ned
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| posted on 10/6/03 at 10:56 AM |
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MK Indy Chassis design
I'm very interested in the MK indy, I saw it at stoneleigh and am impressed with the quality,price and package.
I have since been to see Bob's car and have studied Donut's pictures (apparantly his car is of the latest chassis revision) but have found
some 'niggly' bits in the chassis I don't like.
I've studied 'the book' and work on a race car and am very into my triangulation when it comes to chassis. I've also read
Cymtriks mods to the book chassis which I like the sound of.
My problem with the indy is the chassis members in the nose section that are bent by design. I'd prefer to see them straight and welded. Both
the top bar and the one round the bottom of the engine (see image below).
I'm sure the design isn't problematic, I'm perhaps just something of a purist in the spaceframe department.
Has anyone else modifed their indy chassis' or have any comments on the above?
Picture:
I'm not too worried about the rear end, the front is what takes the brunt of the forces when turning in/cornering and has the weight of the
engine to deal with. I don't fancy my welding skills for building a chassis from scratch and don't want ot rip off anyone else's
design (without them knowing/ok'ing it!).
All help/comments appreciated.
Ned.
beware, I've got yellow skin
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timf
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| posted on 10/6/03 at 11:38 AM |
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Ned
it is often the case that a welded joint is not a good at transfering the loads as one bar which is 'bent' in that a welded bar the point
loads are around the weld.
the MK 'Bent' chassis is very good in that the loads are transfered more evenly into the ajoining frames.
this is why in nascar the majority of the space frame is constructed in long tubes bent to the shape required, not lots of smaller tubes welded
together.
Tim
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ned
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| posted on 10/6/03 at 12:31 PM |
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Tim,
thanks for your comments, thought I think that i'd rather have a triangulated/non bent tube frame then add webbing around any joints that I felt
required additional bracing or took a lot of stress/loading.
Anyone else got any comments?
beware, I've got yellow skin
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Deckman001
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| posted on 10/6/03 at 12:44 PM |
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Ned, try giving M.K. a call, and ask about them doing a 'special'. The worst they can say is no, so not a lot to loose really !
Have fun !!
Jason
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ned
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| posted on 10/6/03 at 01:00 PM |
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Jason,
I think that'll be the way I'll go, just wondered if anyone else had similar ideas/modifications.
Cheers,
Ned.
beware, I've got yellow skin
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GO
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| posted on 11/6/03 at 10:00 AM |
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Just gettin post back to top.
I'd be interested in what Cymtriks has to say about this, what affect the bent bars would have - good or bad?
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GJ Warren
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| posted on 11/6/03 at 12:07 PM |
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The comment that bent bars are better at distributing loads is correct. I dunno what school of spaceframe you come from Ned but you are mistaken. The
best roll cages, designed to be the stongest and safest are infact made outta bent tube. I think you just want to be different rather than chase after
a "pure" design, as welds are normally much more britlle and as already pointed out are the stress points that normally break rather than
flex as in a bend!!!!
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ned
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| posted on 11/6/03 at 12:20 PM |
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My 'pure' space frame would be made up of triangles, correct me if I'm wrong but i thought triangles were the strongest shape. a
square or other quadrilateral will rhombus with stress/load.
How are you meant to have a strong triangle to give strength to the chassis if one side of you triangle is made up of a bent bar.
A bent bar may dispurss load well over a large area on a join, but can't give greater strength to a triangle than straight bars?
quote:
welds are normally much more britlle and as already pointed out are the stress points that normally break rather than flex as in a bend
I don't think the welds will break, and I don't want my chassis to flex or bend,
Ned.
[Edited on 11/6/03 by ned]
beware, I've got yellow skin
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Findlay234
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| posted on 11/6/03 at 01:09 PM |
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Sorry im with ned on this one, in all my schooling on engineering its always been triangulation, i dont think ive every seen a rally roll cage or a
touring car chassis with very many, if any bent tubes........ im not the gospel on this and i may be wrong but id like to be proved otherwise.
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GasGasGas
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| posted on 11/6/03 at 04:34 PM |
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Theres nothing wrong with a good bit of triangulation, but i think you'll find that this little trick on the front of the MK will add a great
deal of torsional rigidity (you know the twisty stuff ) as it appears to act a litle like an anti roll bar, also having seen Donuts chassis, i'd
say these tubes are attached alot more securely (longer welds, Greater contact area) than mere butt welds would offer.
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blueshift
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| posted on 11/6/03 at 04:48 PM |
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ned; your chassis is always going to flex and bend, even if you make it out of a solid block of steel. Personally I'd be happy with bent tubes
rather than welded joints, so long as I / the designer understood the way the metal stressed after bending. I'd certainly trust a bent piece
over my welding at the moment. been reading scary things about E6013 rod not being designed for dynamic loads, and stuff, today..
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carnut
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| posted on 11/6/03 at 05:52 PM |
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I think that the bends on the indy are ok but if i were to make it there is one that i would get rid of. That is the bent tube that sits behind the
diff joining the two tubes that have the upper winshbone mounts on then. It looks like it would flex easily.
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DoctorFunky
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| posted on 11/6/03 at 06:23 PM |
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I'd go with the bends myself. A circle is the strongest shape as it spreads load/stress around its full circumference, therefore distributing
the stress/load more evenly. Although a triangle is strong it focuses all stresses on the corners/welds.
Glad I didn't build a Tiger
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bob
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| posted on 11/6/03 at 07:09 PM |
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An indy crashed last year on the way back from le mans,almost if not a head on with large tree i think.
Evidently the car (chassis) stood up very well,maybe ptm or MK can tell you more but that was a good enough advert for me.
[Edited on 11/6/03 by bob]
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theconrodkid
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| posted on 11/6/03 at 07:57 PM |
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i spose the tree was french and didnt use indicators,typical
who cares who wins
pass the pork pies
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GasGasGas
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| posted on 11/6/03 at 07:59 PM |
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No just on the wrong side of the bloody road
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ned
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| posted on 12/6/03 at 09:26 AM |
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Well,
If all you going to lemans could check the 'french tree situation' as I'd like to know that it's safe to driv over there for
when i go on holiday in the summer.
Points taken on some of the bends. I'll have an chat with MK about the design nearer the time, there must be a compromise / deisgn somewhere
along the line....
Thanks all,
Ned.
beware, I've got yellow skin
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kingr
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| posted on 12/6/03 at 09:52 AM |
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I think there are two different issues here - crash surviving and rigidity. While I suspect curves may be best for crash surviving (my suspisions
would be they would deform at a more gentle rate), I also suspect that welded joints are better for rigidity. I'd be very interested to hear if
this is true.
If it is, then it's a choice between the two as to which one you want in your chassis - I know I'd go for crash surviving as no 7 chassis
seems to particularly want for rigidity or handling.
Kingr
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timf
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| posted on 12/6/03 at 11:31 AM |
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belt and braces
of course ned you could always add the triangulation to the areas your concerned about after you have your chassis.
the cost of getting mk to do it might be more than having them added afterwards
as most chassis are built on jigs that are set up for repeatability. then
you would have the best of both worlds.
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ned
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| posted on 12/6/03 at 12:07 PM |
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timf,
yes, this is another option. just depends on how much i trust my own welding really - i'm out of practise!
Ned.
beware, I've got yellow skin
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GJ Warren
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| posted on 12/6/03 at 12:39 PM |
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Sorry for the late reply to the reply on my post. Take a good look at some roll cages then. the mani bar that goes over the drivers head is always a
one piece bent bar. Just like the rear roll bar of an indy, this is done for strength, as well as the asthetical reasons, there are welds in a roll
cage other wise you wouldn't be able to get it in the car. As already stated a certain degree of flex is always present. From experience a
little flex can actually help on all but the flatest surfaces, we hill climb a 1978 aluminium chasis Chevron in our local hill climb with our old
flexy chass
is on most normal (read bump) roads we find a level of grip that the 96-98 Ralts and Dallara chassis (Carbon tub almost no flex) would dream of. Same
Tyres Avon A40's so i still would like to disagree with your statements Ned
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ned
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| posted on 12/6/03 at 12:41 PM |
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I appreciate what you say about the benefits of a soft chassis, we're running a steel spaceframe car and a lola t86/90 which is an ali tub and
quite soft.
I guess we can agree to disagree on the rest
Ned.
[Edited on 12/6/03 by ned]
beware, I've got yellow skin
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