Two rod straight joints

[raptor93]

Hi everyone,

We are a new FSAE team. We are running short of chassis rods and ordering new rods is not possible.
Is it allowed to join two rods end to end in a straight line? and is that a violation of the triangulation rule?

[Claude Rouelle]

A. I don't understand your question. Maybe others will but I don't. Can you elaborate? Offer a sketch?
B. Why is ordering new rods not possible?

[Big Bird]

I think the original poster is asking if he can butt-weld chassis tubes. My responses:
- irrespective of whether it is legal or not, it is a really bad idea. I sincerely doubt you will match the original tube for strength or straightness
- why can't you order more material? If budget is that tight that you cannot afford some steel tube, then you are in for a rough time when this project starts throwing some real expenses at you

Kind regards,

Geoff

[raptor93]

Dear Big Bird,
yes, we were talking of butt welding. This kind of joint is done only for one straight pipe of chromoly 4130 which is less than half a metre after two straight pipes are butt welded. ordering such a small pipe is not possible because of no access to such pipes in our region. That was unfortunately the last pipe to be welded in the chassis with no leftovers.

Kindly tell if it will be considered as a bent tube requiring any support according to the rule T3.5.5

Thanxxxx in advance.

[Big Bird]

Hi Raptor,

Firstly, I am not someone who can give you official judgement on whether this arrangement is legal or not. I repeat, it is not a good idea though.

A deeper issue is that of your use of 4130. Please excuse me for shouting, but:
YOU DO NOT NEED TO MAKE YOUR CHASSIS OUT OF CHROMOLY

Just in case you missed the point:
YOU DO NOT NEED TO MAKE YOUR CHASSIS OUT OF CHROMOLY

Chromoly, 4130, whatever you want to call it, is a WASTE OF MONEY. It is no stiffer than mild steel, and the extra yield strength is wasted as a chassis should be nowhere near yield anyway.

This point has been made many many times on this forum. Make your chassis out of mild steel - cheaper, and doesn't need heat treatment after welding.

Kind regards,

[Luniz]

Plus: A PIPE is a thing for liquid or gaseous substances to go through, hence it is referenced by its INSIDE Diameter. A TUBE however is a thing made to build structures from.

[Tim.Wright]

Hi Raptor,

Firstly, I am not someone who can give you official judgement on whether this arrangement is legal or not. I repeat, it is not a good idea though.

A deeper issue is that of your use of 4130. Please excuse me for shouting, but:
YOU DO NOT NEED TO MAKE YOUR CHASSIS OUT OF CHROMOLY

Just in case you missed the point:
YOU DO NOT NEED TO MAKE YOUR CHASSIS OUT OF CHROMOLY

Chromoly, 4130, whatever you want to call it, is a WASTE OF MONEY. It is no stiffer than mild steel, and the extra yield strength is wasted as a chassis should be nowhere near yield anyway.

This point has been made many many times on this forum. Make your chassis out of mild steel - cheaper, and doesn't need heat treatment after welding.

Kind regards,

At the risk of opening this can of worms again... wouldn't you accept 4340 as a chassis material for reasons of crash/damage resistance? With the same modulus but higher yield and UTS I'd assume there would be more strain energy to failure for a 4340 structure compared to a 1020 structure?

Perhaps its overkill for FSAE... But if I was designing a steel spaceframe for hillclimbs I'd put a decent amount of thought into what happenes when you slide sideways into a tree.

Tim

[Big Bird]

Hi Tim,
Yes, I certainly would accept chromoly in a form of the sport where it might be likely that you could impact a tree, or another car, or a rhinoceros, or a Bridgeport mill. But in our sport we are exceedingly unlikely to encounter most or all of those things. And when you have situations like this, where a team is compromising their budget and their structural integrity, for the sake of persisting with a material spec suitable for an impact that isn't going to happen, or for a material spec suitable for repair and re-use when effectively the car will only be used once anyway, then we are spending money on a spec not suitable for us.

[Drew Price]

Raptor,

Ask the rules committee directly.

The answer may actually depend on which tube in your chassis you intend to make from more than one piece of material.

If it's the front or main roll hoops for example, the rules specifically say those parts of the structure must be made from one, continuous, un-cut length of material.

No one here can give you an official answer.

And you can weld plain carbon steel tubes to 4130 if that makes it easier for you. Use the same welding rod (or wire) you used for the rest of the chassis.

[Claude Rouelle]

Raptor93,

I was confused by the word rod, rods end etc... You would have used tube (never pipes!) I probably would have got it quicker.

That being said
a. Without any spare tube if you have a crash or a chassis failure and you can't order more tube, what is your plan B?
b. I agree with Geoff that 4130 is a unnecessary expense for a FSAE. What made you decide to got for 4130?
c. If you have headache once or twice a year what do you do? Take an aspirin right? That is what I would do. You will work on the illness ignoring its cause(s). But if you have a headache every day you will probably want to consult a doctor and work on the causes: food allergies, breathing polluted air, too much stress, maybe time to change girlfriend...? I have not seen your chassis drawings but I have seen seen so many first year chassis with so many conceptual design mistakes (even if the chassis passes technical inspection) such as lack of triangulation, suspension pick up points not at a chassis node etc that I fear that you won't be the exception and therefore that would make the choice of 4130 even more a engineering mistake and waste of money. Work on the causes of chassis deflection or break before you work on its consequences.