Turnout operating mechanism

[Richard Hall]

Something that might be of interest.  I'm building a very small layout to use up my last N gauge bits and try some experiments with couplers and ballasting before I take the plunge into 2mm.  Trackwork is Finetrax which is of course very similar to Easitrac, and I needed to come up with a turnout operating mechanism.  The main problem was that I wanted to be able to operate the layout from either side, and for storage reasons I didn't want any control rods etc sticking out of the sides.  I like the simplicity of solenoid point motors, and the built-in switch on the Seep ones makes frog switching very straightforward, but there was no way a Finetrax turnout would survive having one of those connected to it.  And of course with hand-built turnouts the throw and the friction on the tiebar vary from one to another, and there is no over-centre springing to lock the blades in place.  All very tricky.

 

Here's the solution I came up with. This is the fiddle yard turnout which I did first: it has been much butchered in various experiments and looks a bit rough. Blades are in the centre position so that I could centralise the motor.  They don't usually sit like that.

 

 

Cranked arm made from 0.4mm piano wire, running down through a small bore brass tube about 40mm long. The arm needs to be isolated from both rails as the design of the Seep motor means it will be "live" to the centre contact on the built-in polarity switch.

 

 

Forked tube attached to the lower end of the operating pin, upper end cut short.  Piano wire actuator bent over 90 degrees to engage with the fork.  Two slotted mounts from U section brass to adjust the distance between the motor and pivot, allowing the force exerted on the actuator to be varied.  The motor needs to be slid outwards until the point blades only just have enough springing force to stay in contact with the outer rails.  They really are very lightly sprung, which should stop them being hammered to death. There is more than enough friction in the solenoid itself to stop it from creeping back towards the centre position.  Once thrown it stays thrown, even if you try to push the blades across by hand.

 

I have now built three of these and they work nicely.  Since the actuator converts linear to rotary motion the point motor can be positioned anywhere in a 360 degree circle around the pivot tube, which is handy if you have several turnouts close together.  I don't yet know how long the piano wire will last before it fatigues and snaps - I have put one through about fifty cycles before I got bored and it didn't break. It is very easy to replace if it does fail.

 

I will make up some small ramps on pins to plug in over the tiebar and crank, to hide and protect them.  I'm pretty sure this isn't actually my design, but something I read in a model railway magazine a long time ago. Hopefully others will find it useful. I did a fair bit of hunting around on the Internet and couldn't find anything about using solenoids with code 40 track.

[66C]

Hi Richard

 

An even more discreet method is to place a crank under the baseboard and only have the operating wire passing through to the tiebar.

 

The picture shows the method for a Fulgurex motor but solenoid types could be used in a similar manner.

 

 

The omega loop is made from copper electrical cable and protects the tiebar from excessive motor travel and in the case of a solenoid the shock of movement.  Squeezing or stretching the omega loop also provides fine tuning for the tiebar movement.  It is easy to install since the crank can be put in position first and then the motor added.

 

Regards.

[Richard Hall]

I did think about putting the crank underneath the tiebar but that would have made it impossible to change if it broke. Solenoid motors are brutal devices and I'm not sure an Omega loop would be enough to protect the blades, although it might work if it was made from thin piano wire. I still have one turnout to do, and might try using this crank and pin method as I agree it is a lot more discreet.

[Ian Morgan]

I found that the built in 'switch' on Seep motors was rather unreliable, being just a washer sliding across tinned PCB pads. You might find you have to add a proper microswitch to switch the frog at a later date.

[Izzy]

I use piano wire of differing thickness as point acutators with hacked servos and find that it is very resilient and resistant to 'giving' over time. It will fracture/break if bent back and forth at a sharp angle at a fixed point, but is otherwise good and reliable to use.

 

Izzy

[Richard Hall]

I found that the built in 'switch' on Seep motors was rather unreliable, being just a washer sliding across tinned PCB pads. You might find you have to add a proper microswitch to switch the frog at a later date.

 I have found they are usually OK provided the motor is operating along its full travel, but failing that I like to use double-coil self latching relays, 12 volt 2 amp rating.  They switch using the same feed as the motor and have a duty life of around 100,000 operations which should be enough. Omron G6SK-2 or equivalent.