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Just another modeller
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****

NS oxidises quite badly - I had the black stuff that rubs off analysed by a university and it is 95% copper oxide - a great insulator... so you could say that it "rusts" too - but almost invisibly :).

Only NS is used by all the major RTR track people. Silly really.

The problem is most Mfrs use too little Nickel in the mix (less than 17~18%) so its not a good material for rail really - if they used 24% nickel then it would not corrode nearly as much. (Coin grade NS is 25% from memory)

Phosphor bronze never loks realistic even if painted as the railhead is never silvery as it should be on well used track.- and it oxidises worse than NS. to be avoided.

Steel is fine in the average layout environment but as a rule of thumb not in anywhere that gets extremes of temp and humidity as dew point means moisture = surface rust unless treated.

steel files and bends at least as easily as NS and is quite easy to solder as well. In bullhead rail its a super material to work with for hand made pointwork...

C&L do code 82 flatbottom rail and BS95R bulhead is an excellent high nickel version of NS that almost looks like steel - they also do steel rail in both.

Its not logical that NS is the metal used really.... NS is very slippery as an alloy! A loco will pull up to 25% more on steel track. A well chosen grade of stainless steel would be the best answer - none of the down sides of NS and all the benfits of steel.

Anyway... look for a brand that looks less "yellow" the yellower, the less NS is in it. Tilling is a better choice therefore than Peco!
 

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Just another modeller
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9,983 Posts
***True, but NS is like its been soaped compared to steel :). and NS wheels on NS track is so slippery I still can't figure how the brands got it so wrong when it came to choosing what to use.

Here's one for you Paul - and all other engineers on MRF.

I am researching a future project and as part of it, I was interested in the huge reputation of the Portescap motor/gearbox combo sold in UK. Its a very good product that has become very, very expensive, but there is no denying its real world performance

Frankly in most repects the Escap RG4 and RG7 are nothing special as motors go and compared to may Iron core motors, quite wimpy power wise in fact... Anyway - as an offshoot of this overall motor/gearbox related project, I recently received some learned analysis of model railway gearboxes by an august figure in mechanical engineering.

Best efficiency in ANY worm drive gearbox, in any brand, in any ratio, coupled to any motor (motor to wheels power transfer) was 18%. That means less than 20% of the real motor power actually gets to the wheels.

Conversely, using various bevel gears to transfer the power from motor to axle resulted in an always better than 40% efficiency - a really huge practical difference, which explains quite handily why the portescap gets good results from a less than average power coreless motor.

Why is it so extreme?

I accept the numbers, but am still amazed by the huge losses in worm drives. They always appear smooth and well meshed... so...

"why is it so?"

Regards

Richard
 

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Just another modeller
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9,983 Posts
*** Thanks for answers so far - I sort of knew much of it but wanted clarification - other perspectives help.

I suspected that overall friction may be the simple answer, but it still has the same effect on my head that the theory of flight does - I see and comprehend it well enough and can do the math to calculate it.... but the concept of how an aerofoil provides lift still raises an eyebrow when I look at an antonov or an A380 :) :).

Anyway...

Large worms and successfu flywheel effect are counter intuitive given the discussion and the data I have from the report... the larger worm means much more friction via surface contact per revolution so it reduces efficiency .....so the large diameter flywheel effect is a net zero or even less... clearly a "Bachmann marketing thought".. not an engineering one.

One of the conclusions of the report I mentioned was that the worm diameter should be as small as possible and the pitch of the worm thread as large (coarse) as possible to reduce friction and improve efficiency... which means no greater than say 10: 1 ~ 15:1 is really practical in stage 1 (worm and first gear) for reasonable efficiency.

The ONLY loco I have ever seen that came close was an old cold war era PIKO - the worm was fabricated via wire soldered straight to the motor shaft! It explains now why it actually ran very, very well... at the time I just considered it a primitive but clever answer to keeping cost low.

I wonder how practical turning the worm as part of the motor shaft design would be?

Interestingly most US diesels have a 12:1 ratio and are good at slow running and have excellent pulling power, but slow running high torque motors. 8 or ten driven axles is a good way of keeping power transfer acceptable of course... but its still food for thought

......... Hmmm

So a high speed box with a tiny coarse worm being the better compromise - perhaps we need to team them with either with a planetary box before the worm or added spur gear reduction between worm and axle.

Question: I wonder how the cost balance "bevel gear vs worm" looks when this is factored in? I suspect (OK, sort of know :) )that in the end the margin between them is going to be very thin indeed.

I'm sure a few eyes are glazed over about now

But.. It matters to me.... as a loco builder who also nows loco buiders who would also love to be able to use tiny motors with prodigious performance via efficient drives... and... while its not a money spinner.... I'd personally love to produce the answer as a DCCconcepts product as I have the suppliers that can do it... but how many other modellers really care.... Enough to make it worth doing? I wonder....

Richard
 

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Just another modeller
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9,983 Posts
Hi Wayne

How could I have forgotten my Dublo Duchess of Montrose which I was given in 1955 at age 3 as my first ever train set - it did indeed have a turned worm! Doop!

Re the portescap, I also gave up on them, removing the last two as the mosquito impersonation drove me to distraction. Related to this - an interesting true comment - We presented an RG4 to our supplier as an example of a generally suitable design type - the first words out of his mouth after looking it over were "they used the wrong mateial in the gears - I bet its noisy" :) :).

I too love Chris Gibbons / hi-level Gearboxes... I also quite like some of the NWSL stuff, but its getting a bit exxy with the exchange rate.

This whole subject gained momentum a year or so ago... because irrespective of gearbox, Mashima deliery has become to say the least patchy to pathetic and... more importantly, they seem to have changed their spec subtly and now have a tendency to overheat rather too easily when pushed hard compared to earlier models...

So... I've kept the project on the boil as Mashima is a tiny family business with no son to carry it on... and they are close to retirement.

The problem isn't the design any more - thats straightforward enough... its the quantity requirement at this point in time, and the associated commerical risk!

regards

Richard
 
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