Chassis Design

[abisc]

I am a member of an Indian FSAE team, participating in Supra SAE India 2011. I would like to seek assistance on this forum from some highly experienced members as this is the first time that we are participating in a dynamic FSAE event. We have designed a chassis model which is unconventional but we are fairly convinced that it is going to give us some distinct advantages in static as well as dynamic event evaluations.
The distinct feature is the use of long elliptical (closest geometrical resemblance) links in the chassis design in an inverted trapezium configuration \_/ . Please find labelled screenshots below.
We would like to invite views on merits and demerits of our design philosophy. Also let us know if we could PM you the CAD models for in-depth analysis and clearer understanding. Although it makes more sense for us, as first time teams to 'play it safe', but somehow I personally feel that there is a possibility that we maybe let going a winner from our hands by rejecting it on the basis of being an unconventional design. Your able assistance is thus sought.

Kindly remove the spaces from the link to view the images.

h t t p : / / w w w . fl ic kr . c o m / photos / 59283231@N02/

[abisc]

I am a member of an Indian FSAE team, participating in Supra SAE India 2011. I would like to seek assistance on this forum from some highly experienced members as this is the first time that we are participating in a dynamic FSAE event. We have designed a chassis model which is unconventional but we are fairly convinced that it is going to give us some distinct advantages in static as well as dynamic event evaluations.
The distinct feature is the use of long elliptical (closest geometrical resemblance) links in the chassis design in an inverted trapezium configuration \_/ . Please find labelled screenshots below.
We would like to invite views on merits and demerits of our design philosophy. Also let us know if we could PM you the CAD models for in-depth analysis and clearer understanding. Although it makes more sense for us, as first time teams to 'play it safe', but somehow I personally feel that there is a possibility that we maybe let going a winner from our hands by rejecting it on the basis of being an unconventional design. Your able assistance is thus sought.

Kindly remove the spaces from the link to view the images.

h t t p : / / w w w . fl ic kr . c o m / photos / 59283231@N02/

[Chris Craig]

I'd stick with the conventional if i was you and read the rules.

A few pointers

1) Neither chassis's meet the rules
2) The shortest distance between two points is a straight line, why bend a tube if you dont need to
3) A bent tube will buckle sooner than a straight tube
4) Triangulation!!!!!!!!!
5) Torsional Stiffness!!!!!!! Large gaps in spaceframes reduce stiffness
6) Your unconvential chassis is huge!!!!!!!!

You need to get hold of a Mechanics of Solids/Materials book and have a good read, then have a good think about both designs

Regards

[BrendonD]

You are brave to post your work, so kudos for that.

Your "conventional" model is much closer to meeting the rules than your "unconventional" model. Areas of note on the unconventional model include front roll hoop, main roll hoop, main roll hoop supports, and side impact structure.

There looks to be an awful lot of extra space in the front bulkhead, does an increased chassis stiffness justify that?

[Hector]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">3) A bent tube will buckle sooner than a straight tube
</div></BLOCKQUOTE>
Guess you've never seen a suspension bridge, eh?

In all seriousness, it looks like you're optimizing (groan! the O-word again!)for beam stiffness. While some beam stiffness is important, how stiff are you torsionally?

The thing about FSAE cars is that you're going to learn more than you could imagine even building the simplest of cars. Some of the better cars in recent history have been designs that I would deem "simple". Outside of the fun exercise of trying a new design (looks like you're borrowing heavily from beam theory) are you really learning more? Seems like you picked an idea, drew it into a frame, and analyzed it... same as every other team.

Anyways, it would be interesting to see a car like that at competition. Good luck and have fun.

[Xeilos]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BrendonD:
You are brave to post your work, so kudos for that. </div></BLOCKQUOTE>

Amen to that. Kudos as well for posting and asking for feedback; unconventional is sometimes good and sometimes some of the die hard purists of the 'conventional' way of doing things sometimes should keep quiet. Not that they are wrong but that without risks you never innovate and learn.

That is not to say I think it is a good design. The best way to transmit force is in a straight line. There are still glaring gaps in triangulation but that can also be typical of many chassis. It is also huge. Not as in typically huge but huge in that it needs its own back up warning sound huge. But that does also merit mentioning the engine the Formula Supra India SAE race must use.

Also does anyone else think Ariel Atom when they see this; though I am sure we have all thought at one point in time the parallels between the Atom and FSAE.

[thewoundedsoldier]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">1) Neither chassis's meet the rules </div></BLOCKQUOTE>

Do the Indian events have a different rulebook than the others? At first glance, both frames' side impact structure and front bulkhead support structures are inadequate. The conventional model needs a bend at the top of the main hoop, and I am wondering why the main roll hoop of the unconventional model is so wide?

I think it would be rad to see a frame like your unconventional one, but unless your rules are very different from everyone else's, you are fighting an uphill battle.

P.S. -- IMO your conventional-frame triangulation is much better than most. It could be better but don't take any flak about it, especially from teams that simply lay up a carbon tub. Good luck!

[RobbyObby]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Chris Craig:
1) Neither chassis's meet the rules
</div></BLOCKQUOTE>

I wouldnt jump to conclusions. Yes it does not meet the general chassis rules, however it could theoretically pass the new AF rules given that they are proficient enough with FEA.

EDIT: Oops. It seems I jumped the gun. Even through the AF rules you still must meet most of the other general frame requirements as well. My apologies.

Also, a bigger chassis does not necessarily mean it is inferior to a smaller chassis. A larger frame could technically be lighter, stiffer, and have a smaller MOI, through he use of proper tube sizing and triangulation.
Im not saying these designs are good or bad, just dont make those assumptions.

Also, I agree, kudos for posting your work up here. You are already miles ahead of most trollers here in that you have already made a proper attempt at a design before coming for feedback.

[SamB]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BrendonD:
You are brave to post your work, so kudos for that. </div></BLOCKQUOTE>

Ditto.

On first glance it seems you have overcomplicated what can be a relatively simple task through searching for an innovative solution to a problem which doesn't really require one. It looks like you have considered triangulation in some places yet not in others where (it can be argued) that you will require the triangulation more, case in point being the front end which looks far too complex to me - why such a high tube density at the front? Yes, it currently does not meet the rules however a number of positives can be drawn from a first design. What I would recommend is sitting down with your team and scrutinising every single section. Unless you can explain the purpose of every single tube, then your chassis is over complicated.

Unfortunately there is a reason most FS chassis' look the same.

Best of luck, and thanks for not just asking how to design a chassis. It seems that some teams from India are developing a bad reputation on this forum.

Sam

Uni of Manchester
Chassis Guru 09-11

[BrendonD]

The quote from RobbyObby's signature holds particularly true here.

I wouldn't even add weldments until you've got the layout handled, then add the section thicknesses in what's required by the rules and adjust your "free" tube cross-sections to reduce weight and/or increase stiffness.

Another thing of note: Do you know where your suspension points are in 3D space yet? Knowing where those are makes a lot of decisions in the chassis design process. I particularly enjoy the analogy that the frame is just a big bracket that holds everything together. All you have to do is make it as light and as stiff as possible.

[colinE30]

Another thing to point out, how do you plan to bend that tube that fits front to rear on the "unconventional" chassis?

I would run away if our chief engineer gave me a print for that tube.

[Mazur]

Looks like an Ariel Atom.

[Drew Price]

Tata Atom maybe....

[buggaero]

Original attempt stands out heroic.
but don't forget you missed the whole point.
triangulations are missing somewhere and added at other places. Don't forget you should have your material in sight before you opt a particular design...or you might end up with longer members and eventually a heavier chassis.
Heavier Chassis with an extra heavy engine at the rear...plus the poor weight bias plus the wheel to wheel race..... Wake up!