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Link Suspension for Dumb People?

Discussion in 'Center Of Gravity' started by Hossbaby50, Mar 3, 2007.

  1. Hossbaby50

    Hossbaby50 3/4 ton status

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    Does anyone have any good webpages or threads about link suspensions. Pro's, Con's, descriptions, pictures, etc. I have searched around some but what I need to find is the basics of 3 & 4 link suspensions so I can start building my knowledge about what I want in my future plans for a buggy. I have looked around Pirate some but figured I would start my learning hear in a less harsh environment. I am looking for info that someone other then an engineer can understand. Thanks

    Harley
     
  2. gm500hprat

    gm500hprat 1/2 ton status

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  3. blasphemous

    blasphemous 1/2 ton status

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  4. gm500hprat

    gm500hprat 1/2 ton status

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    Yeah its pretty good. I actually printed the pages into microsoft office document image writer and put them into one file so I could refer to them while planning my 4 link. I also used excelcad, I think the guy that made it is on pirate and ck5.
     
  5. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    It wasn't "someone on Pirate", it was our own Triaged (Dan) who did that Excel file along with help from Greg. And the Peterson's article is somewhat useful in a very beginner sense, but there was SO much glossed over or completely ignored that it really serves as only a single partial intro at most. For some of the old links, look at the “top tech” sticky the top of this forum and search for some of the old 4 link threads in here as well.

    When I did mine, it took a great deal of additional research and work to figure out what I wanted to do. The end result was superb, too bad I have not been able to enjoy it much...

    Good luck on your project!
     
  6. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Actually that's close but not quite right......


    ExcelCAD started out as a personal project based on that Peterson's 4WOR "Link Suspensions" article. I took their calculations and created a spreadsheet to model suspensions based on their assertions. After exchanging some emails with Dan (Triaged) about what I was doing he started teaching me basic Mechanical Engineering theory in his spare time (while still a student at Cal Poly) so that I would have the "vocabulary" to understand his suggestions for better ways to calculate things.

    Dan wasn't much of an Excel guy at first, so I continued to send him files and he would double-check the math and send me feedback...often with changes made to improve things. Eventually, I did the graphical views (which I think were around v1.1 or v1.2) That's when Dan got really excited! He hadn't seen Excel used like that before, and basically I was creating CAD drawings to show the link positions and tire locations (which at that point weren't even round, more hexagonal!).

    Shortly thereafter, Dan realized that he'd better teach me vector algebra so that we could model things in 3D space, not just 2D. That was a huge change to the program and that is when Dan became deeply involved and started spending a LOT of time working with me. The 3D models allowed us to show the top and side views and do a lot more with calculating FS values, etc. Plus, the aesthetics of the program were getting a lot nicer. Dan even figured out a way to draw the tires so that they'd be truly ROUND!

    ExcelCAD continued to evolve and Dan was in his senior year of school at that point. I think he was able to use this program for some school credits, since it was getting pretty complicated and he had spent so much time on it.

    Since Dan graduated, he has continued to mess around with ExcelCAD and has created and posted other variations since: 4-bar link and 3-link analyzer, and I have been working on refinements to the original ExcelCAD as well, though I haven't uploaded any new versions in a long time.


    :usaflag:
     
  7. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Sorry for the mistake and thanks for the clarification/history lesson! :waytogo: You guys did a fantastic job, sorry I got the credits screwed up. I'm getting old and the memory aint what it used to be. They say memory is the second thing to go... but I can't remember what the first was... ;)
     
  8. baja-chris

    baja-chris Newbie

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    Is there a version of this spreadsheet that allows you to change the position of the axle within it's travel (drooped, compressed, etc.) without having to re-enter the link positions? Would be useful to see how things like AS and Roll Axis change during the suspension travel. Would also be cool if you could enter the driveshaft u-joint locations to see plunge and u-joint angle change as the suspension cycles. Thanks to Dan & Greg for this cool tool!
     
  9. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Glad you like it!


    A couple of comments:

    I have spent some time working on the suspension travel components you had mentioned...at least as far as having ExcelCAD re-calculate AS and RC values. I was going to have the user input a maximum "bump" travel value and a maximum "droop" travel and then use those as the boundaries for the calcs. Another fun item I had spent some time on was recalculating the AS based on "non-horizontal" terrain (ie. climbing a hill). This was a really important one, since it would REALLY show how badly the AS increases in steep terrain.....and how important it should be to keep that AS value low on level ground and at static ride height.

    I never messed with the u-joint angle calcs, or calcs for caster change (for the front axle) through a range of suspension travel. Those would be nice "validation" points for a design that otherwise looked good....but I suspect they are not an easy modification to make. If I spent the time with it, I'm sure it's solveable....the calculation for driveshaft slip under cycling seems pretty easy to do, though.

    The nice thing about ExcelCAD is that anyone can see the formulas and mess around with it to add features they want. More than anything, that process will teach you a lot about suspension design and how the criteria interract with each other......based on your requests though, it sounds like you are already quite "aware" of what goes on in proper suspension design! :wink1:


    :usaflag:
     
  10. Dr. Custom Werx

    Dr. Custom Werx Registered Member

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    the "non-Horizontal' thing has been bugging me for ever! i've been thinking about taking classes to learn more about vectors and $h!t just to figure it out.

    To figure driveshaft slip you would need to know how much the caster changes throughout the suspension travel. (i use castor because it is directly related to pinion angle and i dont know the technical name for the imaginary line that goes through upper and lower axle link ends). it seems as though it is almost there now, just need to know how far off the origin your u-joint centers are. I don't know how much work that is to do or how much MORE work it is to take offset drivelines into account.

    the u-joint angle thing doesn't matter much to me but i would Love to have the a/s calculated on different angles. i have a system i want to try because it looks like it will work perfect for what i need it to do.... on level ground but for some reason i think it will do some messed up stuff on inclines or flexed out and bound up.
    :doah::doah::confused:
     

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