How do you set/calibrate scale speeds?

[Quacker1964]

How is this done? - nothing worse than having trains flying round in circles at unrealistic speed.  How, dor example, would I set a scale speed of 80mph for a loco hauling coaches?

[zwilnik]

Assuming you've got a reasonably long and easy to measure bit of track on your layout (or know the exact length of a 'lap') you can work out the time it should take for an 80mph train to cover it in N gauge. The scale speed is basically the real speed you want divided by 148 (for British N or 160 for European/US N ).

I work in metric, so here's the maths for 80mph or 128.72kph..

speed in N gauge = 128.72 / 148 = 0.8973 kph

convert to M/s (metres per second) = 0.8973 * 1000 / (3600) = 0.2416

which means your N scale train should travel 0.2416 metres every second when travelling at 80mph scale speed.

So take the length of the track run you want to time over in metres and divide it by 0.2416. This is the time (in seconds) your train should take to complete your run. Now repeatedly run it round your timed loop until you get it near enough to the target time and mark that speed on your controller as 80mph

The only problem is, different engines (with different weights of stock behind them too) will use different amounts of power, so the calibrated setting for one train wouldn't necessarily be right for another.

This is all assuming DC control. I'm not sure if DCC does any of this for you automatically.

One slightly more complicated method to show the scale speed of the train would be to put 2 photosensors under the track with a specific distance between them. You'd then do a circuit to trigger as each one 'blips' from being passed over by the front of the train and use something like an arduino to process the blips and work out the speed to display. That way you'd be able to tell the scale speed of whatever train runs over the track. Going to bug my brother with that one now as he's our electronics go to guy

[Quacker1964]

That first scenario is not as complicated as I first feared as my track (Kato Unitrack) is itemised, so it would be quite easy to calculate.  I was thinking of scale speeds with main and goods lines.  I presume when I add DCC this is when individual values for each loco can pay dividends via CV settings.  I don't know this for sure, just making assumptions that it can be done.  Wonder if anyone can confirm?

A pet hate of mine is seeing train stes/railways setup as glorified Scalextric sets.  Maybe I'm getting old

[zwilnik]

I think it's reasonable to do some scale speed tests at least so you know roughly what sort of speed the trains would run at. Although just as 'perfect' scale doesn't always look right to the eye, sometimes running at a proper scale speed may seem a little too slow and some leeway may be needed with your line's speed limits

[cupoftea]

Hi Quacker

If you are using DC you can use a 'potential divider' to limit the top speed of trains by limiting the max voltage applied to the track. I did a brief tutorial on potential dividers in the N Gauge Tutorials section.

I don't use DCC but I would assume that the max speed can be limited on a DCC controller?

[Quacker1964]

Thanks Cuppa

I'll be using both - though obviously not at the same time.  I now have acquired the Power Cab but might have a DC only track for running in etc.

[cupoftea]

Sounds like a plan. In the distant future (and assuming a lottery win!) I plan to use both DC and DCC on my layout. Ultimately I would like DC on the mainline so I can use a shuttle unit and DCC for the sidings. Don't know if I will ever get to that stage though but I live in hope..............

[Pete Mc]

This is only my experience as i was bored one night and thought I'd measure the length of my trackwork.
This amounted to 1.5 scale miles,so I calculated it would take 90 seconds to complete,which means its going at 60 mph.
As the current fastest loco on my layout is a Deltic,this should complete a full lap of my layout at a scale top speed of 90mph in 60 seconds.
My other locos are classes 37,47,DP1,58 and 2 108 dmu's.

[MJKERR]

At the moment I have a chart with speeds for specific lengths of track
Eventually I will set the CV in each decoder so that all trains travel at or near their maximum speed on maximum throttle
The speed between 0 and 28 will then become a percentage of that (basically a factor of 3 will give the actual speed)

[Donkey]

Using a link that Pendy kindly provided on another thread http://home.cogeco.ca/~trains/rroperat.htm

My Rebuilt Royal Scot hauls 5 Mk 1's at 91mph
My class 45 hauls 5 Mk 1's at 80mph
My B1 hauls 5 Mk 1's at  110mph
My class 37 hauls 5 Mk 1's at 85mph
My Jinty hauls 5 Mk 1's at 127mph!
All of these based on scale of 1:160. I wonder if any of our members could "knock up" a similar calculator tool but for British N scale. I am afraid this is beyond me 

Might slow the Jinty down later but at the moment am loving watching it sail past my expresses lol 

[Greybeema]

Was messing with this myself yesterday.  Loop of track 14.2 ft round...  Built a spreadsheet calibrated 10 - 90 mph with the lap time corresponding to each.  Got the calc out of Ian Mortens Digital Comand & Control book.  Then set the Min, max and middle voltage for my 4 CEP to range between 0 & 70 MPH...  Then set both accelleration and decelleration variables - You know what - this DCC stuff aint so hard afterall....  Just trial & error...

[kiwi1941]

How, for example, would I set a scale speed of 80mph for a loco hauling coaches?

Here's a simple program for those who like computers and visuals. It's a zip file and it does all the calculations for you.

http://www.padsrocks.com/trainspeed/index.htm

Brian

[polo2k]

just because its accurate doesnt mean its appropriate
for example I am building a 5m long layout but this only scales to 1/2 mile. therefore a train doing a scale 60 would cover it in 30 sec. Problem is that the real line was many miles long and had mant stations, the model would look a bit mad passing a station every 10 sec.

When im all up and running, im planning to simply run what feels right and stop twisting the dial then.

There is a CV for max speed, then the chip will automatically scale the speed steps to suit.
you may also want to use a different speed curve. for example a class 08 spends 90% of its life in the yard so you can set the curve so that the first 75% of the throttle, only give you 15mph, then the remaining 25% get you to 70mph.

another useful tip it to place telegraph poles at a set distance (60 ft?) then calculate the time to pass each one at various speeds. Make up a table and post it on the wall next to the poles. this way you can gauge it simply regardless of the loco, and you soon get the feel of whats right for the layout.
i.e. some US modellers know how many 40` boxcars will pass a fixed point in a certain time then its just a case of checking that table again.

[Joe 90]

I wondered if this website would be of help.

http://www.nhsouth.com/crafts/workbench/ssc.htm

[Donkey]

Thank,s Joe and Brian for those links and yes Polo I agree with what you are saying there. I am only just learning to set CV's to give a more realistic speed output/curve.
Much appreciated folks