Loco Detection - How Accurate will it be?

[RDS]

There is discussion at present on another thread, regarding how accurate a train can be positioned or stopped during programming.

I am not sure how this will improve though when Loco Detection (LD) is available. 

When it passes a particular sensor, it will still depend on how fast it is going or how repeatable a particular Loco is, in being able to accurately predict where it will stop or in order to ensure a starting point is always the same.

[gilbo2]

That's a good point and I would imagine that as soon as the program is told by the loco detection system "I'm here", you can then trigger the stop command etc. To my mind, locos with a quicker deceleration may then prove to be more accurate especially if CV 3/4 is set to 0, but we would not want that :-)

This would be far more accurate than today where its purely based on the passing of time in an open loop control system to trigger commands such as stop.

[96RAF]

I think there would have to be a degree of calibration of locos characteristics to make exact stops in the same place for each and every loco after passing a detector.

Some of this could probably be done by the command that is actioned by the system upon such detection event such as the 'decel (x-y)' command discussed elsewhere on the forum. e.g. long heavy train vs light engine.

No doubt the detection system manual will give us a few clues when it arrives.

[RDS]

I have a Turntable on my layout and this is one obvious place (I think) for a sensor, because unless the Loco is very accurately positioned the Turntable is suitable for manual use only and cannot be used by a program.

[St1ngr4y]

@RDS

The following applies to running trains in programs. Currently, you will be timing the start of the deceleration to the stop relative to the start of the program you are running.So that the point the train has reached at the moment deceleration starts at the moment may vary a little depending on how 'normally' the loco has behaved up to that point. I would imagine that when loco detection comes along, the detection of the loco at the sensor would be the trigger for starting the deceleration, so any differences in the speed before reaching the sensor wouldn't matter. You will be restricting the most sensitive section to the deceleration part only, so I would hope that you would get higher accuracy because of this.

Ray

[96RAF]

Ray

As such a sensor position will be fixed relative to the desired stopping point my point was each loco would stop in a different place due to its characteristics hence the need to 'fiddle' with their settings a bit either in CV or by programme command.

Possibly multiple sensors could improve the stop by comparing each locos time over sensor report and altering the stop rate.

[Jailor]

I started the other thread. Now finding this discussion and reading your comments I understand now that I was a bit naive thinking trains stop accurately. At least I know now its not me getting it wrong but find myself a tad disappointed that I can't control the stop, as it means sometimes a loco will derail due to points changing at the wrong time.

[St1ngr4y]

That's if you simply issue a stop command in your program as soon as the loco is detected at the sensor. However, if you use the decelerate command in a program, you have program control over the deceleration rate without having to 'tune' the loco chip CV values.

Ray

[RDS]

Ray

Sorry, I don't understand the 'deceleration rate' argument.  If the Loco's speed varies at the point it passes the sensor will it not stop at a different position each time.

[St1ngr4y]

I think you must have misunderstood me, RDS. What I'm saying is that when a loco detection sensor is available, the program will have started the train and got it going to a 'cruising' speed. Then when it encounters the sensor, this will cause the program to start the decelerate command. So it doesn't matter what happened before it reached the sensor (it might have slowed down slightly at a piece of dirty track, for example), as long as it's going at an expected speed at the sensor, the decelerate command can kick in at that point. It reduces the timing element to the stretch between the sensor and the station, as opposed to the whole journey,.

Ray

[RDS]

Ray

Thanks.  The clue is in your phrase 'as long as it's going at an expected speed at the sensor'.  I think I was forgetting that the Loco would already be under computer control and therefore the speed at the sensor would be more or less the same each time.