programming movements with sound fitted locos

[idlemarvel]

(I am starting this in a new thread.)

The problem I have is trying to control loco movements with sound fitted locos.  The reason I think is this (from previous thread):

"The time between issuing the command and the loco starting to move seems to be variable, depending on how long the loco has been idling.  From startup it is probably consistent (haven't tested this to confirm but I expect so) but from a point after startup it is variable.  With sound turned off I can get locos to stop within a few inches consistently, with sound the variation can be a foot, which componds as you have multiple programmed operations.  I will do some more scientific testing but I would be pleased to hear from anyone else who has tried programming with sound locos."

I have now done some testing.  I have an oval of track, 14 feet long, radius 3 curves, Hornby class 153 DMU (R2757) with LokSound 4 decoder.  I have a simple program which says forward to [10] then stop after 32.7 seconds.  This makes the 153 complete a circuit with sound turned off.  It stops with an inch of the starting point each time, which is pretty good, less than 1% error.

If I turn sound on, I have to increase the run time to 37.0 seconds to allow for the revving up from idle, which is fine, but the end position varies considerably.  Results were, measured in inches +/- the target, ten measurements:
0, -3, +1, -5, 0, -3, -5, +7, +3, +6
A range of a foot.  This makes it difficult to program train movements, without using the "buffer stop" trick, which you can't in through stations for example.

I would like to hear from anyone else who has similar experiences, or has other sound decoders which perhaps don't have the same behaviour.

[St1ngr4y]

Hi Dave,

I have dozens of programs which start and stop sound locos at given points on the layout. However, I rarely use the Forward to [n] command on its own. I find I can get much greater consitency using the accelerate and decelerate commands. Having said that, I have just posted an item complaining about the accelerate command. However...

All of my sound locos have what I would describe as a "pre-movement" sound, such as brake release or revving up. On some locos this may last 4 or 5 seconds before the loco moves, so what I do is something like this:

20 myloco Forward to [2]

27 myloco Accelerate Forward [2] to [50]

Then to stop at a certain point...

80 myloco Decelerate Forward [50] to [2]

132 myloco Stop

These commands, without any extra parameter, vary the speed at about 1 speed step per second, so you can calculate roughly how long each one will take, in the example above 50 - 2 = approx 48 seconds.

Ray

[idlemarvel]

Thanks Ray.  I understand the pre-movement sound is there for a good reason, but it's the unpredictability of the progress beyond that which is the problem.  However I'll try the forward/accellerate/decellerate/stop combo to see if that can provide some consistency.  I'll report back.

[idlemarvel]

So Ray I think you have cracked it.  The "secret" as you probably already know Ray is to get the initial engine revving out of the way whilst minimising the distance travelled.  I tried:
0 forward to 2
7 accel forward 2 to 20
29 decel forward 20 to 2
49 stop

But that didn't help as the forward to 2 wasn't enough to trigger the engine revving (it must be a decoder setting somewhere) so stopping distance was still +/- 6 inches over ten tests.  I then tried:
0 forward to 5  (this did trigger the engine revving)
6 accel forward 5 to 20
...
That was better, got it down to +/- 3 inches.

0 forward to 4
5 accel forward 4 to 20
...
Even better, now +/- 1 inch

Finally
0 forward to 3
5 accel forward 3 to 20
...
This got it down to +/- 0.5 inches which is pretty much perfect.

BTW with this technique you have to be careful to allow enough time for the e.g. Decelerate Forward [20] to [3] to finish before you issue the Stop command, or there is a chance the Stop will not be executed.  In other words in this case allow 17 seconds between the Decelerate and the Stop command ([20]-[3] at default one step per second).  You can change the step time with an extra parameter e.g. Accelerate Forward [3] to [20],0.5 which sets the step time to half a second.

Thanks Ray

[St1ngr4y]

Hi Dave,

Yes, every loco is different in the amount of time you need to allow for the "pre-movement" sound, and experimentation with each one is required. The introduction of the extra parameter gives you even more control of the rate of acceleration or deceleration, and they become very powerful commands.

When loco detection comes along, I can imagine the detection of a loco at a specific point triggering a program which starts with a decelerate command, followed by a stop, to make station stops highly accurate.

One problem which I have with the "pre-movement" sound is when I want to do small intricate movements. For example, I have changed all of the couplings between locos and trains to Kadee, which utilise magnetic uncoupling plates. So firstly, you need tostop the train quite precisely with the couplings above the front of the plate. Then the loco needs to reverse as slowly as possible (2 speed steps) just enough to release the tension. Then to pull forward again slowly. So the Reverse to [2] command is followed by Stop maybe 5 or 6 seconds later, but the loco will have only moved about a quarter of an inch! But using a program is still much more accurate than trying to do this manouevre with the RM slider or the Elite knob.

Ray