blueshift
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| posted on 9/10/04 at 01:35 PM |
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Front suspension design.. any comments?
Before I commit this to DXF for sending off to the laser man I thought I'd chuck up some pictures and see if anyone could spot any other gotchas
that I hadn't.. along the lines of "those wishbones are going to snap!" or "your farnbacker angle is all wrong!".
5.5 degrees castor is built in, and the camber is adjustable from positive to 4.3 degrees negative. The shock modeled is a GTS front shock. The red
diagonal tubes are one of the cymtriks mods (and also support the top wishbone front bracket)
Full size versions of these pictures are
HERE
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sgraber
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| posted on 9/10/04 at 01:58 PM |
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Wouldn't you want your damper to be more upright? Having it more vertical will let it do it's job more effectively. But I wouldn't
move the lower shock mount inwards, I would try to get the upper mount outboard of it's current location. Instead of a bracket pointing straight
down off the top rail as you show, why not one that angles 45degrees outward to give yourself another couple of centimeters.
Just a suggestion, I haven't taken into account the size of the spring coil so maybe you already have it as far outboard as it can go without
interfering with the upper a-arm?
S.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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DaveFJ
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| posted on 9/10/04 at 02:16 PM |
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how thick is the plate on the lower wishbone ?
it looks a little thin in your piccy....
Dave
"In Support of Help the Heroes" - Always
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stressy
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| posted on 9/10/04 at 02:24 PM |
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Hi mate, nice model, heres a few of my thoughts tho.
Q. What diameter and gauge is the tubing on the lower arm, also the thickness of the plate / machining. How are the tubes closed at the ends?
since the plate is on the midplane of the arms were you intended to weld it on both sides???
As graber commented its best to put the shock as upright as possible if there is any opportunity to do so.
the red tube is i believe a stiffness mod and works very well in theory, however, it is not such a good feature if you come a cropper, i.e a HARD
front ender, it makes the front very stiff and as a result if you have a book chassis the loads will end up being much higher when they get back to
where you feet are. just a word of caution. For a road car i would preffer to have a bustable front 12 inches.
On many spaceframe clubman race cars you will find that although they have full triangulation, the material gauge is reduced at impact zones compared
to hte passenger cell to bring back some impact capability.
finally why not move the upper forward braket fully onto the tube.
Cheers mate
c
WHO DARES SPINS
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JB
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| posted on 10/10/04 at 07:30 PM |
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Design Comments
My only thoughts are as follows:-
On the lower wishbone if you can extend the two wishbone tubes all the way out to the ball joint mounting you will avoid the weak point you have at
present between the ends of the tube and the ball joint where it is only plate. The other option is to weld a vertical plate (about 25mm high) from
one tube around the ball joint to the other tube. The main aim is to avoid the thin (relative to the size of the tubes) section of plate.
The important point with the coil over is to mount it so that as much wheel travel as possible is translated into coil over movement. This normally
means moving the lower mount as close to the ball joint as possible (also structually better) and positioning the top mount so the coil over is as
vertical as possible.
JB
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Mark Allanson
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| posted on 10/10/04 at 07:36 PM |
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Looks really good, just one thing, in the second image, it looks like you could not get a socket on the adjustment sleeve bolt due to the clearance on
the rear part of the upper wishbone.
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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MikeRJ
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| posted on 10/10/04 at 09:18 PM |
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Deeper hex head would be the simple solution to that I guess.
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Mix
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| posted on 11/10/04 at 07:24 AM |
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Adjustment
In my view you do not need to get a socket onto the inboard end of the adjuster, just set it to the correct length, restrain the ball joint and
tighten the lock nut. I hope my theory is sound as I've manufactured my adjusters as SVA friendly cylinders 
Mick
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James
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| posted on 11/10/04 at 12:44 PM |
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Looks really good mate.
Wish I'd done something like it myself- would have meant a damn sight less balls-ups along the way!
If I was to do mine again I think I'd move all the wishbones further forward so as to fully mount them on the tubes and prevent the need for 3mm
plates to re-inforce them.
This may then mean the lower, rear bracket/bolt come into collision with FU1/2 but I don't really see why the bottom joint of FU1/2
couldn't be moved inboard of TubeE.
Atb,
James
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blueshift
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| posted on 11/10/04 at 03:45 PM |
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Cheers guys, all very useful comments. I'll reply in full later or tomorrow, things are a bit upside down my end at the moment.
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Mix
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| posted on 12/10/04 at 07:33 AM |
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James
I've moved the bottom of FU1+2 inbord, (see previous post). This has now made the fitting of my lower steering column 'interesting'.
I still think it's a valid option just be aware of the consequences.
Mick
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paulf
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| posted on 12/10/04 at 08:39 PM |
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I also thought i would be clever and do that. I ended up cutting out the steering side tube and repositioing it in the original place.
Paul.
quote:
Originally posted by Mix
James
I've moved the bottom of FU1+2 inbord, (see previous post). This has now made the fitting of my lower steering column 'interesting'.
I still think it's a valid option just be aware of the consequences.
Mick
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blueshift
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| posted on 17/10/04 at 11:27 PM |
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After some tearing of hair..
.. I finally got solidworks to draw some new shock top brackets. That was most annoyingly hard! (3D sketches to the rescue).
I wanted to wait until the revised version was demonstrable before answering everyone's points;
sgraber: Good call on the top bracket. That's exactly what I have done now (though it was more fiddly, so I was avoiding it  )
protofj: The plate is 3mm as are the bits of plate used to make the shock brackets.
stressy: the tube in the arms is 1" OD 16g CDS, chosen after careful consideration of the "bending wishbones" thread. Not sure what
you meant about the machining of the plate.. I'm going to get my mate to cut it on his laser at work.
It's a little unclear on the images but I'm planning to close the tubes with 90 degree wedges cut out of the same tube stock to make 45
degree end caps joining the tubes to the plate.
Interesting point about the extra stiffness at the front, but honestly this car really isn't designed with crashing in mind (apart from the roll
bar it will eventually have). I have enough things to second-guess and worry about without trying to learn about and design in crumple zones and so
on. If the wheels stay on, the brakes work and the suspension geometry doesn't give it lethal handling I'll be happy.
I took your comment about the front bracket on board. It was only there because I was sticking to the book spacing for the bushes. I thought about it
and decided there was no real point, so the wishbone is redesigned and the bush is forward now. thanks.
JB: the tubes do extend to within a couple of mm of the balljoint (taking into account the end caps and welds), I got them as close as I could. I
don't think it'll bend as I think it's as well supported as the book design and some commercial designs. If I was worried I might
think about beefing the plate up a little, to 4 or 5mm maybe..
The bottom shock mounting position was decided by the top mount, the design ride height of the shock and the position of the bottom wishbone at ride
height. After moving the top of the shock out, the bottom is also snug up against the balljoint (and just clears the top bone at full droop.
bonus!)
Mark: Good point! Bollocks!
Mix: Good answer! Phew!
This shows the revisions. Red diagonal in a slightly more pleasing place now it doesn't have to support the back of the top bone front
bracket.
I'm slightly concerned that the new shock top bracket looks a little flimsy, but I thought about it a bit and decided it doesn't need to
be as bombproof laterally as is only takes significant forces in the direction of the shocker. Any thoughts?
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blueshift
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| posted on 20/10/04 at 11:27 PM |
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Wot no comments? Obviously version 2 is so perfect nobody has any criticism.. not even Syd! 
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sgraber
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| posted on 20/10/04 at 11:42 PM |
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quote:
Originally posted by blueshift
Wot no comments? Obviously version 2 is so perfect nobody has any criticism.. not even Syd!
That's it. It's perfect....
Just try to get that damper as upright as possible. So if you can move the upper mount even more that would be good. In regards to the strength of the
steel for the bracket. It should be ok due to the reason you give, but you could always step up to the next thickness of plate for a little
insurance.
[Edited on 10/20/04 by sgraber]
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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blueshift
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| posted on 21/10/04 at 12:30 AM |
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Thanks. The damper is about as upright as I want to get it, it clears the top wishbone gubbins by about 8mm at full droop, and rather nicely snugs up
against the balljoint at the bottom and loads tube J through the centre where it is (rather than twisting it). At best I could get another couple of
degrees on it. It stays put!
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Mix
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| posted on 21/10/04 at 07:13 AM |
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That type of upper damper attachment is one I'm considering at the moment. If I adopt that approach I think I would make the bracket from a
single length of RHS rather than two pieces of flat bar.
Mick
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blueshift
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| posted on 21/10/04 at 08:40 AM |
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Fair enough. if you have it coming down at an angle like I have it, you might find some interesting angles going on. A lot of filing and messing about
will be needed to get a tight fit at the right angle I think. Hopefully since I'm getting stuff lasered from the cad model, all the fiddly
angles are taken care of.
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blueshift
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| posted on 21/10/04 at 10:09 AM |
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Hmm, I might put a small rectangle of 3mm plate on the top and bottom of those lugs, turning it into more of a tube. Thanks for that.
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mackie
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| posted on 21/10/04 at 10:27 AM |
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Would 2 triangular fillets either side of the top shock bracket help (side of bracket to edge or tube)? Should spread the load a bit more I'd
have thought.
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