Whilst rummaging around in the garage looking for a burglar 'deterrent' (i.e. hospitalisation device), I got to considering some 25mm sq 16swg RHS, the material that we're all familiar with through Uncle Rons book. Whilst going the the motions of an imaginary violent 'self-defence' assault, it struck me that the stuff's pretty heavy. So that got me thinking - "There must be a better way".

We create space frames then hang redundant sheets all over them. Could we not use less materials, different materials, different methods that would achieve the same level of stiffness but with less weight at a reasonable cost in our home workshops?

There are the obvious carbon fibre/aramid materials but are very expensive (well, they used to be). Anyone experimented with aluminium honeycomb? Or for the locost idiom end-grain balsa on aluminium sheet? Thinner tubes that are bonded to avoid welding heat distortion?

I sketched out a small chassis a while ago using honeycomb but it dawned on me that I didn't know how to do a decent join with perpendicular faces (and that the design was crap )

To save you typing, I know (roughly) about the FW400

And just think, with the weight you've saved, you could drink more and still be faster.

Cheers,

Neil.

this has been gone over quite a lot before, honeycomb etc was deemed too expencive.

but then, if you wanna do it... do it

i was wondering if fewer big tubes or many small tubes would be better. i decided it was probably dependent on the situation. Also, liberal use of 22g welded sheet.

Cymtriks will undoubtedly be able to cast some light on this thread anyway!

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Originally posted by Staple balls
honeycomb etc was deemed too expencive.

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not too sure.

do a search for honeycomb and maybe composite, should throw up a bit

Someone on the site used to do a 'magic box' front end, with all the brackets in the right place. This could be coupled to a GRP twin skinned monocoque, filled with foam with a similar box at the rear for sierra IRS.

There are a lot of boat designer/builders in my neck of the woods, they use all kinds of techniques to add strength without adding weight, paper rope, cadboard formers etc to create GRP tubes within the structure. I am sure a GRP triangulation within the structure would add as much strength as ERW.

You can buy for around £250 per sheet 8x4 aluminium honeycomb sandwich panels (see technical resin bonders website and hexcel).

These you can route out one skin and fold the other and bond and do overlap joints etc, to form and nice bath tub type chassis. You then need to use bulkheads and machined inserts to take the loads of the things that you bolt to it. All possible, doesn't cost the earth (but far more than steel tube!!) and will be awesomely light and stiff.

The hexcel website tells you all the techniques for fabricating stuff with these panels.

Kind regards,

Darren

The valid reason for going monocoque isn't to save weight but to increase stiffness.
A lot of people in the racing car world have tried honeycomb, only to decide it wasn't iworth the extra hassle except for making a main bulkhead or perhaps a floor from it.

The Locost shape isn't ideal for a monocoque but a stiff structure can be made as per the Qantum (and now even Robin Hood !!!) chassis. Another good monocque material is GRP -- Davrian made good use of it and it.

What about using chromoly? Check out a few homebuilt aircraft sites, they all use chromoly tubing to build their spaceframes. Just checked it comes in all the sizes required by 'the book'.

I've read several fibreglass/composite books and scoured the net looking for details on the construction of fibreglass/foam sandwich monocoques and can't find enough detail. (thickness of foam core,what weight cloth,how many layers,etc) Any ideas???
IIRC it was Merlin that made the "magic box"
Ian

I used to drive seariders in the Navy, we used to drop them 20' into a force 8 sea, with the 85BHP outboard running dry at 8000rpm, smash into heavy seas at 40 knots plus, it never seemed to flex at all, but I did once tear the inflatable bit off the bow and we nearly sank whilst showing off to my parents at Hayle Bar.

I think we should find one, jigsaw it in half, count the laminations and measure the foam thickness, or just fit wheels to the damn thing!

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Originally posted by stutz
What about using chromoly? Check out a few homebuilt aircraft sites, they all use chromoly tubing to build their spaceframes. Just checked it comes in all the sizes required by 'the book'.

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quote:

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Originally posted by robinbastd
I've read several fibreglass/composite books and scoured the net looking for details on the construction of fibreglass/foam sandwich monocoques and can't find enough detail. (thickness of foam core,what weight cloth,how many layers,etc) Any ideas???
Ian

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Hello, first post on here. I have been thining of building a composite Locost chassis once out of uni so am interested in this thread. Carbon Fibre (CFRP) is well out of my budget so GRP is the choice.

It is far more resiliant and repairable tha CFRP but weight vs strength is obviously down.

There are better GRP cars out there. I am building a Clan Crusader that has much much better tosional rigidity and general strength than the Davrian and is made in a different way. The rear cross member mounts all the pick-ups and engine mounts and fits into a moulded recess in the floor pan which bolts through some reinforcing into the chassis basically

One shell I have was rolled at over 100mph and has shown very little in the way of delamination around the seems...

The Clan was designed and built fast road/competition use by former Lotus engineers and is generally considered to be the best and most effective of all Imp derivatives. The chassis is a full monocoque consisting of plywood and GRP with some plates bonded in for mounting the cross member and front wsh bone pick up points. Bonded into the chassis itself was a GRP rollcage that managed support a skip and several tons of water in order for the MSA to pass it for competition use on the Manx.

If you have the budget, you would be daft not to go down the honeycomb route and to glass around it.

You want the minimum number of seams and sharp angles as possible otherwise torsionary rigidity will suffer and fatigue will accelerate due to increased stress concentrations.

As far as copying the marine industries processes, that will be big bucks as they enerally use a mix of Kevlar, Carbon and Nomex board

[Edited on 22/3/04 by imull]

Older rivetted/bonded honeycomb construction tubs are notorious for 'loosening up'. Most of these chassis are in a constant state of repair. Not ideal for a street car. To avoid this you need to use some pretty exotic bonding methods such as those uses by Lotus. However, you can't do this at home because you need an oven to bake the chassis in.

quote:

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Originally posted by imull
snip
out of uni so am interested in this thread. Carbon Fibre (CFRP) is well out of my budget so GRP is the choice.
Yes that is correct

It is far more resiliant and repairable tha CFRP but weight vs strength is obviously down.
Strengthi is not my carbon fibres are use the are STIFFER the glass or kevlar.


There are better GRP cars out there. I am building a Clan Crusader that has much much better tosional rigidity and general strength than the Davrian

Pull the other one ! first you should take a look at THE "works" Clan the ex-Johnnie Blades, ex Kenny Allen works modsport car that has been owned trundled by Stan Share for about 25 years for most of which it has been 10,000 fatigue cracks driving in close formation. It had be raced hard by Blades and with famous successfully by Kenney Allen (mainly due to Allen sorting of the handling and brakes and the ultra special 1140 Carter engine which was without doubt the best Imp engine I have ever driven) but at the end of Allen's steward ship the shell was about raced out.
This works car was a very different annimal from the road shell it was substantially strengthened (where as proper modsport Davrian such as the Mk8 shell made for Ian Forrest were thinner than the road cars) , a few people have tried to build relicas using road Clan shells and failed.



"and is made in a different way. The rear cross member mounts all the pick-ups and engine mounts and fits into a moulded recess in the floor pan which bolts through some reinforcing into the chassis basically"

Actually the floor in front of the (Imp) crossmember was a major failure point on early Washington built Clans, I have seen road going clans split across the full width of the floor in this area.

One shell I have was rolled at over 100mph and has shown very little in the way of delamination around the seems...


The Clan was designed and built fast road/competition use by former Lotus engineers and is generally considered to be the best and most effective of all Imp derivatives. The chassis is a full monocoque consisting of plywood and GRP with some plates bonded in for mounting the cross member and front wsh bone pick up points. Bonded into the chassis itself was a GRP rollcage that managed support a skip and several tons of water in order for the MSA to pass it for competition use on the Manx.

The strength of the "paper" roll cage in the Clan is not in doubt. ****But significantly the the Blades-Allen-Share car has a steel roll cage.


If you have the budget, you would be daft not to go down the honeycomb route and to glass around it.

You want the minimum number of seams and sharp angles as possible otherwise torsionary rigidity will suffer and fatigue will accelerate due to increased stress concentrations.

As far as copying the marine industries processes, that will be big bucks as they enerally use a mix of Kevlar, Carbon and Nomex board

[Edited on 22/3/04 by imull]

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quote:

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Originally posted by britishtrident

snip
out of uni so am interested in this thread. Carbon Fibre (CFRP) is well out of my budget so GRP is the choice.
Yes that is correct

It is far more resiliant and repairable tha CFRP but weight vs strength is obviously down.
Strengthi is not my carbon fibres are use the are STIFFER the glass or kevlar.

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quote:

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There are better GRP cars out there. I am building a Clan Crusader that has much much better tosional rigidity and general strength than the Davrian

Pull the other one ! first you should take a look at THE "works" Clan the ex-Johnnie Blades, ex Kenny Allen works modsport car that has been owned trundled by Stan Share for about 25 years for most of which it has been 10,000 fatigue cracks driving in close formation. It had be raced hard by Blades and with famous successfully by Kenney Allen (mainly due to Allen sorting of the handling and brakes and the ultra special 1140 Carter engine which was without doubt the best Imp engine I have ever driven) but at the end of Allen's steward ship the shell was about raced out.
This works car was a very different annimal from the road shell it was substantially strengthened (where as proper modsport Davrian such as the Mk8 shell made for Ian Forrest were thinner than the road cars) , a few people have tried to build relicas using road Clan shells and failed.

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quote:

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"and is made in a different way. The rear cross member mounts all the pick-ups and engine mounts and fits into a moulded recess in the floor pan which bolts through some reinforcing into the chassis basically"

Actually the floor in front of the (Imp) crossmember was a major failure point on early Washington built Clans, I have seen road going clans split across the full width of the floor in this area.

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quote:

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The strength of the "paper" roll cage in the Clan is not in doubt. ****But significantly the the Blades-Allen-Share car has a steel roll cage.

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Alec Issigonis made some sort of home-brew lightweight special in the 50's that used a laminated balsa (I think) for increased torsional rigidity. I don't think any special high-pressure ovens were constructed to cure it etc.

Surely, if we can bodge home made TIG welders, de-rusting equipment etc, someone must have some super-cheap ideas?

Cheers,

Neil

A technique used in Japan in production-class race cars is to mix up 2-part foam and inject it (with a syringe) into the voids in the unit-body. Although this technique requires bracing of the frame to prevent flexing, the results boost rigidity up to 75% from what I've heard.

2-part foam isn't the lightest thing so it won't help that much for straight line performance, but the increased rigidity will improve handling more than it would be penalized by increased weight.

At the same time, you may be able to use much thinner steel tube to save weight...

Just a thought.

As for Carbon Fiber Monocoque, unless you have the funds for pre-preg cloth, the molds to form it, a room-size curing chamber (with both atmospheric pressure and temperature control) and the means to fuse it to the aluminum honeycomb, it probably isn't a practical possibility.

-MR

quote:

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Originally posted by Noodle
Alec Issigonis made some sort of home-brew lightweight special in the 50's that used a laminated balsa (I think) for increased torsional rigidity. I don't think any special high-pressure ovens were constructed to cure it etc.

Surely, if we can bodge home made TIG welders, de-rusting equipment etc, someone must have some super-cheap ideas?

Cheers,

Neil

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If it's stiffness for minimum weight you want then one tube is best. This is the idea behind backbone chassis as on the Lotus Elan (original) and Esprit. However this kind of chassis requires a much more substantial body shell as this needs to be virtually self supporting away from the central chassis and will also need to support bits that would normally be chassis mounted like the steering column and the door hinges.

The Lowcost chassis can be stiffened up a lot for no extra weight. My suggested mods take the stiffness from around 1200 ftlbs per degree to around 2700, reduce the weight and use less tubes.

If you used my mods but in 18g tube and 20g sheet then you'd have a light weight chassis that would still be 50% stiffer than the book design. The only down side is that you'd need to be carefull about how loads were fed into the chassis. For example tubes G1/G2 may need to be in 1.5 inch deep tube to resist the engine weight or extra triangulation to the engine mounts may be needed.

The standard 16g tube is probably over engineered but is cheep, available, proven and can be made into a stiff structure by an amateur welder.

Anyone looked at RHE's latest offering ?

quote:

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Originally posted by cymtriks
If it's stiffness for minimum weight you want then one tube is best. This is the idea behind backbone chassis as on the Lotus Elan (original) and Esprit. However this kind of chassis requires a much more substantial body shell as this needs to be virtually self supporting away from the central chassis

snip snip snip

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