leto
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| posted on 23/7/03 at 05:54 AM |
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quote:
Originally posted by craig1410
Leif, The weight benefit is not that big IMO............
Craig, IMO 10 - 15 kg is a big benefit. There are not many places on a locost where you can save that much.
Once you decided on the drive train there is not much to do about that. The only other place i can think of right now, is, in my case, the driver 
Leif.
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craig1410
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| posted on 23/7/03 at 09:57 PM |
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Leif,
However, using projectLMP's figures, a 12 square foot section(roughly what I needed for my floor) of 16swg Ally is about 4.8 KG and in 18swg
steel it is 11.6Kg. This is only a saving of 6.8Kg's and doesn't take account of all the extra structural braces you would need to add to
the chassis to replace the strength taken away by using the aluminium and all the rivets which if of the solid type surely must add up to 0.5 to 1Kg
on their own. So I reckon that you will only save maybe 4 or 5 KG's not the 10 to 15Kg's that I originally thought might be possible.
In my humble opinion unless you are building a car purely for competition and probably using aluminium for the spaceframe as well, it is just not
worth the hassle to use aluminium for the floor. You could easily save 6.8 Kg's elsewhere on the chassis and give greater benefit to the overall
design than on an Ally floor.
Using alloy uprights for example or using magnesium wheels. This would cut unsprung weight and give a potentially greater weight saving. You could
reduce the fuel tank size or use lightweight seats or throw out the carpets or lose the radio cassette etc etc.
I appreciate and respect everyone's opinion's completely but for me there is no need for an aluminium floor in a Locost. There....said it,
it's official !
Cheers guys,
Craig.
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Noodle
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| posted on 24/7/03 at 08:03 AM |
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Of course, ignoring the Locost idiom totally, a honeycomb (aluminum, nomex or somesuch (balsa! )) would give superb stiffness and have a lighter
strength to weight ratio.
It'd have to be bonded though, but that would remove any worry about rivets!
Anyone got any stiffness/weight figures to hand?
ATB
Neil.
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David Jenkins
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| posted on 24/7/03 at 08:10 AM |
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Personally, if I were to use aluminium instead of steel, I would feel obliged to go for a thicker section to protect against penetration by rocks,
etc.
I'd probably use 3mm ali instead of 1.6mm steel.
This means that the weight difference would not be so great.
Just my 2p!
David
[Edited on 24/7/03 by David Jenkins]
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kingr
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| posted on 24/7/03 at 08:31 AM |
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Noodle : I think you might be suprised how little difference expensive honeycomb composites make in this application. Cymtriks fairly recently posted
a site of someone who had modified an ultima chassis to make it stiffer and measured the effect of each one, and while some modifications where
extremely effective, putting in an expensive floor, while looking very good made no noticeable difference to the stiffness of the chassis!
This isn't exactly comparing like with like, but it does give some indication.
Kingr
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leto
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| posted on 24/7/03 at 08:35 AM |
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Craig,
thanks for the calculations. With good numbers it's lots easier to make good decisions. 
I think you are right there. There is no point to put down that much work and money to save that little. I'm not very keen on stressed alloy
skins anyway, as they generally fatigue more easily than steel.
Alloy uprights and magnesium wheels is somewhat to the "hicost" side, think I'll stick to saving weight on the driver.
BTW I 'm a little bothered by the lack of "good numbers" in this discussion. Protofj have shared some thumb rules, (thank you
protofj, very useful ) but that's about it. Anyone out there how have any calculations on aluminium gauge, rivet size, rivet c/c, number of
rivets or something like that, for a locost floor?
Cheers Leif
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Noodle
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| posted on 24/7/03 at 08:36 AM |
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Thanks Kingr,
I suppose it's the law of diminishing returns. If the chassis's already stiff and suitably fit-for-purpose it won't make much
difference, good-looking or not.
Has anyone got a CAD modelled chassis that could show how this could affect the Locost?
ATB,
Neil.
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pbura
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| posted on 24/7/03 at 10:52 AM |
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With not so much of a weight penalty for steel, I am considering using 18 ga. steel for the area behind the seats as well.
This would have to help stiffness somewhat, and would get me down to no rivets to speak of (plan to use 3M VHB tape for most ally panels).
Pete B.
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blueshift
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| posted on 24/7/03 at 11:49 AM |
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We have a CAD-modeled chassis, but just for dimensions and fit, not stress analysis. It's more or less a mcsorley 7+4, but we're fooling
around with it a bit.
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Dale
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| posted on 25/7/03 at 11:53 AM |
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Has anyone calculated the weight penalty of using all 18gage or using 20gage one the side and back pannels instead of alloy.
Dale
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Stu16v
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| posted on 25/7/03 at 09:33 PM |
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Dale, couldnt give you accurate figures for replacing panels with steel, but for ease of working aluminium is probably more suitable for these panels.
Ali bends far easier (quite important especially iwth the back panel), and the temptation with steel is to weld to chassis. This will give ultimate
strength, but can mean that the panels are at risk of heat distorting, which will be virtually impossible to remove.
HTH Stu (From the aluminium floor and panel camp )
Dont just build it.....make it!
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craig1410
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| posted on 25/7/03 at 11:37 PM |
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I agree with Stu16v on this one. I'm all for a steel floor as you will know already but for exterior body panels I think that Aluminium is the
way to go for both ease of working and corrosion resistance. However, I will be looking at this magical 3M tape for bonding it rather than messing
about with loads of rivet's. The body panels aren't structural as far as I can see and thus are just for aesthetic value. I may look at
using fibreglass as an alternative too.
My opinion is to use steel for the floor and behind the seats but to use Aluminium for the cosmetic panels.
HTH,
Craig.
[Edited on 25/7/2003 by craig1410]
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Dale
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| posted on 27/7/03 at 03:34 PM |
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has anyone considered attatching a thicker piece of alloy bar on the attatchment points and tapping it so it can be bolted to the steel frame- the
alloy bar and sheet could be welded to each other then bolted on????
Dale
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craig1410
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| posted on 27/7/03 at 06:01 PM |
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Dale,
If I'm understanding you correctly then the only disadvantage I can think of is the need to weld in crush tubes into the steel frame everywhere
that a mounting bolt would be going. I'm sure you are aware that you can't just drill a hole through a tubular member and then put a bolt
through it so maybe you are meaning something else. For example, having small mounting brackets welded to the inside edge of the lower chassis rails
to take little set screws.
You could potentially use rivnut's attached to the lower chassis rails as these don't require crush tubes. You could then use a slightly
thicker ally sheet for the floor (or the flat bar you were talking about here) and using countersunk set screws you could mount the floor.
In any event, I stand by my own statement that aluminium isn't justified for a Locost in all except the purest competition purposes where ANY
extra weight is to be avoided at all costs.
Cheers,
Craig.
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Stu16v
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| posted on 27/7/03 at 06:01 PM |
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Welding thick alloy to light sheet will be virtualy impossible without a lot of distortion.
IMO its best (and simplest) to rivet the panels straight to the frame, sealed and bonded to boot with a decent sealer/adhesive. If you dont like the
rivets showing, wrap the ali round the chassis members.
HTH Stu.
Dont just build it.....make it!
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Surrey Dave
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| posted on 30/7/03 at 05:53 PM |
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Floor
I welded my mild steel floor all the way round the edge, I wanted it water proof!!!!!, There was some distortion but not toooooo bad.
see car at: http://www.groovy42.freeserve.co.uk
[Edited on 30/7/03 by Surrey Dave]
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craig1410
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| posted on 30/7/03 at 06:48 PM |
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That's my theory too, keep the water out (or is it keep the water in...)
More importantly is to keep the water and salt etc out of the seam between chassis and floor or it will rot big time. I intend to seam weld the outer
seam only once I have stitch welded the inner seam (1inch weld, 5inch gap). That should hold everything in place and minimise the amount of heat that
I'm putting in to the metal. Even when I seam weld the underside I will do it alternately on each side and only do 3 inches at a time before
moving elsewhere. At the end of the day who cares about a little bit of distortion as it's under the car anyway.
Cheers,
Craig.
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mranlet
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| posted on 30/7/03 at 07:05 PM |
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As long as the floor is diagonally braced, even with the smaller diameter 1" pipes that are used along the engine bay, the need for any
structurally supporting floor panel is minimal.
I agree that 18swg be better all around than 16 (one could probably even get away with 20swg with Mark's ribs). The transmission tunnel is a
much higher concern for me, and I will most certianly weld 16swg plates along the cabin side of the tunnel to double as structural support and shatter
guard for the driveshaft and transmission (i don't want to be sorry that I chose a 300+hp motor). In order to get an idea how the stress
transmission behaves, build some balsa wood models of the transmission tunnel and side walls and a floor - I know it's not really fair to
transcend materials like that, but the underlying structural ideas carry over from metal to wood - the tunnel and side walls direct much more of the
torsional force through the frame than the floor alone. IMO, if you're going to use heavy pieces, use them here where they will protect you!
I plan to diagonally brace my floor and lay a fiberglass "tub" along the exterior of the frame for the floor. This tub will extend up
along the sides, as well as over the front and rear bulkheads. Given that I can make this tub continuous and enveloping to some of the key frame
members, it will most likely add more structural support than a simple panel of metal. My car will also be closed in from the weather, so I
won't have to worry about rain accumulating on the inside. I will have a gap in the fiberglass to span the underside of the transmission
tunnel, where I will mount a removable panel that is to be raised from the level of the rest of the floor. This panel is mainly to direct air out
from under the car in an effort to generate downforce. Downforce, I imagine, is somewhat of a silly thing to worry about woth Locosts, whereas
I'm building a full-bodied car complete with downforce-inducing panels and planes...
Anyway, I totally agree that the messing around with aluminum is probably not worth the weight savings (except for extreme applications). One thing
that is important to me is to have faith in your engineering: piece of mind is always more important in my book. I am not one to quickly dismiss
saving 10 or 15kg (20 lbs for me ), but I would rather buy a lightweight Kirkey racing seat in leu of a fully upolstered job and be less one gallon
of fuel capacity than wonder if the seal between my floor and frame is going to hold up...
Besides, my girlfriend only weighs 100lbs (45kg)
Hope this helps, and let me know if I'm too much of a loon
-MR
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mranlet
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| posted on 31/7/03 at 08:47 PM |
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quote:
Originally posted by ProjectLMP
A 4' by 12' sheet of 0.063" ali weights about 42.5 lbs (19kg)
The same size and gauge steel about 125 lbs (57kg)
0.050" steel same size weighs about 102lbs (46.5kg)
[Edited on 23/7/03 by ProjectLMP]
If this is the case, your floor is only using a 4' by 4' rectangle IIRC... the .050" steel would be more comperable to the
.063" alu sheet... so, since 4'x4' is 1/3 of 4'x12' we take 1/3 of 102lbs and get 34lbs (15.45) for steel versus
the 14.167lbs (6.44kg) for alu.
Therefore, an alu sheet saves you only 19.833lbs (9.015kg), or the equivalent of about 1 gallon of gasoline and a full stomach. (by the way,
don't race until 20 minutes after eating)
I hope these numbers help you with your decision.
-MR
[Edited on 31/7/03 by mranlet]
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mranlet
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| posted on 31/7/03 at 09:22 PM |
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By the way, I've posted a thread about Carbon Fiber (due to it's availibility on Ebay) in the LOCOST RELATED section. I've thought
about using Carbon cloth for body panels, but could it also be used for frame re-enforcement as well? Maybe a Carbon floor panel?
If anyone knows anything about it (of which I know little) please do comment...
Thanks
-MR
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craig1410
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| posted on 31/7/03 at 09:55 PM |
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mranlet,
Yes I pointed this out on page 3 of the thread and in fact my estimate put the difference at 6.8 KG's due to only needing about 12 sq ft of
steel/ally for the floor. I am gauging this by the fact that I bought a 6ft x 3 ft sheet and still have between 4 and 6 sq ft left. I also pointed out
that this doesn't take account of the weight of all the rivet's and extra structural braces which may be required with aluminium which
aren't needed with steel. Yes the steel welds will weight a little bit but not much if done correctly.
One advantage of Aluminium which I don't think has been mentioned is that it should be quieter and less likely to "drum" like steel
but as Mark pointed out you can achieve this effect with steel by using some 13mm ERW up the underside.
Cheers,
Craig.
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jcduroc
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| posted on 20/9/03 at 11:42 PM |
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ALU HONEYCOMB FLOOR
quote:
Originally posted by leto
On a locost chassis the floor is intended to be a stressed member. Much of the torsional stiffens depends on how well forces are transferred from the
frame to the floor ...
leto
Has anyone considered using aluminium honeycomb plate to make the floor? (My LHS brain cell just popped this idea!...)
If doing so how would you "connect" it to the frame?
JCM
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JoelP
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| posted on 21/9/03 at 12:07 AM |
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it has been mentioned in a thread called 'subject: floor rivet requirements' or something along those lines. if you search for honeycomb
it comes up in a fairly short list.
it was mentioned that it is prone to puncture and delamination.
all hearsay as i dont even know what it is!
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Noodle
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| posted on 21/9/03 at 09:18 AM |
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quote:
Originally posted by jcduroc
Has anyone considered using aluminium honeycomb plate to make the floor? (My LHS brain cell just popped this idea!...)
If doing so how would you "connect" it to the frame?
Hi,
I mentioned this earlier in the thread. The response I got was that it wasn't worth it. As to delamination and what-have-you, I have no
experience, but I would have thought a ready-made Nomex or Aluminum honeycomb would be strong enough.
Come to think of it, if one was to follow this route, why not just stick a few transverse bulkheads on the honeycomb and do away with the steel floor?
I sketched this out last night, with areas cut in the floor for transmission/diff/sump and the sides as structural members. It looks sensible enough,
but manufacturing is beyond me.
Cheers,
Neil.
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Browser
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| posted on 21/9/03 at 10:30 AM |
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quote:
Originally posted by mrantlet: My car will also be closed in from the weather, so I won't have to worry about rain accumulating on the inside
Get yer knife and fork ready, there's a good chance at asome point in the future that at least some of those words will need eating
quote:
Besides, my girlfriend only weighs 100lbs (45kg)
100lbs? That's only just over seven stone! Who the hell is she, Kylie Minogue?
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