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Fulgurex point motor control

22526 Views 70 Replies 13 Participants Last post by  dwb
This week's project is to add control circuitry for a Fulgurex slow motion point motor. The photo below shows the parts I intend to use:

Those familiar with driving Fulgurex will probably think this is a bit over the top, but there is method in my madness and each component has its place in my scheme.

First, it is my intention in the longer term to drive the point motor via DCC, but there may be times when I don't want to have to go to the bother of addressing the motor via the control unit and then selecting the direction I want. To avoid that, I need a local switch. Some DCC point motor controls provide a facility for local buttons, but I'm not sure which those are and whether or not I will use them. In the meantime, I need to control the motor now because unlike Peco solenoids, you can't manually "flick" a Fulgurex. My solution to this need is to use a normally open, momentary action DPDT switch which can be seen in the left of the photo.

The momentary nature of the switch means that once the limit has been reached and the current is switched off, I can release the switch and there will be no current at all. This should avoid conflicts with any DCC control unit I install later. The drawback with this method is that I lose the switch acting as an indicator for the current setting of the point blades. The solution to this problem is to use one set of auxiliary contacts on the Fulgurex to drive the pair of LEDs which are also on the left along with the resistors and matching mounting bezels. This will provide a visual indication by the switch of the current setting. When DCC control is added, any changes caused by the DCC unit will be reflected by the LEDs. This circuit may also double up as input to a pair feedback sensors to provide PC control some time in the distant future.

The ceramic disc capacitor at the bottom of the photo is to provide a degree of noise suppression. According to LDT, the Fulgurex is rather "noisy" electrically and this is a good precaution. Once the motor is installed under the baseboard, I don't fancy lying on my back trying to retrofit these things later, so they're going in now.

The other two devices beside the capacitor are a pair of Zener diodes. This again is an LDT recommendation for reducing the voltage supply to the motor to reduce the change over speed. I'm doing this because the motor will be supplied at about 14v DC which is a bit on the high side.

I will be using the other pair of microswitch contacts to change the frog polarity on the point. The switch blades themselves are hard wired to the outer rails. This eliminates the potential for shorts should the microswitch change over before the moving point blade has ceased making contact with the outer rail. A short on an analogue DC layout is no problem, but it will shut down DCC which is not a good thing.

The black stringy stuff in the top right is heat shrink tubing which I will use to make sure there are no bare wires straggling about.

Now I just need to find something to mount the switch and LEDs on. Panel thickness is a bit of an issue for these LED bezels because the LEDs are quite small.

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Using Fulgurex point motors, or the very similar Lemaco type, with a diode matrix, it is possible to set up routes using a rotary switch. This does away with the need to set each individual point and is very useful for setting routes into storage sidings.

The club layout at the Clay Cross Model Railway Society has an array of 18 roads in the storage sidings, nine in each direction. Each one is long enough to hold two medium length trains, or one full length train. It is only necessary to control the points at the entry to the loops. At the exit from the loops the points blades are not fixed, they are sprung and the train just pushes through. No special wiring is needed to arrange this.

So how does the diode matrix work? The operator simply turns the rotary switch, to road 4, for example. A supply of 16v AC is fed into the rotary switch. Contact no. 4 on the rotary switch is connected into all the point motors driving the array of eight points via a diode for each one which sends positive or negative half wave rectified power to set them in the right direction. Normally it is only necessary to change to the next adjacent track as we run trains in sequence, and so usually only one or two points are changed at a time.

This is a good way to run an exhibition layout as we never need to make a physical check that all the points have been set correctly.

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For the purposes of clarification, I should like to add to the previous posting that each contact on the rotary switch is only connected to those points that you have to set to access that particular loop. For a set of nine storage loops the minimum number of diodes for a symmetrical arrangement would be three per contact, or 27 in total: the maximum for a ladder arrangement would be 45.


Nice looking panel.

I used to cut out a section of the tape equal to the diameter of the hole that I wanted to drill. Then I would use a punch to start the hole before drilling, otherwise the drill tip could wander about.


I agree: get a proper drill stand if you have somewhere to mount it. You will never regret it. I have been able to fabricate all sorts of things since I got mine years ago. I can buy steel offcuts, angle iron and the like, out of the bin at the local steel stock yard quite cheaply.

Engineering could take over from modelling.

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