YOU SIR AND YES I MUST CALL YOU SIR AFTER WHAT YOU'D SHOWED FROM BEING HUMBLE AND DOWN TO EARTH http://fsae.com/groupee_common/emoticons/icon_smile.gif

[exFSAE]

...that's a bit intense.

Some things to think about:

1. If you all you care about is camber change in roll, short VSAL SLA suspension will do that.

2. Or, stiffly sprung - which FSAE teams seem to love to do anyway.

3. Ask yourself if camber even matters much with these tires...

[Z]

Lemon Lime,

In case you don't fully grasp exFSAE's post above, I will expand on it.

1. It has been said many times on this forum that you DO NOT NEED any suspension at all to go fast around an FSAE track. (No one has yet given a compelling argument otherwise.) Your suspension must only provide +/-1" movement to pass scrutineering. After that you can fit springs that make the suspension effectively rigid, thereby solving any camber control problems. Many winning cars have taken this approach.

2. The Sacli suspension you show, as well as the Walker/Dax Rush suspension linked to above (Tim's post) and previously discussed on this forum (in 2005?), are rather complicated systems aimed at giving consistent camber control during body heave, pitch, and roll motions. This camber control can be a good BENEFIT to aim for, but you must also consider the COST involved. Both the Walker and Sacli systems have high cost. Especially the Sacli, which is effectively two complete suspensions in series.

So, other than a completely rigid suspension, are there any other low "cost" options?

Well, you could replace the Sacli's complicated inner double-wishbones with simpler Lancaster-link style lateral-swing-arms, keep the anti-axle-bounce link ("Lock link" in your image) but perhaps make it a little less stiff, and toss the outer sliding-pillar suspensions. This is now a much simpler suspension which is soft in roll but with good camber control, and stiffer in heave and pitch, so the poor camber control there doesn't matter.

Or you could use beam-axles. These can have very soft springs yet still have perfect camber control in heave, pitch, and roll.

The Walker and Sacli systems are really nothing other than reinvented versions of beam-axles, but with a whole lot of complication thrown in so that the dimwits think they are "innovative"! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Z

[Jay Lawrence]

Sorry if this seems dumb, but I don't see how this suspension can work properly. The sliding pillars take care of pitch, but in order to do so they must be quite stiff. This would mean that single wheel bump / heave / warp is also quite stiff, meaning that there's not really any point to such mode separation. Given the stiffness required for the sliding pillars, I imagine any single wheel bump event would be quite unsettling too. Those Lancaster links pretty much eliminate camber change over +/- 1" travel anyway.
Perhaps I'm just confusing myself, and mode separation wasn't actually high on the agenda for this design.

[Pete Marsh]

The system is free in roll except for the dedicated roll springs, so warp would only be dependent on the roll spring choice. (opposed coils is a poor choice for a centring spring though)
Single wheel(depending on how you define it) could be OK with it coming from both warp at the roll rate, and also in series with the hub rate.

I see all sorts of McPherson strut issues x 10! It would be hard to manage both compliance and friction in that little strut/upright. There is a good chance your camber control gains would be flexed away, and the load dependent friction would make a complex damping system even more so.

Still, great to see something different being considered.

Pete

[Z]

Jay,

I'd say that camber control is the priority rather than modal separation.

FWIW, the outer sliding-pillars work just like a normal suspension with equal rates in axle-bounce and axle-roll. So also the same rate in single-wheel-bump (or half that, depending on definition). The inner wishbones have the "Lock link" locking up the axle-bounce-mode (ie. very stiff), and a softer axle-roll rate. The combined rates for inner and outer suspensions are worked out as "springs in series" (ie. the whole is softer than each part).

The Sacli sliding-pillars have 0% Camber Compensation, and the wishbones seem to have about 150% CC. So with the sliding-pillar springs somewhat stiffer than the wishbone roll springs, it should be possible to get close to 100% CC during cornering. Of course (as you suggest) lateral-swing-arms (= Lanc-links) swinging off the car centreline also have 100% CC.
~~~~~o0o~~~~~~

Pete,

I don't see any insurmountable problems with the sliding-pillars. The quite cheap and easy "trick" is to use linear roller bearings. The short travel and clean operating conditions of FSAE makes it quite suitable for sliding-pillars. In fact, for FSAE I reckon tossing the Sacli wishbones and just keeping the sliding-pillars would be better than using the whole Sacli system. (Or just doing Lanc-links with stiff axle-bounce-rate would be better, and Beams even more so, as mentioned before.)
~~~~~o0o~~~~~

Lemon Lime,

Here are links to my previous ramblings on Sliding-Pillars (http://fsae.com/eve/forums/a/tpc/f/125607348/m/73320357151?r=59520287151#59520287151) and Swing-Arms (http://fsae.com/eve/forums/a/tpc/f/125607348/m/73320357151?r=34120987151#34120987151).

Z

[Charles Kaneb]

One thing to note with most FSAE suspensions is that camber deflection is usually in the "wrong" direction - towards negative camber on the inside tires and positive camber on the outside ones.

Having a REALLY flexible portion of the upright between the hub and lower control arm might get you back to zero camber deflection - but TAMU wasn't able to design one with an acceptable fatigue life.

[Claude Rouelle]

Charles,

No need to have a Sacli suspension for good camber control compromise in roll and heave (and steering on front).

During the concept / design
- decent exploitation of tire models coupled with smart suspension kinematics design (especially - but not only - the choice of VSAL and VSAL variation)
- smart design to minimize compliance
and
During testing and development
- smart use of tire temperature sensors and their data analysis

Will lead you (for a given track, given tires ,a given driver and given track conditions) to pretty good camber control; in other words getting the camber you want when you want it, maximizing grip and minimizing wear (and/or uneven wear)

That is why it is worth to have adjustable kinematics pick up points. How can you be sure tat your initial kinematics design is spot on without testing?

Good race cars and FSAE cars / teams have shown it is possible.