Hi Gregory
On (04 Jul 97) Gregory Procter wrote to Alec Cameron...
 -=> Quoting Alec Cameron to Gregory Procter <=-
 AC> Isn't the gearing ALWAYS arranged for ultimate speed? hence freight
 AC> locos geared different from express passenger, and suburban multiple
 AC> untis geared differently again.
 GP> I was refering to the potential speed for the locomotive only, not
 GP> locomotive
 GP> and train.
Gotcha. That seems a rather airy fairy speed that doesn't mean much but I see
what you mean. Rather like holding down the clutch pedal on an automobile at
full throttle. Interesting but keep, out of MY car!! :-)
The record holding TGV (515Km/hr or whatever) gearing was a
 GP> compromise that went only as far as replacement gears which would fit 
he
 GP> standard gear housing and oversize wheels. It's ultimate speed would be
 GP> greater.
 AC> And is compromised by a few other things- like the fact that with
 AC> coupled drive wheels, a slip on greasy or leafy rails leads to almost
 AC> total loss of traction.
 GP> These factors are exactly the same for steam, Diesel, electric and
 GP> etc.
The "factor" may be the same but the results are quite different.
 AC> Not really. Steam locos' drive wheels are always coupled but the
 AC> others, hardly ever.
 GP>  Would you like a list of all the Diesels and Electrics built with rod
 GP> drive?
Sorry I was dealing with the majority, and you are right of course there have
been quite large numbers of weirdos.
 GP> Diesels and elecs having independent drive to
 AC> each axle, some may grip while others slip and a decent drawbar pull
 GP> is
 AC> maintained by the loco as a whole.
 GP>  Once the limit of traction is reached, if one axle slips, the load
 GP> will
 GP> go on
 GP>  to the otheraxles and they will slip to.
Not all the load will transfer, the inevitable drop in speed will see a
reduction in wind and friction forces. I was employed as a mechanic on emu
trains, wheel slip was a single car problem, the other cars in the train
would battle on without loss of adhesion. I lived near the steepest bank on
the local line so wheel slip was a frequently observed situation and
[surprise surprise!] it was the steamers that were most affected. The bank
was such a nuisance that the emergency coupler [emu to steamer] was
permanently kept under a seat in the passenger waiting room of Denistone
down platform.
 GP> some elec
 AC> loco designs used to have a heavy weight in the cab that was rolled
 GP> up
 AC> close to the driver cab, to overcome this weight transfer. At the end
 AC> of the line, the loco returning with the rear cab now at front, would
 AC> have this weght cranked up to the other end ie the "front" of the
 AC> returning train loco.
 GP>  Sounds like "state of the art 1847".
Yes it was old, but importantly! it was informative and gave essential
parameters to an understanding of train dynamics.
 AC> Some "smart" control systems apply less power to the lead axle, while
 AC> loading up those further back. The smartest, just regulate the slip
 GP> so
 AC> that the drive power to each motor is different from all its buddies,
 AC> and the drive power ramps down and up rhythmically at the onset and
 AC> recovery from slip. And the extremely smart locos provide constant
 AC> positive slip at each wheel so as to win adhesion considerably above
 AC> the conventional "25%" figure.
 GP>  You could do the same thing with a 1997 steam locomotive also.
No I couldn't. But yes, NASA or some other smart scientists could do as you
wish given the funds! Where is this 1997 steam loco?! I wanna ride....
 GP> We started this discussion with me postulating a modern steam engine 
ith
 GP> individual axle drive, without coupling or connecting rods to the 
heels.
 GP> A Diesel or electric with coupling rods is not perfect at high speeds.
I don't feel constrained to follow exactly in your steps, discussion- wise.
It is quite hard to consider a modern steam loco, because there are none. If
by individual axle drive you mean electric motors, then that is a gross abuse
of the steam loco design process. A steam loco should have a steam engine fed
by its boiler. I too would like another steam loco design to be undertaken 
nd
more important! would like it to be applauded for its efficiency, durability,
performance and low running cost. I see not the slightest chance, that this
will ever happen.
====
Noted remarks re stiction and pulses
=====
 AC> Sorry, you are not up to date. There are many large locos today where
 AC> positive slip is maintained for long periods. What you have
 AC> [correctly] described is now obsolete technology.
 GP> I admit to not being up to date on the latest technology, but I have a
 GP> passing
 GP> knowledge of the laws of nature, and even a little knowledge of physics. 
I
 GP> assume that the latest technology hasn't managed to by-pass the laws of
 GP> physics?
Those "laws" are changing! Like gravity, Einstein and Newton gave conflicting
"laws" but who cares! The end results are OK whichever physicist is followed.
 GP> I do know that once the wheel slips, the coefficient of friction drops
>> CONTINUED IN NEXT MESSAGE <<
... ....Horsepower was a wonderful thing when only horses had it
--- PPoint 1.92
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