Robin Sundt Echini

Signal Servo Control.

Building my own signals, I have been using HK5330 Ultra-Micro Digital Servos. These servos are very small and I could fit two into a base that was only 25mm diameter or just one as in this ground signal.

IMG_5472.jpg 

I used these servos for the first nine signals that I built but found that they are quite delicate. Of the 15 servos that I have, I lost four. Once programmed and set up they seem to work fine (I do hope they continue to do so!!) but they are prone to rapid “jump” movement while programming them and that destroyed those four. It seems that my signals are stronger than the servos.

For the next set of signals, I also found that I did not have enough space to drill a 25mm hole in the baseboard, so that led to a re-think.

I acquired some rather stronger and bigger servos: Tower Pro SG90s. However that, and the need for a smaller hole in the baseboard, meant redesigning the holder for the servo.

So, back into FreeCAD to create a new holder. This is designed to screw under the baseboard with just a 10mm diameter hole poking through into which the signal is mounted.

FreeCAD Single.jpg 

I created both a single option as above and a double option for junction signals. With the servos mounted, the two types look like this with a single signal and the basic chassis of a junction signal.

IMG_6417.jpg 

 So far, these larger servos have proved to be much more durable. The 3D printer has been working overtime to print the holders and the basic chassis for the next nine signals, which is the easy bit - all the brass and wire parts take lots of time, but being in hibernation means that there IS lots of time!

So, onward and upward.

Stay safe, all the best

Robin

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Penrhos1920
Robin, that second design looks great.  How does the above baseboard part separate from below the baseboard part?
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Robin Sundt Echini
The advantage of the original design with a 25mm hole was that you could build the whole signal and then install it from above the baseboard. The reduction to a 10mm hole meant that it was necessary to compromise. Before installing the signal, the whole unit is put together including the wires (0.4mm) that run from the servo to the balance beam and the servo is adjusted for the correct range of movement. The light is also installed with its cables coming out of the bottom of the signal upright. The actuating wire at the servo end is only bent through 90 deg, so that it can easily be removed from the servo arm.
The base unit, including the servo, is installed under the baseboard. The 10mm cylinder is designed so that you can shorten it for thinner baseboards. The signal is then installed from above, feeding the actuating wire and the light wires through the hole in the middle. The signal upright is a tight fit into the base unit so it is not normally necessary to glue it in place but, if it is a bit loose, I put some contact adhesive round the base of the upright, this hold the signal upright but can fairly easily be removed if necessary. Once installed, the actuating wire has to be reconnected to the servo arm and the end bent over 180deg to keep it in place. 
Reconnecting the servo is a bit fiddly particularly if access is difficult but, for the few times that it needs to be done, it was not worth trying to build a "quick release" mechanism, which would be complicated (in fact, I can't think of an easy way to do it!).
Regards
Robin
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Julian
Snip>>>
Reconnecting the servo is a bit fiddly particularly if access is difficult but, for the few times that it needs to be done, it was not worth trying to build a "quick release" mechanism, which would be complicated (in fact, I can't think of an easy way to do it!).
Regards
Robin

Hi Robin,
you could put the whole Signal/Servo unit together and adjust it before planting it, as you described, but complete the z-bend of the wire in the Servo Arm at that stage.  The Servo Arm can then be unscrewed from the Servo, to separate the signal.  The Servo Arm then stays on the control Wire, to be dropped through the baseboard and then re-placed on the Servo and screwed again.  If required a small split cap, of similar design to the 25mm supplied one, could be dropped in the smaller hole.

Alternately, the Control Wire could be kept absolutely straight and connected to the Servo Arm with a small Pushrod Connector {# 70 3454 from Multiplex Modelsport} {also called Mini E/Z Connector - from Du.Bro}.  Both of these are connectors from the radio controlled aeroplane world, which almost all of those type of shops should have.  You might even have enough room for a collar, obtained from the smallest size Choc-Block brass insert, to join a 2-part Connector Rod.  That's a really cheap joiner and if space is an issue, they can be cut into 2 x single screw Collars.

Julian
{Edit:-  to add that there are 2 sizes of servo arm hole sizes, so it's worth speaking to the shop before purchase of Servo Arm connectors, to get the right size of Connector pin for your Servo size.}  I thought a picture might help, too, obviously it's the brass collar look-alike, with the Connector Rod through it and the clamping screw.
DSC01552.jpg 
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Stephen Buck sbuck
I've been adopting a similar arrangement, assemble on the bench, for New South Wales pattern Upper Quadrant signals.  I've added a 2:1 lever at the base, to make initial setup easier, i.e. to get the servo arm horizontal in the mid (caution) position, and, as the weakest link in case anything goes wrong, the rocker arm breaks, rather than the signal, not that I've had one break yet.  I believe the UK had similar signals on the Great Central.  In NSW, lamps on these signals, and on mainline colour light signals, followed the indications on a mechanical home arm above a distant.  Stop red over red, caution green over red, clear green over green.
   2019-03-24 10.14.00.jpg
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Stephen Buck sbuck
I'm building McKenzie and Holland Ground Shunting Signals and Catchpoint Indicators for my Gordon layout, based on a steam era Sydney suburban station in the 1920s. These signals were supplied to the NSW Railways prior to 1912, and for some decades later to the South Maitland Railway.

While normally ground mounted, the South Maitland Railway had some post mounted examples

They comprise an etch, 3D printed parts and brass tube, and are lit by 0.8 mm dia DCC Concepts nano LEDs. Drive is by a 9g servo. As with other signals I build, they are assembled and tested on the bench and pictures and then placed in a standard socket on the baseboard.

The pictures and short video show a ground shunting signal.

I think they are a particularly smart looking ground signal. The last one was removed from service in Hamilton NSW in 2014. McKenzie and Holland supplied signals to other Australian and New Zealand railways, but this pattern of ground signal was not used by other railways in the region. I'm aware that some UK railways purchased signals from McKenzie and Holland. Did any use these ground signals?


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Bunkerbarge
Superb Stephen, absolutely superb.
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Stephen Buck sbuck
Thanks mate!
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