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Discussion Starter · #1 ·
I'm still in the process of gathering information, ideas and rolling stock for a small DCC N-gauge layout but the question of polarity switching for Electrofrogs (Peco) is bugging me a bit.

Am I right in thinking that provided the turnouts are in good condition and the loco wheels are in tolerance then the switching provided by the blades is adequate? I realise that certain rules must be followed such as feeding power from the toe of the turnout and insulated joiners must be installed generously. Also, that there are certain types of crossings which require frog polarity switching to be used.

I just wondered if there are many of you who have not used extra polarity switching on normal turnouts and have had no problems.

Out of interest, I am using SwitchPilot Servo and small RC servos to operate the turnouts. I will also (belt and braces) add droppers form the Electrofrogs so that later, if needs be, I can add microswitches to change the polarity. I may even, funds permitting, add the SwitchPilot Extension which has built-in relays to do the switching. The switching time can be delayed so that the polarity changes when the blades are in mid-travel, thus avoiding a potential short.

Sorry if this is an oft-repeated subject, just thought I'd ask the question.
 

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My own experience is that frog polarity switching is necessary for Peco N gauge Electrofrogs. I found the blade electrical contact quickly became unreliable. Others may disagree - questions such as whether you plan to weather your track and even room temperature/humidity/cleanliness may make a difference.

The question of wheel tolerance is not relevant to frog polarity switching, it is more related to frog isolation which we've been through at some length several times recently on this forum.
 

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From what Google has told me about the Switchpilot extension then I'm afraid it may not be so simple.

The Extension appears to change the frog polarity via a separate relay at the same time as the motor is changing the point. However if the relay operates too soon, before the point starts moving (or too late when they have finished moving) and the point blades do happen to be in electrical contact then for an instant the frog will be connected to both rails at once! DCC systems are likely to trip out with a short circuit if this happens, and if the relative timing of the relay versus the blades is marginal then you may end up with an intermittent fault of the most irritating kind.

The two best solutions would be either:

Isolate the switch blades from the frog and bond to their stock rails, as I mentioned above this has been discussed at great length so the forum search should find you details.

or:

Instead of using the Extension, change the frog polarity with a switch which is mechanically linked to the point so (once it is set up correctly) the switch only operates with the point in mid-travel. The simplest and cheapest motor including such a switch is probably a Seep PM1 but many of the more sophisticated slow motion machines also have one, or it is possible to fit a separate microswitch.
 

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Discussion Starter · #7 ·
Edwin,

I think the SwitchPilot Servo gets round this problem by allowing the behaviour of the relay switching to be changed so that the relays only switch in the middle between the two end positions of the servo travel. This option can be set for each individual relay in the Extension. I downloaded the SwitchPilot manual (which covers all three flavours of SwitchPilot - ordinary (mainly for solenoid motors), Servo and Extension) and it's covered in section 13. I hope I understand it correctly.

One feature which attracted me to the SwitchPilot Servo is the ability to fine-tune each end position of the servos so I can get a good physical contact between the blades and the stock rails but not exert undue pressure on them. I can also adjust the travelling time up to, I think, 15.75 seconds.

I intend to use the other contacts in the Extension to control red/green LEDs on a mimic diagram - I will no doubt be posting a question or two about this later.

Bluedepot (tim),

I agree with you especially regarding the polarity switching. It seems a bit contradictory to me that Peco (no names no pack drill) make a nice range of electrofrog points and then effectively admit that they are imperfect by making polarity switches (PL-13 and PL-15) for them.
 

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I have at least 25 electrofrog points, none of them are modified and all work as intended

I did forget to set the route once, the loco went over the crossing, causing the DCC system to trip out
Personally, I prefer it that way, otherwise the loco might have stalled / derailed and damaged itself
 

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Discussion Starter · #10 ·
Edwin,

Yes, I have researched this quite a lot and at one time my definite choice was Seep solenoid motors, with the incorporated polarity switch, operated by a Lenz LS150. I also considered the Tortoise motors and similar but to me they seem huge. Then I found that RC servo motors could be used - low current, slow movement and plenty of oomph for the size (they are about 1 x 1 x 0.5 in) and decided that was the way to go. The servos are quite powerful (torque of 2.1 kg/cm) and they only cost a fiver!

As regards removing the over-centre springs, I have read about doing this but wasn't going to do it because I thought it would provide just that little extra bit of location at the end of travel and thus prevent the blades from wandering, especially if there's a bit of play in the linkage. Can you tell me what the advantage of removing these springs would be?

M8 Internet,

Your comment about not having any problems is interesting. I talked to a salesman in a well known chain of model shops and he said he operated his points using push wires and had didn't use extra polarity switching. Never had any problems. However, I'm going to use polarity switching because I think it may be difficult to add at a later stage.

As regards forgetting to set the points, I intend putting insulated joiners about 6 inches downstream (if that's the right term) of the points so that a loco approaching a point not set in its favour will just stop. Obviously this will have no effect if the loco is pushing a load of trucks.
 

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Is turnout polarity switching always necessary?

If you mean frog power feed switching then the simple and factual answer is no. But you are relying on the moving rail blades for making contact and switching power. There are many layouts that rely on this method without major issues such as the large exhibition N gauge layout 'Basingstoke'. If they get the odd problem (which is not that common) it's a simple matter of cleaning the contact area with a bit of paper and that usually resolves the issue.

However, most modellers would recommend adding frog polarity switching for belt and braces operation.

G.
 

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QUOTE (RichardTee @ 4 Feb 2011, 00:34) <{POST_SNAPBACK}>Yes, I have researched this quite a lot and at one time my definite choice was Seep solenoid motors, with the incorporated polarity switch, operated by a Lenz LS150. I also considered the Tortoise motors and similar but to me they seem huge. Then I found that RC servo motors could be used - low current, slow movement and plenty of oomph for the size (they are about 1 x 1 x 0.5 in) and decided that was the way to go. The servos are quite powerful (torque of 2.1 kg/cm) and they only cost a fiver!
Seems a good idea. I'd probably do the same if I was starting my layout today. As it was I went for Seeps.

QUOTE (RichardTee @ 4 Feb 2011, 00:34) <{POST_SNAPBACK}>As regards removing the over-centre springs, I have read about doing this but wasn't going to do it because I thought it would provide just that little extra bit of location at the end of travel and thus prevent the blades from wandering, especially if there's a bit of play in the linkage. Can you tell me what the advantage of removing these springs would be?
The spring means the blades could travel at an uneven speed, slowly at first then very fast as the spring goes over and pushes the blades home. If your servo isn't powerful enough to control this motion (unlikely) or the linkage is a bit sloppy then this may make it difficult to get the relay switching reliably when the blades are always in mid-travel. I'm not familiar with servos but you may be able to set them up to overdrive the blades a bit so they are holding the blade against the stock rail and this might mean the spring is no needed.

QUOTE (RichardTee @ 4 Feb 2011, 00:34) <{POST_SNAPBACK}>As regards forgetting to set the points, I intend putting insulated joiners about 6 inches downstream (if that's the right term) of the points so that a loco approaching a point not set in its favour will just stop. Obviously this will have no effect if the loco is pushing a load of trucks.
If you just leave this 6" section connected to the frog then it won't just stop that loco, it will trip out the command station and stop the rest of the layout too. I'm actually thinking of doing just that in my hidden sidings, but putting them on a separate circuit breaker so any train overrunning its storage track will stop itself and any other trains nearby but not stop the scenic part of the layout. I would need further circuitry to allow for a train bridging between the scenic and hidden sections.

The automatic switch mentioned by Kickstart is probably the "Hex Frog Juicer".
 

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QUOTE (RichardTee @ 3 Feb 2011, 23:34) <{POST_SNAPBACK}>Then I found that RC servo motors could be used - low current, slow movement and plenty of oomph for the size (they are about 1 x 1 x 0.5 in) and decided that was the way to go. The servos are quite powerful (torque of 2.1 kg/cm) and they only cost a fiver!
Richard, what do you use to control them? Do you use a bought controller for each or a home brew version?
 

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Discussion Starter · #15 ·
Edwin,

I think (hope) the servo will be powerful enough to overcome any uneven pressure caused by the spring but if it is not then I'll remove it. Alternatively I could go to more powerful servos but then the size and cost goes up. I need to do a bit of experimenting first. I am a little apprehensive about play creeping into the linkages over time but according to the SwitchPilot Servo manual the end travel positions, determined by CVs, range from 0 to 63. The angle this corresponds to will depend on the servo gearing. I was thinking of adjusting the blade pressure so they just grip a thin piece of paper - the ubiquitous cigarette paper or similar. The end positions can be fine-tuned on the main, as can the traverse time, if the control station supports this. The SwitchPilot family manual explains all this much better than I can. I've read the one I downloaded so much I think I almost understand it now.

I've read about the Hex Frog Juicer somewhere on my literary travels - I'll go back and research it.

LFDRR (Angie),

I'm going to use SwitchPilot Servos, each of which can control four RC servos (as used for model aircraft). These are about £25 each and, in addition to track power, can have an additional AC or DC power supply if necessary. At £6 per point this doesn't seem too bad to me.

Originally I intended switching frog polarity using a micro-switch driven by the servo arms but then realised that the SwitchPilot Extension (also £25) contains 4 double pole relays so I will use one side to do the polarity switching and the other to drive LEDs on a mimic diagram (nothing like being ambitious). The other thing I like about the SwitchPilot Servo is that the servos can be switched by push buttons (I'm going to use biased toggle switches, also on the mimic diagram) in addition to the DCC control.
 
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