Printing Side-Track Ruler

[Mihai]

Hi everyone,

 

I'm doing a simple oval track for testing deceleration and stopping distances for some DCC locomotives. What I'm looking for is a way to have a printed "ruler" right next to the track. So say the locomotive goes at constant speed and trips an optical detector placed at position 0 on the "ruler", which triggers a connected PC to issue a stop DCC command, resulting in the locomotive stopping gently. The end goal is to be able to see - to the millimeter - the distance covered. Does anyone now of a track planning software (eg 3rd Plan It, SCARM, AnyRail, etc) that has such a feature, and which would also allow printing the track plan 1:1 ?

 

 

 

Regards,

Mihai

[The Johnster]

Wouldn't it be easier to measure from the optical detector to the stop point with a piece of string, which you can mark off and lay against a ruler on your workbench?  Or am I spoiling the fun/not understanding the purpose?

[ejstubbs]

Or even, just lay a ruler alongside the track?

 

Really struggling to understand why you'd need to get SCARM/AnyRail involved.

 

FWIW, AnyRail can print 1:1 but I think you'd need to draw a millimetre rule line by line, which would be tedious.

[Mihai]

In the test oval there would be 2 sections of straight track and 2 half-circles. Assume the optical detector is located just as one half-circle ends and a straight section starts. Should the locomotive travel on the straight section of track and stop in a very short distance, sure enough a ruler located right next to the track would immediately indicate the length covered. However, should it stop on the first half-circle or the second one, things get a bit difficult. How would one "bend" the ruler once the first straight section is over ?

[imt]

........................... How would one "bend" the ruler once the first straight section is over ?

 

Hence the suggestion of a piece of string! It goes round corners and can be measured against rulers too!

[Mihai]

True - but to get the exact distance, one would need to mark the spot where the locomotive's reference point (eg tip of the front buffer) reached, remove the locomotive, then get the wire "extended" up to that point. Since the measurement will have to be done right across the center of the track (where the radius is usually measured), the string would have to "follow" perfectly the middle of the track, which - without some form of guides - gets tedious, particularly that the length needs to be marked, then measured. All while looking for a measurement error of below 1 mm.

[Teabag]

Just out of interest, why do you wish to measure the stopping distance with such precision?  I imagine that there will be some variation in this depending on the ambient and motor / bearings temperatures which might exceed the precision you need.

[Mihai]

There is variation, without any doubt. Eg for a linear speed curve of one of the locomotives I've been profiling (Brawa 41030), stopping from external speed 12 will result in distances covered between 29.9 and 31.55 cm, averaging 31.12 cm over the 10 runs used to gather the data). Since the test section of track at the time was the same, and given the measurements were done in a relative small time window, the difference might also have something to do - aside from the internal mechanics - with the precision of the decoder itself (eg how fast it cycles through the speed steps internally). I'm just interested in the range of the values, since based on this I can extract the equations and get the computed stopping distances. Then I get this in my computer code that's doing train control, and the trains get to stop in front of the signals gently.

Why do I want all this precision, since I could already measure to the tenth of a millimetre ? Because that was done using a 50-cm ruler right next to a section of straight track on my layout itself, and stopping from high speeds - with various speed curves - will result in far greater stopping distances than mere 50 cm. An oval track section will solve that problem.

Why do I want to do this instead of using any of the computer software that can do train control (eg Freiwald's Railroad & Co.) ? For the pure fun.

[Memphis32]

You may be better off measuring angle around the curves, and calculating distance from that. However, the fact that the loco is on the curve or straight will have a big impact on the stopping distance...

[Pete the Elaner]

Since the measurement will have to be done right across the center of the track (where the radius is usually measured), the string would have to "follow" perfectly the middle of the track, which - without some form of guides.

You could measure the distance around the outside rail then the inside. The centre would be halfway between the 2.

Taking this one stage further, you may want to factor in the width of the rail & string, then the centre line would be closer to the inside measurement than the outside.

[peter220950]

Just out of interest, why do you wish to measure the stopping distance with such precision?  I imagine that there will be some variation in this depending on the ambient and motor / bearings temperatures which might exceed the precision you need.

There's also the voltage to consider, not sure how well DCC track supply is controlled, but the incoming supply can be fluctuating by about 16%, depending on demand etc.

 

Even if the transformed supply to your equipment was controlled to a fixed voltage, the voltage drop over wiring to various different sections of track would still produce differences to performance in different sections of track.

 

I assume you will have to keep similar loads on loco's at all times, as changes in the number of coaches etc. will also affect performance.

 

Given all these variables I would have thought physical detection of positions to trigger braking and final stop would be a better route to go down than trying to average out a huge number of variables?

 

Peter