MONOSHOCK ??

[JagLite]

I have been unable to find ANYTHING on monoshock suspension design, theory, results, etc. I believe at least one car has used it and I would like to play with design but I hate to reinvent the wheel. Has anybody found any information? Can you give me a clue where to go to read up on it? None of our books have even a mention of it so I am guessing it is newer than the books.

Thanks!
James

[JagLite]

I have been unable to find ANYTHING on monoshock suspension design, theory, results, etc. I believe at least one car has used it and I would like to play with design but I hate to reinvent the wheel. Has anybody found any information? Can you give me a clue where to go to read up on it? None of our books have even a mention of it so I am guessing it is newer than the books.

Thanks!
James

[Mark TMV]

Google 'Dallara Formula 3 car' , you should be able to find some info/pics on monoshock setup. If I'm not mistaken they also use(used?) monoshock on their IRL chassis.

[drivetrainUW-Platt]

search this forum.... there was a big discusstion on it

[Erich Ohlde]

We ran a monoshock in the front last year and will be running it again this year. Our suspension guy last year actually called the Dallara guys to talk to them about their monoshock, they seemed to help quite a bit. If you want to talk more look me up at competition this year.

[EfiOz]

Speak to Jos Claes at Dallara. He's head of the F3 support team and he's always pretty helpful.

[jdstuff]

Try digging around for Formula BMW stuff as well....they're another pro-series (front) monoshock car.

[RacingManiac]

So are the Formula Renault 2000 cars.....the BMW and the Renault, though both monoshock, goes about it quite differently, IMO renault's design is more elegant...but probably harder to execute...

[JagLite]

Thanks!

Now I see it!
(Old movie, "The Hallelujah Trail")

James http://fsae.com/groupee_common/emoticons/icon_cool.gif

[mtg]

Things to watch out for:

- Massive friction due to poor load paths in a shuttle bar system (Formula Renault)

- Lack of roll damping. This is a large effect, and to compensate for no roll damping, the rest of the setup becomes pretty crappy.

The Formula BMW system works well to not produce much friction as it is a T-Bar ARB with the spring/damper connected to the rotation axis of the ARB. Although, it still has no roll damping.

[karter11]

One thing to keep in mind about the FBMW suspension is the extreme lack of suspension movement. It is extremely stiff in roll. I worked for a BMW team for some time this past year and we commonly saw front ride heights of less than 18mm, and no more than 21mm if I can remember correctly (Denver saw the highest ride height). What is most important to BMW suspension set up is bump and rebound settings, but even those don't make a significant difference. These set ups are definately suited for high speed corners and fairly smooth tracks. I'm not sure how well they would work on a slow corner, bumpy surface. I will definately vouch for the effectiveness of the FBMW suspension as we commonly saw sustained g loads of 2.2 and above with the limited aero package we had to work with. But the rear double shock configuration is just phenominal, and overpowers the front end. Just something to keep in mind,

Bill Valet
Lehigh FSAE

[Garlic]

Monoshocks work and have recently been more and more popular on SPEC cars for cost savings reasons. FBMW, Formula Renault, IndyPro, etc.

You have to look VERY hard to find a series that allows a variation of shock options and has a monoshock coming out on top. Something to keep in mind.

The only time I've seen it used when it wasn't required was in F3000, and I never saw it as a common thing. Heck you see three shocks sometimes there.

[Varg]

In Formula Vee some people run a monoshock and no anti roll bar so the cars has no roll resistance at the rear end. The reason for doing it like that is because if one of the cars ends has no roll restiance no weight will be transfered diagnoally like on "normal" cars. That means that the amount of weight transfer at each end of the car is equal to the amount of weight on that end (on a car with 60% rear weight bias the rear will se 60% of the weight transfer). And that method has proven to serve their type of cars (lightweight, low powered, open diff) veary well.

Just something to think about

[Storbeck]

I thought that if one end of the car has no roll resistance then all of the weight is transfered on the other end. There can be no weight transfer if there is no roll resistance, since the weight transfer is a result of the resistance to roll.

However even with no resistance to roll from springs arb's etc, there can still be weight transfer from suspension geometry if your roll center is not at ground plane.

I suspect the reson people might do this in FV is because the rear suspension is swing arms that have a very high roll center, and therefore very high rear geometric roll resistance, so you need very little elastic roll resistance to balance the car.

could be wrong though, I have never had anything to do with a formula V (or any race car really)

Does anybody know if cars with monoshocks tend to have high roll centers on that end of the car?

[Erich Ohlde]

Seems like with a Vee rear monoshock and no anti-roll the car is going to lean to one side or the other, I have my doubts about people doing this and actually going fast.

[JagLite]

Very interesting.

I am not amazed that the designs work well, I am amazed that they work at all considering what must be a ton of friction, and what appears to me to be terrible load path angles. Of course, the less suspension movement, the less it would matter. And I am sure the designers of the systems I found (thanks for all the suggestions) worked through many versions to come up with the ones they use so they must work acceptably well.

I was designing an entirely different monoshock system, one where the bellcranks from the A-arms both push on a single shock, similar to the usual pushrod setup for two shocks. Actually it is a little more involved than that since each bell crank acts on a lever arm that allows one bellcrank to move independently without moving the other side bellcrank while compressing the shock.

My thinking was that by tuning the damping and spring rate for track conditions (straight line bumps, etc.) then when heavy braking & cornering forces come into play the shock would be taking all the load from the one side. No need for an anti-sway bar since the spring rate is now increased. This would also provide for adjustable roll damping as well. Or it might be better to tune the suspension for heavy braking and high G cornering which would make the straight line spring rate half as strong where the highest speeds are attained. Does my description make sense? It could certainly be done by using two shocks also just by connecting the bell cranks with one-way levers so that the loaded wheel is not just pushing the unloaded wheel down.

What do you think?

James

[Erich Ohlde]

I'm not really seeing why your spring rate would be changing.

With any monoshock system you need a rather stiff anti-roll so you can maintain body position otherwise your chassis will lean to one side or the other.

Do you having any pictures of your design or something close?

[karter11]

To be real honest with you, I would suggest against a monoshock configuration for an autocross car. Yeah, the roll rates might seem avantageous at first, but the speeds we are seeing in cornering do not favor a monoshock configuration. We typically see bumpy surfaces at competition which would suggest a double shock configuration to easily deal with different altitudes on each corner. Yes, a monoshock could work, but is it the best solution to slow, rough surfaces commonly seen at FSAE and autocross events?

Bill Valet
Lehigh FSAE

[Erich Ohlde]

I don't know if I would say that. We ran a front Monoshock on our 05 car and we got something like 18th in autocross and something like 9th overall time in endurance (I think). We did pretty well with that setup and we are using it again this year. Also our drivers feel like the car is much more planted in the front in slalom's. This year is going to be different because Ford's proving grounds are so smooth. Should be better for us.

[JagLite]

Hmmm, good points.

No pictures, nothing drawn up yet even. Just the 3D brain version so far. I will try to draw up something so you can see (perhaps) what I am trying to accomplish. However, it does seem much simpler to just go with the normal setup this time.

As for increased spring rate, what I was thinking is that for example: (same hypothetical car) a dual shock/spring using 200# springs will use the 200# per side (400# combined) in a straight line for bumps and braking, but in cornering roll, it drops to the 200# on the loaded side.

Same car with a monoshock with a 400# spring has the same straight line effect but when cornering, the loaded side would have the entire 400# spring available. So it would be similar to using an anti-sway bar without the additional parts and weight.

My example is ignoring partial loads and transitions into and out of the turns but I believe the single shock would still be an advantage then. Why? Because when tuning the damping on the shocks it can be overdamped when both shocks are absorbing a bump and underdamped when cornering and reacting to a similar bump.

Might just be easier to run another set of shocks without springs to tune the corner damping though. I am looking at this from my experience with the very rough parking lots that we use for the local autocross events. Frost heaves, cracks up to 3 inches wide and other problems that would not come up on a real race track. Overly stiff suspension and/or limited travel does not work here as the car bounces too much and the tires lose traction.

James

[Kyle Walther]

I may not be visualizing this correctly, but if both bellcranks are acting on a single shock and are some how decoupled. wouldn't you loose all control of rebound on the unloaded side when the loaded side takes control of the shock?

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by JagLite:
Very interesting.

I was designing an entirely different monoshock system, one where the bellcranks from the A-arms both push on a single shock, similar to the usual pushrod setup for two shocks. Actually it is a little more involved than that since each bell crank acts on a lever arm that allows one bellcrank to move independently without moving the other side bellcrank while compressing the shock.

My thinking was that by tuning the damping and spring rate for track conditions (straight line bumps, etc.) then when heavy braking & cornering forces come into play the shock would be taking all the load from the one side. No need for an anti-sway bar since the spring rate is now increased. This would also provide for adjustable roll damping as well. Or it might be better to tune the suspension for heavy braking and high G cornering which would make the straight line spring rate half as strong where the highest speeds are attained. Does my description make sense? It could certainly be done by using two shocks also just by connecting the bell cranks with one-way levers so that the loaded wheel is not just pushing the unloaded wheel down.

What do you think?

James </div></BLOCKQUOTE>

[JagLite]

I was wondering about that myself actually.
My whole idea may be unworkable. Like most of my "original" ideas. http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

I will have to make a model of it and play around to see if there is a way to do it that is simple. If not, well, back to the drawing board...

James

p.s. Thanks for not laughing at my ideas.