Why not a Monoshock?

[rjwoods77]

Hello,
Just wondering why more people have not tried a monoshock suspension. It seems like it would be good for this application. Loose a little independant wheel tuning for less weight, less cost and less design complication. Anyone?

[Denny Trimble]

It's been done several times including last year. Just make sure you have adequate, tuneable damping in roll...

[rjwoods77]

Tunable with a spring/washer stack on the pivot bar or a separate dampner. WHat do you fell the downsides of it are? Has anyone got it right?

[BryanH]

Rob, you should be asking why Ferrari run 3 in the front.

[Jon]

Generally with a mono shock, you have no roll damping. Whether or not this bothers you, is a decision you'll have to make. You can also have some stiction in the pivot block.

Now, a tri-shock arrangement will give you the benifits of mono-shock (seperating your roll and compression/rebound), but you're also adding an additional shock compared to a "normal" dual-arm, dual shock suspension. Additional weight, cost, and design...

[Kevin Hayward]

Rob,

I think the question should be how much weight you lose vs how much damping performance is lost. A MB shock is roughly half a kilo ... I think. Unless the car is simplified with mounts etc ... which could save more ... I guess.

How much lap time is that worth?

A car with ineffective damping in roll ... what is that worth?

I suppose that damping in roll is pretty important in cars that run on slow tracks with lots of corners ... lucky FSAE is not like that http://fsae.com/groupee_common/emoticons/icon_smile.gif

I have read a paper from a few years back that talked about Jordan's monoshock system. Apparantly the car was really good at high speed sections but lacked grip in low speed. When you think about it this makes quite a bit of sense. I'm yet to hear a decent argument for monoshocks on a FSAE car.

Hopefully one of the monoshock teams will post something in this thread. But unless there is more to it than saving 1/2 a kilo or so then I'd still think its a bad idea.

Kev

[rjwoods77]

Hey Kevin,
I hear what you are saying. I wouldnt just be the weight but the cost as well. Loosing 2 shocks would be tremendous on cost saving. But if you are a well funded team then questions like that never enter the equation. I am building on 8000 bucks. I am also working on the suspension to minimize roll. How effective this will be is an interesting question. We here at University of Buffalo are building something completely different than anything that has been done before. People will love it or hate. But cost is a big reason. The rear suspension has infinite roll stiffness but a completely ajustable roll center(like 1 foot below ground to 1 foot above ground) so I am hoping to work out a solution to maybe minimize roll angle of the car down to nothing much like the DJ Firehawk in Racecar Engineer. No I didnt model its suspension if you were thinking. I agree in a perfect world you should have a dampner for each aspect of the suspension but like much in Formula SAE, everything is way overkill. Just trying to grasp the performance loss if i went with the system.

[Denny Trimble]

When you consider the stiffness of the tires and your structure, nothing is infinitely stiff.

Just semantics, but in Pontiac I bet you'll have some displacement in roll http://fsae.com/groupee_common/emoticons/icon_smile.gif

Hope you're not running a torsen on that ATV rear suspension (just a guess).

[Charlie]

So all your roll stiffness is from hub, upright, suspension and deflection and tire stiffness?

So compliance won't be an issue then, because you won't have any? http://fsae.com/groupee_common/emoticons/icon_confused.gif

[rjwoods77]

Semantics but true. Nothing we are doing has anything to do with an atv. But keep guessing. I'll tell you this. The front bulkhead is inline with the front edge on the front tire in the side view. and has a 65 inch wheelbase. Target weight is 300lbs but we will most likely come in at 325lbs. By the way, love the time you took to make your site look nice. I refer to it all the time. So how did you like the fox shox you ran in 2003? That config in 2003 is one that I was looking into using. I just dont like having to put the rocker pivot and the upper shock mount in the middle of the crossbars between the front hoop and the front bulkhead without any triangulation. I guess thats why everyone runs their pushrod/pullrod setups longitudal.

[rjwoods77]

Charlie,

I am talking about working the front roll center with the rear to help minimize roll, along with the general stiffness of the rear. I am sorry. I didnt mean to say infinite, but the tire deflection will be the roll along with all the other factors. Still working on it. I dont dismiss things till I fully work them out. By the way, Auburn Baja are some of the nicest people on the planet.

[Denny Trimble]

Yeah, the 2003 UW car had serious installed stiffness issues. We learned not to do it that way anymore http://fsae.com/groupee_common/emoticons/icon_smile.gif If you pushed the car in slaloms too hard, it would continue "oscillating" in oversteer. Very odd. Our new car still does it, but much less, because the installed torsional stiffness is twice as much, but still not high enough.

The Fox shocks (at least the old ones) can provide much more force than you need on an FSAE car. But, we didn't like the force/velocity curve shape, so we switched to non-externally-adjustable penskes, with custom pistons and lots of shock dyno time. Not the easy way, but watching our car suck up the nasty bumps in Detroit made it worthwhile http://fsae.com/groupee_common/emoticons/icon_smile.gif

[rjwoods77]

"Serious installed stiffness issues"? Ocillating which direction, up and down or side to side. Are you saying that the lack of support points on those crossmembers was warping you front suspension "box" abd that caused the problems?

[Kevin Hayward]

Rob,

I suppose the cost issue is a valid one. But then if you can't afford two extra mountain bike shocks then I think your teams biggest issues are not technical. Maybe you would benefit by putting more emphasis on raising funds and taking a more conventional design approach.

I am interested to see the high roll stiffness setup. However I don't think it is the way to go at all. With the performance of a fsae car not really dependant on ride height control (ie aero) a little softer suspension will generally help grip.

Furthermore the stiffer the springing the more of an effect the compliance in the system will have. I would imagine to the point that despite your ability to change RC height the roll moment distribution will be effectively set by your weight balance and the amount of compliance and the ratio of compliance front to rear. I would imagine that you would have little ability to tune the RMD at all.

This is a pretty important thing not to be able to tune.

However any car that comes out at 325 lbs with a decent amount of power will probably get away with handling like a pig ... but I wouldn't expect it to dominate.

It appears that there are a lot of people that are prepared to acknowledge grip lost to increased weight but do not acknowledge the grip lost to increased tyre load variation, which is a function of springs and dampers. Probably because the latter is harder to quantify. Furthermore it appears that decent handling behaviour is also comprimised to reduce weight ... again a questionable practice.

Kev

[rjwoods77]

Kevin,
Thanks for letting me pick your brain. I am on a super steep learning curve and really trying to get a "full picture" view. I know all the aspects of the car super well except for suspension setup. I am really just trying to go cheap and light and see where that leaves me. I am not totally convinced that this is the way to design but I am starting here cause' it goes with the concept. The more I talk with people the more I find out I am just gunna have to bite the bullet and go with 4 shocks. Oh well. Gunna have to raise more cash. Won't really add too much weight I guess. Learning is what this is all about right?

[winnie]

Or could you get 2 shocks to do the job of 3?
A mono shock arrangment with a 'horizontally' positioned shock damping equally in extension/compression for the roll damping....
just a thought and not one i have spent time

[Denny Trimble]

Either way, you need at least 4 spring and damper units.

If you want to go ultra-light, use mountain bike air shocks. They're cheaper, too. Cane Creek make some, they got our '99 car to 5th place, but the air damping (!!) and high air seal stiction, plus built-in rising rate, and difficult "rate" change (equivalent to changing steel springs), made them far from ideal.

Even if you have a car that's very soft in ride, but almost infinitely stiff in roll, it will be difficult to drive. One-wheel-bump or warp from an uneven surface will cause much larger disturbing effects on the car. And the Pontiac surface is very uneven and bumpy.

Our '03 car had untriangulated boxes, with the shock and bellcrank mounts on the middle of untriangulated tubes. Horrible! Lost 50% of the frame stiffness through those mounts alone.

"Don't be that guy"

[Kevin Hayward]

Rob,

There is still ways to tune a car with "infinite" roll resistance ... just look at go-karts. These will namely be tyre size and steering geometry. For finer effects you would still have toe and camber angles. There is still certainly something interesting about the quick go-karts which would murder a FSAE car on a similar track ... even with less power.

However we have a bit of extra weight to carry and very different tyres ... but I do accept that someone may make the go-kart approach work really well someday.

But for now I think Denny has hit the nail on the head with the nasty effects of excessively stiff warp and single wheel bump resistance.

...

Denny: I'm not surprised to hear your comments about the air dampers. With such a small air volume the rising rate would alomst certainly be beyond what most people would want and seal stiction just cries out hysteresis. I'm sure oneday we'll get aorung testing one ourselves to confirm what you've mentioned.

Cheers,

Kev

[BryanH]

Denny, why did you need to change the penske pistons?
btw just got a book you may like,
FORMULA ONE unseen archives by Tim Hill
Bryan H

[Denny Trimble]

To increase the low-speed damping force, we had to reduce bleed, by making new pistons with fewer bleed holes.

Also, the shocks come set up uniquely for all four corners of an oval car. So, buy the shim kit too.

[fsae racer]

Denny, why couldn't you just have filled some of the bleeds with some jb. I've never tried it bc we are in fact just trying some new pistons with a different bleed config, but I have heard that it works just fine. Oh and, did the stock pistons have more than one bleed, if so, how many bleeds does you current piston have, if you dont mind sharing?

[Denny Trimble]

Yeah, I guess that's a possibility, but the pistons were so simple, I went ahead an made 20 in two nights.

As for the number of bleed holes, I'll leave that to your imagination... http://fsae.com/groupee_common/emoticons/icon_smile.gif

[drivetrainUW-Platt]

anyone have a picture of this monoshock suspension setup??

[rjwoods77]

http://scarbsf1.com/Monoshock.html
http://www.insideracingtechnology.com/phnxtst.htm

[rjwoods77]

One thing I was discussing with a couple of people was that they said that this does work good on these cars only because they are so stiffly sprung. I still love the idea of using it but I guess a leap of faith would be in order to just go with it and try it out.

[Eddie Martin]

Try to find pictures of the 2001 RIT car. From memory it had a monoshock setup and it was a very good car.

[rjwoods77]

I talked with RIT(i used to live in rochester) and they said that the judges torn them a new one cause' they "did it wrong". I dont know what this means but their car still did good.

[Denny Trimble]

I think their first iteration of that design (in Detroit) used no springs at all on the slider bar (no roll stiffness up front). If I were a judge, I'd be highly suspicious...

I saw rubber bumpers on their car later, in Rochester.

[rjwoods77]

The think did good though. Won or finished 4th in student. I think that was the year they one student so either their car worked good or the brits sucked ass.

[jonnycowboy]

I have some monoshock design ideas but I dont think my team is going to use them due to them wanting to stick with a more conventional setup. It dosen't look anything like the those pictures up there. Hehe I was thinking of patenting it but it's probably already been done before just i've never heard of it. I'll put up some pictures if you want. It's very light, one-spring, one-damper, and has very good anti-roll characteristics.

[Denny Trimble]

When you say "good anti-roll characteristics", do you mean independently tuneable ride and roll spring and damping rates?

[jonnycowboy]

nope!! hehe.
It involves only one spring and one damper (the damper set inside the spring, however this is not good for the damper as the spring has a tendency to rotate when compressed, which is bad for the seals on the damper). This can be changed at the detriment of weight to have 2 dampers on the sides of the rockers. The spring is tuneable in that the spring mounting plates at each end of the damper are on a threaded rod and so can be moved around.
I've attached a picture, please comment it's my first real idea of a radical/different suspension component!
ok so what we have here is two variations on one design. The top one, (my favorite!! http://fsae.com/groupee_common/emoticons/icon_smile.gif ) has one damper and one spring, all mounted on top (providing a neat tunnel for pedalbox) with two rockers mounted near the sides of the frame. The bottom is the same except with independent tunable dampers. The big benefit I see with this is that in corners your inside front wheel tries to lift off the ground - this movement is counteracted by the spring, pushing it back down as well as providing much-needed downforce on the outside front wheel. when the car pitches forward or backward the spring compresses or pulls apart which, using a stiff enough spring will provided enough absorbsion.

[jonnycowboy]

if you have problems seeing the picture i'll try working around it.

[Denny Trimble]

It's asking me to ender my username and password to redbridgesolutions.com.

[Denny Trimble]

I'll give you the benefit of the doubt and assume that the red pushrods are supposed to connect to the lower a-arm, not the upper. Then they would actually be able to support vertical wheel loads.

Still, there's no way this system will resist roll. The whole shock / spring will move laterally, freely, in roll.

[Angry Joe]

In '03 when we were figuring out how to package our large Penske dampers, we messed with the idea of a monoshock connecteced between two bellcranks that provided no roll resistance. Roll stiffness would be provided by a second spring in tension that would resist roll movement (it's hard to explain without a drawing), or by a conventional torsion-type anti roll systen.

We abandoned it because we didn't see a way around adding a second damper, and in the end little if any weight was saved. It was certainly not worth the risk of unpredicable handling characteristics.

It would have been fun to mess with it more, but as it is it never made it past the "doing sketches in the middle of Dynamics class" phase.

[jack]

i thought i would post this picture, not really sure whats going on though.

--allright, it wont work, just have to copy and paste it:

>>>http://car-racing.bravepages.com/20020525-1/15-F3.jpg<<<

[V2 - Italy]

Look at this Formula Renault:

http://www.tatuus.it/HOMEing.htm

and the Dallara too:
http://www.dallara.it/racecars.cfm

We used a mono shock pull actuated, if you want we'll post some pics.
We like it for lightness and reliability.

V2

[coldfire]

our team is starting to discuss monoshock designs...i have found a few setups of other Formula cars using this...

2000 Dallara monoshock front-suspension on a IRL car (coilover):
http://www.insideracingtechnology.com/Resources/monofrnt.jpg

2000 Dallara monoshock rear-suspension, (with seperate springs and dampers):
http://www.insideracingtechnology.com/Resources/monorear.jpg

1997 Formula renault monoshock front-suspension:
http://www.rallye.co.uk/racing/images/fr_frnt.jpg

1994 Formula Ford monoshock front-suspension:
http://www.race-cars.com/carsold/other/vtf941/vtf941ph.jpg

1999 Formula 2000 monoshock front-suspension:
http://www.insideracingtechnology.com/Resources/f2vdmono.jpg

Formula 1 concept monoshock suspension:
http://peter.skorvaga.szm.sk/monoshock_black2A.jpg

[Crimson Racing]

So, as innovative as this looks, I don't understand it's benefits. I'll be the first to say that the majority of y'all know more about suspension design than I do, but where are the performance advantages of this design. Weight would be negligiable because of the massive bracket to house the system and cost is a reltive term also.

[mtg]

The advantage is if you can trick your competitors into using a monoshock design, they end up with a system that has no damping in roll and lots of friction from bad load paths and a heavier front suspension because of the ginormous brackets needed to attach all that crap.

The advantage is to reduce the cost of a spec racing series that uses very expensive dampers. Maybe you could argue that it makes the car easier to setup also.

If you used a non-conventional monoshock system that had improved load paths and roll damping, there's the possibility of producing a system with complete control over spring and damping rates in ride and roll independently of each other.

But if you're going to go through all that trouble, just build a Kinetics style system like UWA.

[js10coastr]

Originally posted by mtg:
The advantage is if you can trick your competitors into using a monoshock design, they end up with a system that has no damping in roll and lots of friction from bad load paths and a heavier front suspension because of the ginormous brackets needed to attach all that crap.

The advantage is to reduce the cost of a spec racing series that uses very expensive dampers. Maybe you could argue that it makes the car easier to setup also.

If you used a non-conventional monoshock system that had improved load paths and roll damping, there's the possibility of producing a system with complete control over spring and damping rates in ride and roll independently of each other.

But if you're going to go through all that trouble, just build a Kinetics style system like UWA.

...or design the car to work like a go-kart, and not allow the suspension to work in roll. Not that any team from CA has tried that with a 450 single, and a carbon front half weighing in at just over 300 lbs.

[HenningO]

The advantage is if you can trick your competitors into using a monoshock design, they end up with a system that has no damping in roll and lots of friction from bad load paths and a heavier front suspension because of the ginormous brackets needed to attach all that crap.

Too bad our system is lighter then our last years car traditional setup. Too bad we can tune roll stiffness without altering wheel rate. Too bad we have adjustable roll damping. Too bad we've reduced overall suspension hysteresis. But I guess you're right... http://fsae.com/groupee_common/emoticons/icon_wink.gif

[JHarshbarger]

Care to explain your setup?

[Marshall Grice]

Originally posted by HenningO:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The advantage is if you can trick your competitors into using a monoshock design, they end up with a system that has no damping in roll and lots of friction from bad load paths and a heavier front suspension because of the ginormous brackets needed to attach all that crap.


Too bad our system is lighter then our last years car traditional setup. Too bad we can tune roll stiffness without altering wheel rate. Too bad we have adjustable roll damping. Too bad we've reduced overall suspension hysteresis. But I guess you're right... http://fsae.com/groupee_common/emoticons/icon_wink.gif </div></BLOCKQUOTE>

alright, one down...150 more to go. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[onemayonaise]

Hi,
i'm new in the forum and i am from the Politecnico di Milano, Italy.
About a monoshock system, i have designed the one installed in our 2007 car: a single unit spring/damper is mounted transversally with respect of the car centerline, activated by bellcranks. bellcrancks activates also a torsional bar through blade bars. the roll damping is obtained with motorcycle's steering dampers rigidly mounted with the bellcrank pivots. we do not save too much weight... but in this manner roll stiffness is completely unrelated to ride stiffness, and the vehicle's ride hieght could be easily changed by increasing the spring preload.

the system is under construction right now... i hope that it will work... http://fsae.com/groupee_common/emoticons/icon_smile.gif

[HenningO]

the roll damping is obtained with motorcycle's steering dampers rigidly mounted with the bellcrank pivots

I take it you are using rotational dampers?

[onemayonaise]

that's right, it is the Ohlins SD431 model

[onemayonaise]

However, i've tried with a multy-body model, to obtain a roll damping with a linear damper. i've tried to do my best with the sketch below http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif
if you use two symmetrical and mirrored bellcranks, and connect the upper part with a linear damper unit, (the horizontal upper line), this unit will take the ride movement. if you connect the upper left joint of the bellcrank with the mirrored point on the other one (the diagonal central line), this unit will take the roll movement and, in the model, it doesn't work while riding (and viceversa...). the idea was not utilized due to packaging problems...

http://img127.imageshack.us/img127/5003/damptt2.jpg

[Rex]

I'm not sure I see how the design sketched above can fully isolate ride and roll. i.e. at first glance, it would appear that ride bump would "pull" the roll damper as well. Unless you just assume that the rising rate/falling rate action there is not significant - which may be the case depending on the actual angles and dimensions involved.

I don't have time right now to sit down and sketch it out myself, but intuitively I can't see it working as described. Of course I realize it's not to scale or anything, but can't envision a scenario where you wouldn't have some kind of rising rate/falling rate issue.

If I'm looking at it wrong, someone please feel free to point me in the right direction.

[onemayonaise]

in these days i'm a little busy (i will graduate this thursday... http://fsae.com/groupee_common/emoticons/icon_smile.gif ). after that i will try to recover some graphs about the simulation mentioned above (i tested it about one year ago...).
maybe the "lucky" point is that i tried it with two 'linear' bellcranks, with right angles between the elements... there was a little pull of the roll damper while riding but it was almost neglected.

[Jerry Lee]

This is bringing up dead threads, but read "Competition Car Suspension" by Alan Staniforth. He has a section on front monoshock designs that had been informative.

I saw pictures of FSAE cars with rear monoshock suspensions. I wonder how much this helps when you can design the rear suspension pretty much however you want..

[flavorPacket]

read mtg's post at the top. he's right.