MERG Servo 4 boards etc

Hi Greg

Our club used to have a switching layout that used three of the Servo 4 boards to operate turnout servos and we used the remote for setting the end points of the servo. The layout was portable so was always being taken out of store, transported by car, set up, taken down again etc. We never had any problems with the Servo 4 boards despite all the above.

We used a push button recessed into the facia to operate the turnouts, with a red light in the button. The light came on when the turnout was set to a diverging road.

good luck

John

Tam Valley

Greg I can highly recommend Tam Valley. Duncan provides exceptional customer service and I have operated several of his Quad Pic decoders for over 10 years without problems.

Can I suggest you carefully read his "Which Servo Decoder" page (Support Menu) to ensure you have chosen the correct product. Your product selection will change depending on use of things like, DCC, Loconet, JMRI etc

Arduino

If you're handy with computers, Arduino is a cheap and easy solution. I'm using Arduino clones, SG90 servo motors and 3D printed brackets with embedded microswitches for a total cost of well under $5 per turnout for DCC-controllable slow-motion turnout motors with switched powered frogs. Routes are also possible -- handy for (staging) yards.

Stand alone is also possible.

I am planning on using toggles with servos. Dave Bodnar on YouTube shows using a 5V power supply and servo tester with resistor can change points with a toggle. I found you can mount the servo with the tester fully on for one side of the switch and back off the potentiometer for the other side. With the toggle soldered into the circuit per his video the servo moves back and forth with it. Albeit not prototypically.  Fascia and signal LEDs are pretty simple to incorporate with a DPDT toggle. I'm mounting a micro switch for the servo lever to change frog polarity. Non-computerized but pretty simple old school with a modern twist.

3d printed mounts

whilst I use tam Valley octopi and really happy with them, I am interested in where you get the mounts or do you print them yourself?

Thenks in advance 

Mounts

The mounts are available from MERG (Model Electronics Railway Group) https://www.merg.org.uk/

You have to be a member to buy from their kit locker. They have a large range of electronic kits and components.

Mounts

Several options exist both Berrett Hill and Iowa Scaled Engineering (MRH sponsors) offer mounts for sale:
http://www.berretthillshop.com/store/products/servo-ut-mount/

http://www.berretthillshop.com/store/products/servo-cradle/

https://www.iascaled.com/store/index.php?route=product/search&search=servo%20mount

You can also 3d print your own at home:
https://www.thingiverse.com/search?sort=relevant&q=model+railroad+servo+mount&type=things&dwh=805acb61d4cf31f

https://www.thingiverse.com/search?sort=relevant&q=turnout+servo+mount&type=things&dwh=15acb6fad1727d

Have shapeways do it:
https://www.shapeways.com/marketplace?type=product&q=railroad+points+servo+mount

Or roll you own option(s):
https://forum.mrhmag.com/post/servos-101-12203325

Appreciate the links

 thanks guys. I make mine from L shaped aluminium (that's how we spell it in this part of the world) but was looking at other options as it's quite time consuming when factoring in micro switches for power routing etc

MERG reply - a disappointment

To me the reply from MERG forum is a disappointment as the power up jerk/bounce/jitter/twitch has nothing to do with connection to semaphores versus turnout points. Semaphores do not bounce when power is applied to the semaphore, but they do bounce in operation.

As you point out power up bounce/jerk has been discussed before on this forum and can be resolved to a great extent by adding a 10K resistor between servo signal and VCC (or GND) lines:  https://forum.mrhmag.com/post/servo-startup-jiggle-with-arduino-control-12206331

As can be seen in this video demonstration of the megapoints controller they do not bounce except at power up and would be fine for controlling turnouts/switches/points.

@Jim

Thanks for this. What is really bothering me is the power up twitch which the video shows. Perhaps I'll play with the Megapoints board and see if a pull up resistor helps with that. The Servo 4 board they sell has this already fitted. 

@Greg

Understood the problem you had with the power up twitch, I was surprised that the MERG forum folks claimed that the megapoints controller was better suited for semaphores because of it! After all it is called a mega POINTS controller which points tends to be the name used outside of North America for a turnout/switch.

I have not been on the MERG forums because I have not joined the group, but have always been impressed with what I have seen from them, so the response you got really surprised me.

Maybe you can look at the Servo 4 board and see where they put the resistor Signal - VCC or Signal - Gnd.

Jim, that's exactly what I've

Jim, that's exactly what I've done. I did order a Servo 4 board. And I have examined the schematic for it and see where they are using a 10k resistor connected to either ground or VCC as you wish to mitigate the twitch. It is configurable with a jumper so you can determine which works best for your particular servo, holding the data pin high or low.

I have to be honest, the response I got wasn't exactly what I expected. As you have said, it has points right in the product description! However, reading further into the Megapoints discussion, it is a source of contention on the board. Many saw taking a commercial product and making it into a MERG kit was the wrong thing to do. I won't get into the details, suffice to say many were upset and the exchanges were tense at times. From this I gather that there isn't a lot of interest in discussion the finer points of the board. It is what it is, it's a volunteer operation. The board works exactly as advertised and I should have done further research into the power on twitch issue which has been discussed in many places that talk about using servos a switch machines. 

Overall I am very impressed with MERG and won't let this issue get in that way. I've also ordered their District Cut Out board which in North American is a circuit breaker. It is designed to work with their booster, which I also have. It is very configurable for current and timing variables. 

Megapoints controller

That is strange to go from a commercial product to "open source" MERG kit I guess I could see how that goes against the MERG model as I know it and be a source of contention.

Oh well, sounds like you have solved your problem - bought the Server 4 board and have a possible solution to the power up of the megapoints controller.

So simple solution

Today I attached a 10k resistor to the data pin of the servo. Applied 5v VCC, twitch gone. 

It is a little baffling why:

1. This isn't already part of the board as it is for the Servo4 board and...

2. Why no one on the MERG forum suggested it.