Servo control of (ground) signals

andrewnummelin
Posts: 169
Joined: Mon Jul 21, 2008 9:43 am

Servo control of (ground) signals

Postby andrewnummelin » Mon Oct 22, 2012 9:24 pm

Having not fully thought out the design of a baseboard, I find myself in the position of having to go for electrical rather than mechanical control of some points and signals and I am without copies of relevant published articles: I had always intended not to need them, intending to use mechanical control like the prototype. I've managed to squeeze in some Tortoise motors for the points, but now it comes to the signals. There's no room for more Tortoises, or similar, so I think the option will be servo control directly under the rotating McKenzie & Holland ground discs. To help me avoid having to re-invent the wheel, I'd very much appreciate help with the following questions:
1. Are there smaller control boards than those produced by GF Controls, Heathcote Electronics or Model Signal Engineering ? These are all too big to be installed easily near the servos.
2. Can the control boards be located far from the servos? (In, or near, the layout control panel a few meters away.)
3. Where can I buy 3 pin plugs & sockets and appropriate wire for linking servos to the control boards?
4. I will have 4 signals on one particular baseboard. If the servo control boards can be fitted on the baseboard, 8 wires (4*2) will need to go to the control panel - these could be conveniently routed via a 9 pin D-sub connector (Of course, plus 2 for the power supply). If the control panels are mounted off the baseboard then at first sight 12 wires (4*3) will need to go from the baseboard: is there any way of using a "common return" to reduce the need to 9 wires (4*2+1)?
Regards,

Andrew Nummelin

nigelcliffe
Posts: 456
Joined: Mon Jul 21, 2008 8:31 am

Re: Servo control of (ground) signals

Postby nigelcliffe » Mon Oct 22, 2012 10:44 pm

andrewnummelin wrote: To help me avoid having to re-invent the wheel, I'd very much appreciate help with the following questions:
1. Are there smaller control boards than those produced by GF Controls, Heathcote Electronics or Model Signal Engineering ? These are all too big to be installed easily near the servos.

Can't answer on sizes, but their are a few others you might consider, eg: Tam Valley and MERG (kit form).

MERG do two designs, the original Servo4 (controls 4 servos independently) and the Servo1 (controls one, but its more complex to build due to type of components). The Servo4 costs £6 for the kit of parts, can be configured (throw angles, speed of throw, etc) with a serial lead to a computer, or via another "settings box" kit. You must have a method to configure it, but once set you disconnect the configuration device and use the board on its own.

2. Can the control boards be located far from the servos? (In, or near, the layout control panel a few meters away.)


Yes for a few feet, perhaps a meter or two, but not sure of the maximum distance.


3. Where can I buy 3 pin plugs & sockets and appropriate wire for linking servos to the control boards?


Radio controlled aircraft/boat specialists, should be available in various lengths pre-wired with a plug and socket on them.
I bought mine online from "Giant Cod", but the firm changed hands earlier this year and is now "Giant Shark" and online reports suggest its not as cheap and quick as it used to be.


4. I will have 4 signals on one particular baseboard. If the servo control boards can be fitted on the baseboard, 8 wires (4*2) will need to go to the control panel - these could be conveniently routed via a 9 pin D-sub connector (Of course, plus 2 for the power supply). If the control panels are mounted off the baseboard then at first sight 12 wires (4*3) will need to go from the baseboard: is there any way of using a "common return" to reduce the need to 9 wires (4*2+1)?


Depends on the design of the Servo Control board, though I'd expect most can have a common switch return.
The MERG Servo4 has a common return on its input switches, so you'd need 5 wires to the panel (4+1), plus the power supply to the board (2 wires). I've built MERG Servo4 boards with a 12vDC power supply which use the same 0v as the common input switches, so its six wires to a board (4 signal inputs, 0v, 12v), and its five wires to a panel (4 signal inputs, 0v).



- Nigel

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grovenor-2685
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Re: Servo control of (ground) signals

Postby grovenor-2685 » Mon Oct 22, 2012 11:02 pm

I have extended Servo cables up to a metre but I don't think I would want to go much further, it seems more straightforward to just plug in the servo lead to a local control board,
However, the 3 wires to the servo consist of +5V, 0V and a control signal. So you can common the two power supply wires and just have single control wires to each servo, so needing only 6 wires for 4 servos. Don't modify the servo cables just plug them in a local connector block assembled on stripboard and wire that back to the control board, then if you do find problems with the length of cable you can still change to a local control board and plug the servos onto it.
Mike Peascod is using the MERG servo board for just such rotating type ground signals.
Regards
Keith

Alan Turner
Posts: 503
Joined: Sun Jul 20, 2008 4:24 pm

Re: Servo control of (ground) signals

Postby Alan Turner » Tue Oct 23, 2012 8:27 am

I have built rotating ground signals for Ellerton Road using the MERG Servo1 board. Ellerton Road is of course S7 but the principle is the same.

Here are some photos that show the set up. As you can see the Servo1 sits immediately below the signal. The Servo1 to the right of the first photo controls the turnout.

IMG_2547.jpg
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IMG_2548.jpg
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IMG_2549.jpg
IMG_2549.jpg (33.35 KiB) Viewed 5673 times
IMG_2550.jpg
IMG_2550.jpg (35.88 KiB) Viewed 5673 times


regards

Alan

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Jol Wilkinson
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Re: Servo control of (ground) signals

Postby Jol Wilkinson » Tue Oct 23, 2012 12:19 pm

Andrew,

I have used servos with the MERG servo boards to drive LNWR rotating ground signals. I mounted the servos remotely from the signals, driving them thorough a simple linkage and rod system. The MERG servo boards and portable control box are straightforward to build and very good value.

I found that the servos had less than 90 deg. (around 80 deg.) maximum rotation when set up with the MERG control box, so had to make the linkage arms of a suitable length to compensate. The amount of servo rotation is more than enough for my other application, operating post signals.

Jol

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grovenor-2685
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Re: Servo control of (ground) signals

Postby grovenor-2685 » Tue Oct 23, 2012 2:02 pm

We now have firmware available for the servo4 board to give up to 180 degrees rotation if needed, but I'm not sure if it can be set up with the setting box or will need a PC. Something to check.
Regards
Keith

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newport_rod
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Re: Servo control of (ground) signals

Postby newport_rod » Wed Oct 24, 2012 12:10 pm

Andrew
If you want to see for yourself we have implemented servo control with the MERG servo boards on the Fiddle Yard for Little Mill Junction (see http://www.newportmrs.com/clubgoingson.htm, towards the middle of the page). Come along to a Nagnag meeting (second and last Tuesdays of the month) in Newport and you can see how we've done it.
Regards
Rod

andrewnummelin
Posts: 169
Joined: Mon Jul 21, 2008 9:43 am

Re: Servo control of (ground) signals

Postby andrewnummelin » Wed Oct 24, 2012 10:26 pm

Gents,
Very many thanks for all the useful and interesting information, and the invitation. You've given me the leads I need to have a go to see see if I can achieve what I want.
Regards,

Andrew Nummelin


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