A new team needs some help in framework

[The Mechanic]

Hello everyone!
We are a first year team. We represent Nazarbayev University FS Racing Team "G-Gear" and have almost finished our frame design. However, we are still not quite sure about some parts of our assembly, e.g. front hoop bracing members, which are intersecting in the middle of the front bulkhead, or main hoop bracing, so we are looking forward to seeing your advices and comments regarding the whole structure.
Thank you in advance for your time.

Here is our frame's picture:
http://i.imgur.com/D5QAdTd.png?1?8884

149

[Pat Clarke]

Mechanic,

Yours is probably the most common rookie mistake! The chassis design does not come first!

The chassis is really just a complicated bracket that holds all the components together whilst accommodating the driver and abiding by the rules.

So, it cannot be designed before all the components are selected and modelled.

Making the chassis first and then adapting all the componentry to it is not Design, but 'making it up as you go along'! The result will be heavy, ugly and compliant and the judges will hate it.

It also follows that no-one can make much of a constructive comment on your drawings.

It also might be a good idea to introduce yourself and mention the team you represent. Have you read the 'Read this before posting' thread?

Pat Clarke

[a.basov]

Hello to russian-speaking team!
I agree with Mr. Clarke, but will try to make specific advices.
Front and main hoop braces seems to be ok but check rule T3.14.4 and T3.13.4.
Did you check template passing? I have some doubts especially about cockpit cross section template(strange tube across front hoop).
You should support bends of main hoop by rule T3.11.5.
Frame is missing structure to support seat, that will also lead to poor stiffness in horizontal plane.
Your frame is missing sholuder harnees attachment points.
What about engine mounts? It will be better to make rigid triangulated structure to support, not just cantilever tubes.
Also did you think how to mount steering column, steering rack, pedal box?
Jacking point?
Is it square tubes at bottom of the frame? It could be hard to prepare tube ends at nodes with square and round tubes.
I think chain drive will intersect with square tube behind the engine.
And of course what about mounts of wishbones, dampers, rockers, arb? Try to place it to frame nodes to avoid bending.

[The Mechanic]

Dear Mr. Clarke,

Thank you for your response. We edited our post.

Initially, we believed that by choosing an appropriate engine and measured pilot's metrics, we could proceed further and design the frame.

Now we think we will reconsider the whole process of our design, because not only the result is important, but also the procedure.

Kind regards,
NU Formula Student Racing Team “G-Gear”
JSC Nazarbayev University
Email:nu.formula.student@nu.edu.kz

[The Mechanic]

Hi Andrey,

We are also glad to see a russian-speaking team here.
Thank you for your valuable comment. If we go step by step then:
1. We checked and witnessed that our braces are correct.
2. The thing we now make a stress on is the template passing. Regarding tube across front hoop - we found it necessary for the dashboard, steering rack and steering column; it also does not disturb the template’s pass . The thing which prevents templates passing is the front bulkhead width and now we realized that we should make it larger. The frame is rebuilt.
3. We double checked the main hoop. Though it seems that the hoop has a bending in the side view, it actually should not - the model is now rebuilt.
4. We added the seat supports and shoulder harnessing bar, and again rebuilt the model.
5. Well, to be honest, we have not developed all mountings yet, because we designed frame first and only then intended to mount other staff.
6. We are going to use the rear part of the frame as the jacking point. The issue is that we are not sure whether it should be a distinct member attached to the rear part of the frame or the exact rear member of the existing frame. If the second, can we make only this member circular and others keep rectangular?
7. Regarding the square tubes, we believe that they have a higher stiffness comparing to pipes, don’t they?

Also, can you please clarify which part did you mean as the cantilever?

The updated model: http://i.imgur.com/CQnLT6O.png?1

[a.basov]

1)ok
2)ok
3)I always thought that T3.11.5 says about ANY bends in the Main Roll Hoop above its attachment point to the Major Structure, not only bends projected to symmetry plane. Try to submit rule question to the Rules Committee. And I really don't like unsupported bends (you reduce critical buckling load).
4)ok
5)~ok
6)smart idea, it should be ok if you will use round tube. 6.1) I think you can.
7)square tube have larger moment of inertia in two directions in compare with round tube with equal area, but there is no advantages in tension-compression. To make frame stiffer try to avoid bending loads and make a triangulation so frame will work only for tension-compression.
8)I meant that there is no engine mount in your frame, and there is no frame nodes near supposed engine attachment points. So engine mount tubes could be long.

[The Mechanic]

Andrey, thank you very much for your feedback!
Your comments are important for us as a beginner team. We will take into consideration your suggestions.

[Claude Rouelle]

The Mechanic,

No engine mounting points and I do not see where the suspension pick up points are. As Pat Clarke mentioned the Chassis is "just" a huge bracket which must
a) connect all the different car elements (engine, transmission, cooling system, steering, seat belt points, etc.... Have you make a list of these elements....?)
b) respect the templates. I would have these "volumes" integrated in a light transparent color in my design
c) preserve the safety of the driver
d) get the best compromise between rigidity-weight-easiness and cost of manufacturing and repair
d) allow easy repair and maintenance work on the car (think about engine change, access to pedal box for example)..

For example... If you have double wishbone (there are other solutions but it is what the majority of team use) every suspension linkage axis is supposed to pass through one of the chassis node then you must have huge front lower wishbone between the front bulkhead and the front roll hoop.....

[Charles Kaneb]

That rear suspension box will be very flexible. It'll drive you up a wall trying to tune it. FSAE car setups are now VERY stiff because of our el-floppo tires.

I think the only value of a chassis drawing this early is to show 1) what's required to comply with the rules 2) where the major stuff (driver, engine, driveline, 16x suspension hardpoints) will be going.

[SomeOldGuy]

As others have said.

Build the frame to all the critical mounting points(engine, suspension, etc.)
Build around the templates.

Also I would add that building a mock up(from wood or pvc pipe)chassis is very helpful to understand where all the controls will fit without hitting templates while still be easy to use for the driver. Build the top of the cockpit opening strong so that you can use it to do egress, and see how easy or awkward that may be.

[The Mechanic]

Mr. Rouelle, thank you for your valuable comments.


We see now that we have chosen the wrong approach and started modelling the frame prior to the choosing mountings instead of the opposite.

We have already written a list of mechanisms to be mounted and work on them.
We are rebuilding the frame based on mounting points and make a stress on the templates pass. Of course, we do not forget the driver’s safety and try to find the balance between the safety, rigidity and accessibility

[The Mechanic]

Mr.Kaneb,

can you please tell us what does el-floppo tires stand for?

[Pat Clarke]

Mechanic,
Charles Kaneb's use of the word 'el-floppo' to describe tyres is probably a poor use of slang.
What he is talking about is a current generation of FS tyres that have high grip but low lateral stiffness, especially at low inflation pressures. Hence they tend to 'flop' around somewhat in use.

Remember, the choice of tyres should be made very early in the design process. Make sure you read the 'sticky' tread here regarding the 'Tire Testing Consortium' or 'TTC' as there is a lot of knowledge there about tyres.

Pat

[Charles Kaneb]

"el-floppo" is an entirely appropriate use of slang here!

Our tires give over 1" of lateral deflection at maximum load. If your design does not account for that, you will choose different front and rear track widths than if you do. They also deflect vertically - enough to give .3 deg/g roll in the tires alone. You can find yourself scraping things you wouldn't think would get near the ground.

[Pat Clarke]

Charlie,

I never disagreed with your summation of current tyres, just that I suspect 'el-floppo' probably doesn't translate well into Kazakh!

Pat

[The Mechanic]

Mr. Clarke,

Yes, you are right. We just couldn't find the equivalent translation for that tyres. Thank you for description.

[The Mechanic]

Mr. Kaneb,

Thank you for your comment.