Chassis Rules - Definition of Triangulation

[jon_stafford_fbr]

Hi Everbody,

This is my first time designing an FS chassis, so I may be making a basic error here.
I've checked the rules and the forums and haven't managed to find a satisfactory answer so any help would be greatly appreciated.

In the 2015 - 2016 FSAE rules, section "T3.3 point l" (page 26) states that triangulation is defined as;


"Node-to-node triangulation – An arrangement of frame members projected onto a plane, where a
co-planar load applied in any direction, at any node, results in only tensile or compressive forces
in the frame members. This is also what is meant by “properly triangulated”.


To me, this means that bars in a chassis can form a rectangle so long as all of the bars are braced so that if a force was applied at any point,
it would be transmitted in tension and compression only. (i.e. no bars in bending).

However, we've had some internal team debating about whether this is unacceptable because it forms a mechanism.
I feel that that would be true in 2D, but in 3D that doesn't apply because the bars can be constrained in different planes.

Below are images of our proposed 2017 chassis. What do you think of the bars attaching to the top of the front roll hoop?
It appears to form a four bar linkage in the side view. Is this allowed by the rules? Is there a rule or a forum I've missed?

Angle 1.jpgLeft.jpg

Any help would be greatly appreciated.
Thanks for taking the time to read this post

Jon

[onemaniac]

You'll get the most accurate answer by contacting the Formula SAE Rules Committee.

Meanwhile from what I know, the two bars at the top are not required by rule (but I haven't updated myself since 2014.. so it may have changed. Check the section where it describes the front bulkhead bracing).

Technically, any tubes that are not part of required structure do not necessarily fall under the triangulation rule.

But here's my question... what are those two tubes put in for? They don't seem to help either torsional rigidity or bending too much with current configuration.

[Adman]

As onemaniac has said you're best off contacting the official rules committee; an opinion from an internet forum is nothing to go by.

In saying that, I believe your chassis fails rule T3.19.2, in particular part C. You must have an upper, lower and diagonal 'brace' from the front bulkhead to the front rollhoop. Brace is paraphrased because they can be multiple or bent tubes, so long as they are triangulated. However part C states that the diagonal brace must properly triagnulate the upper and lower support members, which I think yours does not.

To correct this, I would suggest bring those upper tubes to the node where the diagonal member currently meets the diagonal tube coming from the main roll hoop. Not only will this fix your rule issue, but currently the two upper tubes leading to the front roll hoop (a) put the front roll hoop in bending in the event of an impact and (b) don't offer much in the way of torsional rigidity, as the suspension points will not be supported in any way due to their current configuration.

Adam.

[Z]

Jon,

Search the web for Appendix T-4 of the FSAE 2017/8 Rules. (Hint: It is linked to the 2017/18 Rules, but they have cleverly hidden it in a file of another name.) There you will find 35 different examples of side-views of the FRH to FB bracing, roughly half being "OK" and the other half "Not OK".

Your side-view picture is quite similar to Appendix T-4's Figure 11, which is labelled "OK". In fact, your frame includes the same members as Fig 11, plus a whole lot more, so should pass scrutineering.
~~~o0o~~~

However, the really sad thing is how many of Appendix T-4's "OK" examples are UTTER ABOMINATIONS!
Groooaaannnn!!! [Insert vomitting emoji.]

Jon's frame is likewise, though even worse because even more useless tubes in even more useless places.

How are all these stupid Rules supposed to improve the education of young engineers?

Will I EVER see an FSAE spaceframe that makes me think "Yep, looks neat...".???

Z

[jon_stafford_fbr]

Thanks for all the replys,

I'll deffinatly submit a Formula SAE Rules Committee enquiry and post the reply here for completeness.
Z, I've been looking for those chassis pictures for ages but had no idea what they were called so have never managed to find them. Thank you so much.

To answer a few questions about the other bars / the chassis in general. Bellow are two labled pictures showing where our VD points are, and which bars serves to meet specific rules.


VD.jpg In this photo;

-The red dot is the damper mount (we run struts).
-The orange points are for wishbones.


Bar descriptions.jpg In this photo;

-Brown is the "lower support member"
-Green is the "Upper support member" - with the dotted lines being the bracing (because the bar is bent).
-Gray is the "diagonal brace" - with the dotted lines being the bracing (because the bar is bent).
Blue is the "Front Hoop Bracing"

The reason we have the front hoop bracing at the top of the roll hoop is because, the top is more than 50mm from the next node on the roll hoop. (T3.14.4)
This means we can't just join the two green bars together. If we lowered the roll hoop top by 25mm then we could do this. (This is what we did last year). But at competition our drivers all complained that the steering was really heavy and that they needed a bigger
wheel. As this is the only bit of driver feedback we've ever got from comp (we don't race very often) I thought I should try and accomodate this by raising the top point allowing a bigger wheel. (T3.12.4)

Hopfully that shows some of the reasons behind our chassis decisions. I know its not a very neat sollution and some of my logic is pretty flawed.

Thank you for all the advice given in the posts above. I think have a play arround with the front to try and improve it.

Jon

[DougMilliken]

... As this is the only bit of driver feedback we've ever got from comp (we don't race very often) I thought I should try and accomodate this by raising the top point allowing a bigger wheel.

Have you looked any further into why the steering was heavy? This is the sort of thing that I question when design judging, and relatively few teams have good documentation of their design/analysis/testing process for the steering system.
While I personally dislike really tiny steering wheels, simply increasing the diameter to reduce the rim force may actually be a patch on a bad steering system design?

[jon_stafford_fbr]

*** UPDATE ***

Just received confirmation from the rules committee that its fine;

Your Front Bulkhead Support (FBHS) structure is properly triangulated.
In this configuration, the Front Roll Hoop Brace (FRHB) is not considered part of the FBHS Structure and so does not need to be part of the triangulation.

Cheers for all advice, it has been so helpful for a first-time chassis designer.

Jon

[BillCobb]

Have you looked any further into why the steering was heavy? This is the sort of thing that I question when design judging, and relatively few teams have good documentation of their design/analysis/testing process for the steering system.
While I personally dislike really tiny steering wheels, simply increasing the diameter to reduce the rim force may actually be a patch on a bad steering system design?

Ah yes, the classic Mercedes oversized steering wheel....

You would not need all these rules if you dropped the top 5 or 10 cars nose down from a crane. I have the portable crane. It will go up 35 feet. Extra credit if the driver goes along for the ride. Failure and disqualification if any bleeding occurs.

[Drew Price]

The very clever teams will drain the blood beforehand, also gaining the benefit of reduced mass mounted high up in the car decreasing RMOI.