query re: locomotive weights

"Christopher A. Lee" wrote:


You got me! ;-) I've been a fan of Mike Sharman ever since he published some of his techniques in the 60s-70s. My models tend to be from the end of the eighteenth century rather than the beginning but the same techniques work. I tend to favour heavier construction than the etched brass frames common in UK kits and most of my compensation is based around milled blocks of brass rather than flimsy sheet. (etched detail overlay) I tried and rejected Sharman's gearing system with pinion reduction before worm gearing - I tend to used worm on the motor shaft and spur reduction between the worm gear and driven axle(s) Spur gears at motor speed are too noisy for my liking.
Greg.P.
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Hi,
On 03/09/2011 08:00 AM, Twibil wrote:

...
Take a moment, draw a box (outline of your loco) and add in the points where the wheels contact the rail and the coupler. Now draw the relevant vectors of force, acting on the loco. This will be *gravity, *drawbar power. They will originate from the Center of Gravity. The gravity goes straight downwards, while the drawbar power intersects the drawbar center.
The result from adding the two vectors gives a combined one pointing to the rear and downward. You should have a diamond-shaped thingy with the resulting force vector being the longer diagonal line in the diamond.
Now, when you look at the resulting vector, it becomes obvious that the loco's front will lift from the rails once the resulting vector points /behind/ the rear wheels. It should also be obvious that the efective force on the wheels shifts quite a bit backwards compared to the gravity vector. But the axle height does not have any influence.
As a result, one could say, the lower the drawbar the better. Also, a loco being nose-heavy is likely ok, as long as it keeps pulling in the same direction. The resulting vector (above) will work out well.
Also, adding weight will increase pulling power, just draw the longer weight vector and update the diagram. The rear wheels should stall first ;-)
But on any loco that will run both directions or run inside a consist or train, it might be better to center the weight over the drivers ;-)
Have fun...
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Twibil wrote:

Ok, ok, a slight misuse of language :-) As I generally model small locos I sometimes use part of the tender frame resting on the loco rear beam. The forward bogie of the tender is loose vertically so all the tender weight forward of the rear axle (three axle tender) rests on the loco frame.
Greg.P.
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ray wrote:

N scale weighting has a very simple formula: "make your loco as heavy as is possible." You can't overweight an N gauge loco. Extra weight has 3 main advantages: - better traction current collection. - smoother running through greater momentum. - better tractive effort.
Rolling stock weight then becomes a balancing act between the length of train able to be pulled and trackability. (abilty to stay on the track.
Greg.P. NZ
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