01-02-2009, 05:17 AM
There was a short article on this in the September 2003 issue of RMC magazine. The basic formula for scale miles per hour (S.M.P.H.) is:
S.M.P.H.= .6818 x Scale Factor x Distance (in decimal feet) / Time
The number .6818 is a constant
The Scale Factor is dependent on the scale, and is as follows O = 48, S + 64, HO = 87.1, N = 160, Z = 220
The decimal distance means 6" = .5', 9" = .75', etc.
The time is measured in seconds
So, for example, if an N scale loco travels two feet in 4.32 seconds, the formula gives us .6818 x 160 x 2 divided by 4.32 or 218.176 / 4.32 = 50.5 S.M.P.H.
Because this method is rather cumbersome and requires a stopwatch, the author, Ron LaFever, constructed a table in 5 s.m.p.h. increments. From the example above, 218.176 / s.m.p.h. = seconds, so 218.176 / 5 s.m.p.h. = 43.64 seconds. From this it was easy to calculate that a loco at 10 s.m.p.h. would take half the time to cover the 2' distance, etc., etc. He then marked a tie on his layout with a dot of paint, and another 2' away with a second dot. With the table posted on the layout facia, and a wristwatch with a second hand, an operator can get a good sense of what the actual train speed would be.
He also did a table for his HO scale switching layout, using a 1' long measuring area, due to the limited space and slow speeds. His table shows that it takes 59.39 seconds for an HO scale loco to cover the 1' distance at a speed of 1 s.m.p.h., and, at 5 s.m.p.h., the elapsed time was 11.88 seconds.
He notes two general rules of thumb: the slower the speed being measured, the shorter the distance should be, and the faster the speed, the longer the distance.
I already have speed limit signs on my layout, and plan to incorporated several speed "traps", using signs to denote the "START" and "END" points. Most areas of my layout are 30 s.m.p.h. or less, due to curves and/or grades. You can make the measuring area on straight track or curved track (for curved track, assemble enough cars together to equal the desired length, then run them to the curve you wish to use). Most will find that your trains are running faster than you thought, and I think a couple of these speed zones will get you used to running at more prototypical speeds. For most of us, that will increase the running time between destinations, which will contribute to making your layout feel larger. You'll probably become accustomed to more prototypical speeds, too, and won't need to do frequent speed checks. However, they'll still be useful when you have visiting operators - you have to ensure they obey the posted speed limits.
[album]287[/album]
Of course, Mikey's link is even easier.
Wayne
S.M.P.H.= .6818 x Scale Factor x Distance (in decimal feet) / Time
The number .6818 is a constant
The Scale Factor is dependent on the scale, and is as follows O = 48, S + 64, HO = 87.1, N = 160, Z = 220
The decimal distance means 6" = .5', 9" = .75', etc.
The time is measured in seconds
So, for example, if an N scale loco travels two feet in 4.32 seconds, the formula gives us .6818 x 160 x 2 divided by 4.32 or 218.176 / 4.32 = 50.5 S.M.P.H.
Because this method is rather cumbersome and requires a stopwatch, the author, Ron LaFever, constructed a table in 5 s.m.p.h. increments. From the example above, 218.176 / s.m.p.h. = seconds, so 218.176 / 5 s.m.p.h. = 43.64 seconds. From this it was easy to calculate that a loco at 10 s.m.p.h. would take half the time to cover the 2' distance, etc., etc. He then marked a tie on his layout with a dot of paint, and another 2' away with a second dot. With the table posted on the layout facia, and a wristwatch with a second hand, an operator can get a good sense of what the actual train speed would be.
He also did a table for his HO scale switching layout, using a 1' long measuring area, due to the limited space and slow speeds. His table shows that it takes 59.39 seconds for an HO scale loco to cover the 1' distance at a speed of 1 s.m.p.h., and, at 5 s.m.p.h., the elapsed time was 11.88 seconds.
He notes two general rules of thumb: the slower the speed being measured, the shorter the distance should be, and the faster the speed, the longer the distance.
I already have speed limit signs on my layout, and plan to incorporated several speed "traps", using signs to denote the "START" and "END" points. Most areas of my layout are 30 s.m.p.h. or less, due to curves and/or grades. You can make the measuring area on straight track or curved track (for curved track, assemble enough cars together to equal the desired length, then run them to the curve you wish to use). Most will find that your trains are running faster than you thought, and I think a couple of these speed zones will get you used to running at more prototypical speeds. For most of us, that will increase the running time between destinations, which will contribute to making your layout feel larger. You'll probably become accustomed to more prototypical speeds, too, and won't need to do frequent speed checks. However, they'll still be useful when you have visiting operators - you have to ensure they obey the posted speed limits.
[album]287[/album]
Of course, Mikey's link is even easier.
Wayne