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Frog polarity switching


philsandy
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I want to operate 4 hand built points on a small shunting layout using tube in wire or push pull rods, operated by slide switches. I have done searches on the subject but there are a couple of thing I'm not sure of.

As well as the DPDT slide switches being used to mechanically operate the points, can they be wired so they also change the frog polarity, ie. no need for micro switches?

If so, would the wires from the DPDT centre terminals both go to the frog, and can the power to the switches be taken direct from a DCC power supply?

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Yes, and yes. I use DPDT switches and one ‘side’ can change the polarity leaving the other free for other uses. A feed from the DCC bus is all you need, to the outer pins, centre to the frog. I generally use small brass rod and you can drill a hole through the switch for this and have bits of tube either side of the rod soldered in place to set the actual travel distance. Others prefer omega type devices to absorb the excess movement.  It’s all nice and easy and simple to do.
 

Izzy

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2 hours ago, Izzy said:

Yes, and yes. I use DPDT switches and one ‘side’ can change the polarity leaving the other free for other uses. A feed from the DCC bus is all you need, to the outer pins, centre to the frog. I generally use small brass rod and you can drill a hole through the switch for this and have bits of tube either side of the rod soldered in place to set the actual travel distance. Others prefer omega type devices to absorb the excess movement.  It’s all nice and easy and simple to do.
 

Izzy

 

Izzy thanks for your reply.

Re. the excess movement. On the slide switches there is 5.5 mm travel, and the point blades only move approx. 2 mm at most. If  the switch travel is restricted to 2 mm by using stops soldered in place, does this not effect the DPDT contacts to switch the polarity, because it is only travelling less than half the distance?

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Phil, I think you may vaguely remember this from when you came over.P1010603.JPG.b4a05f21cc2b5149145c3beea24919ec.JPG

0.6 or 0.7mm piano wire and a 1mm hole in the slide switch.

Edited by dhjgreen
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32 minutes ago, philsandy said:

 

Izzy thanks for your reply.

Re. the excess movement. On the slide switches there is 5.5 mm travel, and the point blades only move approx. 2 mm at most. If  the switch travel is restricted to 2 mm by using stops soldered in place, does this not effect the DPDT contacts to switch the polarity, because it is only travelling less than half the distance?

 

Yes, the idea of the stops is to absorb the excess travel, so in the measurements above just move the rod that 2mm. The post above shows how omega loops do the job allied to wire-in-tube. It looks very neat and tidy.

 

Perhaps this shot will help explain. The idea is to put minimal pressure on the point tie-bar, many home made tie-bars such as those I make/use can't cope with high loads or lots of 'thumping' of solenoids etc.

 

The rod goes through the switch, this is 0.9mm brass rod as the layout is 2mm/2FS. The switches are from Expo tools - usual disclaimer - because they are easy to get, and softly sprung with a measure of 'give' in them, and reasonably priced.

 

On the left the switch is pushed forward and the tube in the front is hard up against it. On the right it's pulled back and the rear one is pulling the tube the needed distance. Their positions are set after installation, to just move the rod the required distance so the point blades are hard up against the stock rail but just enough to make sure they are secure in place. And of course with care they can be moved to obtain best position. Care because excess heat will melt the switch a bit.......

686528663_RMwebT18.jpg.ac2379676b714822d2a2fe09739b1539.jpg

 

Hope this explains it.

 

Izzy

 

 

 

 

Edited by Izzy
only half the post loaded!
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On 04/07/2020 at 15:28, dhjgreen said:

Phil, I think you may vaguely remember this from when you came over.P1010603.JPG.b4a05f21cc2b5149145c3beea24919ec.JPG

0.6 or 0.7mm piano wire and a 1mm hole in the slide switch.

 

Yes David I do remember it. So the switch travels the full distance each way and the Omega wire takes up the excess travel?

Did you make the Omegas yourself?

 

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Just now, philsandy said:

 

Yes David I do remember it. So the switch travels the full distance each way and the Omega wire takes up the excess travel?

Did you make the Omegas yourself?

 

Correct and yes.

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On 04/07/2020 at 15:51, Izzy said:

 

Yes, the idea of the stops is to absorb the excess travel, so in the measurements above just move the rod that 2mm. The post above shows how omega loops do the job allied to wire-in-tube. It looks very neat and tidy.

 

Perhaps this shot will help explain. The idea is to put minimal pressure on the point tie-bar, many home made tie-bars such as those I make/use can't cope with high loads or lots of 'thumping' of solenoids etc.

 

The rod goes through the switch, this is 0.9mm brass rod as the layout is 2mm/2FS. The switches are from Expo tools - usual disclaimer - because they are easy to get, and softly sprung with a measure of 'give' in them, and reasonably priced.

 

On the left the switch is pushed forward and the tube in the front is hard up against it. On the right it's pulled back and the rear one is pulling the tube the needed distance. Their positions are set after installation, to just move the rod the required distance so the point blades are hard up against the stock rail but just enough to make sure they are secure in place. And of course with care they can be moved to obtain best position. Care because excess heat will melt the switch a bit.......

686528663_RMwebT18.jpg.ac2379676b714822d2a2fe09739b1539.jpg

 

Hope this explains it.

 

Izzy

 

 

 

 

 

Izzy thanks for your reply.

Sorry I'm missing something obvious here. I  can see how an Omega wire takes up the excess travel, but not this. 

As you pull or push the operating rod it's the soldered tube that actually pushes/pulls the switch with it? But isn't the rod still moving the full distance of the switch travel, (eg. 5.5 mm for the switches I have).

It obviously works, I've just got a blind spot here.

 

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It looks to me like the stop points are set at the required distances according to the amount of travel required up to a max of 5.5mm.

So for your movement of 2mm and with a 5.5mm switch, the distance of the stop point is 3.5mm. So the total distance between the two stoppoints is 9mm

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2 hours ago, philsandy said:

 

Izzy thanks for your reply.

Sorry I'm missing something obvious here. I  can see how an Omega wire takes up the excess travel, but not this. 

As you pull or push the operating rod it's the soldered tube that actually pushes/pulls the switch with it? But isn't the rod still moving the full distance of the switch travel, (eg. 5.5 mm for the switches I have).

It obviously works, I've just got a blind spot here.

 

Maybe I'm wrong, but the rod will slide through the switch and do nothing until it hits the soldered sleeve, then move the rod the remaining distance.

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27 minutes ago, kevinlms said:

Maybe I'm wrong, but the rod will slide through the switch and do nothing until it hits the soldered sleeve, then move the rod the remaining distance.

 

That's how I see it.  

I've done similar mechanisms before, often using a couple of nuts on a threaded shaft, so they are adjustable.  If there is some varnish (or other sticky stuff) on the threads, the nuts don't move easily, so tend to stay where they are put.  The alternative is pairs of nuts tightened against each other.

 

- Nigel

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31 minutes ago, kevinlms said:

Maybe I'm wrong, but the rod will slide through the switch and do nothing until it hits the soldered sleeve, then move the rod the remaining distance.

 

Ah! yes, (slaps forehead with hand),  I've got it now, Doh!  Thanks.

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