Servo controlled points

[david_wakefield]

Hi All

In the latest edition of the Hornby magazine there is a good article on controlling points by using servos. Not a new concept of course but it does make a great way of slow motion realistic operation. There are several dcc servo decoders and analogue controllers on the market, hopefully a Hornby one soon.

Regardless of the control method you have got to connect a servo to a point. This how I do it for what it's worth.

In the first picture you can see that each servo is attached to a furniture corner block with a cable tie. This makes a convenient way to mount your servo. Pull the cable tie tight to secure the servo. The piece of white tube is used for a bearing for the control wire.

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I use a paper clip for the control wire, it has a bit of give in it which helps protect the point from servo over run.

Drill a small hole through the baseboard between the rails at the join where the lead in track meets  the point. Insert the tube to act as a bearing.

Form a 90º bend in the wire with a small peg bent in the end to locate in the point controll bar hole.  Thread the other end through the bearing.  Mount a second corner block with a hole drilled through to take the paperclip wire. Form the wire as in the picture and mount the servo. Hope you find it useful.

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[RB51]

Very clever David. This is the system I shall be using when I get round to Layout V2. Credit to Dave Fenton of Megapointscontrollers. (no affiliation). Here I have used 15x15x15mm aluminium channel with a paper clip in a 1.5mm hole which acts as the fulcrum. /media/tinymce_upload/2c9a54a4929e935713a967e8db624faf.jpg

 

The opposite lug to the one marked needs to be removed so the motor sits flush in the channeling.

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Top view.

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The motors shown here are a little narrower than 15mm so I squeezed the sides in a vice to give a tight fit.

R-

[david_wakefield]

Now this is why I love this forum. Good ideas and good discussion.  I like your mounting system Roger its simple and practical. Reminds me of a well known slow motion point motor only about a tenth of the cost.

I will be using servos on my garden railway (thread "Hornby garden railway" in General Discussion) as they will be under the baseboard and out of direct weather I think they will be fine.

I have used the white block and paperclip system on my indoor layout for ages with no problems. Servos are the way to go I recon, they are so versatile.  I have also used them to operate Hornby semaphore signals and crossing barriers. There are plenty of YouTube videos with other applications. 

Dave

[RB51]

Sounds good. What system do you use to control the servos David? R-

[david_wakefield]

I have tried most of the servo dcc decoders on the market with mixed results.

Most of them are difficult to setup and some give servo buzz all are quite expensive.

I discovered a guy on eBay that makes his own dcc system. He has a different approach to DCC.  A small dcc master module gives a dcc output to up to 10 slave decoders, these could be servo, light signal, point motor or relays. They just work and very reasonable in price. They also work perfectly with Rail master which is my primary dcc system.

Have a look at arosamia6 on eBay.

 For the garden railway I am using tam depot pic dcc controllers with manual sqwitching.

I'll post some pictures tomorrow.

Dave

[Chrissaf]

It is not immediately obvious how to search ebay for a seller. The search function is geared towards searching for products. To help out anybody who is interested, I have searched ebay for seller arosamia6 using the 'advanced search function' and found this:

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http://www.ebay.co.uk/sch/arosamia6/m.html?_ipg=50&_sop=12&_rdc=1

[RB51]

Crikey Dave - they are certainly very reasonably priced. Thanks.

 

Thanks also to Crissaf. I have searched for sellers before, but I agree - it is not easy to find out how to do it.

 

R-

[Chrissaf]

David,

A few questions:

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1. Are they DCC address self learning i.e you do something like pressing a switch to put in learning mode on main track and then send an operational address from your controller to set the address(s).
2. Does it just set the first address (port 1) and it allocates a range of addresses automatically based upon how many slaves are attached, or do you have to address all the servos individually.
3. Do they come with full detailed documentation, there is no mention of the level of documentation provided in the ebay listing that I can find.

Cheers.....

[david_wakefield]

Hi Chris 

You can set each slave decoder to a base address and the rest follow. Certain functions can be adjusted at CV level depending on the type of decoder. The led signal one for example you can adjust the brightness and the fade speed.

Each unit comes with full documentation plus Szabi (Szabolcs Beke)Is very contactable and helpful he is a Check lad living in Ireland and very knowledgeable.

I recon he has a small cottage industry making these units. Check out the Maximouse it's brilliant. (I was lucky enough to get the first one)

I hope this helps.

Dave

[david_wakefield]

Yes that was my reaction when I first saw them. I ordered a servo decoder and a master unit with out much faith in them. Too good to be true and all that.

I directly replaced a way switch pilot servo decoder that buzzed every servo.

I programmed the first address and selected the point on railmaster and hey presto, perfect. All my decoders are Szabi made now. The relay decoder has 4 relays with an address each. I use mine to power building and Street lights.

He has a few YouTube videos that are worth a look.

Dave

[david_wakefield]

As promised here are PCs of servo control panels for my indoor and outdoor layouts. Both are under construction as I have just relocated my indoor layout into a purpose built RCshed.

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This is the Szabi system for the indoor layout. Top left, relay decoder middle & bottom left led signals decoders. Top right servo decoders and middle point motor decoder and bottom another signal decoder. They are not wired up yet.

[david_wakefield]

Here is the servo panel for the garden railway. I'm using two Tam Valley Depot dcc/analogue decoders with switch controllers. Powered by a 1500mAh LiPo battery.

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I opted for rca plugs for connecting to the servos cos I had a load in the spares box.

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This is just an ornament at the moment as I haven't installed the servos yet.

Dave

[RB51]

Thanks, David, I have ordered some kit and will post on here how I get on. It all looks very straightforward and the chap has said that I can contact him if I need any help. R-

[david_wakefield]

Good oh Roger. I have been using this kit for around a year now. All I can say is that it works well and is reliable. Just give the master module 18volts (AC or DC) and dcc from your controller. Connect the slave decoder and off you go. Out of the box they are set to address 1 to 4 so for evaluation you can just plug and play.

I will be most interested in hearing your views on the kit when it arrives.

Dave

[RB51]

Certainly. Did you find there was any "sensitivity" to the decoder type when configuring the motor in point settings? I imagine one of the DCC Cobalt type options (AD4) would be suitable? R-

[RB51]

That's all very neat Dave. Your post (above) had to wait overnight for approval, so you may have missed my question just above it. I have asked Adam to forward an e-mail from me to you in the hope that I can pick your brains off-line 😎. Happy to share the summary on here of what I am up to for anyone who is interested. R-

[RB51]

I amended my order so it is not here yet. In the meantime, I have been trying to find out a bit about servos motors and good / poor brands, and in this context, I am grateful to Suzie on another forum for this insight, as in a senior moment I ordered a substandard servo (SG90) instead of the (what I now know to be) better quality SG92R. I asked Suzie what the main differences might be and replicate her response here in case anyone else is looking into using servos.

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There are two key differences:-- SG90 is analogue while SG92R is digital.- SG90 has plastic gears while SG92R has carbon fibre.In practice neither of these will make much difference if installed carefully. The gears on the SG92R are very tough and impossible to strip, whereas the SG90 gears are more delicate and you will need to be careful about overloading the servo arm. Use an omega loop or similar to be on the safe side. The biggest issue you are likely to see is that the SG90 is a bit more prone to twitching because it does not have the signal conditioning that you find in digital servos. The SG90 will be a bit quieter though since it should stay put once in position, and the low torque should see it not move very quickly even if it does hunt around a little bit.I don't know what type if fixing arrangement you are using, but a cam type actuator like the Signalist SB1 should eliminate any potential problems.

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Although the principle of a "cam type actuator" has been explained I can't visualise it - and I work much better with things explained with pictures, so if anyone can help with that I, and maybe others, would be grateful. 

 

 

R-

[RB51]

This is a photo I have been trying (for most of the day) to upload to show what the Omega Loop looks like against the standard set-up. Personally, I think the wire, a paper clip in this case, will be too robust to allow it to carry out its intended function. R-

 

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[david_wakefield]

Ah the old ohm spring ploy.  I wonder if the wire is too thick for the ohm spring to be effective. I notice that you have to mount the servo outside of the channel. That rather spoils your original design which is very neat.  

[RB51]

I agree - there is no doubt that a paper clip will not have sufficient springiness for the O Loop to work. I was just trying to show the principle. I will not be using it. R-

[96RAF]

Off to your local aeromodelling shop Rog for some piano wire, which is much stronger for much thinner and much more springy, and it wont break due to fatigue like the paper clip,will,after a few bends.

[RB51]

Thanks Rob - yes, already have several kilometres of piano wire. Mainly not using the Omega loop due to having to establish another fulcrum point if I put the motor back in the channelling. Personally I am going to try 0.8mm piano string in a straight shot from the servo horn through the channelling and into the tie bar. R-

[2e0dtoeric]

Roger B quoted - The SG90 will be a bit quieter though since it should stay put once in position, and the low torque should see it not move very quickly even if it does hunt around a little bit.

As an r/c model flyer, as well as a railway modeller, I can tell you that the SG90 will be fine for what you want (and a sight cheaper!) All you need to do is ensure that the mechanical movement of the pushrod isn't less or greater than the tie-bar movement! If less, obviously the point will not switch cleanly, and if greater, the gear-train and motor will be under constant load because the servo will have stalled at less than it's full travel.

Servos usually travel about 90' from end to end, depending on the controlling signal, of course! In most cases the controller can have the 'end-points' adjusted - ie how far it tells the servo to move, or of course you can use simple mechanical adjustment, (move the push-rod in or out one hole on the servo arm for less or more movement of the point).

Digital (nothing to do with DCC) servos have a different electronics board inside, which is a lot more precise in it's position-monitoring, and as a result, all digital servos can be heard to be buzzing all the time, as the motor is constantly being driven back and to a tiny amount, (using power) whereas a basic analogue servo just goes to the instructed point, and stops, unless you try to force it away from it's position by twisting the output arm. (That's a good way of breaking the plastic gear-teeth off!)

Any servo that is overloaded or stalled will buzz merrily until the motor gives up or the electronics melt. (Just like your analogue loco on a DCC track!)

[RB51]

Thanks 2e0, Yes, thanks, I have realised that the swing of the servo arm and more precisely the start and stop points are crucial to correct operation. Although the SG90 is cheap, you don't want to waste too many! R-

[2e0dtoeric]

As a p.s. - the digital versus analogue servo naming isn't really correct, both types are 'digital', as they both receive a series of pulses of data from whatever source (controller - radio receiver) based around a 1.5 millisecond 'frame'. This 'frame' can be squashed down, or stretched out (electronically!) between around 1 and 2 m/seconds in length, and the little circuit board inside the servo 'reads' it, and winds the motor, and thus the gears and the tiny potentiometer, round until it's internal pulse length matches the one coming in from 'outside'.