DCC controlled Hornby turntable using Rail master

[Howhoward7]

Hornby recommend using a loco decoder to control their turntable. Have any of you guys made this conversion and if so is it necessary to program the decoder and if so how or is this done within the Rail-master track edit screen? If it is programmed from

 

rail-master what are the settings?

 

Thanks

 

Howard

[David55]

 

If you look on page 51 of the Railmaster instruction manual, it gives you details about this and mentions instructions for conversion to DCC can be found on this site.

 

 

[David55]

[reply]David55 said:

 

 

If you look on page 51 of the Railmaster instruction manual, it gives you details about this and mentions instructions for conversion to DCC can be found on this site.

 

Should have said go to downlaods and accessary

 

and set manuals, the turntable is at the top

[Fishmanoz]

To confirm, when you look at those manuals, you do indeed use a loco decoder to control the TT if you want to do it under RM. it is after all just another motor.

 

As far as converting it to DCC, yes Hornby has a method, but I suggest you take a

 

look at a recent TT thread in the DCC Forum for better ways, in my opinion and the opinion of others, to do it.

[Fishmanoz]

Oops, this is the DCC Forum, was thinking we were in the RM Forum. Take a look at the thread 5 down in the list with Wiring a TT in its title.

[Howhoward7]

Hi again

 

Thanks for the response. I have read all the recommended stuff on the TT & Fish do know if the TT Bridge on the Hornby TT is powered via a split ring? Also does "better way" that you refer to mean leaving in place the bridge contacts and

 

using insulated rail joiners between the TT and all the connecting rails? Also when turning a loco around 180deg does this change the polarity of the bridge rails and if so would the rotated loco cause a short as it left the TT bridge? I thought simplicity

 

was the essence of good design! May be its me thats simple!

[Fishmanoz]

Yes, the Hornby TT is a slip ring design so, yes, when it goes through 180, the polarity will be reversed.

 

The important part to isolate is the inlet track between the bridge pickups under it and the bridge, otherwise you get shorts when the opposite

 

tracks connect as the bridge rotates, if you understand what I mean.

 

If the outlets go to sidings that aren't otherwise connected to the layout, no isolation is necessary and the bridge polarity doesn't matter as it is the only connection so won't

 

cause a short. However, if an outlet connects to the layout, then the polarity must be the same between the bridge and that connection. And it must be isolated by IRJs or such to avoid shorts when the bridge rotates, just like the inlet track.

 

Hope

 

that all makes sense. It does to me as I can visualise it in my head, but that doesn't mean you can see my visualisation.

[Howhoward7]

Thanks for that Fish. I do understand what you mean but what I cant get my head round is; having turned a loco through 180deg and therefor, changed the polarity of the TT bridge rails is, why is there not a short circuit as the loco is driven from the

 

bridge back on to the main feeder line? What have I missed this time?

[Fishmanoz]

Post a new reply...made me think but answer is simple. Put yourself in line with the inlet track and the connections are left inlet track to left bridge track and right inlet track to right bridge track. Turn the bridge 180 and you now have left inlet

 

to right bridge and right inlet to left bridge. But the bridge polarity has reversed, so effectively it's rails have swapped and so the correct connections are still being made. The problem would be there if you didn't use slip rings and you would have to

 

use a reverse loop module instead.

 

Is it doesn't matter which end of the bridge is connected to an inlet or outlet, the polarity at any one of them will always be the same. Half will be the same as the inlet, and the other half will be reversed - all

 

the time.

[Blackbird]

The term 'polarity' can be confused when use DCC, and in this case the tuntable and it's rotation. With the basic DC system, polariy determines the direction of rotation of the loco's DC motor. The turntable will reverse the 'polariy' for half of the outlets

 

with a basic DC supply. But with DCC the 'polariy' isn't +ve or -ve, it is AC, alternating current, it is the cross connection (short circuit) that has to be avoided. As long as isolation is provided when the turntable is rotated, the 'polarity' isn't of consequence,

 

any of the DCC connections will be secure, no RLMs required.

[Fishmanoz]

.blackbird, I beg to differ about polarity being a DC only concept. I think it works just as well in AC, or in this instance DCC. I would be happy to be perfectly correct and talk about in phase or 180 out of phase but that is getting a little technical.

 

And the fact is, even with isolation, if an outlet connects to the layout 180 degrees out of phase, you will still get a short circuit.

 

In summary, I stick by my last post.

 

Also, if what you are saying is correct, are you trying to say an RLM

 

is never needed in DCC, even to run a reversing loop?

[Howhoward7]

Fish, I agree with you but what ever one calls polarity it is necessary ,as we all know to ensure that, "A" is always connected "A" and B to B to use Hornby's notation to avoid a short. You made the point Fish, that the approach track has to be isolated

 

from the TT bridge to avoid a short after a 180deg turn due to the TT bridge rails then being the opposite polarity to the approach track. Now the task of a RLM is as I understand it, to ensure that section of isolated track fed by the RLM will be switch to

 

the same polarity of the main line at the instant that the train comes into contact with the opposite polarity of the main line.

 

Going back to the TT where the 180 rotation has the opposite polarity of opposing tracks ie the TT bridge and the approach

 

track, will there not be a short circuit as the train traverses the isolated join. If not What have I missed this time?

[Fishmanoz]

Howard, as I said 2 of my posts ago, when you turn the bridge 180, the polarity reversal means physically, bridge tracks A and B are swapped. So, going through 180 swaps them once but the slip ring arrangement (think of it as a virtual swap of A and B)

 

swaps them back (2 reversals mean no reversal) so polarity is still correct at the inlet track.

[Howhoward7]

Thanks Fish. Sorry to frustrate you and I can see that to be the case. I looked at the link you mentioned again just now and compared the split ring ordination shown on the TT wiring diagram and compared it with the instructions for a peco TT that I am

 

putting in on another layout. The difference is that the diagram on the site from the link shows the split ring division parallel to the approach track which of corse provides the operation you describe. The peco instructions specify that the split ring division

 

at right angles to the approach track and I think that will give me a problem if I leave il that way. I presume that the Hornby TT I hope to get next week for my own layout will have its ring division is parallel to the inlet track.

 

I hope I have not

 

missed anything this time and thanks for your posts

[Fishmanoz]

Howard, for polarity at any point, the angle of the slip rings is irrelevant. The only thing that the angle determines is which of the outlets are reversed. Think about it, it should become clear.

 

And no, not frustrated, happy to help.

[Howhoward7]

Thanks for your help Fish

[Howhoward7]

Thanks for your help Fish

[Howhoward7]

I successfully converted my Hornby turntable to run using DCC with Railmaster today and temporarily set it ip for test and it worked immediately. I operated it first on DC by simply connecting the TT motor directly to an old analog controller. It whizzed

 

round like a fairground ride at high speed and ran poorly at slow speed. At slow stalled when the bridge rail contacts touched the approach rails. For this reason I used Hornby's conversion method of removing the bridge rail contacts so when running DCC it

 

was able to align smoothly with the approach track. Using Railmaster it was very easy to operate and Fish, it will come as no surprise to you that having turned through 180deg I drove it off. No prob. Eventually it stopped maligned and I positioned it using

 

the Elite as per the instructions.

 

Thanks for the help

[Fishmanoz]

Good result. The only thing now is that you will need to power all of your sidings with the contacts missing, and make sure you get the polarity correct depending on whether they are reversed or not. Not a bad thing as you'll then be able to manoeuvre

 

on them without the bridge turned to them, or have sounds continue uninterrupted.

 

And should you get the polarity wrong, you'll find out instantly when a loco starts to drive off and everything comes to a halt.

[LMSTim]

HowHoward, I have found that if you fine-tune the turntable rotation speed and time (within the RailMaster.ini file) you can get it very precise. I used a stopwatch to time how long it takes to run from one lane to the next to the middle of the idle. The

 

motors may be slightly different from one turntable to another.

 

If you then couple this with trying to ensure that if you do do a 180 degree turn, say clockwise, that you should try to the do anti-clockwise rotations so that you get back to roughly

 

your starting position eventually. This minimises mis-alignment after a long period of operating. I successfully ran the turntable in programs under RailMaster control at a recent exhibition for a whole day without ever having to align it manually.

 

The

 

nice thing about RailMaster is that it runs the turntable at a much more realistic speed and without the attendant noise (like a plane taking off) when running it at full pelt in DC.

 

[walkingthedog]

In days far off before DCC I had a Hornby TT and put some resistors in the feed to slow it down.

[Fishmanoz]

How yesterday WTD, now we write a program in RM that tells the motor to run like it has series resistors installed.

 

Seriously though, more then one way to skin a cat.

[walkingthedog]

That's right fishy. I trained as a telephone engineer in the mid 60's. In those days it was all electro mechanical and I was in my element repairing equipment.

Thankfully I left and joined air traffic control but a mate of mine remained and retired

 

a few years ago. He ended up spending his time replacing circuit boards if a fault developed. It would have driven me mad.

They call it progress, which of course it is, but I prefer the engineering path.

 

[Fishmanoz]

Understand exactly what you mean WTD but the problem is simple - it costs less to drop in a replacement board from the production line than it does to have you spending expensive man hours doing the fault finding and replacing the faulty component. Not

 

to mention the saving in the test equipment and jigs you need to work on the board in the first place.

 

I seem to remember my computer programmer wife from a previous lifetime being critical of programmers who didn't spend the time to make their programs

 

perfect and bug free before submitting their job for running. But that was in the days when the mainframe cost a fortune and programmers were cheap. Now the hardware comes in corn flakes packets and the programmer is expensive, so the job changes to make the

 

most efficient use of programmer time.

[Fishmanoz]

In the mid sixties, I was doing electrical engineering at university. But the only thing I like to see moving is the electrons. Stuff like cross bar exchange equipment or earlier would have driven me batty.