Re: MR engine reviews

On Tue, 25 Jul 2006 10:41:02 -0400, David Starr
<dstarrboston@xxxxxxxxxxxx> wrote:

Dan Merkel wrote:
One small complaint that I have about MODEL RAILROADER's engine reviews is
that they will talk about an engine like it has a lot of power but when you
look at the drawbar pull vs. the "average" locomotive, it is often much
weaker. While I like nice looking engines, I also want to know how they
pull. What is an "average" locomotive anyway? : )

dlm
---------------------------
Dan Merkel


Model locomotive pull is proportional to weight. Heavier locomotives
pull more. The motors always have enough torque to spin the wheels, so
tractive effort is limited by the onset of wheel spin. For metal wheels
on nickel silver rail, the coefficient of friction is about 0.25. The
means the wheels start to slip when the tractive effort is 0.25 *
locomotive weight. So a 16 oz locomotive can create 4 oz of draw bar
pull. Double the weight and you double the draw bar pull.
The only way to improve on this is to improve the coefficient of
friction by the use of rubber traction tires. Rubber on nickel silver
has a coefficient of friction of 0.5 or better, so you get double the
pull for the same locomotive weight.
HO diesels pull better than HO steamers, especially plastic HO
steamers. All my diesels pull enough cars up my grades. None of my
steamers pulls as many cars as I would like. I have packed as much lead
as will fit into all of them, and they still don't pull as much as I
would like.
If you like steamers, consider keeping the grades gentle to give your
locomotives a break.


Properly designed, weighted and balanced steam can pull.

Example I have a old (late 60s early 70s)GN O-8 2-8-2 from PFM
Tenshodo, NOT re motored yet so it's the original Pittman open frame,
I also have a similar GN S-1 4-8-4. On our club layout either of these
will take 40 loaded Athearn 34 foot twin hoppers cars up a 110 ft long
2.2% uncompensated grade. There is also a 90 degree 36" curve followed
15' later by a 180 degree 36" curve at the end of the yard at the
bottom of the climb so the train hits these right after leaving the
yard.

I have two Sunset Q-2 2-10-2s, and an O-8 imported in the mid 80s and
made by Samhongsa. None of these engines can pull that train unless
double headed. I was told not to add weight to these due to the belt
drive and they are lighter than the Tenshodo by a lot. The tender
trucks are much more free rolling than the Tenshodo but that does not
help. I suspect it's partly a lack of torque in the Canon CN-22 motor
provided in these engines in addition to the weight and drive system
differences. They seem balanced properly so I don't think that's an
issue (The stock Athearn USRA light 2-8-2 is tail heavy and balances
over the third driver so the first driver does almost no work) Also
the springing in the lead and trailing truck seem OK so I doubt they
are taking much of the weight. Mind you they are much better detailed
then the older engines but can't pull like them.

I'm going to test the USRA light 2-10-2 tomorrow night (CN version
with the stock Bachman DCC) to see how it does.

--

"I believe there are more instances of the abridgement
of the freedom of the people by gradual and silent
encroachments of those in power than by violent and
sudden usurpations." - US President James Madison

"To be a social conservative is to believe that the
poor have too much money, and the rich don't have
enough." - J.K. Galbraith


"You need only reflect that one of the best ways to get
yourself a reputation as a dangerous citizen these days
is to go about repeating the very phrases which our
founding fathers used in the struggle for independence."
- Charles Austin Beard
.

Relevant Pages

  • Re: Cultivators with electric start
    ... >>Electronic ignition won't make it any easier to pull the starter cord, ... OP's got a dodgy right arm and can't pull the cord at all. ... of the B&S engines used to have a pre-wound spring starter. ...
    (uk.rec.gardening)
  • Re: briggs&stratton starting problem
    ... I have to pull many, many times, and after a while the engine starts to ... and I can see gas splash up in the carb ... I have seen other Briggs engines do this, and I have never figured out ...
    (alt.home.repair)
  • Re: Saving a sunk 1959 CC SeaSkiff
    ... Even though the engines have been pickled. ... Pull the spark plugs and crank the engine over to get rid of ... be checked over because there's been water in the bearings, ... The water did NOT hit the gages.. ...
    (rec.boats)
  • Re: whats the bridge between a cruiser and a sportbike...
    ... The stators on lots of mid-80s Honda engines tended to quit. ... also needed to pull the engine to fix it. ...
    (rec.motorcycles)
  • Re: Bachmann Standard 5MT
    ... The Standard 5MT seems fine except for a lack of weight, ... some weight to the Loco it comfortably pulls the full train and 25 wagons ... I am going to get my fishing pull scales and see just how much ... > coaches, and whilst it didn't reach the same speeds as the Class 40 still ...
    (uk.rec.models.rail)