M Menu
b 0 Items s

Fishmanoz

Signature: and thanks for all the fish

Bio: 65 years old and new to railway modelling

All Posts

Fishmanoz

9753 posts

Chris, could you please reconsider your text equating analog, DC and a PWM signal.  Although I do get your reason for saying so.

 

A quick Fourier analysis will put the lie to a PWM signal being DC.  It is a square wave of relatively high frequency with modulated or varying mark space ratio.  In fact, in this regard it is analogous to the stretched zero bit that Rob describes for address 0 DC loco operation.  In both cases the motor sees this variable mark space ratio square wave but, being highly reactive, filters out all of the high or non-zero frequency components (again Mr Fourier can help here) by being (almost) open circuit to them, leaving only the average DC value to drive the motor.

 

However, just as the DCC frequencies are high but not infinite, so the motor is not actually open circuit to them but high impedance, so is affected by them to some extent.  Hence the buzzing you hear with a DC motor on a DCC track as the motor moves backward and forward slightly to follow the square wave frequency.

 

PS.  Fourier analysis, or frequency domain analysis, doesn’t look at how the signal varies over time, rather it looks at a particular time only and sees what frequencies are contained in the signal.  In a square wave, the frequencies present are the fundamental frequency of the wave plus various harmonics of the fundamental frequency with decreasing amplitude as the harmonic number increases.

and thanks for all the fish

Fishmanoz

9753 posts

It should be there in the list as R3663T, not TTS.  If not, report it to HRMS as Rob says.

and thanks for all the fish

Fishmanoz

9753 posts

Thanks Chris. I still think it may have been handled differently many moons ago, but irrelevant now.

and thanks for all the fish

Fishmanoz

9753 posts

Now that this thread has been made more “moderate”, may I repeat my view that an auto-lock function after a period of inactivity is all I see as practical. I don’t support deleting threads and anything requiring manual intervention to determine ongoing relevance v waffle is going to consume considerable time and energy for those involved.  While storage space permits, just letting such threads age into obscurity seems far simpler. They are unlikely to be resurrected by subsequent forum searches either.

 

PS.  Question for moderators - on finding my post moderated out of this thread, I checked to see if it was still in my posting history, it isn’t (I was seeing if I could copy and paste what I’d said about thread locking).  It used to be the case though that, even if a whole thread had been removed, the individual posts in it were still in the posters’ history.  Is this still the case?

and thanks for all the fish

Fishmanoz

9753 posts

Flipped it mirror image Rob, I take it that was before ballasting?

and thanks for all the fish

Fishmanoz

9753 posts

Boring Rob, no spark that way!

and thanks for all the fish

Fishmanoz

9753 posts

What about a simple swap of decoders between drive cars, or just make the other one the reversed one without swapping?

and thanks for all the fish

Fishmanoz

9753 posts

To explain a little further without getting the full story from Chris’s excellent tutorial, RLMs are connected to isolated sections of track and switch the polarity (phase) of the DCC signal in the section to match an end where a train is entering or leaving.  If something then enters or leaves the other end at the same time, the RLM will be trying to switch for that too, meaning it will be switching back and forth rapidly and most likely fail to do its job, leading to an overload fault. 

 

If you now connect the RLM to 2 isolated sections in 2 reverse loops, you multiply the chances of the above happening as soon as you have trains operating in both reverse loops.

and thanks for all the fish

Fishmanoz

9753 posts

Derek, if you isolate the track, there will be no power to run the train.  So, apart from having it in something like a siding you can isolate by throwing the point away from the siding, no you can’t. Usually with DCC, you try to make the entire layout live all of the time via a DCC bus or initially using DCC point clips.  But you can leave the clips off siding points if you only want to run trains in and out of the siding and not move around on the siding by itself. 

and thanks for all the fish

Fishmanoz

9753 posts

Hi javes, welcome to the forums. It would seem pretty clear that you have a short somewhere/somehow in your Class 47, the question is how to find it.

 

For a start, my physics professor is having conniptions about the short occurring with just one wheel on the track.  With just one wheel in contact, there is no return path to draw current, so no way an overload can occur.  Can you check that out again please.

 

Then you need to check out the loco itself off the track.  Can you see anything stray that is causing a short?  Do you have a multimeter to check further on the ohms range from the wheels to pickups to the motor itself?  If you put a 9V battery in direct contact with the wheels, does it run or do you just get sparks?

 

Let us know how it goes please.  And having just seen Rob’s reply, I agree but you can still look for anything stray and try the 9V battery first before returning.

and thanks for all the fish

Forum Rules

  • The Hornby Forum is intended for discussion of all things model railways. Primarily a place for newcomers to ask questions and seek assistance from like-minded individuals, the Hornby Forum offers a user community for all those interested in railways.
  • Discussion of non-Hornby brands is allowed, however, active promotion or advertising of these brands is not permitted.
  • Please keep in mind that the Hornby Forum is a publicly viewable space and you should never post personal information (including email addresses). 
  • While every effort is made to contact you before any censorship, we reserve the right to amend or remove any content without explanation.
  • All customer service enquiries should be directed to Hornby Customer Services.

Useful Links

Forum Guidelines

Membership Restricted Product