Alan B
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| posted on 8/5/04 at 06:08 PM |
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quote:
Originally posted by britishtrident
Since when did steel stock holders accept orders of tube in terms of "moment of inertia" ?........
Never, and you know it...or ought to...
You also know it's the designers job to specify a material with appropriate "I" value for the intended application...
So, what was the point of that remark?
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Noodle
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| posted on 8/5/04 at 07:01 PM |
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quote:
Originally posted by NS Dev
Gosh, I have found somebody on the forum that I don't feel compelled to argue with!!
I agree once more Syd! Just as an aside, have a look at www.beardmorebros.co.uk, and take a look at the suspension design, chassis design etc on the
"New Project"
John Beardmore is one of the few people who designs things which I have great difficulty in criticising!! He should be at Curborough with it tomorrow
so I should be popping over for a look. Incidentally, Allan Staniforth has been looking at this car and has just done an article on the design etc of
it!
He's taking the Moggy? I might just drag the kids over to see it. Do you what tomorrow's events are? I couldn't see it on the
Curborough site.
Cheers,
Neil.
Your sort make me sick
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NS Dev
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| posted on 9/5/04 at 08:44 PM |
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Noodle, did you get to Curborough?
It was a Nott's club event, and John Beardmore + moggy were there! Had a good chat with him over one thing and another.
His car is stunningly well presented and every detail is done because it was thought out that way (by him not on other advice!!) and it went extremely
well!
He could do with some more power/less weight but a time at Curborough of 39.32 on his first timed run (first time out in car and first time at
Curborough) was not bad at all. Didn't see his last run so may have been quicker again (would think so, his paractice times were falling and the
first timed was the quickest until I left!)
To anybody that hasn't seen it have a look at his website. (anybody easily upset please stop reading now)
His engineering as simple and carefully thought out and is not diverted by the bull byproduct that seems to flow on this forum from time to time! His
car just goes to prove that sound engineering is no black art, if something is right in principle then it will work, and well!!!
A good day was had, the rain kept off nicely!(and my XR4x4 got the chance to "stretch it's legs" on some dry roads for a
change......doh....need new tyres now....wish it was a bit lighter, might not kill them so fast!!....doh again....new brake pads needed too!!! ah
well, best get on with the locost then!)
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cymtriks
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| posted on 9/5/04 at 09:51 PM |
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Loads in the suspension?
Come on Darren/Dozracing
Tell us if you have any guidelines for what the loads on the suspension might be. Do you know how these numbers would be estimated for a race car?
I've assumed a 3g bump with a factor of 2 in my calculations but I suspect this is high for a locost.
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Bob C
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| posted on 9/5/04 at 10:58 PM |
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OK ERW tube - there's a seam in it. Now lets say you want to put a bending stress on the tube- Where would you ideally put the seam?
Top? (OK I'm thinking of a book lower front wishbone here...) No shear stress across the weld but weld could act as trigger point for
crumplage.
Side? wouldn't have thought so - max shear AND excuse to fold for aforesaid crumplage.
Bottom? looks favourite to me.
Anyone got test results (preferred) or old wives tales to pass on?
Oval ERW tube - where's the seam on that then?
And I want to know what stresses are used professionally for suspension designs too. I've heard a blithe "stressed to 3g" comment
from long ago - fair enough - but how do you calculate the effect of running into a pothole?? This looks to me like hitting your suspension with a 1/2
ton sledgehammer doing 40mph!!!
Cheers
Bob C
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dozracing
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| posted on 10/5/04 at 09:11 AM |
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Wishbone loads?
Anyones guess! F1 cars are strain guaged so we know what they see, but, as they generate 4g in cornering and braking they are well over what you would
get close to even with a fat boy 7.
Rally cars are usually designed to take 5g bump loads, and Safari rally cars usually 7g bump. In my opinion the bump loads are not the major concern
in a Locost, i think you'd have a hard time bending them due to bump alone. All the stories i've heard previously have related to hitting
kerbs etc, where you get a horizontal load into the tyre and wheel.
I still believe you want the wishbone to fail if you hit kerbs hard etc, as otherwise the chassis and brackets will get damaged and they are harder
and more expensive to replace. Race cars and modern road cars are expected to loose their suspension members before the chassis is damaged.
3g bump is probably a fair loading, but, you should consider what braking loads you get and what a pothole might reasonably do to you as well.
Nice little project for you cymtricks.
I might get round to FE'ing for a laugh and see what happens.
I think you want the seam on the minimum bending stress line, so the tube has the best structure at the max stress and max displacement. Shear stress
i'm not sure i'm so worried about it in comparison, considering the way its then likely to fail.
Darren
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PLEASE NOTE: This user is a trader who has not signed up for the LocostBuilders registration scheme. If this post is advertising a commercial product or service, please report it by clicking here.
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stephen_gusterson
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| posted on 10/5/04 at 09:48 AM |
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I whacked a rover 600 into the kerb at 50 drifting out of a roundabout I took too fast in 1996.
It caused 2,500 of damage to the car. The front suspension bent, and the front subframe was also shagged. Nothing atually broke away, but the wheel
ended up with about 30 degrees negative camber.
The 'something should break' requirment didnt seem part of that rover / honda design!
atb
steve
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Bob C
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| posted on 10/5/04 at 11:29 AM |
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<I think you want the seam on the minimum bending stress line, so the tube has the best structure at the max stress and max displacement.>
cheers - but would that be top, side, bottom or somewhere in between?
I feel a home made test coming on(!), ain't worked out how to do it yet though...
Bob
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Dougw
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| posted on 10/5/04 at 02:13 PM |
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maybe it is a combination of things
1 Is the tube thick/heavy enough
2 Has the weld nearby altered the structral strength of the tube??
3 I cant believe it is anything to do with the engine weight as the rover V8 is light for its size therefore must be either inherent to the tube OR
design issue
3mm walled tube at that length should withstand about 4 ton of force ? is it coincidence that it has done the same thing twice
4 Has the manufacturer offered to replace the wishbone?
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cymtriks
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| posted on 10/5/04 at 08:46 PM |
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Very nice wishbones
Check out this site. Very nice suspension on the front of the silver car.
Note how close the spring is to the hub (low bending moment to reduce stresses).
Note how the tubes form a V with the lower hub joint at the point, no offset as on the book locost design (just like Caterham, lowers stresses).
Note the aero tubing and the detailing. (looks good and works if the bending loads are reduced this much).
http://www.elfin.com.au/index.html
Darren/dozracing
What kind of upright does your choice of lower ball joint fit? Your wishbones look like a pure V shape.
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Dave Gilling
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| posted on 22/5/04 at 10:55 AM |
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Tiger have put a recall on kits using oval wishbone tube, finished cars will be collected and new (round tube?) wishbones fitted for free! 22mm dia.X
3mm CDS tubing for me thanks.
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MikeR
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| posted on 22/5/04 at 11:44 AM |
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Hmmm, interesting, do we know what the oval where made of and why they are being recalled?
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britishtrident
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| posted on 22/5/04 at 12:52 PM |
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quote:
Originally posted by Dave Gilling
Tiger have put a recall on kits using oval wishbone tube, finished cars will be collected and new (round tube?) wishbones fitted for free! 22mm dia.X
3mm CDS tubing for me thanks.
Is this another recall ? from memory there was one about 2 years ago ?
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Dave Gilling
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| posted on 22/5/04 at 01:37 PM |
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Very little info, only what is in WK & KC mags (KC page 9,WK page 11 above the article about Richard Stewart wanting £1.5mill for Robin Hood )
only lower wishbone affected, but that makes sense.
[Edited on 22/5/04 by Dave Gilling]
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SR2
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| posted on 27/6/04 at 11:34 AM |
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Hate to point out the obvious but I think we have a basic design flaw here folks. Surley the gusset plate needs a curved as opposed straight edge to
avoid the stress point that caused the failure.
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JoelP
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| posted on 27/6/04 at 12:02 PM |
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thats been pointed out a few times up the thread, but its worth mentioning again.
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Chris_G
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| posted on 27/6/04 at 01:16 PM |
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This is a long thread now, but if you read right the way through you will see that the first images were of a 'home made design' without
the curve in the plate, however that was replaced with a commercial part of 'book' design ie with the curved plate...BUT, this also
failed!!!
Since it has been 'beefed-up' all seems well, touch wood.
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Rob Lane
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| posted on 29/6/04 at 12:50 PM |
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Don't know if this was mentioned in long thread.
MK had a problem with a batch of wishbones he made up at very start.
They were CDS tube BUT were of a soft steel. He withdrew ALL the wishbones, non going to customers but some to two resellers who returned them.
Martin then did a redesign and used thicker wall CDS tube and then eventually oval tube with much thicker wall.
He and I were well aware of the weld stress riser point.
In fact I posted about this very problem in relation to wing stay failures.
So much so I recommended at least 12mm solid bar as uprights and 25x3mm flat for wing mount.
Interestingly my wing stays have stayed intact since I over built them BUT the triangular mounting plate on one has started to fracture now! On a weld
stress point!!
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geezer
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 posted on 4/10/04 at 08:16 PM |
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bendy arms
looks fairly obvious to me - not enough length ( oh er missus ) in your coil springs , spring are binding up when suspension is loaded up hence
running out of suspension movement but car continues to load up suspension and somethings got to give, forces, reactions, opposites, angle of the
dangle, blah blah blah.
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JoelP
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| posted on 4/10/04 at 09:56 PM |
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not guarenteed though. 300 pounds per inch springs that can compress 4 inches will obviously take around 1200 pounds, This could bend a bad bone
before it runs out of travel.
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Chris_G
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| posted on 4/10/04 at 11:03 PM |
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quote:
Originally posted by geezer
looks fairly obvious to me - not enough length ( oh er missus ) in your coil springs , spring are binding up when suspension is loaded up hence
running out of suspension movement but car continues to load up suspension and somethings got to give, forces, reactions, opposites, angle of the
dangle, blah blah
blah.
Geezer,
That wasn't the case here, it was tested by wrapping a blue-tac 'sausage' around a coil and monitoring it. It did not get anywhere
near pinched to the point the coils would have been bound!
Anyway the problem now seems to have been solved by beefing the wishbones up.
Chris
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Peteff
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| posted on 5/10/04 at 09:13 AM |
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"beefing it up"
Sausages, mmmmmmmm!!!!!! If it bends make it stronger, seems obvious. We had to do the same with a panhard rod which had been made from pipe and did a
banana impression. Remade in bigger seamless tube cured it.
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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Tigers
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| posted on 5/10/04 at 05:12 PM |
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He, he...
I'm making my wishbones out of 25x3mm seamless tube. Was hell to bend them in tube bender (don't know how this this is called correctly)
with 1 meter extension tube.
My wishbones will be the last thing that bends. Of coure they weight a lot, but I couldn't get better tube. And saftey first
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stantheman
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| posted on 18/10/04 at 10:26 PM |
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its like groundhog day
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erbieb02
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| posted on 3/8/05 at 01:34 AM |
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In my student engineering opinion there was just to much bending going on. One wants their A-arms to be loaded only in tension and compression, no
bending. Having the shock mounted so far from the upright's lower ball joint makes the A-arm bend downwards in the middle due to the
shock's loading. That coupled with the bend placed into the A-arm just inboard of the mounting plate creates a stress raiser.
Baisically I chalk it up to it being under engineered, I suggest triangulating the Arm vertically, in a sort of pyramid shape if you want to keep the
shock in its current mouted location.
Eric B.
Eric B
So many choices, way to much time (until I can afford to build).
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