Balancing, Counterbalancing and Dynamics

[NW Mailing List]

Thanks, Gary.

I realize that in counterbalancing drivers you're trying to come up with a fixed or static solution for a dynamic problem that is changing constantly (I guess that's redundant) and you have to come up with the best compromise possible to enable the locomotive to reach a top desired speed while not doing damage to the track, the moving components of the loco drive system and the fixed parts of the locomotive--frame, cylinders, etc.  And it has to stay on the track!  I just had never noticed counterweights that didn't at least appear to be centered directly across the axle from the rod pins.  I'm know there's a good engineering reason why weights are put where they are and my bias toward the centered location is just an observational bias not a reasoned one.  I took enough engineering before becoming an English major that I could probably follow the vectors, polar moments, etc. that would explain the forces leading to the location decisions.  And if not, I could just nod.

Sam

----- Original Message ----- 
  From: NW Mailing List 
  To: 'NW Mailing List' 
  Sent: Wednesday, March 25, 2009 8:06 PM
  Subject: Balancing, Counterbalancing and Dynamics


  Remember that the counterbalancing is not for a STATIC case but a DYNAMIC case with the mass of the drivers and rods included and rotating at different speeds.  In addition there are first mode, second mode, third mode and so on, that is, different dynamic loading per frequency at multiples of the running rpm.  Depending on a bunch of different things, the second, third fourth or other modes might be the most significant loading comparing a dynamic loading situation to a strictly static one.  In reality, you have the rotating drivers plus the oscillating rods moving back and forth and going around the driver pin so those loads are part rotating and part horizontal and vertical loads. Plus the loads from one side are transmitted to the other side and vice-versa.

   

  Thinking about the situation in 'common sense' static balance thinking is pretty far off from what actually happens in a dynamic situation. 

   

  In physics or vibration calculations/modeling, this is a complex system requiring some pretty sophisticated analysis.  The Roanoke engineers would have loved to have had a computer to model what they had to estimate with a slide rule.

   

  Part of the issue with the RF&P 4-8-4's and their poor high speed balancing problems were that the published state-of-the-art calculation methods didn't work (1927).  The N&W didn't do the calculations that way for the A and the J.  (The AT&SF engineers didn't follow the published methods either for their high speed locomotives.) 

   

  Gary Rolih

  Cincinnati ( and a Mechanical Engineer)

   

   


------------------------------------------------------------------------------

  From: nw-mailing-list-bounces at nwhs.org [mailto:nw-mailing-list-bounces at nwhs.org] On Behalf Of NW Mailing List
  Sent: Wednesday, March 25, 2009 3:54 PM
  To: NW Mailing List
  Subject: Re: Wheel spokes

   

  Very interesting.  I had always assumed that counterweights were centered exactly opposite the pin holding the rods.  While that appears true for the front and middle A drivers, it is obvious from the drawing that it is not true for the main driver.  Would this be because the added weight of the main rod throws the balance off-center?

   

  Sam Putney

   

    ----- Original Message ----- 

    From: NW Mailing List 

    To: NW Mailing List 

    Sent: Monday, March 23, 2009 8:20 PM

    Subject: Re: Wheel spokes

     

    Richard,

    I'm surprised no one else has answered this yet. The number is 15. 

    You can see drawings of the drivers at the following addresses:

    Front Driving Wheel http://www.nwhs.org/archivesdb/detail.php?ID=23293
    Intermediate Driving Wheel http://www.nwhs.org/archivesdb/detail.php?ID=23187
    Main Driving Wheel http://www.nwhs.org/archivesdb/detail.php?ID=23192

    Listing of more Class A wheel drawings is at http://www.nwhs.org/archivesdb/listdocs.php?index=rs&id=161&Searchword=wheel 

    Ron Davis

    At 03:15 PM 3/20/2009, you wrote:



    Hi chaps
    Can somebody tell me the exact number of spokes on a Class A driving wheel, thanks in advance
     
    Regards Richard in UK
    ________________________________________
    NW-Mailing-List at nwhs.org
    To change your subscription go to
    http://list.nwhs.org/mailman/options/nw-mailing-list
    Browse the NW-Mailing-List archives at
    http://list.nwhs.org/pipermail/nw-mailing-list/


----------------------------------------------------------------------------

    ________________________________________
    NW-Mailing-List at nwhs.org
    To change your subscription go to
    http://list.nwhs.org/mailman/options/nw-mailing-list
    Browse the NW-Mailing-List archives at
    http://list.nwhs.org/pipermail/nw-mailing-list/



------------------------------------------------------------------------------


  ________________________________________
  NW-Mailing-List at nwhs.org
  To change your subscription go to
  http://list.nwhs.org/mailman/options/nw-mailing-list
  Browse the NW-Mailing-List archives at
  http://list.nwhs.org/pipermail/nw-mailing-list/
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://six.pairlist.net/pipermail/nw-mailing-list/attachments/20090326/905638d5/attachment-0001.html>