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Projects '31 A FHC build (design?) thread

Discussion in 'The Hokey Ass Message Board' started by Ned Ludd, Jun 25, 2009.

  1. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,839

    Ned Ludd
    Member

    I'm loth to call this a build thread, as it's very much in the design development/technical documentation stage. Hopefully it'll morph into a physical build in due course.

    What I intend to do is post my CAD drawings for the project here until such time as the physical work starts. There will probably be a few false starts, and consequent redesigns.

    The project is a '31 A with a fabric fixed-head coupé body, on a fabricated frame, z'd 6¼" in front and underslung at the back, on a 116" wheelbase.

    Apart from collecting parts (a process that happens haphazardly and without any structure as to the importance of the parts involved, so that I might end up with enough mirrors for six cars left over) the first job is to generate an accurate and detailed drawing of the frame, complete with all holes and brackets and tabs and lugs. I know that some of these will change when it comes to the actual build: the trick is to incorporate some allowance for variation at the other end of things to where they are critical.

    I've laid out the rails. Here's a .jpg-plot I'd taken a while ago. The drawing has since progressed quite a bit:
    [​IMG]

    I've since concentrated on the front end. Here's a front view:
    [​IMG]
    The axle is a fabricated tube axle. I've spoken to an acquaintance who owns a machine shop, and he is confident that he can do the 900mm CLR bend smoothly. The Mumford linkage will be behind and below the radiator. Note the roll centre height.

    Also shown are the single air spring and the cylinders for the hydraulic roll control system. The bell cranks are notional, as the longitudinal placement of all that stuff still needs to be finalized.
     
  2. -Brent-
    Joined: Nov 20, 2006
    Posts: 4,730

    -Brent-
    Member

    I read patents for a living and I'm not embarrassed to say, I don't understand what the heck is going on with this plan. This is a traditional hot rod website. Although I dig CAD drawings what's up with Mumford linkage and air bag assisted suspension?

    What's the motivation here, Ned?
     
  3. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,839

    Ned Ludd
    Member

    Hi Brent

    As I say, it's a work in progress. The bag is the primary suspension medium: it keeps the front end up. There'll be another at the back doing the same job. The car will be kept from falling over by a double-acting, double-rod-ended hydraulic cylinder at each corner. They'll be cross-interlinked side to side and straight-interlinked front to rear. You'll see that that results in two separate hydraulic circuits. Each of those will be pressurized by a steel coil spring and damped by a valve block. Hopefully all that will become clear as the design develops.

    The purpose of all this is a warp-flexible system (tunable by varying the leverage of the bell-cranks onto the hydraulic cylinders) that will take the torsions that result from differential suspension loadings out of the frame, and therefore collapse the advantage that a unibody, space-frame, or monocoque has over a ladder frame. And that's where tradition comes in: I'm trying to improve the ride/handling product of a ladder frame with solid axles, without recourse to electronics.

    Because all this, the hydraulics, the interlinking, the bags; it's all in the thinking that was happening in the '30s, '40s, and '50s. I don't know when Mumford came up with his linkage, but it's pure '50s/'60s suspension thinking (that is, geometric rather than cybernetic).

    Where I do deviate from tradition is that I am working from first principles and not from example. Tradition works by presenting examples from which others can work, without the need to go into abstruse theory. It allows non-rocket-scientists to do stuff on their own, and achieve something without living in the pocket of some centralized power. That's why I'm all for tradition.

    But tradition is always overlaid with a bit of wizardry, that is, weird stuff that works from first principles. Wizardry feeds tradition, otherwise tradition won't have anything to pass on. So, I'm trying my hand at wizardry, and that knowing that I'm not the only wizard on the HAMB, not by a long shot.

    Make sense?
     
  4. Um... What's wrong with a spring?
     
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  5. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,839

    Ned Ludd
    Member

    Nothing: but I'm looking for a lower spring rate at ride height than is practical with a steel spring. It'll either be stiffer than I want or it'll bottom out too easily. The 8" bag set up that way will, by contrast, almost double its spring rate over 1½" of bump. I'm just trying to go beyond the performance expectations we have.
     
  6. n.z.rodder
    Joined: Nov 18, 2008
    Posts: 1,016

    n.z.rodder
    Member

    Ok, so the airbag is linked to both bell cranks and not to a point on the chassis, if this is so when the left wheel moves up it pushes on the airbag and the right hand bell crank moves that wheel down (chassis up). ???
     
  7. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,839

    Ned Ludd
    Member

    Exactly. The bag doesn't contribute any roll stiffness.
     
  8. This is really interesting. No roll stiffness with the bag - so what will give you that back? This Mumford linkage? (That I freely admit to never having heard of!)

    I´m a fan of things like this. I´ll be watching this develop.
     
  9. n.z.rodder
    Joined: Nov 18, 2008
    Posts: 1,016

    n.z.rodder
    Member

    I count 16 pivot points, add add another 8 for 4 bars ( have you taken into account axle twist with all those pivots ? ) thats a busy front-end. How much gain are you expecting over a leaf with a panard bar?
     
  10. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,839

    Ned Ludd
    Member

    The roll stiffness will come from the four hydraulic cylinders, two of which you can see on the drawing: the rectangular things 15º off vertical with the bellows top and bottom. I still have to go and talk to hydraulics people to be sure what the physical size and shape of those things will be: what I've drawn is an educated guess.

    They're double-acting, double-rod-ended, so their upper and lower chamber displacements are the same. So, cross-interlinked side to side, as long as both front wheels move together displacement from top/left simply flows to bottom/right and vice versa, and there's no pressure change. During roll the volume, and hence pressure, of TL+BR will be unequal to TR+BL: pressure in one circuit rises and pressure in the other falls. This is resisted by another cylinder, damping valves, and spring in each circuit. Why not an anti-roll bar? Because a) I can't damp that and b) that doesn't let me interlink front and rear and thus make the system warp-flexible.
     
  11. n.z.rodder
    Joined: Nov 18, 2008
    Posts: 1,016

    n.z.rodder
    Member

    Ok just googled Mumford suspensions and found some better diagrams of what this is, and now understand the principle of this design, I'm still unsure about the air bag in the mix though. Will keep an eye on this.
     
  12. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,839

    Ned Ludd
    Member

    I don't know! I hope to find out. But keep in mind that the pivots aren't all in series, which would have been a lost-motion nightmare.

    Three bars. That lets me set up for anti-dive without bar flex in roll.
     
  13. Ah, so something like the old Citroen system? Clever stuff if you can get it to work as you want.
    Am I right in thinking that its the rate of flow of hydraulic fluid through this system that will control how quick the body roll can occur?
     
  14. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,839

    Ned Ludd
    Member

    No, this'll be a static system, no pumps, no constant flow; more like the BMC Hydralastic/Hydragas systems, except that it controls roll only. Roll is resisted by two steel springs. The hydraulic system is only a transfer system, to get the relevant forces where I want them: think brake system. As with a brake system it is actually simpler to do hydraulically than with mechanical linkages, as I found after long deliberation.
     
    Last edited: Jun 25, 2009
  15. 55chevr
    Joined: Jul 12, 2008
    Posts: 959

    55chevr
    Member

    You are on the wrong website ... this site focuses on traditional hot rods ...
     
  16. :rolleyes: Oh dear.
     
  17. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,839

    Ned Ludd
    Member

    Am I? I'd rather have, "this is a site for traditional hot rods" than, "why don't you bodge it right with electronics?" At least here nobody's going to ask if I realise it's 2009!
     
  18. Heretic! Coming on here with your new fangled "hydraulics" and fancy "bell cranks"!:D
     
  19. Phil1934
    Joined: Jun 24, 2001
    Posts: 2,608

    Phil1934
    Member

    I don't see this. If it is anchored to a flexible frame, you should not be able to make it stiffer.
     
  20. Silent_Orchestra
    Joined: Jun 17, 2007
    Posts: 1,313

    Silent_Orchestra
    BANNED
    from Omaha, NE

    Hmmm this is interesting even though I don't understand much of it..I'll be watching this one, hopefully it all becomes a little more understandable...I did just wake up to though that could be an issue...

    As long as you don't toss around ideas of sticking casters on the frame rails I think you may get a few decent replys.

    BTW is that your project idea in your avatar?
     
  21. hot rod pro
    Joined: Jun 1, 2005
    Posts: 2,668

    hot rod pro
    Member
    from spring tx.


    let the guy at least show some pictures of the work in progress,before we start this crap.i want to see this drawing turned into metal before i add my opinion.

    -danny
     
  22. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,839

    Ned Ludd
    Member

    The need for rigidity is eliminated because the apportionment of roll loads front to rear is determined by the roll-control system through a combination of piston area and mechanical advantage. Think of the balance bar in a dual-master-cylinder braking system: the apportionment is determined by the position of the pedal link along the bar, even though the link is free to pivot on the bar. Now think of a balance bar the length of the car (or, because that would be hugely heavy, an hydraulic system instead that does the same thing.)

    The hydraulic apportionment sets up a virtual pivot somewhere along the wheelbase. The frame can flex all it wants and not move that pivot forwards or back; it just flexes around the pivot. The front-rear apportionment therefore doesn't change. But by the same token, a lot of the forces that generate flex in the first place are eliminated by introducing that pivotedness. This is hard to explain without pictures!

    Or, if it were a toy car, you'd be able to hold it by the front wheels with one hand and by the rear wheels with the other, with your thumbs and forefingers in the dishes of the wheels. You're only touching the wheels. If you were then to rotate the axles in relation to one another, as if to twist the car, i.e. one axle rolling left and the other rolling right, there'd be no resistance until you hit the bump stops. Because there's no resistance you can twist all you want (in that range) and not impart any torque onto the toy car itself. Does that explain it better?

    Of course it's still a good idea to have a reasonably rigid frame, it's just practical, but the need is a fraction of what it would be with a conventional system. It's a different order of magnitude.
     
  23. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,839

    Ned Ludd
    Member

    No casters, don't worry!

    My avatar is a previous stage in the development of the idea; or rather, it's a short detour during which it was a '27 T before it turned back into a '31 A. It was briefly an MG K3 replica, too, at another time.
     
  24. Can´t escape the feeling that you have an entirely inappropriate user name!
     
  25. 28hiboy
    Joined: Feb 2, 2007
    Posts: 397

    28hiboy
    Member
    from milton fl

    I want to see the body design stuff.
     
  26. Ned Ludd
    Joined: May 15, 2009
    Posts: 3,839

    Ned Ludd
    Member

    It's because I don't like electronic controls, mass production, and unfixable stuff. The original Luddites weren't against technology, they just wanted the sorts of technology they could engage with.
     
  27. Ah - Well then, I´m with you all the way on that one!:)
     
  28. TCURRIER
    Joined: Mar 7, 2005
    Posts: 88

    TCURRIER
    Alliance Vendor
    from michigan

    there is commercials all nite long on the t.v tellin me to send some cash to poor little haboob down in africa for food, and youre drawing shit on cad, wtf? i want my money back!!
     
  29. kurtis
    Joined: Mar 13, 2009
    Posts: 1,990

    kurtis
    Member
    from Australia

    Excellent thread Dawie.
    Now to the questions, and there will be alot. What is the theory concerning the 15degree angle on the cylinders?Why not straight up? Why four of them? Surely two would be enough for this application considering they are hydraulic.
     
  30. BarryA
    Joined: Apr 22, 2007
    Posts: 643

    BarryA
    Member

    Africa is a big place - with poor, rich and some in the middle much like anywhere else......OK maybe a few more poor!

    Dawie I am watching this with interest, like some of your other posts/ideas.
    Some of it goes a little over my head though, and I must say that given what goes into getting a car built, the ideas are great to theorise about, but I'm probably goning to go with the tried and tested (and relatively freely available) in order to get my build on the road sooner.
    That said, if no-one thought out the box we wouldn't have progress (for better or worse!!)

    Barry
     

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