7mm Yorky D's Küchentisch - Slides - Something industrial. Totternhoe Chalk Pit 1960

Discussion in 'Area 51' started by Yorkshire Dave, 30 May 2016.

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  1. Yorkshire Dave

    Yorkshire Dave Western Thunderer

    Not yet, it's still on the list but the recent weather has hardly been conducive for going out.

    I decided to remove a set of rear wheels to make it into a lighter truck..... ;)
     
  2. Heather Kay

    Heather Kay Western Thunderer

    Perhaps a little overdone, but for a tired old truck it’s okay. A small but definite improvement. :thumbs:

    Now, what’s the plan with the Blitz?
     
  3. Yorkshire Dave

    Yorkshire Dave Western Thunderer

    The Blitz is to be mutated into a 1936 Bedford.

    Like the Ford AA it has to be converted to left hand drive.
     
  4. Heather Kay

    Heather Kay Western Thunderer

    Tidy. The Opel cab will need some work, as the Bedford is a deal more square. I shall look forward to seeing this come together. :drool:
     
  5. Dog Star

    Dog Star Western Thunderer

    What Heather is describing in regard to the wheels being at different angles is a design intention of Ackermann steering.

    I believe that the self-centring characteristic of the front wheels comes from the degree by which the caster angle leans forward of the (imaginary) axle centre line..
     
    Last edited: 15 February 2020
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  6. simond

    simond Western Thunderer

    Indeed.
    Toe in or out is the non-parallelism in plan view. It contributes to the stability of the steering, but is not the primary reason for self-centering.
    Camber is non parallelism in end view, positive camber, as described above, is when the wheels are sitting perpendicular to a normal convex road, negative camber is the opposite, visible to a greater or lesser degree on lots of cars with sporting ambitions. It is used to compensate for the deflection of the tyres in such vehicles. I don’t have any idea why older vehicles used considerable positive camber, unless they used cart wheels, where the dishing is very limited. Ideally you would want the kingpin axis to coincide with the tyre contact patch in the end view, which requires the wheels to be dished.
    Caster angle is more easily seen on a motorbike, the forks are typically parallel to, but offset from, the steering axis. Producing the axis of the steering until it his the road allows you to measure the trail which is the distance from this intersection to the centre of the contact patch. The angle effectively means that steering the wheel away from straight lifts the front of the vehicle, so gravity tends to bring the wheels to the straight ahead position. Trail does the same thing.

    Sorry, rabbit hole...

    atb
    Simon
     
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  7. Osgood

    Osgood Western Thunderer

    Picard.png
    Here is a Ford Model AA axle - just look at that KPI!
    So when a wheel is turned inwards (e.g. RH wheel turning left) the bottom of the wheel will tuck under, and when turned outwards it tucks under.
    Ford AA front axle.jpg
    Interestingly (or probably otherwise :))), positive or negative caster (another factor in non-upright wheels) is usually adjusted on truck axles by means of tapered wedges between axle and spring - with KPI and camber you are stuck with what it is, but the turning effect can be compensated for by the castor angle.
    Screen Shot 2020-02-15 at 13.54.11.png
     
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  8. Dog Star

    Dog Star Western Thunderer

    After such a lesson in steering ideas, Simon, you shall no doubt enjoy the simplicity of the Land Rover front axle (say SIII ) with:-

    * positive camber for the wheel;
    * toe-in of variable nature;
    * camber for the virtual king pin (actually top and bottom swivel pins);
    * camber through the placing of the top and bottom pin bushes in the swivel hub housing,

    All in all a neat solution to the problem of going round corners. What has never been explained to me is how the 88" WB and 109" WB steering set-ups are the same since that ought not to be the case given the basis of Ackermann geometry.

    Tony, (@Osgood), I did get around to adding king pin inclination into the discussion - at the same time as you were typing. I stopped short of mentioning KPI because of how LR achieved the requirements through the design of assymetric swivel hub - assembling hubs the wrong way converts the KPI angle between negative and positive with interesting effects.
     
    Last edited: 15 February 2020
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  9. Osgood

    Osgood Western Thunderer

    Same with all those cheap short wheelbase tractor unit chassis that turned into flatbed recovery trucks by doubling the wheelbase!
     
  10. Overseer

    Overseer Western Thunderer

    Spotted on the Isle of Dogs
    image.jpg
     
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  11. Yorkshire Dave

    Yorkshire Dave Western Thunderer

    An interesting photo all round - truncated railway arch, garage/workshop under the arches, advertising mural.
     
  12. Yorkshire Dave

    Yorkshire Dave Western Thunderer

    Tony, Simon, Dog Star - thanks for the detailed information - yet more to store in the old grey matter. I never knew steering was that scientific.
     
  13. Threadmark: GMC
    Yorkshire Dave

    Yorkshire Dave Western Thunderer

    Following Heather's observations regarding the cab shape on the Opel Blitz I've had another look and it'll be tricky to convert to a Bedford cab...... I'll take the lazy option and build it as Dutch or German civilian vehicle - so some Hauler etched parts are on their way :) .

    In the meantime a start has been made on the US 6x6 aircraft fuel tanker.

    Chassis - the 'sagged' wheels are from the DEF Model range.

    GMC 002.jpg

    And yes, they are Uniroyal tyres....

    GMC 003.jpg
     
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  14. AJC

    AJC Western Thunderer

    There were at least a handful of Opels imported before hostilities commenced - there was a picture of one in traffic in the centre of Bristol (trams and all) published in one of the vintage commercials magazines, recently, but not, I suspect, one of a statistically significant number!

    Adam
     
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  15. adrian

    adrian Flying Squad

    My understanding (which may well be wrong!) is that there were a couple of reasons. For early vehicles suspension geometry was in its infancy and so things were kept simple. As the suspension gets loaded then they would move towards a neutral or negative camber. So when cornering as the vehicle rolls then the outside wheel would load up and move to a neutral camber - making the best contact patch by having the wheel perpendicular to the road. I have also seen comments that the positive camber lightened the steering load, useful in the days before power steering although I'm still try to figure out how that works. I can see how extreme negative camber makes the vehicle very stable in a straight line. You only have to look at the para-Olympics all the wheelchair athletes using significant negative camber. So presumable positve camber works the other way.
     
  16. simond

    simond Western Thunderer

    Yep, another element in attempting to get the king pin axis to coincide in end view with the centre of the contact patch!

    again, the dishing of the wheel is relevant.

    Atb
    Simon
     
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  17. simond

    simond Western Thunderer

    vehicles with a beam axle do not change their camber with added load, though the castor angle and trail may change. Vehicles with independent suspension do change camber with load (and dynamically).

    I’ll have a ponder about the wheelchairs, though I suspect it may be more to do with the ergonomics of riders’ arms reaching the hand-wheel than anything to do with steering, or cornering stability.

    As an aside, in my Mini days, (many moons ago) I fitted neg camber lower arms to the front suspension. It stopped understeering very noticeably. Once it did let go at the front (at much higher cornering g) it was a bit digital, all or nothing, not progressive like a standard Mini. You were not going to get it back unless you had acres of space, or you stopped...

    They are dead easy to make if you can weld, or can find a welder you can trust. Chop the lower arms, roughly in the middle. Place a suitable piece of steel, maybe 3-6mm thick between the ends, and tack back together. Check it’s all straight, then weld a couple of 1/4” rods in the web of the arms. The ones I made were about 4” long. I can’t remember the calculation of extended lower arm to degrees of camber, but it wasn’t hard to work out. A few mm makes quite a difference!

    Atb
    Simon
     
  18. Rob R

    Rob R Western Thunderer

    The erstwhile Millwall Extension Railway. When I get to the pc I will try and work out which way the photographer is pointing.
    Rob
     
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  19. Overseer

    Overseer Western Thunderer

    It is the north abutment of the steel bridge across Manchester Road (or is it still Westferry Rd there) taken from what was then Johnson St. The photographer had his back to the North Greenwich station building and the Thames. This was after it closed the first time and the steel bridge was removed. A new bridge was built for the DLR but that has now gone. The brick viaduct survives but unused again since the tunnel under the Thames was built.
     
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  20. Osgood

    Osgood Western Thunderer

    Those Uniroyals look positively new - unlike the tyres on this GMC refueler (poor quality pic but you can see missing tread!!):

    CCKW refueler.jpg

    Note the (red?) flag - only pic I've found of a GMC refueler with a flag.
     
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