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Monoshock front suspension

Started by zac510 , May 24 2006 14:12

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29 replies to this topic

#1 zac510

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Posted 24 May 2006 - 14:12

I've become interested in this suspension since viewing one such setup on a Force chassis (can't recall whcih one inparticular) at Shelsley a few weeks ago. Photographed here, for interest: Photo link

As all of our threads are locked up in the archive vault, I decided to start a new one. Perhaps the most notable thread is this one which includes a diagram by scarbs: Thread link

I was just interested in continuing the discussion a bit. Does the location of the assembly need to be above the geometric roll centre for any reason?

In the thread linked above, in MattPete's quote about Formula Vee - do they run an open rear differential?

It sounds like it was popular in F1 a few years ago but has fallen out of fashion. It seems like if you just replaced a typical F1 sway/antiroll bar with a solid rod joining the rockers you would achieve a similar suspension to this monoshock setup with damping if you retained the dampers (of course spring rates would be wrong too).

Thoughts, discussion, random mumbling..

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#2 Greg Locock

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Posted 24 May 2006 - 22:35

I can't see any reason why the shock needs to be anywhere in particular, it just needs to be able to react the forces. After all, at the contact patch you can't easily tell if you have a leaf spring or a coil spring or a torsion spring or a gas spring, so the position of the actuator itself is a detail.

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#3 scarbs

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Posted 25 May 2006 - 09:14

I have to say monoshock installations are undenialy neat.

Monoshocks do incorporate some roll compliance, in the photo you posted the bar the assembly pivots on has a stack of belleville springs, however the roll resisitance isnt damped only sprung (normally the pair of dampers do this). Inhehrently monoshocks are set up very stiff, they tend only to be used for cars with large aero loads to keep the cars attitude under control.

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#4 zac510

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Posted 25 May 2006 - 13:09

Yeah I agree, they are neat and interesting. I doubt this car was producing masses of downforce. It was winged so relative to its weight it might be producing a reasonable amount, but hillclimb top speeds aren't enormous.

When I am trying to imagine roll condition, is there always going to be a little bit of compression/bump of the spring/damper and thus the inside wheel will be pulled 'up' like a traditional sway bar?

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#5 scarbs

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Posted 25 May 2006 - 13:55

No roll is decoupled from pitch, it is possible for the car to roll across the pivot without having to compress the springdamper. But yes the inside wheel will lift in roll

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#6 zac510

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Posted 25 May 2006 - 14:22

But what about in practice, will there always be some compression occuring at racing speed (especially with aero loading)?
In the other thread you said that the inside wheel would be in droop. I can't see how this is beneficial for front end grip. I still have to think about this some more

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#7 Fat Boy

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Posted 25 May 2006 - 15:21

Originally posted by scarbs
I have to say monoshock installations are undenialy neat.

Ummmm, I'm going to have to say that they're neat in about the same way that a De Dion rear suspension is neat or an old drive donut is neat.

Probably the word that comes to mind for me is 'kluge'.

The monoshock is championed by aero engineers. They see that they can lock the front ride height solid and fall in love. They are _horrible_ for mechanical grip. They are so bad for mechanical grip that the 2 series that are controlled by aero loads, F1 and IRL, have both given up the concept. The only place that a monoshock is competitive is when only racing against other monoshocks. That's not completely true. For some reason, they love the mono in F3, where you can use 4 (or 5) if you want to. My guess is since everyone is using the mono and the Dallara is a nice car, no one really cares about running a proper suspension. As the saying goes, in the land of the blind, the one-eyed man is king.

The Lola has a 3,4, and 5 shock arrangement. Despite being underfunded and massively out-numbered it has won races. My guess is that they are also underpowered, aren't quite as good in the aero department, but have a massive suspension advantage. Having said all of this, I've never raced F3, this is all 'from the outside looking in'.

The main spring does compress somewhat in roll, which gives a small amount of roll damping. The main roll damping is taken on the rear (the end with 2 shocks). On the damping side, whenever you're looking at the friction in the system helping things, you know it's a bad idea.

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#8 Ross Stonefeld

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Posted 25 May 2006 - 15:26

So why are there monoshocks on race winning Formula Fords vs 4-damper systems? And I dont mean club 1600s, I mean at the height of the 1800 Zetec cost wars.

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#9 zac510

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Posted 25 May 2006 - 16:19

Thanks for the frank reply Fat Boy

Ross I am not very familiar with those series, but are they 'overtyred' relative to the aero grip? Might they be trying to favour a rearward weight bias?

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#10 Ben

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Posted 25 May 2006 - 19:00

Originally posted by Ross Stonefeld
So why are there monoshocks on race winning Formula Fords vs 4-damper systems? And I dont mean club 1600s, I mean at the height of the 1800 Zetec cost wars.

FF have low CG heights and very wide track widths. On smooth tracks the disadvantages are minimised. Having said that "so and so won using a monoshock" isn't a good technical justification.

I'm with Fat Boy on this. A twin shock layout (with a third) spring should be better provided you can set it up right. This is I guess the caveate for lower formulae where time and skills are less abundent.

BTW I've been doing a bit of data engineering (posh term for driver babysitting) in BGT this year and we share a paddock with British F3. There is more than one Dallara with two shocks at the front. One team runs two Lolas - one mono, one twin.

Anyone got any shots of any Euroseries Dallaras?

Ben

Edit - not matter what any clubman competitor says about his/her monoshock a big part of it is replacing one £500 damper with a couple of quid's worth of disc springs. Never underestimate economic factors. Particularly in the aforementioned Formula Ford

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#11 Fat Boy

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Posted 25 May 2006 - 19:10

Originally posted by Ross Stonefeld
So why are there monoshocks on race winning Formula Fords vs 4-damper systems? And I dont mean club 1600s, I mean at the height of the 1800 Zetec cost wars.

Well, who did you have running? Van Diemen, Mygale, Tattuus, maybe a Vector? They were all running monoshocks. If everyone has the same handicap, then the playing field is equal.

I can tell you that in 1991 and 1996 Van Diemen brought the mono to the US and in both situations it was considered a worse car than it's predecessor. The '96 Van Diemen won races in '96, mainly by the factory team. They had the best drivers, best engines, and best teams. The 'old' cars were ran by guys who had less money, less power, and lesser teams. In '97 Van Diemen changed back to a 4 shock arrangement for the US and has never tried the mono again.

In the US, the tracks tend to be bumpier than the Euro tracks. This probably is another reason why the mono is such a massive disadvantage in the US. Regardless of where you're racing, though, there are advantages to riding curbs and controlling the car over bumps. If a 4-shock car is losing to a 3-shock car, then the guy with the 4-shock car doesn't know what he's doing. That can either be driver or engineer, but someone is not getting it done.

To answer Zac's question, the 1800 Zetec cars have very little aerodynamics at work, and I have yet to stumble across a racecar that has too much tire. The Zetec cars ran a treaded street tire, so they wouldn't fall into that catagory for anyone.

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#12 zac510

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Posted 26 May 2006 - 08:56

Thanks, nice discussion. Hopefully soon I can check out the Pilbeam and Gould top end hillclimb chassis soon but after this dicussion I expect they are running a two spring front setup or maybe even 3.

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#13 GregorV

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Posted 26 May 2006 - 09:35

Fat Boy, thanks for your explanation. I was thinking that I am missing something patently obvious when thinking that the monoshock arrangement is horribly wrong; good to see I am not the only one ;).

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#14 Lukin

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Posted 26 May 2006 - 10:16

The VD RF94's came mono-shock to Australia and a fair few of them were converted (Stealth Spec it was called) and are still run competitively in state series.

At the AGP I noticed a few of the older F3 cars ran monoshock. Never worked on a car with a monoshock.

Im guessing they would have a pretty stiff front ARB to maintain a sensible roll stiffness distribution?

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#15 LMP900

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Posted 26 May 2006 - 13:38

Being involved in both Euro and British F3, I can tell you that most Euro cars use the mono, and most British cars use twin, and this also applies to the teams I'm working with. Pragmatically, the worst thing you can do is try to test the two systems back-to-back, because they both work well, with one superior depending on the track and the ambient conditions: you end up misled and confused. The advantages of the mono have been touched on here - the de-coupling of spring and damper in roll and heave. In my opinion, the decoupling of the damper is the more important, because the roll inertia of these cars is very small compared to the heave inertia. A well-engineered 3-shock arrangement may combine the good points of both, but it would also be expensive and heavy and raise the CG. Having said that, such a system will be seen in F3 this season...

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#16 Ross Stonefeld

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Posted 26 May 2006 - 14:15

The British teams using twin, is that a relatively new thing? For as long as I could remmeber they were running monoshocks, even the Lolas, which surprised me.

Fat Boy / Ben I agree with you regarding the 4 vs 3, I just always wondered why such supposedly clever people didnt figure it out.

As far as Lola v Dallara, its impossible to say, Lola has never had a really serious go at it. Not to criticise them, but they've always been a few steps behind in having any chance against beating Dallara.

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#17 LMP900

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Posted 26 May 2006 - 14:49

Twin isn't that new in British F3.

The British series is off to Pau next week, probably the most bumpy track in Europe, and I guess most people will opt for twin-shock. However, Knockhill is also a pretty brutal track (leaping over kerbs and such), yet a monoshock car was quick there last year. Having said that, "my" car (on twin) won both races...

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#18 LMP900

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Posted 26 May 2006 - 18:08

Another advantage of the mono (as engineered by Dallara) over the twin is its facility to shape the roll stiffness/displacement curve. The belleville washer stacks that are used for lateral springing can be preloaded, either independently or oppositionally. So you can have a curve that is linear, progressive or regressive. All you need then is the brainpower to compute the best set-up, and the track time to test it, so most people set it and forget it!

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#19 desmo

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Posted 26 May 2006 - 19:19

Aren't Bellevilles still common as third springs in F1? I'd always thought the ability to tune rate against position was the primary motivation. Easier to swap out discs than to mess with geometries.

Surely a monoshock setup is harder to completely lose the plot on as there are fewer variables to get wrong.

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#20 LMP900

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Posted 26 May 2006 - 19:35

I haven't seen an F1 installation that uses Bellevilles for roll, rather than heave, control, but there may be one out there. In heave, you never really look for anything other than linear or rising rate.

Regarding losing the plot - no, it's theoretically easier with a (Dallara) monoshock, purely because of all the infinite/double/rising rate/falling rate/zero roll stiffness options it provides. The trouble is, I don't think anyone really uses all its capabilities.

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#21 Andrei

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Posted 28 September 2006 - 18:18

Hello to all,

i've got inveolved in the Formula BMW in Germany and was looking now to make some basic calculation on the car to figure out some details about it.

The problem is that I have never worked with monoshock suspensions and do not realy know how to cuantify a single spring in the suspension. What I am looking for are some general hints to calculate the spring frequency, wheel rate and so on.
Obviously, I know how to do it for usual layout's with 1 spring on each wheel, but what are the non suspended mass, etc, etc, in this layout?

Thank you!

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#22 Greg Locock

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Posted 28 September 2006 - 23:11

Draw your suspension out at design. Now move it by say 10mm up. Now remeasure all the spring lengths. that gives you the motion ratios. Draw free body diagrams for each linkage, and you'll know the forces. Work back to the wheel centre, and you know your wheel rate. Then you can figure out the linear and angular velocities, and from that work out the unsprung mass. I usually use an energy approach for unsprung mass, that is, 1/2 * munsprung* Vwheelcentre^2=sum (all the rotational and translational kinetic energies in the system)

Note that with a third spring you'll get different unsprung masses in heave and roll.

or you throw the whole lot into an MBS modelling package and try and figure out what the results mean.

The first method is initially faster, reasonably accurate, and increases your understanding.

The second method is easier, reasonably accurate, and allows for quicker changes.

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#23 Paul Ranson

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Posted 29 September 2006 - 19:39

Thanks, nice discussion. Hopefully soon I can check out the Pilbeam and Gould top end hillclimb chassis soon but after this dicussion I expect they are running a two spring front setup or maybe even 3.

The Pilbeams are all 2 spring/damper fronts, sometimes with additional springs acting as droop limiters.

The Goulds (excepting the older Ralt F3 based versions) are all monoshock front and 2 or 3 spring with (so far) 2 dampers at the back. This is deliberate rather than for fashion or cost reasons.

Sort of shows front, http://2t4t.dnsalias...es/PICT2708.jpg

I can't find a good photo of the rear yet. It's possibly interesting because the third spring only comes into play after the downforce has built up. http://2t4t.dnsalias...es/P1020084.jpg makes a nice placeholder.

Paul

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#24 Andrei

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Posted 30 September 2006 - 15:26

Hey Greg,
thank you for your answer.
Unfortunately, I have lost you in the second row because I do not really understand what do you mean with a free body diagram.
And how do you calculate the translational and rotational energies in the system?

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#25 Greg Locock

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Posted 30 September 2006 - 22:27

An FBD is a picture of each mass, with all the forces acting on it. The vector sum of the forces, divided by the mass, will be the acceleration of the mass, the sum of the forces *moment arms +torques about an axis divided by the moment of inertia of the mass around that axis will be the angular acceleration. OK, that is very complicated, you need an applied mechanics book.

translational KE=1/2*m*v^2 for each mass
rotational KE= 1/2*I*w^2 for each mass

You know v and w because you've already worked out how far each part moves in a given time interval, from the deflection test.

Again, you probably need a mechanics book for that. I've no particular recommendation, the title would probably be "Introduction to statics and dynamics" or something like that. Check in the index, if it mentions coriolis, dot products and d'Alembert forces or pseudo-forces then it is the right sort of book. If it mentions Hamiltonians then it is probably too complicated.

You might get by with a copy of Shigley, that's what I use, but he pretty much assumes you know what is going on.

http://www.mhhe.com/...s/mech/shigley/

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#26 Fat Boy

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Posted 01 October 2006 - 05:29

[i]You might get by with a copy of Shigley, that's what I use, but he pretty much assumes you know what is going on.

http://www.mhhe.com/...s/mech/shigley/ [/B]

I second the recommendation. Shigley or Shigley and Mischkey are really good engineering authors.

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#27 Andrei

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Posted 01 October 2006 - 13:53

Thank you, now I have understood.
I hope to get all the required data next week and than be able to start make some calculations.

That Shigley book seems to be very interesting, think that I'm going to get one copy.

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#28 zac510

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Posted 03 October 2006 - 10:09

Originally posted by Paul Ranson

The Goulds (excepting the older Ralt F3 based versions) are all monoshock front and 2 or 3 spring with (so far) 2 dampers at the back. This is deliberate rather than for fashion or cost reasons.

Cheers Paul, I have since seen you and the rest at Gurston Downs a few months ago. I got a few good pictures of the Goulds close up but they just don't break down often enough so nobody takes them panels off

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#29 barthe

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Posted 01 September 2008 - 15:49

Hello From French

Do you speck French ?

How to calculate the monochock ? no software...

and How to calculate the RC ( roulis center) with triangle anti-cabrage...

thank you

pbarthe@cascades-europe.com