rallyslag
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| posted on 21/9/02 at 06:54 PM |
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strengh - will it be enough
i know the standard locost chassis is strong
but i am buiding a locost yank tank with a stupid amount of ponies and torque 
will the 1" 16swg be enough?
or should i use a thicker metal tube
or could i just get away with adding a few more supports here and there?
thanks
Old chinese proverb: "If a man speaks in a forest, and no woman hears him, is he still wrong?"
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Alan B
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| posted on 21/9/02 at 08:36 PM |
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Adding some more, strategically placed, diagonals will always be more effective than just upping the thickness right through.
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rallyslag
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| posted on 21/9/02 at 09:01 PM |
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where would you recommend i add the extra support?
Old chinese proverb: "If a man speaks in a forest, and no woman hears him, is he still wrong?"
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Alan B
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| posted on 21/9/02 at 09:20 PM |
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My build is nothing like the book so I'm the wrong guy to ask about specifics, but I'm sure some will pick up on this and advise you.
Mine's an MR2 powered mid-engined jobbie
http://www.desicodesign.com/meerkat/
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bob
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| posted on 21/9/02 at 09:27 PM |
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hicost runs nearly 400brake without the NOS,his chassis is as book but a bit wider and a tad longer and copes well enough. 
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cymtriks
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| posted on 24/9/02 at 08:00 PM |
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A while ago I posted the results of my finite element analysis of the lowcost chassis. This type of analysis is used by major manufacturers to assess
their designs. This is how to up rate the standard lowcost chassis.
All tubes in the original design remain as in the book. Extra tubes are assumed to be 1 inch square with 16 gauge wall thickness. All steel panels,
except for the seat belt mount reinforcements, are 18 gauge.
Form a V joining the centre of tube LC to the ends of tube LD. This triangulates the front with the tubes running immediately behind the radiator. The
reduction in airflow will be minimal. If radiator, fan or water pipe clearance is a problem then a diagonal or X brace across the chassis in this
position may be used. Alternatively a similar modification connecting the ends of tubes FU1 and FU2 may be used but may cause clearance problems with
the front of some engine ancillaries.
Form two diagonal braces, one on each side of the chassis, between the tops of tubes LA and LB and the bottoms of tubes FU1 and FU2. This carries the
triangulation of the chassis sides right to the front of the chassis and crosses the rectangular hole in each side of the chassis roughly defined by
the top and bottom wishbone mounting points. Check that there is room for the steering rack.
Weld in a panel across the bottom of the chassis between tubes E and LD. This replaces the alloy panel referred to in the book.
The next step is to box in the transmission tunnel from tube O3 to tube P. If you are concerned about weight it is worth noting that the ¾ inch tubes
forming the frame of the transmission tunnel do nothing if this modification is done. Check a Caterham chassis if you find this hard to believe, it
has a very light structure in this region indeed. A single arch over tube B2 may be required to give local reinforcement to support the handbrake or
gearshift mechanisms.
Some lowcost builders have reported that the floor is prone to flexing when thin gauge steel is used. Floor reinforcing tubes, running parallel to B2
and just in front of or under the front of the seats may be welded in, one on each side of the car.
We now have:
Chassis with modified front, 18 gauge sheet steel panels and boxed in tunnel with no internal ¾ inch tubes
The stiffness is 2449 ftlbs per degree of twist and the weight is 144 lbs
Thats a good all round improvement for not much effort.
Note that the weight is lower, the stiffness much higher and the number of tubes is reduced compared to the basic chassis built to the book which
proves that extra strength need not mean extra weight or complication.
Note that if a Satchel link is used to locate a live axle or Deon axle or if an independent double wishbone suspension is used then the tubes around
the back of the transmission tunnel will need to be stronger than ¾ inch and should be 1 inch square as a minimum.
A lot of builders seem to think that extra bracing or welded in panels will just add weight and simply omit it. This is a false economy as a properly
braced frame can be made out of smaller or thinner walled tubes thus more than compensating for the extra tubes. My modifications for the lowcost,
given above, actually reduce the overall number of tubes by making the remaining tubes work a bit harder for their keep.
All the above was aimed at a standard build. For a bigger engine, especially a US V8, I would suggest using one and a half inch deep upper and lower
tubes on the chassis sides (tubes N, J, A, D and F) and on tubes C, G and E. I would also suggest replacing tubes TR with tubes running from the top
rails where they join tubes H and FU to the engine mount base positions. This creates a V brace each side of the chassis with the engine mount
positions at the point of the V and the tops of tubes FU and H (on the outside of the chassis, not the inside H tubes)at the ends of the V arms.
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James
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| posted on 24/9/02 at 09:25 PM |
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Hi Cymtriks,
Really interesting stuff.
What I did notice was that you said it'd be lighter but I can't see from the below info' where you've removed any tubes.
It's probably just me being blind so point out what I've missed willya please! 
Thanks,
James
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stephen_gusterson
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| posted on 24/9/02 at 10:15 PM |
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he uses 18 swg for the floor instead of 16, and had omitted the tranny tunnel.
atb
steve
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rallyslag
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| posted on 25/9/02 at 03:01 AM |
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well weight isnt the problem really as im using a big iron V8 anyway i just wanna make sure it doesnt bannana under throttle
Old chinese proverb: "If a man speaks in a forest, and no woman hears him, is he still wrong?"
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cymtriks
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| posted on 25/9/02 at 07:25 PM |
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The weight saving is due to the transmission tunnel tubes being deleted and the sheet steel being replaced by 18 gauge. The transmission tunnel is not
deleted; it is replaced by a sheet steel structure of the same size as the original tunnel and is important to the overall chassis behaviour.
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twentyover
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| posted on 4/10/02 at 09:58 PM |
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This question, I guess, is targeted at cymtriks.
I would think that widening the spaceframe 2 to 4 inches as some have done, or raising it an inch or two would have a significant positive impact
torsional strength, in addition to fitting my lard butt better. Without trying to quantify it, do you believe this would improve the strength of the
chassis?
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cymtriks
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| posted on 7/10/02 at 09:02 PM |
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making the sides deeper and the frame slightly wider should make things slightly better. I have done a comparison of ladder frame chassis designs and
they get stiffer as they get wider. Going from a narrow body, like the lowcost, to full width with the frame side members in the sills, like a Cobra
kit, adds about 25% to an X braced ladder frame. I might have a look at wider and deeper finite element models as these seem to be common alterations.
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cymtriks
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| posted on 8/10/02 at 09:04 PM |
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I have just checked it out by moving the chassis sides 2 inches out on each side from the front to the back of the chassis. The stiffnes goes up to
12% over the book chassis.
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rallyslag
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| posted on 9/10/02 at 01:59 AM |
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how accurate are these messurements?
i know they are done by computer and this is no disrespect towards you
but surley untill somthing like this is tested the stiffness cant really be measured?
Old chinese proverb: "If a man speaks in a forest, and no woman hears him, is he still wrong?"
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cymtriks
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| posted on 16/10/02 at 09:40 PM |
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That's a very good question. I honestly don't mind being asked as I was expecting it sooner or later and I'm used to it at work. My experience
suggests that my models are within 10% and possibly within 95% of accuracy. I know someone at work who got a finite element analysis result of
1500ftlbs per degree for a Westfield which is similar to my result of 1200 to 1400 for a lowcost depending on the build. I think that my model is
slightly more realistic as theirs assumed that the alloy panels were fully load bearing while I assumed they weren't. I know that the two chassis
aren't exactly the same but this is a reasonable cross check. As for real tests I got 6300ftlbs for a Stratos replica that acheived "over 6000"
when tested and got 7000ftlbs for the Elise which Lotus claimed to have 7350. I would emphasise that finite element results are allways approimate
especially with something like the lowcost or other kit car chassis. It is important to know what is and isn't accounted for. All my results are
based on the welded steel structure only and do not include fine details such as the shape of suspension mounts and the effect of access holes or
brackets. Individual builds can vary a bit one to another so it probably isn't worth going to greater accuracy.
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wayner
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 posted on 17/10/02 at 09:12 PM |
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Cymtriks are you able to analyse steel frames if carbon fibre strengthening panels are added, I'm interested in a mid mount very light weight BEC and
think that if the basic frame is built to locate the suspension and then infill using carbon foam carbon to absorb the flex, it will allow a much
narrower front.
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cymtriks
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| posted on 22/10/02 at 04:45 PM |
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In theory, yes. This would add a lot more variables to the model. There is more than one type of carbon fibre panel and, likewise, several different
ways that such a panel could be fitted to a chassis. At the moment my chassis models are simple, from an FEA point of view, and are aimed mainly at
giving good results for overall distortion and showing up any grossly overstressed regions. Adding composite panels would probably require a much more
complex and time consuming model that I might not be able to fit in around my real work. I'm just guessing here as, though I work in the aerospace
industry, the work I do relates to metal parts and structures mostly of steel, aluminium and titanium. I would suggest that a better solution for a
very light weight chassis may be to use all my suggested mods but with 18 gauge tubes and 20 gauge panels for the whole chassis, except seat belt,
drive train and suspension mounts. This would still give a stiffer structure than the book chassis (circa 1800 versus circa 1200/1400) but would be
25% lighter. If your whole car is very light you will get away with 18 gauge for the tubes as some race cars use this tube wall thickness. It may be a
good idea to either retain 16 gauge where loads are fed into the structure or to use 1 x 1 and 1/2 inch 18 gauge tubes with the 1 inch face facing the
load. Hope this helps.
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wayner
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| posted on 23/10/02 at 03:42 PM |
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Thanks, I had hoped to " tape ( bond using 50mm wide epoxy soaked tape )" in the composite panel as having to rivet in side panels etc is a bit
agricultural and we have to fit side panels floors etc any way, why not just make them structural.
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Nuclear Jimbo
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| posted on 23/10/02 at 07:52 PM |
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Hmm, I'd considered bonding the ally side panels to the chassis with structural epoxy and 'belt and braces' Cherrylock rivets - if it works for
Thrust SSC, it'll work for a Locost...
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paulbeyer
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| posted on 23/10/02 at 09:17 PM |
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What the hell are cherrylock rivets? and what other flavours can you get? 
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Nuclear Jimbo
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| posted on 24/10/02 at 08:18 PM |
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quote:
Originally posted by paulbeyer
What the hell are cherrylock rivets? and what other flavours can you get?
Cherrylocks are structural pop rivets. In a 'normal' rivet, the two panels are held together with what is basically a thinwall aluminium tube as
the steel mandrel has been pulled out by the rivet gun. With a Cherrylock, the mandrel stays within the 'tube' and breaks off flush with the head
of the rivet. Because of the extra bit of steel they're about twice as strong as an ordinary rivet and are used in aircraft structures. Cherrymax
rivets have a separate collar which locks into the head and are even stronger but are expensive with a capital 'F'
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jcduroc
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| posted on 31/10/02 at 03:06 PM |
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quote:
Originally posted by cymtriks
The next step is to box in the transmission tunnel from tube O3 to tube P. If you are concerned about weight it is worth noting that the ¾ inch tubes
forming the frame of the transmission tunnel do nothing if this modification is done. (...) Some lowcost builders have reported that the floor is
prone to flexing when thin gauge steel is used. Floor reinforcing tubes, running parallel to B2 and just in front of or under the front of the seats
may be welded in, one on each side of the car.
Following 'cymtricks' explanation I wonder if this central section could not be made of carbon fibre, for the same stifness and rigidity and less
weight? Structure and padding should be done in one, with quite a "look".
Could you estimate the figures resulting from such a mod?
Comments please.
Joćo C.M.
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stephen_gusterson
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| posted on 31/10/02 at 08:17 PM |
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quote:
Originally posted by Nuclear Jimbo
Hmm, I'd considered bonding the ally side panels to the chassis with structural epoxy and 'belt and braces' Cherrylock rivets - if it works for
Thrust SSC, it'll work for a Locost...
I have actually met andy green and mr noble, and touched and been at a presentation of thrust ssc.
We were told that SSC could not have stood too many more runs as it was breaking so many rivets and structural parts every time it went out.
fantastic acheivement.
atb
steve
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cymtriks
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| posted on 6/11/02 at 10:05 PM |
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composite tunnel
I agree that a carbon tunnel would combine a great look with, possibly, a better structure for the chasis. The big problem with this is how it is
fixed to the rest of the chassis. Bonded in, riveted or bolted? If boding is used what will happen if rust gets in between the carbon and the steel?
Rusting internals can burst open a carbon panel. I'm not sure how to approach a worthwhile FE model of this as not only are there several different
ways of fixing the carbon tunnel but there are also a lot of variations of carbon and resin for the tunel itself. A complex model may be the answer
but I can't fit this sort of job into spare coffee breaks and lunch breaks! If I can get hold of a simple method of looking at this I'll let you
know.
In the mean time I've often thought that a round top, as on a Caterham, looks better and is slightly better from a weight point of view as well. If
it is possible to weld stainless steel to ordinary steel then this could look good especially if given a "turned" finish as on vintage race car
dashboards.
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jcduroc
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| posted on 26/11/02 at 05:39 PM |
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Chassis FEA
quote:
Originally posted by cymtriks
I would suggest that a better solution for a very light weight chassis may be to use all my suggested mods but with 18 gauge tubes and 20 gauge panels
for the whole chassis, except seat belt, drive train and suspension mounts. This would still give a stiffer structure than the book chassis (circa
1800 versus circa 1200/1400) but would be 25% lighter. If your whole car is very light you will get away with 18 gauge for the tubes as some race cars
use this tube wall thickness. It may be a good idea to either retain 16 gauge where loads are fed into the structure or to use 1 x 1 and 1/2 inch 18
gauge tubes with the 1 inch face facing the load. Hope this helps.
Have you ever analysed an Elan backbone chassis? Or the Spyder replacement one?
Wouldn't a Locost chassis based on that layout, with 18 swg tubes and welded 20 swg steel panels, supplemented by side rails (top and bottom) be more
rigid than the book one?
Joćo Matoso
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