Bits chopped out...
       GP> than a non-equalized loco.
 RA> Actually, no. The main rod's mass may be resolved into two: One
 RA> mounted at the crankpin, moving in a circle; and the other at
 RA> the crosshead joint, moving _horizontaly_. The crankpin mass may
 RA> be counterballanced in the wheels, as any other rotating mass.
 Yup!
 RA> It's the horizontal component that can't be ballanced, which
 RA> provides torque around a vertical axis. Since the horizontal
 RA> component is at right angles to the equalization, there is no
 RA> interference. The mass of the other side rods can be completely
 RA> counterballanced, as their centers of mass describe a circle
 RA> (not an elipse as the main rods' do). Notice that the counter-
 RA> weights on the main drivers are larger than those of the others?
 RA> That's why.
      The coupling rods are completely ballanced, as you say.
      The connecting rod forces describe the elipse as you say.
      The counterweight could be, and was (1820 - 1870) made to balance the
      rotating component of the motion.
      Your loco it then left with, for example: (per revolution of drivers)
      a rearward force, left side
      a forward force, right side
      a forward force, left side
      a rearward force, right side
      It is a complicated dance step, guarrenteed to trip you or a 4.4.0 up 
t
      any speed so the designers were forced with 4.6.0s and 2.8.0s to trade
off
      some of the rotational counterbalancing of the connecting rod for fore
and
      aft balancing. (The con-rod needs to be longer on 4.6.0s and 2.8.0s 
han
      4.4.0s to reach the second driven axle)
 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.
 GP> (If all axles are equalized, the loco will flop forward or
 GP> backwards to the limit of axle travel. Its been built! ;-)
 RA> You are quite right. You have caught me in an oversimplification.
 RA> Depending on the design of a particular locomotive, axles are
 RA> grouped into sections which are not equalized with each other.
 RA> Consider the common 8- or 10-wheeled locomotive: a 4-4-0 or a
 RA> 4-6-0. The lead truck will be equalized within itself, and the
 RA> drive axles among themselves. The locomotive would then be
 RA> supported at three points: the pivot of the lead truck, and the
 RA> centers of support of the left and right sides.
      Modern Locos are equalised per bogie (truck) so they are supported at 4
      points which makes them more stable. The weight distribution suffers in
      theory against 3 point support but with lots of wheels the difference 
s
      negligable.
      The torque
 RA> resulting from (forward) tractive effort will shift some of the
 RA> locomotive's weight from the lead truck, onto the drivers.
 RA> The drivers may share this added burden equally.
      It worked in the locos favour on the Norris 4.2.0s, it was all downhill
      from there ;-)
 RA> I think I may elaborate on this in another message; look for
 RA> "Steam Loco Design", or some such topic, to "All".
      Greg.
  
... Catch the Blue Wave!
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