Secondary and Primary members |
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aalekh
Bolt Sorter Joined: Sep/18/2012 Location: India Status: Offline Points: 11 |
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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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Soccerdan7
Organizer Joined: Sep/22/2010 Location: CA Status: Offline Points: 780 |
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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.
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Danny
Cornell (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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tmenzefricke
Milling Master Joined: Oct/01/2012 Location: Montreal Status: Offline Points: 46 |
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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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aalekh
Bolt Sorter Joined: Sep/18/2012 Location: India Status: Offline Points: 11 |
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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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Soccerdan7
Organizer Joined: Sep/22/2010 Location: CA Status: Offline Points: 780 |
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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?
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Danny
Cornell (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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aalekh
Bolt Sorter Joined: Sep/18/2012 Location: India Status: Offline Points: 11 |
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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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Soccerdan7
Organizer Joined: Sep/22/2010 Location: CA Status: Offline Points: 780 |
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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.
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Danny
Cornell (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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Priyank
Welding Master I don't search Joined: Jul/04/2011 Status: Offline Points: 241 |
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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.
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You never stop learning.
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aalekh
Bolt Sorter Joined: Sep/18/2012 Location: India Status: Offline Points: 11 |
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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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Soccerdan7
Organizer Joined: Sep/22/2010 Location: CA Status: Offline Points: 780 |
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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.
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Danny
Cornell (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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