Doug68
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| posted on 23/10/07 at 04:15 AM |
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quote:
Originally posted by Peteff
Even Rossi can't accelerate with his knee down in a bend 
Complete cobblers even I could do it on the 1991 TZ-250 I used to have. Getting on the throttle and sliding the back wheel with knee still down was a
relatively common event.
There's been no discussion on this thread regarding the Second moment of area,
Stiffness is a function of that and not directly the tensile strength of the material.
However the stiffness of members in a Locost frame is not really the issue as their designed not to be loaded in bending.
But the Second moment of area is a input into working out the buckling loads a member can take.
In short citing examples of things that haven't and haven't worked in the past will only get you so far and in the end you'll need
to do the math for yourself to see if its acceptable.
Doug. 1TG
Sports Car Builders WA
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short track 123
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| posted on 23/10/07 at 07:58 AM |
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Peteff
Play in any joint connected to a chassis is a different issue and will all ways fail SVA/MOT bike or car.
I used a race a Norton commando along with a few other bikes and in an attempt to make it handle stiffened the chassis so much it handled worse then
for a bit of fun put some slicks on it and it then was much better than it ever was so flex is the chassis was good for this e.g as in that class we
were not aloud slicks.
Ti is Titanium.
All materials have a life span with regards to flexing and will be reduced by being flexed.
Take a valve spring on a standard road car in an attempt to improve performance you could reduce the load it puts on the cam thus reducing friction
and increasing performance. In standard from the spring is designed to " flex " and should run for a fair few miles. If we reduce the wire
size of the spring it will ( if we go to far ) reduce the life of the spring and it will fail. The same applies to any material in any shape
A good e.g is a kart chassis which is designed to flex some modern ones have torsion bars so the chassis can be tuned for different conditions i.e
make it flex more or less. And as tyres have become more gripy over the years the chassis need to flex less ( be stiffer ). But in the wet more flex
will give you more grip. So we design more flex into the chassis.
Ally box chassis have been done ( see Werner Van Loock post for link ) and have worked before. I would build one but my ally welding is just not as
good as it could be for a chassis so for now will not attempt a chassis in ally box. I would if money was no object do a bonded ally honeycomb
chassis.
rebelrider have you any photos? I for one would be pleased to see them.
And good luck with the build
Jason
[Edited on 23/10/07 by short track 123]
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Lippoman
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| posted on 23/10/07 at 08:55 AM |
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Karts are made to flex because they have no suspension.
The main reason to have a stiff frame and let the suspension do the work to keep the tires in/under control is that suspension is "easily"
damped and tuneable while the flex in a frame is not.
If you stiffen the frame you will have to retune your suspension as it is now working under totally different circumstances.
When stiffening a frame, care needs to be taken that transitions from stiff to less stiff sections are made gradually. You want to avoid
"hinge" effects that concentrate the bending action (and the stress) to a small part of the structure.
To use another material effectively you should redesign taking all the properties of the material in consideration. Substituting one material with an
other has spelled disaster many times before. Aluminum alloys are very different, to state that a frame is made of aluminum is like saying it is made
of metal.
The properties of Al-alloys also vary with heat treatment/temper.
So bottom line: If you undertake such a feat, do so with proper equipment, materials and know-how. Talk to (a lot of)people who do structural work in
Al-alloys, most likely you find them in aerospace or the higher echelons of motorsport.
You can do anything in a number of ways, but there is a difference between doing it right and just getting away with it.
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D Beddows
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| posted on 23/10/07 at 09:34 AM |
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Surely the aluminium frame in the link was realy just a lightweight framework to which to bond the honeycomb panels (which actually formed the main
structural component of the chassis) rather than any form of space frame chassis.
If you look at the end of the page it didn't end up being an awful lot lighter than a properly triangulated steel spaceframe either! stiffer
though.....
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iank
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| posted on 23/10/07 at 09:46 AM |
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The whole saving weight in the chassis thing is less valuable than people think anyway. A steel locost chassis is <10% of the weight of the
finished car before you even step into it.
Better to do the safe stuff, i.e. fit carbon bodywork, aluminium diff casings, triming bolts to exactly the right length etc etc etc before getting
into shaving a couple of kilo's off the chassis.
To design with a material with different physical properties requires a different design. It's not a complicated concept is it? As ^^^
different grades/alloys of aluminium will need different designs between themselves to work.
Bringing Titanium into the argument is missing the point as it has completely different properties to both aluminium and steel.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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Peteff
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| posted on 23/10/07 at 10:17 AM |
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Getting on the throttle and sliding the back wheel with knee still down was a relatively common event.
Stunt riding stuff, you're not accelerating while the wheel's spinning. There's an avatar on here with someone doing it one handed.
You will only accelerate when the tyre grips and if you're still leaning it will spit you off the high side. Been there done that, took an hour
to get the bike out of the ditch, too old and chicken for it now. There's at least one killed a week round here in Summer from trying to do it
and getting thrown into oncoming traffic up Matlock. The amount of grip available from your tyre was not like the superbikes now have. A friend of
mine still has a TZ and they are like pram tyres compared to Blade and ZX9 rears.
I had a blank there on the ti sorry Jason. Round here it stood for Tube Industries. I used to work in a foundry in the 70s where we cast titanium,
mostly turbine rotors. It was relatively experimental then and it was lighter and stronger than steel but the brittleness (is that a word?) was a
problem then till it had been heat treated. As with steel you can make springs from it but I've not seen any made from aluminium. Old Norton
frames were never renowned for their stiffness, some of my friends had them and claimed they were better after they had been crashed. The name
"Featherbed" was one that immediately sprang to mind as my uncle had one.
[Edited on 23/10/07 by Peteff]
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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short track 123
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| posted on 23/10/07 at 10:53 AM |
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I know what you mean by they were better after being crashed I was never shore if it seemed to improve because i had crashed or because it got stiffer
as i repaired it each time. That's why I went over the top with the stiffening. I have bonded plates to ally bike chassis to make them flex less
but was never able to tell if it made them better or not ( not as good at riding them as I could be )
Jason
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Doug68
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| posted on 23/10/07 at 11:31 AM |
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I didn't say spinning I said sliding more like the feeling of walking, I'd describe it as and quite controllable.
Also I think you're thinking of the old 1980's TZ's the tyre size I ran on the rear was a 160 which I think is close to whats still
being run at world GP level today in the 250 class.
Below is a picture of the bike in question note the 'frilly' edges of the tyres.
BTW I am definately not trying to insinuate I'm any sort of riding legend in Australia I was graded as a 'C' grade rider which I think
was right. I'm sure anyone else who's raced motorcycles for any length of time particularly on slicks will be able to relay the same
experiece.
 
Rescued attachment BikeRear.jpg
Doug. 1TG
Sports Car Builders WA
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Peteff
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| posted on 23/10/07 at 11:59 AM |
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I didn't say spinning I said sliding more like the feeling of walking,
If it's leaving black lines it's spinning up, that's why the edge is frilly. Should have said Stoner as an example, sorry 
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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Doug68
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| posted on 23/10/07 at 12:18 PM |
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Anyway... back closer to the subject of the thread...
A quote from Peter Elleray, the Chief Designer for the 2003 Le Mans winning Bentley EXP LMGTP:
"As regards the overall level of stiffness, it is an order of magnitude higher than the roll stiffness of the suspension, which is usually a
good rule of thumb to work to…"
Which I take to mean if the force to induce 1 degree of roll is X then the frame stiffness should be 10X as a minimum.
Quote came from here
Doug. 1TG
Sports Car Builders WA
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short track 123
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| posted on 23/10/07 at 04:06 PM |
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"As regards the overall level of stiffness, it is an order of magnitude higher than the roll stiffness of the suspension, which is usually a
good rule of thumb to work to…"
Which I take to mean if the force to induce 1 degree of roll is X then the frame stiffness should be 10X as a minimum
We would have solid bars instead of springs if it was the other way round.
Jason
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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