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my new double A chassis idea fro comment


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#1 mariner

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Posted 05 January 2013 - 19:33

I started drawing racing car chassis in my school books at 14 so I can’t stop now. Turning the drawings in to cars is much harder than doing them in the first place. The biggest problem (apart from lack of talent and money!) is the need for complex jigs, especially fro a monocoque chassis. That has led me to the design idea I am offering here for comment.

It’s not intended to be the best in terms of weight to stiffness but rather something that could be built in workshop with basic metalworking tools and no large jigs. The construction relies on two things – sheets of larger than the old “8*4” and a metal folder capable of folding up to 3metres. I have established that both are available in the UK at least. I have also made up a little model, its not exactly to scale due to fastener sizes etc.

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Basically the chassis is two opposing “A” frames sandwiching a central alloy plate or honeycomb bulkhead to which all the high load bits are mounted – front of engine, roll hoop, seat belt mounts, battery and oil tank etc. It is stabilised by the seat back which has an access hole for servicing front belts, pumps etc.

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The side member are simple top hat sections which self- jig the chassis , as they are very stiff you can rivet them to the floors without jigs. Because the side beams have simple flanges all riveting can be with hard rivets bucked from underneath.

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The whole chassis is made from only 14 parts as shown here.

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The design isn’t very complex but it does give good side impact and front impact protection.

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One downside is the tapering limits foot room but this shouldn’t be problem in racer as there usually isn’t a requirement – in a road car the passenger would have to pull their legs up bit.

Hopefully the pics of my little model give an idea of the layout – any comments are very welcome


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#2 rachael

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Posted 06 January 2013 - 11:11

Neat! I think that might have quite a respectable torsional stiffness.

Is it going to stay as just a model?

#3 gruntguru

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Posted 07 January 2013 - 00:38

I like it too!

Suggestion. If the "top hat" beams are to be custom folded, why not taper them somewhat such that the section is larger at the bulkhead? this will increase the stiffness/weight ratio.

#4 Kelpiecross

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Posted 07 January 2013 - 13:28


Nice model. Does the front "A" need to come to a point? Maybe it could be squared off a little. How are you going tp join the two"A"s together? Remember a car needs almost endless numbers of brackets/attachment points for suspension, steering, pedals etc. etc.

#5 mariner

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Posted 07 January 2013 - 19:10

Thank you all for the input. To answer the comments in turn!

- I hope to go further and at least do a layout of the parts needed to cut and fabricate the design so I can get quotes for the cutting/bending.

- I like Gruntguru's idea of widening the boxes near the centre as it doesn't make it any harder to build and ,as well as boosting torsional stiffness, it would make the bag tanks a better shape.

- The ends of the A frames are connected by "U" shaped members which attach to the tops and bottoms of the side arms - as shown on the model. That imparts a stiffness to the ends of the frames.

- Ive tried to simplify all the usual brackets in three ways

1) As much as possible of the mechanics are hung on the central bulkhead which is either 3mm plate or honeycomb so it can take loads without extra bits. The battery, oil tank, roll bar, safety belts etc go there as does the engine front end support and header tanks etc.

2) The three steel box section suspension cross members are used to carry things like the top steering mount. etc.

3) The actual suspension mounts are the bits shown as dotted lines through the box membes. All are basically identical except in length. Just a 75mm * 50mm ERW square tube with a plate welded on one end . You drill the actual suspension holes after its installed ( the one bit requiring a jig).

Hope that makes sense!!



#6 MatsNorway

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Posted 08 January 2013 - 14:35

If you scale it up how much would it weight?

#7 mariner

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Posted 09 January 2013 - 15:36

To answer Mat's question, assuming the following

- wheelbase of 2.3 to 2.5m ( i.e the classic 90 - 100")

- width of 1.82m

- engine bay sized to a SB chevy with front engine plate mounting

- 18G alloy for all panels

-18G steel for the box members

- 25mm honeycomb with 0.5mm skins for the central bulkhead

- 5kg for fasteners/adhesives

the all up weight would be about 80kg or 160lb