Turntable DCC conversion

[crosbystills]

I have fitted a decoder to control the tuntable motor from a loco address. This works perfectly with the ability to vary the speed of rotation in either direction. (Using Elite)

Why am I being advised to modify the turntable further? i.e. removing contacts and wiring up outlet tracks?

[5Dublo2]

I believe it is to avoid short-circuit conditions as the turntable moves (related to the track, not the motor drive of the turntable)

 

With DC operation the track leading to the turntable and the deck of the turntable are not always live (as you don't move the the loco on the turntable when moving the turntable). Hence no issues when turning

 

With DCC operation the tracks are always live so accidental contact as the turntable moves can cause issues

[Chrissaf]

See these links. As 5Dublo2 says. Because in DCC layouts the track is always live. The rotating bridge rails touch layout track rails of opposing phase (polarity) and create a 'short circuit'. The 'removing contacts' modification you have referenced is a 'sledgehammer to crack a nut' solution. The solution documented in the posts below are more gentle and just as effective.

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R070 Turn Table DCC Modification

http://www.hornby.com/uk-en/forum/r070-hornby-turn-table-to-dcc-including-images/?p=1

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R070 DCC Conversion – my version with a detailed drawing

https://www.hornby.com/uk-en/forum/post/view/topic_id/27722/?p=2

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Note ... making links clickable on this forum is broken at present [see post in forum feedback section]. So you will need to 'copy and paste' the link text above into your browser.

[mjb1961]

If are following hornbys instructions then you have to remove them and anything else ,there is another version by one of the members on this forum which means you don't have to remove the contacts etc ,,,someone will no doubt put up a link for you .

[crosbystills]

I only need the track leading off the TT to be live when lined with the TT? So I don't see why I need to modify the TT track? The motor is controlled separately by loco address.

[St1ngr4y]

What about the track leading onto your TT from the rest of your layout? If the bridge is lined up to this track, you can drive a loco onto the bridge, no problem. However, as soon as the TT starts to rotate, it is possible for the left rail of the bridge to make contact with the right rail of the inlet track (or vice versa depending on direction of rotation) causing the DCC to short out. This is why the solution is to remove the brass contacts from the end of the bridge rails.

 

Ray

[5Dublo2]

For DCC the inbound track to the turntable will always be live, the track across the middle of the turntable will also always be live as unmodified it is connected to the inbound track

 

When the turntable is aligned with the inbound track, no issue, but as it starts to turn the left hand rail on the inbound track can touch the right hand rail on the powered track on the turntable itself (or vice-versa) this causes a short if not isolated

 

Personally I would go with St1ngr4y / Chrissafs solutions - as the turntable can easily be put back to default (DC) operation, if you only detach the underneath wires and then isolate each stub track with IRJs

[Chrissaf]

Also, if you don't go with the forum solution and wire up the outlet tracks, the outlet tracks will become dead tracks when the bridge is not aligned to them. Not particularly useful for DCC locos that have lights and particularly not useful if they have sound as well.

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So yes you can get away with just dealing with the inlet track [as others have said an unmodified inlet track will generate a short circuit as soon as you try and rotate the bridge ... so that track has to be modified for DCC as you will find out if you choose to ignore the forum advice that is being given to you], but why reduce the functionality of a DCC modified TT by 90% just because you are reluctant to go that extra mile and do a proper conversion of all the outlet tracks as well.

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And as I said in my original reply, the Hornby documented method of removing the contacts at the end of the bridge rails is a 'sledgehammer to crack a nut'. Why?. Because the contacts have a dual function. Not only do they transfer power to the outlet tracks, they are also used to provide an element of positive alignment. Removing the contacts can potentially affect the robustness and reliability of rail alignment. Using the forum method with Insulated Rail Joiners also means that the TT can be easily regressed back to DC operation as 5Dublo2 outlined in his reply.

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The Hornby R070 is designed for DC Analogue layouts and needs modification for DCC. The DCC modification is all about eliminating the track 'short circuit' issues that is inherent in the DC Analogue design of the R070 turntable and has got absolutely nothing to do with using a DCC decoder to rotate the bridge motor. In fact you can just as easily use a DCC modified R070 turntable on a DCC layout and still rotate the bridge motor using DC Analogue without a installing a decoder. The decoder is totally optional for DCC turntable operation.

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