Frog Polarity switching: Relay or Microswitch ?

[RedgateModels]

On 24/07/2020 at 08:21, Izzy said:

 

The problem is RFI/EMI (radio frequency/electro magnetic interference). It is this that is the issue of the older Farish locos disrupting the servo signals. This disruption can arise from many sources, mine went haywire whenever my DCC system was switched on, it didn’t even have to be plugged into the layout! Needless to say I dumped servo control as such, managed to sell off the MERG servo 4 boards - as you say a lot of people have no problems at all - and now use ‘ hacked’ servos. They just run off 1.2 -1.5v DC via DPDT centre off switches. 
 

 

 

Many attempts have been made to eliminate servo twitch on start up at MERG, the current idea that myself and Geoff Church amongst others are championing is the use of an LM217/317 regulator configured to provide a delayed 5v supply to the servos independent of the control circuitry. In this way the PIC is up to speed and ready to control the servo way before it has enough voltage to start working. 

 

Seems to have solved the problem for us. I have produced my own PCB too

 

 

Much smaller than the standard MERG offering, with a few niceties that I don't use (ICSP series resistor network on the inputs) removed. I have included AC/DCC rectification though as the next generation of standard MERG pcbs will be 12v DC powered only.

 

I have found that simply gluing aluminium foil on the underside of the baseboard where the servo wires run connected to 0v has removed all twitching caused by the passage of locos over them. The Servo4 boards have always had one fixing hole connected to 0v which with a metal spacer onto the foil provides a handy connection. 

Edited July 12, 2022 by RedgateModels

[RedgateModels]

On the original question, I use microswitches on the MERG servo mounts, I don't find any problems with them TBH. MERG are producing a single servo driver PCB though that can include a relay, very much a personal choice really. 

 

Oh and I have used a frog juicer where I have no moving blade on a fixed crossing, but then I am DCC and always will be

[Oldddudders]

7 hours ago, WIMorrison said:

I think that the term you meant to use is 'consist' and not 'lash up' which has a rather different connotation.

No. While unaccountably the US model hobby has foist the term 'consist' upon us, when many of us have been used to that term describing the train that is being hauled, rather than the power at its head, multiple locos are indeed referred to in the US railfanning community - and thus probably by US railroaders - as a 'lash-up'. It clearly has no connotation of an imperfect arrangement, to which you allude.   

Edited July 24, 2020 by Oldddudders

[Chris M]

10 hours ago, ikcdab said:

Not sure why you say this.  A peco point motor retails around £7. A 9g servo (hobbyking hk15168) is £2.29. If you use MERG drivers, these are £5 to power four servos (servo4 kit). So servo drive is around £4 plus a few pence for aluminium channel mount. Switches are the same in both cases, though with the servo just needing a simple on/off switch rather than a momentary contact it is simpler and easier. If you need to add a relays or mixroswitch than that added another £1 to the servo option, but even so it's less than the cost of a peco solenoid. And of course, with the servo, you avoid the horrible "thump" of solenoids and impart far less wear and tear on the tiebar.

Well it cost a lot more than that per point at our club. How do you mount the micro switches if you use aluminium channel for servo mount. The club used those badly designed MERG plastic mounts some of which broke. There were  boards in the control panels to generate the code for the receivers. When we gave up on trying to use microswitches we wasted more money on the MERG electronic switching which also turned out to be a total pain. And points continued to change all by themselves even when running modern locos.

There is a huge hidden cost with MERG - your time as you first try to understand it and then have to build all the units. Like I say I know it has worked for some but for us it has been an unmitigated disaster. This is a shame because it is a good idea in theory.

I like the satisfying clunk of a solenoid and have never seen tiebar damage due to the solenoid in 50 years of using solenoids.

[Chris M]

On my own layout I have very happily and reliably used a Peco smartswitch to control servos for my signals which shows I'm not against servos.

[Izzy]

4 hours ago, WIMorrison said:

The short happens because when you throe the DPDT switch the blade is still in contact with the stock rail thus at one polarity, but the frog polarity changes when the DPDT switch has been changed but the delay in the servo moving the point blades causes a track short until the blade has left the stock rail.

 

Ah, thanks, so only if you have points that have an 'all-in-one' blades and closure rails construction, as per the old Peco way. The newer unifrogs are of course different as is hand built stuff where the crossings are isolated from the blades/closure rail.

 

Izzy

[ikcdab]

4 hours ago, Chris M said:

Well it cost a lot more than that per point at our club. How do you mount the micro switches if you use aluminium channel for servo mount. The club used those badly designed MERG plastic mounts some of which broke. There were  boards in the control panels to generate the code for the receivers. When we gave up on trying to use microswitches we wasted more money on the MERG electronic switching which also turned out to be a total pain. And points continued to change all by themselves even when running modern locos.

There is a huge hidden cost with MERG - your time as you first try to understand it and then have to build all the units. Like I say I know it has worked for some but for us it has been an unmitigated disaster. This is a shame because it is a good idea in theory.

I like the satisfying clunk of a solenoid and have never seen tiebar damage due to the solenoid in 50 years of using solenoids.

It's a pity it didn't work out for you.  I get away with the channel as I now use relays so no need for fixing microswitches. 

[dasatcopthorne]

On 20/07/2020 at 17:49, DGO said:

OK so I've decided to come back to model railways after a short 40 year gap, I've also decided I'm going to switch my turnouts with servos though I've yet to decide on exactly how. But then I come to controlling the polarity of the frog. So as I see it I can either switch the polarity using a relay at the same time as I send the command to the servo (or use sensors to tell the system the servo is moving and change)  or I can stick one or two micro switches on the other end of the servo arm to the turnout and use that to switch the polarity, Are there any clear advantages or disadvantages to either method ?

 

Currently my thinking is that I'd use a pair of microswitches to control the feed, that way whilst the turnout is actually moving the frog will be isolated completely 

 

DGO.

 

I've used these Servo mounts. They are brilliant. Maybe they do cost a bit more but I feel they are worth it.

 

The MERG servo 4 is good but if you have more than 4 turnouts then the MERG kit for the Megapoints board if worth considering.

 

Choose whether they are DC or DCC. The Megapoints offers 3 pre-set routes as well.

 

Dave Smith

 

http://www.dingoservo.co.uk/

[DGO]

54 minutes ago, dasatcopthorne said:

 

DGO.

 

I've used these Servo mounts. They are brilliant. Maybe they do cost a bit more but I feel they are worth it.

 

The MERG servo 4 is good but if you have more than 4 turnouts then the MERG kit for the Megapoints board if worth considering.

 

Choose whether they are DC or DCC. The Megapoints offers 3 pre-set routes as well.

 

Dave Smith

 

http://www.dingoservo.co.uk/

 

I will admit those mounts are very nice, if I do what I intend though I'll need custom mounts because rack rail points are so much more complicated ... did I mention I may be mad ? .... 

[Junctionmad]

On 24/07/2020 at 14:48, WIMorrison said:

The short happens because when you throe the DPDT switch the blade is still in contact with the stock rail thus at one polarity, but the frog polarity changes when the DPDT switch has been changed but the delay in the servo moving the point blades causes a track short until the blade has left the stock rail.

Err ,  normally if you switch the frog , you would also bond the switch rails to their respective stock rails , then there is no issues switching the frog to any polarity at any time and no shorts occur 

Edited July 26, 2020 by Junctionmad

[Dagworth]

30 minutes ago, Junctionmad said:

Err ,  normally if you switch the frog , you would also bond the switch rails to their respective stock rails , then there is no issues switching the frog to any polarity at any time and no shorts occur 

You can only do that though if you have cuts in the rails between switch rails and frog. if the rails are continuous (as supplied by Peco, particularly the code 100 electrofrog range) then the frog *has* to be switched when the blades are mid way. Either that or rely on the switch rails making good enough contact with the stock rails to carry power - no thanks!

 

Andi

[WIMorrison]

6 hours ago, Junctionmad said:

Err ,  normally if you switch the frog , you would also bond the switch rails to their respective stock rails , then there is no issues switching the frog to any polarity at any time and no shorts occur 

 

How nice it would be to live in such a perfect world that this was always possible and where everyone possessed the skills to modify turnouts to meet your normality.

Edited July 26, 2020 by WIMorrison

[Oldddudders]

3 minutes ago, WIMorrison said:

 

How nice it would be to live in such a perfect world that this was always possible and where everyone possessed the skills to modify turnouts to meet your normality.

I think Peco Electrofrog points offer the facility and instructions to do this, right down to factory-attached leads to the frog etc. I am no great modeller, but the simplest soldering skills will provide a point that does what is wanted. 

[WIMorrison]

Not all scales have turnouts built in the same way that 00 points are, many are still using designs that are old therefore the statement is only valid for the limited range of products that have been redesigned and retooled to provide this capability - though given the number of questions asked about which links to cut  on retooled turnouts suggests the process isn't as simple or easy as expected. 

[Suzie]

If you are using servos then you have a couple of options:-

 

1. Use a servo controller with built in frog switching. The Peco/ANE PLS100 solution uses an add-on to switch the frog polarity at the same time that the servo moves, or you can use something like the Signalist SC2 which has frog switching as standard.
2. Use a servo based motor that integrates the switching with microswitches. There are quite a few simple mounts available, and you can probably make something suitable from a bit of sheet aluminium, but if your controller is prone to twitching a servo motor that limits the movement and uses the full range of travel of the servo can be a good idea, and it will have plenty of torque to operate the microswitches.

Here is a Signalist SB1 motor which can actuate a pair of microswitches (one at each end of travel). It can be mounted below the baseboard and be fitted with a pin too.

[Stubby47]

@WIMorrison so what would be your 100% perfect solution for DGO, given that AFAIK he's not mentioned scale, make of point or track layout, soldering skills or wiring ability but he is using DC (an assumption from the sub-forum title) ?

[WIMorrison]

it is simple - a switch operated by the mechanism throwing the turnout, which is the way that has been tried and proven over many years by many modellers across many model railways of all scales, gauges and electrical supplies.

Edited July 26, 2020 by WIMorrison

[Junctionmad]

On 26/07/2020 at 08:48, Stubby47 said:

@WIMorrison so what would be your 100% perfect solution for DGO, given that AFAIK he's not mentioned scale, make of point or track layout, soldering skills or wiring ability but he is using DC (an assumption from the sub-forum title) ?

The simplest is to buy a tortoise or cobalt point motor , which is ready to go , has the switches built in and is easy to install, no further electronics required 

[WIMorrison]

4 minutes ago, Junctionmad said:

The simplest is to buy a tortoise or cobalt point motor , which is ready to go , has the switches built in and is easy to install, no further electronics required 

 

I would tend to agree, and that is why I used to use Cobalt IP motors, however I now use MTB MP1 motors which also have inbuilt microswitches which can be used to change the polarity. 

 

 

[Enterprisingwestern]

 

A purely personal observation, but layout placement comes into the equation. My trainsets have to cope with an ambient temperature range of 6°c to 55°c in their current environment, and although the servos are mounted on steel mounts the microswitches were constantly going off piste, so frog juicers reduce one of my issues.

The temperature fluctuations don't do the trackwork any favours either, but that's another matter!

 

Mike.

[WIMorrison]

Do 'frog juicers' work with DC?

[ejstubbs]

On 26/07/2020 at 02:09, Dagworth said:

if the rails are continuous (as supplied by Peco, particularly the code 100 electrofrog range) then the frog *has* to be switched when the blades are mid way

 

Most modern* Peco code 100 electrofrog points have rail gaps between the frog and the switch rails which are bridged by a wire under the turnout.  It's straightforward to snip the bridging wires in order to insolate the frog from the switch rails, and indeed Peco used to have the instructions for doing this on their web site.  Unfortunately those useful snippets of information seem to have disappeared since the web site was redesigned a couple of years ago (though you might be able to get them by contacting their technical department directly).

 

The one code 100 electrofrog point I know of (there may be others) that doesn't have rail gaps 'out of the box' is the short Y.  To be fair to Peco there isn't a whole lot of real estate available on that turnout to fit them in.  IIRC there is at least one thread on RMWeb, possibly more, about how tricky this is for the end user to do as well, for that same reason.

 

* By "modern" I mean the ones I've bought since I started to get back in to the hobby six years ago.  They've mostly been brand new but some have been second-hand off Bay and might date from before 2014.

Edited July 30, 2020 by ejstubbs

[kevinlms]

2 hours ago, WIMorrison said:

Do 'frog juicers' work with DC?

No, so they don't belong in this topic.

[AndyID]

10 hours ago, WIMorrison said:

Do 'frog juicers' work with DC?

 

This one does but you'll have to make it yourself. It only works in one direction (trailing) although it probably could be adapted to work in either direction.

 

 

 

[AndyID]

On 24/07/2020 at 00:21, Izzy said:

I have come to understand that there is no real problem with radio controlled servos per se, but that trying to adapt them for model railway use can cause issues that can arise with them becoming an obstacle to usage, depending on the particular layout setup and where the layout is situated, where it is erected for use at any particular time. 
 

The problem is RFI/EMI (radio frequency/electro magnetic interference). It is this that is the issue of the older Farish locos disrupting the servo signals. This disruption can arise from many sources, mine went haywire whenever my DCC system was switched on, it didn’t even have to be plugged into the layout! Needless to say I dumped servo control as such, managed to sell off the MERG servo 4 boards - as you say a lot of people have no problems at all - and now use ‘ hacked’ servos. They just run off 1.2 -1.5v DC via DPDT centre off switches. 
 

I did use an alternative design which I posted in the 2mm section which might suit your club. https://www.rmweb.co.uk/community/index.php?/topic/112916-hacked-servo-point-control/

 

Anything is better than sledgehammer solenoid point motor control.

 

Izzy

 

Servos have lousy noise immunity. That's not a problem in a RC boat or aircraft but it's a problem on model railways. The solution is to eliminate the antenna effect on the input to the servo and this is one way to do that.

 

Try as I might I could not make them twitch under any circumstances with this method. I don't know if anyone else has tried it but I'd be interested to hear how they got on.