Junctionmad

As I mentioned elsewhere  here’s my circuit , positioned close to the servo 

personally , and testing the configuration there are two benefits 

(a) the major benefit is the reduction of input resistance of the servo control line. This to me is the single biggest issue that is resolved 

(b) the introduction of a floating servo pwr , as far as the servo is concerned , ie no local GND , this means we get some additional noise immunity from induced noise shifting gnd or 5V or the signal line to the opto. 
 

the other area to take care off is the configuration of the drive signal , or a pull down resistor is useful for this ( for positive logic ) , this handles the issue of inadvertent transitions on the io line   

Pete Waterman’s extremely large O gauge layout is controlled exclusively by MERG CBUS 

Yes the nightmare that is SEEP point motors. 

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with SEEP motors (the built in auxiliary switch will activate the frog).

you'll regret that decision

By the way 

my latest panel is 3mm dibond in white 

this is then drilled for 3mm flat top leds that lie flush with the surface Using a copy mimic as a drilling template 

the mimic is printed on transparent acrylic vinyl and glued to the dibond 

hence no holes in the vinyl means easy cleaning , no rough edges and the precision of the holes  doesn’t have to be exactly precise 

Dave 

22 hours ago, BusDriverMan said:

Oh my gosh, that's adorable and also extremely cool.

And VERY expensive 

heres my actual circuit  R1 = 680R , R2 = 1K , R3 suits LED  ( this is to support a signal lamp Led) 

The opto wired to active pull up with a resistor for pull down , is the best option as the default unpowered position will be low input 

place the opto within the standard servo cable distance 

noise on the 5V is balanced by the same noise on the OV , so my recommendation is to feed servo power And GND , from the servo control board, and hence in effect implement a balanced line. The alternative is bussing around gnd which isn’t as good. 
 

in my experience , the solution is excellent 

My merg boards do. ?  In that I have a miniature SMD board with the opto close to the servo and a live driver board with the merg servo software 
 

my own view would be that the opto at the servo exposes a low ( lower ) input resistance and this resolves the noise immunity issue 

the common mode benefit is rather circumspect since many people will power the servos from the servo board so for the purposes of the servo , it’s a balanced line anyway. 
 

I did a big minic using 3mm dibond and simply had the plan printed locally on outdoor vinyl 

i then drilled 3mm as required about 200 holes in all 

the drill leaves the vinyl slightly ragged but not bad 

Worked well 

6 hours ago, Chris M said:

 

You may well be right, I left it to those who thought servos/MERG was a good idea to set everything up. They tried very hard to make it work but didn't succeed. From what I saw of it the MERG electronics appear to be somewhat flaky.

Given the merg modules are fine, I suspect the issue was the people involved may not have understood the issues around deploying servos 

9 hours ago, AndyID said:

 

That's very good to know.

 

Did you position the opto-isolators close to the servos? That seems like the most logical place to put them and it's what I did with my immunity tests but I have sometimes wondered if they might be as effective if they were at the controller end instead. (Handy Hint: People that sell servo point controllers might consider trying that.)

 

I might give it a shot myself, if I ever get around to it

Yes the opto is positioned right at the servo. 
 

the whole idea is to decrease the input resistance of the servo control line , that solves almost all issues 

 I’ve tried experiments with power sequencing and I’m not convinced it adds anything to resolving the issue 

the main point seems to be to allow the control signal to be correctly established  before the servo is powered up. But I’ve found appropriate pull up or down resistors achieve that and power sequencing adds nothing 

as a MERG member I can say their various servo boards are as good if not better then anything else on the market 

On 29/07/2020 at 14:50, kevinlms said:

I know they used to make/find resistor values like this. But isn't the manufacturing process now sufficiently good, that they just make the required value in batch form? Even computerised testing of each one, would blow the price to unacceptable levels, for the average user.

Military specs would be different.

Actually each metal film resistor is laser trimmed to the required resistance and tolerance 

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Solenoids just work with a satisfying clunk. You fit them under the point put a couple of switches in your control panel and you have a perfectly reliable and cost effective means of changing points. A complete and simple solution that works. Servos just seem to be a pain so far as N gauge points are concerned .  And what on earth servos “being a component of the solution “ is all about I don’t know.  All you need is to press a button and have the point change; there’s no more to it than that. I’m glad some folk enjoy using servos to change points but so far as I am concerned solenoids are for points and servos for signals. That’s what works for me. 


At our club a few people were dead keen to use servos and pressurised the rest of the crew into agreeing. Two and a half years of pain and delay later we are stripping out MERG and servos and installing solenoids. Maybe a different (and more expensive) servo based solution would have worked better.
 

What I meant about set is being a component of a solution is that on their own they are not a complete solution to point control , unlike say a Colbalt point motor 

using servos requires electronic drive control , you then need to add frog switching either electronically , by relay or physical micro switches 

you also need to understand the issue around power sequencing and long live drivers to ensure that they don’t twitch etc. 
 

As I said , they are a “ component “ not a solution 

since 1000s are in use happily switching points and signals, including many merg members layouts , I suggest the issues you had may be a function of your setup rather then any fundamental issue with deploying servos 

16 hours ago, AndyID said:

 

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.

 

 

 

Andy , I’ve used the opto method to drive the servo line , no twitches 

I’ve about 30 driving signals on a big O gauge so plenty of dcc current floating about

servos are great , but they are a component of the solution not a complete solution , those that run into problems don’t seem to appreciate that 

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 

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 

On 15/07/2020 at 10:19, Nearholmer said:

Sir Topham

 

Seeing this and your other "electrical" questions, you might want to start with a very basic intro to electricity.

 

This one is pretty good, and it does quickly get on to using a multimeter https://www.explainthatstuff.com/electricity.html#:~:text=Electricity is a type of energy that can,one place to another is called current electricity.

 

BBC Bitesize also has quite good material, although their resources are so many that I find using them involves looking for the most suitable needle in the haystack first.

 

Apologies if these are patronisingly junior introductions, but the danger of RMWeb for something like this is that it has members who are experts, but tend to take off at the deep end, and members who are actually  a tad confused themselves.

 

As an aside, a multimeter is definitely in the "luxury" class of tools when it comes to railway modelling - you can well get by without one. I'm an electrical engineer by profession, have been playing trains for a lifetime, and own a multimeter which comes out of the drawer probably no more than once a year!

 

Kevin

To suggest a £10-£20 DMM is a luxury for an hobby powered by low voltage electricity is rather far fetched 

As a person that started with copper clad and now uses ply sleepers and plastic chairs , I’d say the 2nd method is far far better , you get correct rail height , wooden sleepers , and the ease of assembly of functional plastic chairs. Copper clad is now much more expensive then it used to be. I create my own ply sleepers from AA grade 4 sheets of ply and saw them up on a little proxxon table saw. 
 

don’t bother with pre made crossings and switch blades , make your own , it’s very easy once you’ve have made one or two. 
 

00-SF , ie 1mm flangeways and 16.2 track gauge is a fabulous compromise for points. I flare back out to 16.5 and use conventional commercial track for straights. 
 

ive used peco bull head , c&L, Smp , and dcc Concepts.   I won’t use stainless track ever again , thank you. 
the reality is that any of them used as straight track , ballasted , weathered etc , looks good. 
 

use commercial straight track , hand build the points , best compromise and remember while we are attempting to model a railway , it’s all an illusion , and a good illusion isn’t about precise numerical relationships. 

We built all our large O gauge layout baseboards , 20 baseboards , some as big as 5’ x 2’6” from 6mm high quality moisture resistant Scandinavian  or Russian birch ply. We use 6mm 120mm deep sides and Centre longitudinals as well as diagonals , no screws or nails , hot glued initially , then PVA and fiberglass tape to all joins. Extremely rigid and light for their size 
 

end cheeks carrying pattern maker dowels are 12mm birch ply 

three years later and several exhibitions , it’s bomb proof , we tested each board by placing a 9 stone man sitting in the middle of the baseboard supported on its outer end , maximum deflection was 2mm 

All major dimensions were CNC saw cut. 

don’t use the cheap “ dark “ far eastern or Asian ply , it’s junk , birch ply is nearly white. 
 

and definitely don’t use MDF ( except in a enclosed stove) 

it takes track pins and screws very nicely 

ps. We investigated fully laser cut , but we wanted the ability to move the cross bracing based on the track diagram to ensure point motors could be fitted , so we have asymmetric box sections underneath busy track work boards 

By the way mention was made of using scopes, unless you have , an isolated scope, battery powered scope , differential probes, or setup to use two inputs in differential mode , don’t connect a standard scope probe across a DCC track , as the scope probe  gnd  is at mains ground and will short out the DCC track. 

On 27/06/2020 at 23:50, melmerby said:

My scope does this:

Nice.  Built in DCC decoder , what scope is it 

On 04/06/2020 at 19:50, WIMorrison said:

I don't understand the Railcom issues with the older decoders as the Railcom standard hasnt changed and I have some ancient Lenz decoders that still work with RailCom now - but the motor control is awful so they are getting changed for Zimo

many of the issues relate to the fact that the RailCom spec as adopted by the NMRA , isnt sufficient to fully define everything .  its not helped by the fact that Lenz itself then changed the byte order in the second channel themselves , leaving Zimo in the dark .  

Railcom plus will never be a MRA standard as Lenz have not released the protocol into the public domain and the distrust that Lenz engendered over RailCom , means that no-one will touch any further proposal from them with a barge pole 

Ive designed a railcom decoder , the " standard " has many holes in it unfortunately , and many manufactures of decoders didnt implement the standard correctly either . There is also the issue of the number of preambles your control station supports , hence limiting you to 1 channel RailCom in certain cases, which means you cant detect multiple decoders on the same track section etc 

having said that the Z21 RailCom decoder is good , its what I use in my testing etc 

MERG has a little servo board that can use the servo signal to switch a relay , you set the switch over point 

On 25/05/2020 at 21:02, Grovenor said:

Depends on how much work you are prepared to do, most etched frames such as the Scalefour Society one can be adapted to use Servos as electric locks. We have at least one member in MERG who has done that. I am not aware of anything that can just be used as it comes.

I built these ( the scalefour ones . MK1 & Mk2)  , they are not easily modified to some form of electrically driven Locking operation . I abandoned using them and developed by own that are explicitly designed for electrical operation and controlled . They are  3Dprinted with 4mm aluminium levers. Pull plates can be fitted as the levers are large ( 14mm centres for the purposes of indicating scale ) 

The levers are both capable of being locked normal or reverse and can also be moved by the servos ( to facilitate  dual panels or where layout automation is also used ) 

The bicolour led on each lever can be used to indicate the locked status , or errors in lever positioning where  mechanical locking isnt  desired . Im currently developing the PCB board that all this sits on and the control hardware and software 

There is a little video showing the operation  YouTube video - Leverframe