-=> Quoting Reggie Arford to Alec Cameron <=-
 RA> No. (I did a senior project with the stuff in University.)
 Interesting subject! I like hearing such info!
 AC>You have proposed that a rigid set of drivers as in conventional
 RA> steam locos, is sprung and equalised sufficiently for you to compare
 RA> with elec motor bogies.
 RA> "Rigid" set of drivers? Not hardly! Look closely...
 RA> The side rods have joints near each crank pin, except at the ends.
 RA> The drive axle journal bearings are in blocks, which float up and
 RA> down in slots designed into the loco frame. Note that this vertical
 RA> motion is at right angles to the drive forces applied by the rods,
 RA> so the two are independant.
      Not quite independent, the driving force from the connecting rod 
imparts a
 load against the journal block to slot face, which restricts the free 
movement
 of the axle in the frame. Recent suspension systems for high speed work
 generally use radius arms rather than slots. The axle movement is then an 
rc
 rather than a straight vertical movement. There is little effective 
difference
 for one axle, but it would be a different (impractical?) matter for coupled
 axles.
      The leaf springs above each journal are
 RA> linked at the ends to the next one over, so that all work together
 RA> equalizing the weight from one axle to the next, and the next after
 RA> that... The suspension on a steamer is much more complicated than
 RA> the drive rod system! Note also that the rotating mass of all the
 RA> drive rods, and half (exactly) of the main rods, can be counter-
 RA> ballanced in the wheels.
      This remaining "half" becomes a major problem, it could be as much as 1
 tonne moving up and down at 4 times per second on one axle, which is a force
 to be reckoned with! If the driven axle is equalized with its neighbours, 
he
 "hammer blow force" is spread over all the equalized springs, not just the
 single driven axle spring. So a result of equalization is that the loco is 
less
 able to cope with with the unbalanced forces than a non-equalized loco.
 RA> [fully] sprung and equalized. The equalizing system adjusts
 RA> the spring tensions so that all axles receive their share of
 RA> the burden. Note that lead and trailing truck axles are
 RA> typicaly included, but at a lesser rated burden.
(If all axles are equalized, the loco will flop forward or backwards to the
limit of axle travel. Its been built! ;-)
 RA> I have no problem with the dynamics of the lead and trail bogies. The
 RA> springing of these could be as good as on a Bo Bo elec or de body.
      But why include unpowered carrying axles when the point of the exercise 
is
      to provide traction?
 But
 RA> I won't buy the principle that the main drive wheels of a conventional
 RA> steamer, are uniformly sharing the burden of the train on- the- move.
 RA> Because-
 > The drive wheels and axles have very high mass hence inertia, and
 RA> will more slowly respond to the ups and downs of the rail head.
 RA> * Not relative to the vertical forces involved; plus the track
 RA> doesn't go up & down that sharply. Rail doesn't bend that way.
 > The heavy side rods, pinned to each drive wheel, also restrain any
 RA> independence of vertical movement of any single axle as IT passes over
 RA> a valley or hill in the rail head.
 RA> * No; as I said, they're jointed near the middle crank(s).
      There is appreciable friction in the coupling rod bearings, evidenced 
y
 the reduction in friction achieved by fitting roller bearings in later years 
of
 steam.
 > The springs that serve each axle are much "harder" than those
 RA> of a conventional motor bogie. The bogie of today has multiple
 RA> springs and links. Not just one spring per axle box!
 RA> * No; if you consider the (change in force) per (unit traveled),
 RA> the steam loco's spring /system/ is MUCH softer than "bogies".
      This is offset by the much worse ratio of sprung/unsprung weight of the
 steamers wheels and rods.
 >And, I don't think there is much scope for designing springing
 >improvements into a set of 6, 8 or 10 couple drive wheelsets.
 RA> Not necessary. It's already quite soft & flexable.
      Greg.P.
  
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