ProjectLMP
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| posted on 7/8/03 at 04:01 PM |
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I would think the best way to reduce weight would be to use 3/4 round for diagonal bracing and substitute some of the less highly stressed members for
18g tubing instead of 16g.
Home of the Astronomicalcost Mid engined LMP project
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mranlet
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| posted on 7/8/03 at 04:48 PM |
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LOL, we all kinda got a little absorbed into the idea of exotic materials, huh? 
You could probably preserve the torsional rigidity if you essentially build one big trans. tunnel that would hook up to the front and rear
suspensions.
One of my origional plans was pretty much one big piece that looked somewhat like a chicken bone with a groove cut out of it on the top side to hold
the engine. The addition a thin bulkhead front and thinner one rear joined together by 1.5" RHS beams outboard and 3/4" tubes cross
braced gave a very rigid frame considering its simplicity. The frame that I have now is really just a beefed up version of the same thing in order to
accomodate the higher power levels that I have planned for it. Although, my current concept has really been developed into something more than the
origional.
With a strong enough torque tube, you might be able to bold seats, suspension, steering, and fuel tank to it and have yourself a superlight - just
don't get in an crash.
-MR
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twentyover
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| posted on 7/8/03 at 06:36 PM |
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Well, for me at least-
Taking 30 pounds off the driver is the most cost effective way of getting a lighter car. Except for the cost of my new wardrobe.
My take on this is that it is easiest to get weight reductions by attacking the heavy stuff first. I saw one engine that a guy spent 3 months in
evenings cleaning up the block of EVERY casting feature that wasn't required. Seems it pulled 15 pounds of. Smokey Yunick, on one of the
stockblock chevrolet Indycar engines in the early '70's ground close to 30 pound off an engine block.
Do we really need big car (2500lb) rear axles for these things? Can we get away with a Spridget or (in the US) a Datsun 1200 axle? The banjo axle in
my MGB weighs about 40 pounds less than the later tube type. So I guess I don't need to loose those 30 pounds- and it's unsprung to
boot.
Same with the fronts- are we putting big brakes on for street cred or do we really NEED them on a 1200 pound car
The attraction for me in BEC is that you cut out 150-200 pounds off the CEC configurations.
Want to take some weight off the frame? Look at larger thinner section steel tubes. I think cymtriks underestimated here- I believe it's the 4th
power of diameter change, not the 3rd, that affects tube stiffness as a function of cross section. This tubes will have the same load carrying ability
in tension and compression as the smaller tubes, but may well be lighter (haven't done the calculations, so I'm not going to state this as
fact.)
Everyone must (and should) follow their own path. Listen to others, and follow your own advice.
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TheGecko
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| posted on 8/8/03 at 01:01 AM |
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quote:
Originally posted by mranlet
You could probably preserve the torsional rigidity if you essentially build one big trans. tunnel that would hook up to the front and rear
suspensions.
Sound like the STP turbine Indy car "Silent Sam" which had the gas turbine on one side of the backbone and the driver on the other. Oh,
and 4WD and inboard suspension etc etc etc. Very nice for the time.
Food for thought? Maybe not 
For what it's worth anyway,
Dominic
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mranlet
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| posted on 8/8/03 at 12:47 PM |
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That's almost exactly what I'm talking about!!! Great picture Gecko!
With a little re-proportioning, that is essentially my frame plus a little extra metal for footwells, side rails, roof, etc. for protection...Oh, and
I use a mundane RB26DETT in lieu of a turbine
How would you harness a turbine's power into shaft drive anyway? Do you just hook a shaft to the turbine's shaft?
Ned - There you go, frame simplicity at its finest!
-MR
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cymtriks
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| posted on 9/8/03 at 11:50 AM |
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alloy and tube sizes
Regarding the responses to my earlier post an aluminium part of the same size as a steel part will have about one third of the stiffness. For a
spaceframe this means that you need three times the cross sectional area as its stiffness is mainly derived from tubes in tension or compression. So
no weight saving for a true spaceframe of the same stiffness. Strength is different. A high quality material alloy part may be stronger than a low
quality material steel part. It will still bend or twist three times as much though. Many components are overengineered anyway so changing to alloy
often gives a worthwhile weight saving for no real world reduction in strength. If stiffness is an issue then for beams, as in ladder frame tubes,
levers and bell cranks, the part can be made about 50% deeper in cross section which restores the stiffness and still lets you have a 50% weight
saving.
As for tube sizes, for a given wall thickness, the relative bending and torsional stiffness is proportional to the cube of the size. The actual
stiffness is the fourth power as pointed out above.
Must dash! We have to be somewhere else and the wife wants to be on the road.
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Afro
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| posted on 15/8/03 at 07:35 PM |
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If you look at say mountain bike frames, alu frames are significantly lighter than steel frames, last for years, and can be stiffer too, all at the
same time. The stiffest frame Ive ever rode was a specialized M2 made from an Ally based alloy, (Duralcan I think), which was featherweight and
extremely stiff.
The tubes on ally frames are generally of greater diameter than their steel counterparts, but of thin wall section. If you tried to build an Ali
chassis with tubes the same small diameter as in the steel version you could be on to a loser, but if you up the diamter of the tubes, then you get
the stiffness required to avoid fatigue and can use fairly thin guage to save weight...
I would actually like to know if anyone has much knowledge of using Cro-Moly as a chassis material and the ins and outs of construction methods using
it.. ie welding / brazing and whether heat treatment to de-stress it is required??
If it aint broke... it will be soon
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stephen_gusterson
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| posted on 15/8/03 at 10:46 PM |
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quote:
How would you harness a turbine's power into shaft drive anyway? Do you just hook a shaft to the turbine's shaft?
-MR
AFAIK
a jet helicopter uses a drive from a turbine shaft, not the actual thrust produced.
atb
steve
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stephen_gusterson
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| posted on 15/8/03 at 10:52 PM |
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these weight arguments are so pedantic.
At the moment I am cleaning my front uprights/ hubs - sierras. Each hub weighs a shyte load.
I havnt measured it, but i have been told they are 15 kilos - gotta be at least that.
Whats the point of going to the trouble of making a light chassis unless you go the whole hog and take the philosophy all the way.
Thats alu chasis, light hubs, bike engine, a weightwatchers course (all F1 drivers diet) dont paint it (paint is weight), get ultra light alloys, sit
on frame only seats, - in fact just fit one seat, etc, etc. Dont even fit a roll bar. Why waste 8 kilos or so when its only your head thats at risk -
its a big weight saving.
15 kilos approx a hub - and there are four (in kind) so thats 60 kilos of hub. Thats gotta be more than the chassis you are trying to save weight
on!
The std chassis looks way to minimal to me already. There is hardly a tube in the design that could fail and maintain the integrity.
atb
steve
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ProjectLMP
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| posted on 15/8/03 at 11:58 PM |
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I've got to agree with Stephen. The chassis only represents about 10% of the overall weight of the car. To me that is the last area to optimize
given its critical nature. Far more gains can be achieved by fitting lighter wheels, uprights, brakes, axles, bodywork, ali floor etc. Without
compromizing strength/rigidity the best I think you could save on the chassis would be around 20 to 30 lbs if your lucky.
Home of the Astronomicalcost Mid engined LMP project
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Afro
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| posted on 16/8/03 at 10:15 AM |
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Definately agree with the above comments about saving weight in other areas, as there are some serious chunks of heavy metal around the car (and
possibly on ur radio ). To make the expense and difficulty of building an ally or other material chassis in order to save weight worthwhile then
you would have to do the weight savings elsewhere aswell.
I imagine that a lot of people are building these things with parts that 'do the job' and once on the road will over time upgrade bits and
bobs. Building a fully sorted chassis from the outset means that you can bolt these bits on without thinking 'is my chassis worth hanging these
expensive parts on?'
A bit of food for thought: In MTB'ing there was a massive fad for people to buy titanium or aluminium bolts for holding on brake calipers, water
bottles etc etc. to save a few grams off their bike.. Invariably it p***ed it down with rain and the course became a mudbath with everyone carting
several kilos of mud around on their bikes making 20 grams saved irrelevant.. the money could have been better spent on a bit of polish to stop the
heavy mud sticking to the bike so much...
mmm chewy
If it aint broke... it will be soon
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