Open for suggestion and criticism first car

[Thiago Gabardo]

Hello Guys,

I'm the team leader and my university in Brasil just implemented the FSAE Project. My first proposal was to make a tubular frame so that way we can acquire experience and than move up to the monocoque. But the university was very incisive about doing the monocoque. So I'm here to ask you guys some advice and/or criticism. We're going for the electric design. Because the project just started this month, we have some design objectives but we don't have yet the motor, the batteries, control unit.

http://flic.kr/p/e1Fvqf
http://flic.kr/p/e1zQx4
http://flic.kr/p/e1zQtz
http://flic.kr/p/e1FvdG
http://flic.kr/p/e1FvuE
http://flic.kr/p/e1FvAw
http://flic.kr/p/e1FvEE

Thanks in advance.

[Ben K]

Don't have rod-ends in bending.

I also recommend telling your university that a spaceframe is much, MUCH better for a first year team.

Ben

[Kirk Feldkamp]

Nice start. There are two basic things that pop out at me at first glance:

1. The driver looks stuffed in there. At the very least, he's going to want more elbow room. It's wise for any new team to build a "seating buck" or "mock chassis" to work out some realistic driver ergonomics and packaging. You will save a lot of resources by doing that early on, thus avoiding rework when you realize the driver simply can't fit or drive properly. It's also worth seeking out as many "real" racecars as you can to see how certain positions feel to you. Some cars are *much* more comfortable than others. A comfortable driver is usually a quick driver.

2. If you're going to use Catia, do yourself a favor and learn as much as you can about the powerful surfacing capabilities that the program offers. Doing a composite structure is cool and all, but designing it as a series of slab panels with constant radius curves between them is a shame. Learn about curvature and acceleration, and how they can be used to make more attractive shapes. It's not really "mechanical engineering" per se, but it certainly has its place within the automotive realm. Understanding that sort of surface design will also open up the world of efficient aerodynamics to you too.

-Kirk

[rjwoods77]

Go visit a team in Brazil that has a good history of international competition so you can touch and feel the car to get a better idea of what you are doing.

[Warpspeed]

Agree with Kirk.
Begin with a very crude full scale mock up.

Get some PVC electrical conduit and a hot air gun to bend the stuff, and put together a rough skeletal outline frame to locate all the major components.
A physical 3D frame you can actually walk around, sit in, and view from any angle will be very helpful in tweaking your CAD dimensions to fit a human driver.

Cardboard and duct tape make a terrific monocoque.

If you can fabricate a torsionally stiff chassis out of PVC conduit and cardboard, you are definitely on the right track.
It's fast, cheap, fun, and very instructive.

[jlangholzj]

Originally posted by Warpspeed:
Agree with Kirk.
Begin with a very crude full scale mock up.

Get some PVC electrical conduit and a hot air gun to bend the stuff, and put together a rough skeletal outline frame to locate all the major components.
A physical 3D frame you can actually walk around, sit in, and view from any angle will be very helpful in tweaking your CAD dimensions to fit a human driver.

Cardboard and duct tape make a terrific monocoque.

If you can fabricate a torsionally stiff chassis out of PVC conduit and cardboard, you are definitely on the right track.
It's fast, cheap, fun, and very instructive.

this would make a GREAT inter-team competition. We make our actual "racecars" but It'd be hilarious to see what kind of a soapbox car we could make given only wood, screws, PVC and cardboard.....with some duct tape obviously

[Freddie]

I agree with all said above, and would like to add :

If you really have to make a monocoque, maybe the Oxford Brookes way of making it (folding a sandwich material instead of using molds) can make it a bit easier? To me it seems that it would be easier to make a new, revised monocoque if you realise that there is some problem that can't be fixed otherwise.

Do you have any contact with other Brazilian FSAE teams? If not; make contacts as soon as possible! When we started, we had one guy that had FSAE experience, contacts with the other Swedish teams and a couple of us had visited teams and seen actual cars/facilites and talked to people involved. That helps a lot! Experience in any way, shape or form is needed.

Also, measure everyone that wants to drive and make CAD models that you know are accurate of the max/min length that the rules dictate, as well as your standard driver. As Kirk said, it's not that fun to have to try and "find" a couple of centimeters somewhere when the chassis is produced and you realise that something doesn't add up ...

When looking at the car itself, it seems to be a bit too high and/or tight around the drivers sides.

[Warpspeed]

A couple of centimeters, or a hard surface right where your knees or elbows keep wanting to go can be no fun at all to drive.

[Charles Kaneb]

At Case Western, we built a plywood mockup of the cockpit and the rear-end packaging before we built our chassis.

We really should've just added the steel roll hoops and raced the plywood car!

[Big Bird]

Hi Thiago,

It was very brave of you to offer your design for our feedbacck, and for this you have my full respect. Politely, I offer the following:

1. As you will get deeper into your design, you will realize that the chassis is just a big bracket, that holds all the components where they need to be. Therefore from a mechanical design point of view, design your chassis last, after you know where everything else needs to go.
From a marketing point of view, design your chassis first - so you have something to "sell".
From a real world point of view - do both. Use your first iteration chassis to draw attention, but do not marry yourself to that first design. Be prepared to change, and iterate.

2. From top view, your rear a-arms are at a very shallow included angle - and will experience huge loads under cornering. Be careful

3. This is your project, your design, for your education. That is priority one for your team. Do not let yourselves become free labour building a showpiece for your school. I've been in a situation where the latter objective took priority over the former. It is a horrible place to be.

Unis are notoriously heavy on the ground with technophiles, who will often have a marvellous repertoire of well-practised arguments as to why their pet technology needs to be on your car. Usually, such people have never designed anything more complex than the string of words coming out of their mouths.

If the uni is dictating a design solution, then walk away until they have delivered that solution. They demand a carbon tub? OK, they can deliver you a carbon tub. Let them wear the consequences of their decisions. Do NOT let yourself get in a position where the uni makes the decisions and you become their lackeys. I can assure you, when the fit hits the shan and their decision is proven a poor one, you dont want to be in any way exposed when they start deflecting the blame.

Good luck!

[TMichaels]

You might also want to consider that many experienced teams struggle with the resistance requirements of FSAE Electric when building monocoques.

[Adambomb]

Ha, not much I can add that hasn't been said already! Big Bird, as usual, hit the most important things. My only tidbits to add:

1. Chassis design, taking the "one big bracket" idea further:

~~a. Get shocks, rockers, push/pull rods located very very soon in the process, as that's a large part of where your wheel loads go, and with a small car it can be very difficult to integrate them well later.

~~b. Kinematics? Without a complete set of a-arms I can already see that the front roll center is a "normal-ish" height, but the rear is probably going to be around the CG. Might want to consider that. Also looks like the a-arms are nearly equal length...another thing to consider.

~~c. Size: Last year our team built a car with the templates being the #1 size criteria. That's all great in tech inspection, but then when the real world hits and you need add a shifter, wiring, etc., you have created a ton of headaches. I also found that car unbearable to sit in, and despite many years experience with FSAE cars I could not pass egress at Formula North. I gave it about a dozen tries, kicked the floor pan out, and then decided to quit before I damaged anything else. At that point I couldn't get under 7s, and in the past it never took more than a couple tries. For the record I'm 6 ft., 195 lbs (about a 90% male), and in pretty good physical condition. It sucks spending so much time and effort designing and building a car that less than 90% of your team are physically able to drive.

~~d. Size part II: Few people in FSAE think about serviceability. Small cars, especially monocoques, are impossible to work on. And if you don't think you are going to spend a significant amount of time fixing things on the car, you should stop and get back in touch with reality. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

2. A-arms:

~~a. As mentioned, don't use rod ends in bending (aka REIB...it's a big enough problem it has its own acronym). Google that for an article from Pat's Corner that goes into detail on that.

~~b. Also as mentioned, with the shallow angle a-arm loads will be huge, even more so with the rear-swept a-arms. I would be doubly worried about the mounts pulling out of the monocoque.

3. Big Bird is spot-on with the types of personalities you will most likely unfortunately have to deal with. The majority have all the ego that comes with being published in many journals, but are completely lost in a shop, and even more lost on a racetrack. They live in a magical dream world where any parts that need to be fabricated are sent off to a magic machine shop in the sky, and cost is often not nearly as much of a practical concern. And god speed on working with them...that is yet another one of the inherent challenges with FSAE.

[RStory]

To add to the comments above about monocoque size, if you have not already I would suggest doing some test samples and figuring out what you need to meet the SES requirements, especially the side impact rules. It's hard to see in the pictures how close the templates are to the outside surface of the monocoque, assuming you have a female mold you need to make sure you have enough space to fit in a structure that is thick enough to meet the stiffness and strength requirements in the rules.

[mech5496]

Robert is right, we almost missed a season due to that very fact, and we had to come up with some radical metal/CF combination in certain areas to avoid excessing local bending deformation...

[Thiago Gabardo]

Hey guys,

Sorry for the long time to respond, we were occupied doing some paper work.

Replying to everybody.

We already started a new cockpit concept. We changed the ergonomics and we made it a little bigger to enhance the rear suspension geometry.

The REIB seems like a problem very difficult to overcome, but we're making a deeper research and always suggestions are welcome.

We're using Optimum g software to assist us locate the suspension parts and trying to achieve our initial goals.

At the moment we're doing your schedule, looking for sponsor and new team members.

I'll be posting pictures in the future.

Thanks you guys. You gave us some really good points to work on. Much appreciated!!!

[Bemo]

To overcome REIB isn't so hard. Just use ball bearings in a milled part. I think the reason why teams are continuing doing it, is they think of it as a comfortable way to adjust camber.
But there are much more elegant ways of solving that problem than using REIB, which have to be of ridiculous dimension to withstand the bending loads.
This is a design competition! Look at solutions from other teams. There's quite a lot of material around the internet.

[Z]

Thiago,

REIB (http://fsae.com/eve/forums/a/tpc/f/125607348/m/52120148151?r=38120648151#38120648151), from a different point of view.

Z