Chassis Trouble

[Archit]

http://postimage.org/image/1x8n754qs/ http://postimage.org/image/1x8ljls90/ http://postimage.org/image/1x8i8j39g/ http://postimage.org/image/1x8exge9w/ http://postimage.org/image/1x89yucsk/ http://postimage.org/image/1x86nrnt0/
hey guys
I m a member of Team BHR India and we have designed two chassis for the FSAE India 2011
and now we dont know which one to choose
So I need hellp of the wise minds out here to solve this problem.
so i have posted the images of both the chassis
Please reply asap.
thanks.

[Archit]

http://postimage.org/image/1x8n754qs/ http://postimage.org/image/1x8ljls90/ http://postimage.org/image/1x8i8j39g/ http://postimage.org/image/1x8exge9w/ http://postimage.org/image/1x89yucsk/ http://postimage.org/image/1x86nrnt0/
hey guys
I m a member of Team BHR India and we have designed two chassis for the FSAE India 2011
and now we dont know which one to choose
So I need hellp of the wise minds out here to solve this problem.
so i have posted the images of both the chassis
Please reply asap.
thanks.

[The AFX Master]

Your images don´t work

[moose]

Might I recommend a quantitative based decision? Posting 6 pictures here won't really help you justify which is better or right for the team. It’s the old internet common sense rule – just because someone on the internet says that something is right surely doesn’t make it so.

If you have approximate weights, stiffness characteristics, other design tradeoffs to post in addition to to the isometric & side views I’m guessing you tried to post (since I can’t see the pictures) and your/the team's opinion, I’d bet an informed discussion could ensue.

I’m not saying that any of those is the ultimate deciding characteristic either, just some of the information you should think about when making the decision. Saving 5 lbs and losing some stiffness might be ok, but it all goes back to what the design goals are.

[Nick Renold]

After some small amount of copy/pasting, I was able to view the images. I would choose "Chassis 2" because "Chassis 1" will not pass tech due to not having proper Main Roll Hoop Bracing. I also do not think that "Chassis 2" has properly triangulated "Main Roll Hoop Bracing Supports". Also, your rear box on "Chassis 2" is lacking triangulation, which will cost you on stiffness. You should read through all the rules to make sure you aren't missing anything else.

Interesting idea with the curved tubes for Chassis 1, but I don't think that will add stiffness versus having separate straight sections. Long bends like that might be difficult to make as well.

[Bemo]

I definitely agree with Nick.

Chassis 1 is missing main hoop bracing. And making these very long bends will be a pain in the ass.
The major problem with chassis 2 is that the whole rear part won't be stiff at all. Some more tubes for triangulation will add some extra weight, but having a stiff chassis is totally worth that.
And as Nick already stated, the main hoop bracing support has to be properly triangulated. If I were a scrutineer, I wouldn't accept both chassis like they are now.

You have to ask yourself what the major goals in your design are. And rules compliancy has always to be number one. If a design isn't rules compliant, no matter in which field of the car, it's absolutely useless!

[Chris Craig]

Once again i agree with both Bemo and Nick, Chassis 1 wouldn't pass scrutineering, Chassis 2 might but its debatable and it looks to have a lack of stiffness.

It looks to me like you have a very heavy, stiff chassis that wouldn't meet the rules, and a light unstiff chassis that may meet the rules.

With respect to bending tubes, the shortest distance between two points is a straight line, so bent tubes are always heavier.
Also beam buckling theory will show you why bent tubes are worse in compression so they need to be kept to a minimum, really only roll hoops should be bent if you can get away with it.

I'd have a good read of the rules if i were you and think a bit more about your load paths and triangulation at the rear aswell.

[moose]

A bit more on chassis 2 (hopefully some helpful comments) - you probably need to add a couple of .065 (maybe .095) tubes underneath the seat to mount the seat belts to. Also you need some .095 (I believe) tubing behind the seat for the shoulder belts (can't tell if something is there) and just be careful with mounting as the rules are fairly specific there now.

The front bulkhead is another area to doublecheck against the rules, be careful that all of the required tubes are there, I think its ok - but there are lots of pictures on the old FAQ forum / postings on the SAE site with what is and isn't OK. They may even be in the rule book these days. Its been a couple years for me, so I don't know every rule cold anymore (which is why I don't want to guess).

Also - what are the orphaned tubes up in the bulkhead for? Some sort of steering mount?
If that's where your bellcrank mounts, from what I can tell its going to flex like crazy in that plane.

[Ben K]

I think the chassis 1 looks awfully similar to an Ariel Atom....

Straight lines won't look as cool, but will likely increase your frame's strength/weight ratio.

Ben