Model Railway Forum

Walkingthedog wrote: ↑Mon Jul 05, 2021 5:20 pm

Brian wrote: ↑Mon Jul 05, 2021 5:00 pm

Walkingthedog wrote: ↑Mon Jul 05, 2021 3:53 pm Surely that only applies if all wheels are metal and there is a good chance of one of these wheels shorting out an IRJ.

Yes I does. There are very few carriages or wagons sold today that have all plastic wheels. Detailing on items today demands metal wheel sets.

A wheel trad will easily bridge a gap of IRJ spacing when the rails are close together even the end post of an IRJ offer a close fitting rail to rail joint.

Thanks Brian. When I had one I guess I must have been lucky. The polarity was changed by switches on the points.

Hi
If the reverse loops rails polarity is changed by a DPDT switch fitted onto and operated by a point motor/point direction, then the loops rails will always be set correctly before the loco reaches the IRJs of the loop, assuming the point is set prior to the arrival of the loco. So there will not be any shorting of IRJs by metal wheels occurring.

Using points fitted with a DPDT switches leading into and out of a Reverse Loop is an excellent way of controlling the loops rail polarity and it will always be set for the correct direction, assuming the point(s) are set correctly. Basically its automatic switching of the reverse loop by the point(s) position.

When I did it I didn’t know there was any other way of doing it.

Brian wrote: ↑Tue Jul 06, 2021 9:01 am

Walkingthedog wrote: ↑Mon Jul 05, 2021 5:20 pm

Brian wrote: ↑Mon Jul 05, 2021 5:00 pm

Walkingthedog wrote: ↑Mon Jul 05, 2021 3:53 pm Surely that only applies if all wheels are metal and there is a good chance of one of these wheels shorting out an IRJ.

Yes I does. There are very few carriages or wagons sold today that have all plastic wheels. Detailing on items today demands metal wheel sets.

A wheel trad will easily bridge a gap of IRJ spacing when the rails are close together even the end post of an IRJ offer a close fitting rail to rail joint.

Thanks Brian. When I had one I guess I must have been lucky. The polarity was changed by switches on the points.

Hi
If the reverse loops rails polarity is changed by a DPDT switch fitted onto and operated by a point motor/point direction, then the loops rails will always be set correctly before the loco reaches the IRJs of the loop, assuming the point is set prior to the arrival of the loco. So there will not be any shorting of IRJs by metal wheels occurring.

Using points fitted with a DPDT switches leading into and out of a Reverse Loop is an excellent way of controlling the loops rail polarity and it will always be set for the correct direction, assuming the point(s) are set correctly. Basically its automatic switching of the reverse loop by the point(s) position.

I had thought about that in the past, but I never got to try it out as I did not have a layout at the time to try the idea out on. I am glad that you have confirmed to me that the idea works... But my thoughts are that (Trying to get my brain into gear) isn't it possible to have a senario where both points could be set to run round but create a short by doing so? Or prehaps not because of the rest of the curve leading off the loop... Sorry. I am trying to think. I would need to draw it to work it out in my mind.

Ammended. No, you are right because the leading point would be isolated (I am using insulating frog points in my mind to get myself to understand it in simple terms) and so therefore will avoid a direct short... (If I tried to think in live frog terms I would have lost my train of thought. ).

You must have IRJs fitted in both rails at all entrances and exits to a Reverse Loop. Therefore the minimum is four IRJs, but the maximum number is dependent on the number of alternative entrances or exits to the Reverse Loop.
In the amended image I provided on page 1, there is one point controlling the entrance and exit to the loop - top of drawing near to the Point A that I marked. This, if fitted with a DPDT switch, would work the reverse area automatically.

Yes. But my initial thought was if both points are set at the same time but I get where my thinking has gone wrong now.

There is an example of this in the latest Hornby track plan guide. I can scan and upload a copy if there’s still interest in this thread.

Hi Buffer, it would be interesting to see the plan. This loop is working but it might not be the last one I make, its always good to have alternatives.

Dave.

If points on the plan I've marked as A and lower B are set to the reverse loop then you will get a full short circuit if no IRJs and no switching of some sort isnt used!
Very simply print the plan and take a red pen or pencil and mark the upper (outer) rail in red. Follow this all around the track and into the loop rails. Now change pen colour and use a black pen or pencil and track the inner rail. Between the two points - red will abut onto black Result Short circuit! See my (poor) drawing attached.
Hence the need for IRJs and some form of polarity switching for the reverse loops rails.

Yes. With IRJ's on both rails it would not be an issue.

It would as soon as a loco bridges the IRJs.. That is why IRJs are installed in both rails at all entrance and exit places - Minimum of 4 IRJs, unlimited maximum depending on the number of tracks leading into or out of the loop area.