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Secondary and Primary members

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aalekh View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote aalekh Quote  Post ReplyReply Direct Link To This Post Topic: Secondary and Primary members
    Posted: Nov/16/2012 at 11:18pm
Are the A arms considered as secondaary or primary members?I went through the rule book and couldn't find this anywhere.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Soccerdan7 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/17/2012 at 12:56am
Originally posted by aalekh aalekh wrote:

Are the A arms considered as secondaary or primary members?I went through the rule book and couldn't find this anywhere.

Neither. The primary and secondary members rules only apply to the required members of the rollcage. Suspension is totally unrestricted (in this aspect) and other bars for bracing and mounting things on the frame are not regulated either. This is basically down to a simple safety rule. The rules set the minimum so drivers don't get hurt, and then leave the rest up to the discretion of the teams to balance out cost, weight, durability, etc.
Danny

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10 races, 7 top ten's, 2 overall wins
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tmenzefricke Quote  Post ReplyReply Direct Link To This Post Posted: Nov/17/2012 at 12:57am
As far as I'm aware they don't count as frame and are therefore neither primary nor secondary. As such I don't think there are any requirements on tube sizes and material (if thats what you're after) although obviously I wouldn't use 1x0.035 for any tube a shock will mount on.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote aalekh Quote  Post ReplyReply Direct Link To This Post Posted: Nov/27/2012 at 1:38am
We were planning to use the primary member size for our arms and therefore we needed to confirm this.Now its all clear.Thanks a lot.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Soccerdan7 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/27/2012 at 10:08am
Originally posted by aalekh aalekh wrote:

We were planning to use the primary member size for our arms and therefore we needed to confirm this.Now its all clear.Thanks a lot.

Primary members (1.25" x 0.065" 4130 or 1" x 0.12" mild) are definitely overkill for your a arms, especially those that do not have shock mounts. Think about bending, tension / compression and denting, as well as how you plan to fabricate them. It is easy to do a simple hand calc for these components to select a tubing size without any complicated FEA model and still be plenty strong. Why do you want to use primary? 
Danny

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Post Options Post Options   Thanks (0) Thanks(0)   Quote aalekh Quote  Post ReplyReply Direct Link To This Post Posted: Nov/30/2012 at 5:43am
Well the only reason was that the supplier wasnt ready to give us a separate size of about 40 feet length for the arms.So we had no option.But now we got him to give us 25mmX2mm pipes.We plan to use them now.And what calculations are involved?Cause i have nevr come across this.It would be really helpful.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Soccerdan7 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/30/2012 at 10:18am
Originally posted by aalekh aalekh wrote:

Well the only reason was that the supplier wasnt ready to give us a separate size of about 40 feet length for the arms.So we had no option.But now we got him to give us 25mmX2mm pipes.We plan to use them now.And what calculations are involved?Cause i have nevr come across this.It would be really helpful.

What material is that tubing? It seems decent for shock mounted tubes and probably still way overkill for non-shock tube depending on your design.

I mean simple hand calculations for a 3 point bend due to the shock, tension / compression loads from tire side loads, frontal impact loads (tension, compression, and maybe bending depending on your pivots). You can use a simple geometry since they are just tubes and take into account a strength knockdown for welding (usually ~15%). Obviously FEA would be better to optimize the geometry, but if you are going to stick to one tube size, you need to at least check that it should be strong enough. I hate seeing cars getting towed back to the pits after the first few laps of endurance with a wheel flopping around or totally missing when a simple series of calculations that you could do in an afternoon will alert you to this problem before hand.
Danny

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Priyank Quote  Post ReplyReply Direct Link To This Post Posted: Nov/30/2012 at 8:27pm
For the arm calculations, you can consider it as a beam, and take the load points as per your design.. You know the section, an so you can calculate the amount of loads, if there is.
Like, if you're at a 2G bump, you know the cars bumps down on the arms through the shocks, but the end at the upright will create a normal force.
Hence, beam.
We're using the primary member size for our shock arms.
You never stop learning.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote aalekh Quote  Post ReplyReply Direct Link To This Post Posted: Dec/10/2012 at 11:04am
The tubing material is DIN 2391.I suppose they should be strong enough.But i will still apply the calculations that you'll are speaking about.Dont want a wheel flopping out there.Thanks guys.
What size tubing are you'll using?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Soccerdan7 Quote  Post ReplyReply Direct Link To This Post Posted: Dec/10/2012 at 12:00pm
Originally posted by aalekh aalekh wrote:

What size tubing are you'll using?

Anywhere from 3/4" x 0.028" to 1" x 0.065" 4130 and we have dabbled with carbon and aluminum as well. It all depends on how you direct the loads by using tabs, gussets, bracing tubes, type of pivots, etc. Heat treating also makes a big difference depending on your alloy.
Danny

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(fall'07 - spring'12)
Former Captain / MEng / that guy with all the carbon
10 races, 7 top ten's, 2 overall wins
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