Starting Suspension

[typeh]

We are second year team with totally new members.
my questions is about suspension. We started our work based on last year suspension design and just tested it on Lotus suspension and played with geometry to optimize curves and are waiting tire data to finalize it.
I think in this way we are not going in right way as we didn't started with traditional way (front view geometry/ side view geometry/ 3d plans then optimization).
Are we working on good track? and please supply me with advice you can

thanks

[JDS]

That completely depends on how well the suspension was designed last year I suppose. If it was designed well last year, for last years tires, I would not wait on getting tire new tire data before finalizing the designs. The differences will not be big enough to justify moving on with other designs.

[Chris B]

yeah i agree with JDS it totaly depends on the previous car and how much info/data etc you have about that car and how it ran.

im currently 2 days out from finishing a final year project designing our teams 2012 suspension and we started first off by identifying what the problems were with the current suspension. that then set the tone for what we'd spend the year trying to fix. after that we tried to get as much data on the 4 physical tires that we had on the car at comp last year as possible (i.e temps, how worn the tires were, how hard, wear patterns, etc). from those two tasks we were then able to work out what we wanted the new suspension to do.

[typeh]

Thank you a lot.

The car wasn't working due to problem in half shafts and it wasn't built on tire data. would that change anything?
so out task now is to optimize curves only? no more?

[M. Nader]

Hi i think we are more or less in the same boat, we are from Cairo University

regarding your question, I am no expert as i don't have enough experience but i know there are a lot of ways to design a suspension, you can adjust the curves with no tire data and this way you would have a very functional design but you will not be optimizing the use of your tires, which is quite suitable for teams of our current state (starting). just a word of caution i was told before: Tire data is not an easy solution and it certainly is not instant as you will need to work on it LOTS of time just to be able to get near what you think you need, You guys have more experience than us so my humble opinion is just to fix what was broken and improve things and then think about optimizing. You want tire data but you don't need it, this should be your selection criteria. and if you decide to go for it just make sure that you have enough time to be devoted to first understand the tire data and then to implement it in your designs.

Again I am in no position to give you advice as your position is better than ours since you have more experience, I am just trying to be helpful.

[typeh]

Thank you Nader for your interest.

Tire data is very important starting from basic decisions on your system to advanced and complicated calculations to know how your system will perform and make best use of tires as you stated.

We try not to do mistakes our older team did. We reached good curves but want optimize our design.

rbna m3akom we m3ana isa http://fsae.com/groupee_common/emoticons/icon_smile.gif

[RollingCamel]

Hmm....someone scrutineering the dark side of my work...http://www.insektenfang.com/ipforum/public/style_emoticons/default/whistle.gif

Beware! It is a land so dark and dangerous that you will need a complete redesign. I'd do that myself.

PS. Did you try to draw a random geometry in SW? Using a kinematics software without before drawing it yourself is an inverted operation. Check RCVD chapter 17, iirc, and see if you can draw it right. Assume anything, just do it to know how to learn how to draw it.

[typeh]

Akram you mean by redesign it tire data or that way we worked isn't right?

We optimized curves we had from your car but almost changed all data such as KPI,castor,..etc

I am not worried about sketching it in solidworks as if we start by sketch we will modify it depending on optimization through Lotuse right? , but i asked to restart work we did if we aren't right. Waiting your advice.

[RollingCamel]

We didn't know what tyre we CAN get and wether we would be able to get any racing tyres at all, many thanks to our sponsor (really you should give them special treatment, they will support you in the future if they get more in return). So without knowing what tyre we will be using and time was running out we had to start something. I used some basic recommendations as not letting the wheel get into positive camber cornering, decrease bump steer to min and have good camber change range (subjectively).Packaging and rules template volume was kept in check as possible and tried to properly transfer the loads into the chassis.

Anyways, if you have looked at the car you'll see that the wheel packaging is crap and the dampers fixture location should be changed. Every small change will change the geometry. Furthermore, in reality you'll be very lucky to get anywhere near the theoretical design.

You should be worried about sketching in SW, it is called suspension geometry. Where is your geometry? The kinematics software is a simulation program. How can you simulate if you don't have the object you want to simulate on? How will you check the clearances and etc?

It can't be done in reverse. Stop looking at the previous work, it will poison and limit your thoughts. Why do you think I didn't give you the 3D model?

[M. Nader]

I would recommend checking out the "why do we need tire data" thread, should help you a bit know what you want from what you need

[RollingCamel]

Take care that there tons of other small details mostly clearance and manufacturing issues that will break your design. I'd recommend not to spend too much time on curves and theory work and learn what will make a car work. There is no optimum result just goal priorities, compromises and time limit.

[typeh]

If i don't realize tire data importance won't waste money neither time to get it.

[RollingCamel]

I'm not talking about tire data, sure the tire data is utmost important but also knowing how to use it and understanding that a good deal of the job remains after cars start rolling. You will be working on assumptions that will depend on how close it is to the finished product. It requires testing and experience. You will assume target weight and dimensions while not having most of the components weighed and placed in position to get a close CG assumption.

You will need some time to understand tire models and how to utilize the data, then look at curves and data coming out of the kinematics software. You'll need to set a strict time limit for it which I would give one month from now, since you really need to start building the chassis already.

[typeh]

We are already took assumptions, targeted values for C.G height and that stuff and did preliminary calculations according to it and waiting tire data to confirm assumptions and modify it. We aim to finalize all maximum 2 weeks after getting tire data. I'm working according to your advice on sketching geometry in Solidowrks.

Thank you rolling camel http://fsae.com/groupee_common/emoticons/icon_wink.gif

[LemonFool]

We started our work based on last year suspension design and just tested it on Lotus suspension and played with geometry to optimize curves and are waiting tire data to finalize it.

Based on this statement, it sounds like you're in better position to move on with your design than wait on tire data. Although it's hard to know what information last year's design incorporated, and the information you gathered, I would assume based on some statements the necessary information isn't there. There are more basic things a second year team need.

I think Nader and RollingCamel have made some great points. I'd listen to them from a practical perspective. You're better off with an extra month on a reasonable suspension than 3 months behind on a theoretical attempt. Unless you're on a multi-year plan, you should be starting the chassis. A month to incorporate tire data is extremely optimistic. If you know RCVD inside and out, intimately know a number of software programs to incorporate all of the information, and have little time taken up by school, a month could be done.

Otherwise, I would plan and learn for next year with tire data. There's no doubt the tire data is important for a thorough design, but working out major problems with last year's car sounds like greater importance. Without the knowledge base other teams have from senior members/faculty, you're looking at months of comprehending the information and working with models you set up, not programs that attempt do it for you (G.I.G.O.).

It's all a trade off. You have lots of time and money ahead in tire data for 10-20% gain, you have lots of time and money in fixing some of the other suggestions like improving your manufacture, and your mentioned drivetrain failures.

[typeh]

We are building totally new car so we don't solve problems with old car. So my question was obvious that working on last year geometry and modifying them is right or better start again.
I'm not going to repair car or power train or that stuff.

[RollingCamel]

I'm talking from a design point of view, you need to start the design from scratch.

[typeh]

I would like to see your opinion about results which reached
front:
http://imageshack.us/photo/my-images/265/frontddy.jpg/
http://imageshack.us/photo/my-images/151/front2jn.jpg/

front track 1300 mm
front roll center 64 mm
camber -3.5 deg
toe out 2 deg
toe change range 0.07 deg
with enough anti-dive

Rear:

http://imageshack.us/photo/my-images/864/rear2z.jpg/
http://imageshack.us/photo/my-images/856/rearz.jpg/

rear track 1200 mm
roll center 73 mm
toe zero
toe change range 0.04 degree
anti-squat 13%

is roll center height difference good? i think difference should be a bit more

is toe change good? i think good but rear wheel toe out in case of bump and as mr.Pat mentioned before car will be unstable if toe out in bump but even if it's in maximum bump 0.04 deg?

camber change is high i.e from -5 to -2 things like this. i don't care about it as it stays negative .am i right?

[Zac]

For what is essentially a first year team, the numbers you are quoting are fine. What is a lot more important is figuring out how to package components, properly react loads into the chassis, and work out some efficient manufacturing processes in order to actually have a running car at competition.

[typeh]

thanks now working on chassis but if there is something to modify so we must do it.

[Z]

Originally posted by typeh:
I would like to see your opinion about results which reached

typeh,

Your images don't appear on my screen, so it is hard to form an opinion.

Nevertheless, I guess you are using a double-wishbone suspension.

Why?

But if so, then why are your "roll centres" (or n-line slopes) so high?

And why have you chosen rear bump toe-out (albeit, negligibly small)?

All the above choices are unjustifiable, IMO.

Lastly, I hope you have already done the "holistic" design of the car? If so, then what is it?

Or to put it another way, have you read Geoff Pearson's "Reasoning..." thread?

Z

[arohit1911]

Images not visible.
Heed RollingCamel advice. You can design infact the whole car from tire data.Suspension,steering,drivetrain gear ratio,chassis are the things that even I know. But I will not put my 2nd year inexperienced resources to this task. Your task should be to improve the packaging and reduce the weight. Optimization from tire data and by data acquisition should be your last frontiers.

[typeh]

Sorry i will try fix pics and here are pics for toe results in bump and roll
http://imageshack.us/photo/my-images/21/frontrei.jpg/

http://imageshack.us/photo/my-images/15/rearxy.jpg/

http://imageshack.us/photo/my-images/607/toef.jpg/

http://imageshack.us/photo/my-images/412/toer.jpg/

i hope it works and will upload pics again but i tried it and worked by right clik on it and open in new tab

[typeh]

pics of previous post:
http://imageshack.us/photo/my-...es/265/frontddy.jpg/ (http://imageshack.us/photo/my-images/265/frontddy.jpg/)

http://imageshack.us/photo/my-...es/151/front2jn.jpg/ (http://imageshack.us/photo/my-images/151/front2jn.jpg/)

http://imageshack.us/photo/my-images/864/rear2z.jpg/

http://imageshack.us/photo/my-images/856/rearz.jpg/

[typeh]

Originally posted by Z:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by typeh:
I would like to see your opinion about results which reached

typeh,

Your images don't appear on my screen, so it is hard to form an opinion.

Nevertheless, I guess you are using a double-wishbone suspension.

Why?

But if so, then why are your "roll centres" (or n-line slopes) so high?

And why have you chosen rear bump toe-out (albeit, negligibly small)?

All the above choices are unjustifiable, IMO.

Lastly, I hope you have already done the "holistic" design of the car? If so, then what is it?

Or to put it another way, have you read Geoff Pearson's "Reasoning..." thread?

Z </div></BLOCKQUOTE>

better control for wheel and packaging and roll center slope is very small just 4 mm or 3 mm difference between front and rear and i tried to make all toe change negligible as it's desired to remove effects for bump and roll steer to improve stability.

[Z]

typeh,

You are going about this "suspension design" the wrong way. I know this because of the number of times you use the word "optimise".

Let's just focus on the RC heights. As you know, double-wishbones let you have the RCs above ground, below ground, or pretty much anywhere.

So why have you decided they should be 64mm front, and 73mm rear?

You say "better control for wheel and packaging", but frankly, that is meaningless.

I suspect you have simply thrown some darts at the dartboard and written down the numbers. I use this system when doing my tax return http://fsae.com/groupee_common/emoticons/icon_smile.gif, but it is not a good system for suspension design. The Design judges will recognise your lack of understanding and award low points. Worse yet, your car will recognise this, and will handle like a dog.

So, as practice for when you are in the Design tent at the end of the year, try now to give a rational justification for why your RC's are as high as they are.

Or better yet, think about where else they could be, and what would be the consequences.

Z

[typeh]

as i stated earlier i worked on old geometry and i know it was mistake and not right sequence to design and had to finish it quickly to continue work in other parts and others here also advised me optimize old graphs and they do same if i have chance to work in same project next year of course will do the right way as rolling camel stated and as shown in RCVD.
roll center height in my case was number i try to reduce and make different between front and rear small without loss performance of other terms and i know it's not the right way but had to accept it. http://fsae.com/groupee_common/emoticons/icon_frown.gif and also get best performance from that system.

[Z]

typeh,

I have tried to help you, but with no result. RollingCamel and LemonFool have also given you useful advice. Geoff Pearson spent a lot of time on his "Reasoning..." thread, mainly to help new teams like yours. Unfortunately, it seems all this effort is wasted.

This is not meant as a direct criticism of yourself. The criticism is directed at your whole team, or whoever are the most influencial members.

Your team's problem is that it has been too lazy to do the hard thinking at the beginning of the project. Instead, your team has decided to take the easy option;

"We will keep doing what we have always done, but this year we will optimise everything!"

Of course, the end result will be "... we will keep getting what we have always got...", which is failure. And that will come after a lot of very long hours of very hard, but ultimately futile, work.

I know this is only your second year. But it is very likely that next year will be the same. And the year after......

The really sad part is that it seems that your society is currently going through a similar situation. There is the opportunity for a fresh start, but it looks like all the same old mistakes are being made again, and you will all end up in the same place you started.

Z

[typeh]

yes i know it's my team mistake and being lazy of suspension guy who made us late for months and months with no results and i had to finish it as quick as i can for chassis team. whole team will loose because of this and i appreciate your advice and if have time will try start this design from draft. one of horrible things that we had no solidworks for it and had to export points to solidworks i will try work on it these few days and see if i get results and will share it would like to see your opinion.
thanks for help and criticism it's severe but all what u said is true.

[RollingCamel]

I was really frustrated to know that you managed to get our model and use it. What you did, or trying to do, is to polish a turd and the polishing process isn't even clear.

I'm more and more frustrated when all the advice fall on dead ears, and repeating the same mistakes we've done.

Yes, I didn't receive well my cousin's advice too, but I had my reasons that 8 years difference is huge gap between what Egypt was and is.

Anyways, thinking positively, the best part of the learning process comes in you start designing for manufacturing and glad that you reached it. This is the fun part.....

[typeh]

Originally posted by RollingCamel:
I was really frustrated to know that you managed to get our model and use it. What you did, or trying to do, is to polish a turd and the polishing process isn't even clear.

I'm more and more frustrated when all the advice fall on dead ears, and repeating the same mistakes we've done.

Yes, I didn't receive well my cousin's advice too, but I had my reasons that 8 years difference is huge gap between what Egypt was and is.

Anyways, thinking positively, the best part of the learning process comes in you start designing for manufacturing and glad that you reached it. This is the fun part.....
Rolling camel i fought but you know whom you should blame. last meeting we stayed hours but sorry for wasting your time they did what they want.