Tubes diameter and thickness

[Xabi Tecnun]

Hi everyone!

We are just new in the fsae competition, this is our first year in the competition.

I have some doubts about the chassis, that's the part I choose. We almost have finished building it in the computer, and we achieve a rigidity of 6800 kg*m/º with a weight of 32 kg. This is too much for us, because we were thinking in 4000 rigidity. So, we can make our chassis lighter to have a well balanced car. The question is: in the Front Bulkhead Support, which tubes need to be in concordance to the 3.3.1 rule? And also, 'til which point extends this Bulkhead Support? I mean, can we put lighter tubing after the front suspension first joints? Other whise, how can we reduce our weihgt?

I add some pictures, so you can make a little idea where we are. By the way, we would like to know which are your opinions about the chassis.

Thanks all of you!

http://farm4.static.flickr.com/3502/3294235933_04b48a4df3.jpg?v=0
http://farm4.static.flickr.com/3574/3303480082_a1c559bb48.jpg?v=0
http://farm4.static.flickr.com/3460/3302650307_f6fac35b9b.jpg?v=0

[Xabi Tecnun]

Hi everyone!

We are just new in the fsae competition, this is our first year in the competition.

I have some doubts about the chassis, that's the part I choose. We almost have finished building it in the computer, and we achieve a rigidity of 6800 kg*m/º with a weight of 32 kg. This is too much for us, because we were thinking in 4000 rigidity. So, we can make our chassis lighter to have a well balanced car. The question is: in the Front Bulkhead Support, which tubes need to be in concordance to the 3.3.1 rule? And also, 'til which point extends this Bulkhead Support? I mean, can we put lighter tubing after the front suspension first joints? Other whise, how can we reduce our weihgt?

I add some pictures, so you can make a little idea where we are. By the way, we would like to know which are your opinions about the chassis.

Thanks all of you!

http://farm4.static.flickr.com/3502/3294235933_04b48a4df3.jpg?v=0
http://farm4.static.flickr.com/3574/3303480082_a1c559bb48.jpg?v=0
http://farm4.static.flickr.com/3460/3302650307_f6fac35b9b.jpg?v=0

[exFSAE]

You PREDICT you will get 6800 kg*m/deg. In reality with all the compliance that's going to inevitably exist, when you weld it and assemble everything, it will be much lower (hub to hub)

Make it rigid. 32kg isn't that heavy for a steel FSAE frame anyway.

[Xabi Tecnun]

Sorry, I just realised that the pictures does not apear. How can I put them correctly?

[exFSAE]

Use a photo hosting site that isn't password protected.

Photobucket.com works well.

[Tilman]

You are a first year team? Do not go for weight. Go for reliability and try not to do any mistakes. Go for a design without flaws. Reliability comes first, removing weight will be your goal in five years.

Conclusion: Go for a rigid frame. And the design you posted will not be very rigid. Triangles are rigid, quadrangles are not. Look at this: http://www.sardinien.com/vonabisz/kidsundco/images/plastwood/harley_400.jpg Almost everything is made out of triangles http://fsae.com/groupee_common/emoticons/icon_wink.gif

Good luck.

[L B0MB]

How are you modelling it to get 6800kg*m/degree?

I used to restrain the rear bulkhead at the 4 suspenion pickup locations and apply a torque to the chassis about the longitudinal axis via the front pickup points

With this method I have seen 3153Nm/deg and 28.8kg (with a mock up tubular engine in the model as it adds heaps of rigidity, its mass ingnored in overall chassis weight)

Perhaps try this method before reducing section sizes or removing bars...

[Xabi Tecnun]

Yes L Bomb, that's the way I test it. I fix the back points of the rear suspension and apply a torque in the front points of the front suspension. This gives me the degrees that turns that point, and with it and the torque apply I deduce the rigidity.

I really apreciate your help. So, this year you recomend me to get worry about rigidity. I think that a rigidity of 6000 is quite enought, taking into account that it would be lower in reality.

Thank you all.

http://farm4.static.flickr.com/3469/3308941542_4e79033573.jpg?v=0

By the way, the bars in red, could be in any tube diameter and thikness?