johnston
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| posted on 4/4/03 at 05:47 PM |
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Makin uprights
Right i'm makin uprights out of a set of macpherson struts
will the distantce between the bottom bj and top make any difference as long as i get my wishbone lengths worked out right ??????????
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Alan B
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| posted on 4/4/03 at 06:44 PM |
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It's not just the wishbone lenghths...there are other factors..you need to look at the whole geometry of it...
But, in theory it should be quite doable...of course if you stay close dimensionally to a known upright then you'll have an easier job....
It really isn't too difficult...you just got to do it right...
I'm sure Rorty can add something?
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stephen_gusterson
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| posted on 4/4/03 at 07:13 PM |
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as alan says, the geometry matters, The bones are unequal lenght to control the hub so it goes up and down essentially vertical.
I am not a cad person, so I 'modelled' mine on the back of wallpaper.
draw the side of your chassis at full scale inc susp points.
Draw the wishbone at the bottom level, and draw a 'block' to take the place of the hub at the end, with the ball joint positions marked
top and bottom.
Draw the top bone.
Thats yous suspension in static load.
Now, scribe an arc from the upper and lower susp points, that mark the arc formed by the ball joints from the bone chassis pivots.
Now, at a suitable height above and below level, draw the hub in upper and lower positions, using the pivot points as datums for the 'hub
block'.
If you have got it right, the hub will still be vertical in both lowest and highest positions.
Bet you it wont be!
You can play with the bone lengths and pivot points to see the effect of alterations.
Then, once you have sorted that, you will have the interesting problem of bump steer.
Im no suspension specialist, but this looks like sensible logic to me.
Another thing is to download the 'suspension helper' software in the TOL files area. You can change dimensions and watch the effect on the
screen of your PC. Its interesting to see how 10mm one way or another in wishbone length can change things.
atb
steve
[Edited on 4/4/03 by stephen_gusterson]
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Rorty
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| posted on 5/4/03 at 02:48 AM |
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It's absolutely crucial to get the various suspension points spot on. You'd be amazed how much difference even 0.25mm can make!
I too used 1/2 scale cardboard "uprights" for about 20 years, until I got a couple of CAD programs. I still wonder at times if CAD has
improved that particular task!
As Steve says, draw it out, even 1/2 scale would do, but do your homework on scrub radius, castor and camber (static and induced). If you don't
fully understand all the functions and actions, ask someone here to help you.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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Stu16v
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| posted on 5/4/03 at 09:59 PM |
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Just to pick up on one of Steve's points, the hub doesnt have to be vertical in lowest and highest positions. The hub/wheel needs to stay
vertical to the ground (theoretically) when the car rolls during cornering. Two very different things. If the hub stays vertical through it's
suspension travel, when the car 'leans' during cornering, the wheel will too-and by the same amount, decreasing grip to the very tyre(s)
that need it most.
Cheers, Stu.
Dont just build it.....make it!
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johnston
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| posted on 8/4/03 at 10:01 PM |
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im keeping the bottom wishbone to the same as the donor the track rod sits at the same level so keeping bump steer to a min (hopefully)
but what im worried about is i have top and bottom bjs too close will it put any more strain on the top wishbone than having them further apart
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Rorty
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| posted on 9/4/03 at 04:44 AM |
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Copying a manufacturers dimensions/positions for steering gear is notoriously fallible. It's one of the last areas given consideration when
packaging suspension.
quote:
but what im worried about is i have top and bottom bjs too close will it put any more strain on the top wishbone than having them further apart
You can't just go altering the relationship of the suspension points willy-nilly. It's Impossible to explain concisely, but you're
courting disaster if you tackle it blindly.
The bottom wishbone/joints will always take the lion's share of stress (with the exception of some instances where the shock/spring is mounted
to the top wishbone)
As suggested previously, draw it out to scale, and model it with "cardboard uprights", and you'll see for yourself what difference
0.25mm can make!
I'm sure there are plenty of experienced people on this list who could assist you. Allan springs to mind, and he's got nothing much to do
at the moment anyway!. I'm happy to help, but I've got another lengthy stay in hospital looming imminently. But, if you're not in a
hurry........
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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Alan B
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| posted on 9/4/03 at 01:22 PM |
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quote:
Originally posted by Rorty
........I'm sure there are plenty of experienced people on this list who could assist you. Allan springs to mind, and he's got nothing
much to do at the moment anyway!......
You must think I'm just sat here waiting to jump in........
Erm......look's like I am I guess.....
Check out my post called "bump steer animation" on March 23rd.....it shows how I can model suspension movements.....send my some info, and
Ill see what I can do....
It's really only glorified cardboard and pins...erm...and in 3D......but a bit cooler...
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Simon
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| posted on 9/4/03 at 03:16 PM |
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Rorty
"I'm happy to help, but I've got another lengthy stay in hospital looming imminently"
Without expecting the details on a public site, I hope all goes well for a speedy recovery.
ATB
Simon
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Rorty
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| posted on 10/4/03 at 03:24 AM |
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Alan, sorry for dumping you in it, but the bloke is obviously stuck, and at the point where he could do something nasty.
Simon:
quote:
Without expecting the details on a public site, I hope all goes well for a speedy recovery.
It's not life-threatening, just complicated, with long recovery time. Thanks for the kind wishes.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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eddymcclements
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| posted on 10/4/03 at 08:41 AM |
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quote:
Originally posted by stephen_gusterson
The bones are unequal lenght to control the hub so it goes up and down essentially vertical.
and
If you have got it right, the hub will still be vertical in both lowest and highest positions.
[Edited on 4/4/03 by stephen_gusterson]
It is possible to get the hub/upright to remain vertical, using parallel, equal-length wishbones. Of course this would be a daft thing to do because
as the car goes into roll (while cornering) the outer tyre will take on a positive camber, losing loads of grip. This system has been used on
home-built specials and hillclimbers in the past, but they were on very skinny crossplies back then, and loss of grip due to camber change
wasn't as serious as it is on today's wide, stiffly-braced radials.
What you need to aim for is to match the camber change of the upright during suspension travel to the body roll of the vehicle during cornering, so
that the contact patch of the tyre remains firmly in contact with the road surface. This is of course impossible to do under all situations, so what
you end up with is a compromise based on the purpose of the vehicle.
One way to ensure the tyre is kept in contact with the road is to have such hard springs and anti-roll bars that the suspension doesn't move at
all. Voila - the current F1 car!
I realise that this is all very general, and probably not a help - Alan B's and Rorty's suggestions about CAD or card-and-paper models are
the best starting point.
Cheers,
Eddy
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Alan B
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| posted on 10/4/03 at 12:29 PM |
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quote:
Originally posted by Rorty
Alan, sorry for dumping you in it, but the bloke is obviously stuck, and at the point where he could do something nasty.
Hey Rorty, absolutely no problem, I was flattered....love to help as much as time allows..glad you mentioned me...I'll just await some
feedback....
Hope you get well soon...
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johnston
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| posted on 10/4/03 at 05:27 PM |
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dont worry not goin to jump in and do somethin stupid (first time for everything)
ive got all the stuff on roll centres and camber changes scrub radius bump steer etc etc pretty much sorted
but i'm just worried that i might get it all theoritically right only to have too much load on top wishbone or somethin daft like that
but my plans to have everything worked out and ready to start building over easter have taken a down fall cos cant get of work and i got told
lastnight i'm away doin the circuit of ireland
and im really glad you offered help alan cos i was goin to go book locost till i seen your site so its all your fault 
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Stu16v
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| posted on 10/4/03 at 08:02 PM |
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Eddy, thats pretty much what I said, but with a lot less words!
Cheers, Stu.
Dont just build it.....make it!
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eddymcclements
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| posted on 11/4/03 at 07:55 AM |
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quote:
Originally posted by Stu16v
Eddy, thats pretty much what I said, but with a lot less words!
Cheers, Stu.
Oops! Hadn't read the thread properly. A thousand apologies.
Cheers,
Eddy
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Stu16v
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| posted on 11/4/03 at 04:41 PM |
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LOL!
No worries mate....
Dont just build it.....make it!
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