Answers on a postcard.....
[Edited on 26/1/08 by Jesus-Ninja]
File below is now "out of date", and has errors. A corrected version is now in a post further down.
[Edited on 22/1/08 by Jesus-Ninja]
As I keep adding updates, please go to the last post (with an attachment) for the latest version.
[Edited on 4/2/08 by Jesus-Ninja]
[Edited on 4/2/08 by Jesus-Ninja]
OK, found the first problem. Using a positive value for h seems to make the double wishbone go screwy...
what does it all mean?
now i know why it's always been hammered into me to always label axes and give graphs proper meaningful titles
tom
i think , its just showing the change in KPI , ive plugged mine in - over the deflection i experience i get about 4 degrees KPI change .
it doesnt take into account the roll angle tho , but at least it shows how much camber gain you will likely see - whoever did it , needs to put more
documentation to it . my arm lengths were also negative so as not to upset it . might play with it now to see if i can reduce it a bit more .
Righto - I was certainly quite premature with the first post. Last night, I sat down and went back to basics and started it propertly, rather than
stiching together bits from elsewhere. The result is attached.
I've not made any changes to the first page which models McPherson strut. This was the starting point for me, as this is my current set up, and I
wanted to define the change in KPI, and hence camber gain, relative to the vehicle, to help define a starting point for replacing the strut with an
upper wishbone.
Documentation is not extensive, but things slightly better labelled.
As a rough guide, input your key attibutes: lengths of wishbones, length of upright, and position of upper bone pickup relative to lower bone
pickup.
The graph with the curve will show KPI, relative to chassis, over a large range of wheel deflection (relative to chassis) (-200mm to +200mm!)#
Pick the range in which you want to visualise motion (min and max), and the starting (or rest) deflection. Hit "Go", you will see a
graphical representation of the wishbones and upright moving through the range defined. A single bar with KPI (relative to vehicle, of course) will
change (I found this useful for seeing the range). A pink dot will also move over the curve, as an indicator of the range you are looking at.
The thing that this really threw out was how small changes to any value can make marked differences to the main curve - ie how steep the curve is,
where the range lies etc. Additionally, it was interesting to note how the curves for McP and double wishbone differ, mainy in that one is
inverted.
Hope this is a little clearer. The attached XLS works for any values you put in, with in reason. Some combinations of values are clearly
impossible.
Not sure how to delete the one in the first post, but if someone could, then that would be helpful.
OK, another update. After BAGS of trig, it now (i believe...!) calculates both instantaneous roll centres, and hence the swing axle lengths and the
dynamic roll centre. This can be viewed by clicking either of the buttons - one "bounces" the car to show bump and droop. The other rolls
the car between two extremes. Of course, it doesn't consider an anti roll bar, or spring rate, but does give an idea of where roll centre is.
More to follow. May knock this up in a java app, rather than a spreadsheet, if it's useful.
There are a few basic programs already out there. The one attached may help. If I remember right it does front view geometry only.
Cheers.
EDIT: file below doesn't work. See later post.
[Edited on 25/1/08 by C10CoryM]
quote:
Originally posted by C10CoryM
There are a few basic programs already out there. The one attached may help. If I remember right it does front view geometry only.
Cheers.
quote:
Originally posted by Jesus-Ninja
OK, another update. After BAGS of trig, it now (i believe...!) calculates both instantaneous roll centres, and hence the swing axle lengths and the dynamic roll centre. This can be viewed by clicking either of the buttons - one "bounces" the car to show bump and droop. The other rolls the car between two extremes. Of course, it doesn't consider an anti roll bar, or spring rate, but does give an idea of where roll centre is.
More to follow. May knock this up in a java app, rather than a spreadsheet, if it's useful.
quote:
Originally posted by t.j.
Zip file doesn't open!
quote:
Originally posted by C10CoryM
There are a few basic programs already out there.
Odd, some reason the forums upload didn't like it. Here it is again and it appears to work.
http://www3.telus.net/public/corym/susp.zip
It's your typical front view only, dos based program but its easy enough to figure out where your swing arms, camber curve and roll center are.
For a free program is might help some people.
Cheers.
I think it's nearly there. Version 11 attached. Tried to make it a bit nicer and fluffier, and solved some geometric "niggles".
Answers on a postcard.....
[Edited on 26/1/08 by Jesus-Ninja]
I've split it down into two seperate workbooks: 1 for Double Wish, and one for McPherson Strut.
This is the driver behind all of this, of course, as I am moving from McP to double wishbone, and want to compare what I have with what I could
have....
[Edited on 28/1/08 by Jesus-Ninja]
And the most recent Double Wishbone one...
Added some more functionality. Both sheets can be controlled using ALT + arrow keys. Up and down change bump, left and right change roll.
Remember to use the ALT key with the arrows!
I've found this actually better than the automated system, as you can change a bit of roll, a bit of bump, a bit of roll......
Oh, and there's two little graphs that show the change in KPI and the change in shock length, on the assumption that the double wishbone uses a
diagonal shock / spring from the lower ball joint up to the top wishbone mounting point.
And of course in the case of McPherson, the strut is not, strictly speaking, the line from the ball joint to the top mount, but the strut and upright
are fixed together, so it's still usefull to see the amount of compression compared to bump.
Well, it is for me, anyway!
He's the latest double wishbone sheet
[Edited on 29/1/08 by Jesus-Ninja]
[Edited on 29/1/08 by Jesus-Ninja]
That looks ever so good: I'll plug my suspension values in & see how it compares to my calculations (of 3 years ago....)
Bob
here's the McPherson one. Apologies if anyone downloaded this in the last hour. I just found a + where there should have been - which was making the strut get longer under compression!!
quote:
Originally posted by Bob C
That looks ever so good: I'll plug my suspension values in & see how it compares to my calculations (of 3 years ago....)
Bob
OK - dialled in my home-brew rear suspension & was rewarded with results very like I was expecting. It was quite a job digging up measurements
fron 2 years ago (all in inches too.....)
Comments -
1) bump/droop scale - there's about enough droop but not enough bump (on the moving bargraph at the top - I want at least 75mm
2) the 'starting bump' (D16) didn't seem to update on the fly - I thought it wasn't working at all until I switched off XL then
back on again (the [zero] button didn't do anything, I couldn't find the [set] button)
I was using your version 13.
Overall - I wish I'd had this when I was designing my suspension, excellent tool, well done! (I used that DOS thing that crashes & locks
up)
Bob
Edited after I put my front in too - point 2 above - seems to an issue with the zero button - this levels the bottom wishbone rather than setting it
to its starting value. I think that the latter would be more useful as it's likely to correspond to the static position.
[Edited on 30/1/08 by Bob C]
hanks for the feedback, Bob.
1) bump/droop scale - there's about enough droop but not enough bump (on the moving bargraph at the top - I want at least 75mm
OK, easily fixed by rescaling the chart. This is one of the reasons for leaving it in Excel. It's easy to change things like this yourself
My current set up has 35mm bump and 15 mm droop, so that's why it's a little "tight"
2) the 'starting bump' (D16) didn't seem to update on the fly - I thought it wasn't working at all until I switched off XL then
back on again (the [zero] button didn't do anything, I couldn't find the [set] button)
Yeah - my apologies - I forgot to add the set button (it's in the McP one).
Here's the latest Wishbone sheet with the set button!
Of course - I should have thought of that (I'm a big fan of XL...)
Does Pbura still post on here? he helped me a lot when I was looking at this stuff & I sure he'd be interested in this.
Bob
PS do you mind if I give this spreadsheet away to other folk with an interest in suspensions?
[Edited on 31/1/08 by Bob C]
quote:Mate - feel free! Open source is the way forward!!!
Originally posted by Bob C
Of course - I should have thought of that (I'm a big fan of XL...)
Does Pbura still post on here? he helped me a lot when I was looking at this stuff & I sure he'd be interested in this.
Bob
PS do you mind if I give this spreadsheet away to other folk with an interest in suspensions?
[Edited on 31/1/08 by Bob C]
Anyone have any clue as to where the attachments went? I've lost my files, and was hoping to get some copies back from here. If anyone still has any, that would be perfect!
Panic over - I found them. Here's links to them on my server:
http://jesus-ninja.dyndns.org/public/suspension_geometry/
Good stuff dear sir!