quote:

You (and Matt) say that my solution (a direct-to-wheel coilover with no rocker) "would probably end up heavier". How so? I would take your existing coilover, attach the bottom 1/4 of your pushrod as an extension of the damper shaft, and throw away the upper 3/4 of the pushrod, the rocker, and the rocker mounting bracket. Surely this is losing weight? Furthermore, I would attach the coilover to the chassis just above the upper-wishbone rear chassis mount, which is already a "strong point" and probably part of your dashboard bulkhead (or front-roll-hoop?). Moving this coilover chassis mount closer to the centre of the car makes for a shorter stressed chassis, so less weight again (do similar at rear). Also this angle of coilover is more aligned with the worst case forces on the front wheels (ie. from wheelprint to CG), so it reduces the loads on the lower wishbone, so again less weight.

Z,

We've heard volumes about what you would do?
Blah, blah blah...I think that you offer some good insight and ideas. But, What have you actually done? How have your projects performed?
Care to put your money where your mouth is? Are you actually gonna build an FSAE car?

Chris

Hey Z,I guess we agree somewhat. I considered using a shock extension similiar to what you described, but was concerned about puting the buckling load on the shock, so we did this.

Motion ratio almost exactly .5, and very linear.

I hope this image thing worked out.

http://photobucket.com/albums/v191/doc1320/FSAE/?action...current=100_2735.jpg

Chris,

Am I "actually gonna build an FSAE car"? No. I explained this before, I am not eligible - I left school probably before you were born . I could probably sign up for some kind of teaching role at my old university and get involved in FSAE that way, but I'm too busy building other stuff (well, when I'm not in front of this screen!). When I finish this house and another shed, and some other stuff, I'll get back into off-roading...

Anyway, I have ulterior motives for my postings here. I have become bored with a lot of modern motorsport, especially circuit racing, and I want to see something interesting/exiting! Where are the Colin Chapmans and Jim Halls, and all their radical cars? They are certainly not to be found in mainstream road racing (there is some interesting stuff off-road). There is some mild innovation in FSAE, such as CVT's, but even these have been around for ages (unfortunately, the boneheaded organizers of most current formula (eg. FIA) have banned them!). Trying yet another variation of a pushrod and rocker, even if it is in carbonfibre, is NOT innovation - it is just following fashion.

Worldwide, there are probably ten thousand bright, well-educated, young students involved in FSAE. Because of the necessary turnover, in five years time there will be another ten thousand. Surely some of these students can come up with something really new or exiting? I'm thinking of something that so dominates the opposition that the organizers will have to ban it (like many of CC's or JH's creations). Would this be a bad thing for the builders of these cars? No! Forcing a rule change is undoubtedly the best compliment you can get! And since you are out of the competition in a few years anyway, the more restrictive rules don't matter.

To finish this rant, I realise that a few of you have taken offense to some of my criticisms/comments. Get used to it guys, it is going to get much worse when you get a "real" job . My intention is NOT to be a nagging, critical, pain-in-the-arse. Instead, I am trying to provide a supportive voice to those who want to build a slightly "different" car, in the hope that they can get an edge on all those "standard car" teams out there.


Storbeck,

Yep, good solution (IMHO). Simpler, stiffer, less friction, etc., etc., than a pushrod/rocker. Nice graphics too!

Did you have any trouble getting it past the "design review committee" (aka the "fashion police")?

Z

quote:

Originally posted by Z:
My intention is NOT to be a nagging, critical, pain-in-the-arse. Instead, I am trying to provide a supportive voice to those who want to build a slightly "different" car, in the hope that they can get an edge on all those "standard car" teams out there.

Z, after reading quite a few of your posts and being quite annoyed with you more than a few times, may I offer some advice.

I think you have good points and, at least to some extent, the direction you are trying to lead anyone that will listen is a good one.

But damn, the way you do it is awful. Your comments come in threads where people are trying to introduce thier car, put photos up, show off thier hard work. People have a hard enough time taking criticism from design judges, mentors, people they are face to face with, and (usually) have at least some respect for. They are much less likely to be receptive to someone they've never met, know nothing about, and has nothing good to say.

As closely knit as the FSAE community seems to be, you don't just offend that particular team, but most everyone else too!

Of course people get criticism from your boss, parents, etc. But either they respect those people or they at least respect the fact they have to try and listen. If you are faceless and nameless, you better be tactful if you want to sway opinions.

I don't suggest you say nothing. If you see something that 90% of FSAE teams do, and you think it makes no sense, start a new post. make an arguement. People will listen and this is a great place for discussion when there isn't percieved ill will.

Charlie,

Sure, I'm not tactful, but then again I'm not trying to be. I'm not trying to sell anything here. Since most readers of these posts are adult engineers (and not little children, or menopausal women undergoing stress counselling), I really don't think they should get too upset when their designs or pet ideas are questioned in a rational (and frankly, rather boring) manner. Like I said, it gets a lot tougher when you move into the real world.

Most of my "criticisms" have actually been in the form of questions along the lines of "I can't see a reason for that part. Please explain how the extra weight/complexity/cost of that part improves the car's performance?". Apparently Socrates' philosophical style was to walk the streets of Athens asking people various questions about their beliefs. Then, after Socrates asked some deeper questions, the person would often contradict themselves, and thus find out for themselves that their original opinion was wrong. This is a legitimate and well respected method for getting at "the truth" of a matter (it is called the Socratic method). Of course, when Socrates was about 70 the government of the day decided that he was guilty of shit-stirring or some such crime (actually "impiety and corrupting the youth"), and sentenced him to death. Given your above post, Charlie, I wonder if our modern society has progressed?

Getting back to pushrods and rockers. I've asked "Why?" in two threads now, and I still haven't heard any compelling reasons for using them. Since, as you say, ~90% of the cars are using them, and there is at least some doubt as to their benefit, then shouldn't there be more discussion of their merits, or otherwise (of a boring, technical, and unemotional nature)? You suggest that I have "nothing good to say". Well, I pointed out many advantages of NOT using rockers, and I suggested a possible alternative. I also said that I think Storbeck's design is a good approach. So what helpful comments do you have about the pros and cons of rockers?

I would also note that while there is no end of praise for complicated versions of the "standard car", both from the students and the design judges, there is still very little praise for simple and effective solutions (like no rockers). I am trying to provide some support for those solutions.

Z

Z,

You have misunderstood Socrates in comparing yourself to him.

It was his style to ask questions ... not give answers. One of his claims to fame was to claim his own ignorance.

The Socratic method of teaching entails the teacher first approaching with apparent ignorance (humility). Once the student has admitted his own ignorance the questions would then turn to finding out the truth of the matter. The summary of the answers would lead to true knowledge of the subject and the conclusion that the student did indeed posess the knowledge required.

The response at large of the forum viewers appears to match the response Athens gave Socrates, in that you are similar. However we are yet to see you admit ignorance, feigned or otherwise.

So while I admire the questioning to keep the great men of Athens (the forums) honest, the act of supplanting yourself as the source of wisdom is much less appealing. Especially when the people of the forums have no way to assess the validity of your wisdom by viewing the end results of your work. (Beyond the small amount of converstaion on these forums.)

Still it makes for interesting reading.

Kev

p.s. By the way this is not an attack at you, but at the analogy ... especially after a well thought out reply to the other post.

Kevin,

No, I am not comparing myself with Socrates. I am just trying to use (some of) his method.

And yes, I am very ignorant on a lot of matters (apparently, tact is one of them ). But to use the full Socratic method (of lots of questions and answers) in this forum would take a very long time, and probably not get a result. So I have posted a few of the ideas that I have some inkling about (its faster, and I think more helpful).

Should people believe me? No way! I don't even trust myself! You've got to work it out for yourselves, guys.

Z

Z,

Yea, we've all got stuff to do. I'm working on a house....etc....A 240Z also awaits a nice resto-mod in the garage. Hmmmm...LS1?

So, you've managed to avoid my question? What have you actually built to completion and competed with? Here....I'll start. I'm not bragging, because things can always be improved, but I, as with many other FSAE'ers, have designed engine packages, electronics, wiring systems, intake, exhaust. Each design was better than the previous and I ended up learning more than I ever would have thought.

http://www.unm.edu/~fsae (shameless plug)

Delft has this beautiful composite featherweight car that I'm sure they put enourmous amounts of effort into. But, where is your stuff? I would like to see some photos or videos of your stuff. I would like to be able to say..."what the hell did you do that for?, why didn't mount the engine much lower, it totally messed up your CG."

" Like I said, it gets a lot tougher when you move into the real world." In the real world, money talks and bullshit walks. So, show us the money! All of my experiences have benefitted me greatly in the "real world". System integration, teamwork, engineering anaylsis, etc, etc. Even if we are following "fashion", at least we did our homework, did the anaylsis, worked out the problems, built the stuff, tested it, drove it, broke it, and learned from it.

Z,

Keep being a bastard. Its more fun that way.

Chris,

That is what I am doing after i get out of school. Ls1 240z. Love those cars.

Chris,

What have I actually done? I've posted briefly on this before, but to keep the answer simple, I've been nowhere, done nothing, and know nothing! And all that in a working career longer than your lifetime. But I am very lazy . (Note to Kevin, is that the correct way to start - your above post, paragraph 3.) So does that mean that I'm not allowed to ask questions, or express opinions? Is a person's reputation really that much more important than their reasoning?

I am guessing that you like pushrods and rockers. Maybe it was your job to do "the homework,... the analysis", etc.? If so, then how did you justify them? What did you learn from them?

Z

Getting back to the first step off-topic:

On the issue of bellcranks, or not, here was our basic reasoning for going with a bellcrank setup.

Pros (for bellcranks):
-They allow us to position the shocks completely within the bodywork, looks nicer compared to direct-acting coil-overs. This probably does not affect performance much in FSAE, since drag isn't huge, but we like the way it looks.
-Since this is a prototype, it's entirely possible that we find in testing that our motion ratio is completely off (whether our goal or some aspect of our design was off is irrelevant). A new set of bellcranks can be substituted in to remedy the situation, whereas this isn't necessarily the case for direct coil-overs.
-We run sway-bars, and the packaging of these is a lot cleaner and lighter with inboard shocks.
-Inboard shocks mean lower moments of inertia unless done horribly.
-This may seem like a lousy reason, but we've done it before and have some experience making such a setup work pretty well
-The way we're thinking of doing it this year, the stressed part of the chassis would be shorter than direct acting coilovers

Cons:
-More places for friction
-Maybe slightly heavier
-Seems like a "everyone does it so we will" kind of solution"

We did the whole QFD and Pugh's matrix dealie, and we came up with a bellcrank setup, which was our gut feeling anyways. So for our design criteria, a bellcrank setup is optimal

And I've been thinking about it, and Delft's setup seems a lot like the Michigan Tech one you lauded. I kind of see the bar connecting the shock mount to the lower a-arm mounts as a kind of bellcrank (with welded connections in place of pivots). But for the kind of wheel displacements we see in FSAE, I wouldn't be surprised if the Delft guys can achieve the same kind of motion ratios, at the expense of a little more friction. And I'm willing to bet that their little rinky-dink rocker weighs less than the two tubes that are welded to michigan tech's lower a-arm.

And maybe the rocker design Delft uses isn't as simple as your proposal, but it's one of the simpler rocker setups I've seen.

Matt Gignac
McGill Racing Team

Z,

You wont find me too strong a supporter of the Socratic method of teaching ... It would make me too much of a hypocrite

As for the whole rocker non-rocker debate there are a couple of things distinctly in favour of rockers. As one of the previous posters mentioned the bending loads applied to the damper can be a sizeable issue. It can affect the durability of your piston rod seals, their ability to seal, and add unwanted friction to your dampers. This is less of a problem with a lot of the dampers that people are using due to the high piston rod to bore ratio. Most of the mountain bike shocks do the majority of their compression damping with the fluid displaced by the rod. I think this is a pretty crappy way of doing things. If you were to make your own dampers I would recommend using a much smaller piston rod to bore ratio. Also to decrease rod seal friction there are certain things that can be done as well. However all of this increases the problems with seal durability and leakage due to bending loads applied to the damper. However I doubt this is a big issue with most of the dampers that teams run.

Another issue is the flexibility the rockers offer in the design build stage. Given the nature of the build cycle (at least for our team) the chassis needs to be designed and started construction earlier than quite a lot of the things that bolt to it. This means that either you allow for some later flexibility in your design or commit to a lot of decisions early and live with the consequences. Again it is probably better practice to commit early but flexibility does not hurt. A rocker system allows you to make some very radical changes late in the piece if you wish to, or if you find your initial decision were way off base. With a damper development program having rockers on old cars allows you to test radically different dampers that require radically different motion ratios without too much of a problem. This approach was incredibly handy for us in our first year, as well as our most recent. When adopting the new custom dampers we needed to be able to retrofit the car with different units if we hit some big problems. Fortunately we didn't but I appreciate having the option to be able to do so.

There is at least one more advantage we had using rockers that relates to our adoption of the Kinetics style system, which boils down to a way to alter roll moment distribution considerably if we were off the mark. It sort of fits in with the whole flexibility point though. I would hazard a guess that this flexibility may be more of a curse than a blessing to most teams. If you are not getting considerable testing mileage or testing different damper solutions then the complexity of the rocker system may outweight the benefits. The whole flexibility issue is also probably more of a problem with monocoque chassis' than it is with spaceframes. The trusty steel spaceframe has a hell of a lot of flexibility in the later build stages. One of the big advantages of implementing a steel spaceframe.

A minor issue is the problems associated with increased progression with most implementations of outboard shocks. I must admit very little experience with outboard shocks, but have worked on a couple of cases non-fsae related. This problem becomes more extreme the further out your uprights are from the body of the car. This causes the shock to have to lay on a fairly shallow angle, decreasing motion ratio and increasing progression. However there are ways around this and within reason it is not a major problem.

All said and done I think that Z is probably right for a lot of the cars (and the dampers they use) in FSAE. It is a much simpler implementation and I agree with him that rollbars are not really that important (which is also a plus for a lot of rocker setups). Having presented to a fair few design judges I doubt that many that I have met would find exception to using outboard shocks. In fact I think at least a few would applaud the simplicity and reduced weight. But with all things design judge related it would depend on your justification.

Cheers,

Kev

Just two quick points.

Matt,

You say " The way we're thinking of doing it this year, the stressed part of the chassis would be shorter.. (with rockers)".

The stressed part of the chassis, as far as torsion is concerned, is between the front and rear rocker mounts (rocker mount to damper chassis mount is only a local stressing). So my suggestion (earlier posts) was that you could run the coilovers direct from the wheels to wherever the rocker mount is, ie. along the line of the pushrod. This gives the same length of stressed chassis.


Kevin,

Regarding progression: I assume you mean rising or falling rate. If you draw a triangle connecting the two BJ's of a direct-to-wheel coilover and the lower-wishbone chassis BJ, and if either of the coilover BJ angles is a right angle, then you have a linear rate (at the instant). The upper BJ of Storbeck's car has this right angle, hence linear. Similarly, it is easy to see if a car has rising or falling rates depending on whether some angles are acute or obtuse... but easier to show on a drawing!


Apologies to the Delft team for hijacking their thread. (I just asked a little question... .)

Z

Z,

I am aware of how to calculate the progression (and yes I do mean rising or falling rate rather than progressive or digressive damping) of the outboard shocks and that it is very visible as to how much there is.

As I mentioned in my earlier post I think this is a minor issue and there are work-arounds. I still argree that setting up the a-arms (or other) witht he shocks to produce the desired effect is probably simpler than doing so with a rocker system. However it still does introduce a problem to be solved. I know that it would have meant a few changes to our chassis / suspension last in the past few years to accomodate it.

Kev

quote:

I am guessing that you like pushrods and rockers. Maybe it was your job to do "the homework,... the analysis", etc.? If so, then how did you justify them? What did you learn from them?

Pushrods, pullrods, outboard: Each configuration has it's advantage's and disadvantages. I agree that an outboard configuration can be clean and simple, minimizes components, reduces stiction, and
could offer more stiffness through simpler linkage. But as others have pointed out, a rocker system can give you increased flexibility when it comes to development.

But you can be like a freakin bull in a china closet when it comes to ripping peoples stuff apart and it's time to get out the cattle prod.
Present your case all you want.....but continuous criticism and monday morning quarterbacks are annoying. Anyway...enough arguing. But, I will throw you a bone and admit that you sound like you know your stuff. And maybe you're a cyncical old fart for a good reason: you've been there and done that.

quote:

Originally posted by Z:
Of course, when Socrates was about 70 the government of the day decided that he was guilty of shit-stirring or some such crime (actually "impiety and corrupting the youth"), and sentenced him to death. Given your above post, Charlie, I wonder if our modern society has progressed?

Ha, take it easy Are you saying my post is the equivalent to the death penalty? Wow I never knew my words were so sharp, heh.

Just some advice... like yours to other FSAEers, it doesn't require you to take any action if you disagree.

As far as the reaction of the design judges to the outboard shocks on our car, our design presentation was a complete cluster F#%$, but at least one judge seemed to really like the idea, and none of them said anything negative about it.

The Delft car is a work of ART. That it had minor tech issues on track was irrevalent.

Cris please consider an RB26 in your 240Z, It is one of the toughest proddy engines ever built and just looks so right in a 240Z
An LS-1 as mch as I like tuning them would be bastardisation in your car. Speaking of Bastards, I reckon some of us have the wrong idea of Z, he is not a bastard, but he is breathtakingly ignorant of real world racecar setup and design in a kind of Forrest Gump kind of way.
Bryan H (2 state titles & 1 Nat title in last 3 years)

An LS1 would be pretty damn cool though!
See off topic posts.

quote:

Originally posted by Z:

....When I finish this house and another shed, and some other stuff, I'll get back into off-roading....

Z

Are you going with bellcranks and pushrods or just a straight up foundation for that house of yours....