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A prototype TOU


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I've nearly finished laying track on my P4 competition layout, so my thoughts turned to how to drive the turnouts. At the Tonbridge show this year I picked up one of the C&L memory wire experimenter kits, and my first tests seem to have great potential. I've used two sizes of Evergreen extrusion that fit nicely together, and all the working parts are internal, so it's screened from draughts and suchlike, (which reportedly seems to be an issue). The basic mechanism is working well, now all I need to do is fine tune the throw, and work out a way to drive the microswitches to switch polarity. More will follow.

 

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Well, I've managed to overheat my first piece of memory wire! With the short throw I require, (about 1.5mm) I was using a wire with a working length of 50mm, and there just wasn't enough pull to operate a microswitch positively, and cranking up the power to see if that would help wasn't entirely successful. :)

 

So, I need to rethink how I rig the wire to see if I can get a couple of lengths in there to increase the pull, hopefully wired in series to avoid the resistance dropping too low.

 

Oh, and as I had to take it apart again, here's a pic of the innards:

 

post-6908-12591568560291_thumb.jpg

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Success! The Mark II version seems to work well. The wire is now twice as long, with a loop around the sprung end. The instructions warn against sharp bends, so it's looped around two pins this time to avoid this. Here's a pic that I've roughly sketched the internal layout on, hope it makes sense:

 

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I've fixed an offcut of the smaller diameter box section onto the slider to act on the microswitch, which for the moment is just tacked on. Epoxy should do the job for the final fix. I'll also fit a mounting plate on the bottom once I find my 40 thou plasticard.

 

Now to work out dimensions for the install units.

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  • 1 month later...
  • RMweb Gold

A neat and impressive design! Far better than the cobbled together lash-up I just spent the last two days on... wish I'd found this post before!

Incidentally, I've opted to use double pole switches for turnouts to avoid the need for microswitches. One less complication!

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Hi Adrian

 

It's changed again, slightly! The basic concept is the same, but I've had to add an external spring as the internal one just wasn't quite strong enough to hold the switch blades closed. I'm also driving them from a DPDT relay now, one side for the supply current, and the other to switch the V. I'll post a pic later, as the camera is on charge at the moment.

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Here's the pics I promised:

 

post-6908-12626914680257_thumb.jpg

 

The relay is switched by a Hornby accessory controller, and the power to the TOU is from a 5V bus, (the yellow and black wires). The other side of the relay does the vee. You can see how I've modified the original, the actuator is rotated through 90 degrees so it's wide side down, I've added mounting brackets with outsize holes to tweak the dead position, (you'll see why in the next pic), and the drive pin is now mounted in a bit of brass tube. I've also added a 2.2Ohm 5W resistor to prevent any excess current draw and slow down the actuation slightly.

 

And the tiebars:

 

post-6908-12626917581174_thumb.jpg

 

This is the one I'm fitting at the moment, as you can see, it's not quite aligned correctly, so the outsize mounting holes will allow me to shift it around 'till it's nicely lined up.

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Hi

That is a very neat job.

A couple of questions if I may...

 

How long does it take to move the point blades from one side to the other?

 

Also have you had any issues using the relay to switch both operation and frog polarity?

I was wondering that as the relay would operate immediately and the switch rail would still be closed onto their stock rail a short would occur within the frog. Unless the switch rails are bonded to the adjacent stock rail and insulated gaps have been left somewhere in the closure rails, making the frog totally insulated from the rest of the point? As there is no picture of the whole point I'm unable to tell if this is the case. :unsure: :unsure:

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  • RMweb Gold

Thanks for the update Al. Along with Brian I also have a query. I note you're not using a safety spring in addition to the return spring. Do you feel that's unecessary or are you just happy to take the risk!

 

In answer to Brian's question, hand-built turnouts will always have crossings that are electrically isolated from the switch blades, so there is no danger of a short.

 

With my experiments I find the initial throw is fairly quick (1 sec?) but the return takes a little longer (3 secs or so)

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That is a very neat job.

 

Ta!

 

A couple of questions if I may...

 

Of course. :)

 

How long does it take to move the point blades from one side to the other?

 

Not timed it precisely, but I'd guess about half a second. You could change this with a different resistor and playing with the spring tension if you wanted, but it looks about right to me.

 

I was wondering that as the relay would operate immediately and the switch rail would still be closed onto their stock rail a short would occur. Unless the switch rails are bonded to the adjacent stock rail and insulated gaps have been left somewhere in the closure rails, making the frog totally insulated from the rest of the point?

 

I did originally have the switch rails wired to the vee, but on further thought, came to the same conclusion as you, so now they're bonded to the stock rails. They were always isolated from the vee.

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Thanks for the update Al. Along with Brian I also have a query. I note you're not using a safety spring in addition to the return spring. Do you feel that's unecessary or are you just happy to take the risk!

 

Frankly, it just struck me as over-engineering. With the way I have things set up, the only risk of damage is if someone physically tries to move the switch blades/tiebar whilst the TOU is activated, and that struck me as unlikely. There is enough play in the system to allow for, say, a wagon being pushed backwards through the point set the wrong way, I think that's where the closer tolerances of P4 help.

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  • RMweb Gold

Frankly, it just struck me as over-engineering. With the way I have things set up, the only risk of damage is if someone physically tries to move the switch blades/tiebar whilst the TOU is activated, and that struck me as unlikely. There is enough play in the system to allow for, say, a wagon being pushed backwards through the point set the wrong way, I think that's where the closer tolerances of P4 help.

 

Ok Al, sounds reasonable to me! I think the idea of the safety spring in the C&L notes was to prevent damage from the memory wire itself introducing too much stress. I guess if your calculations for length of wire is accurate enough then this will be overkill.

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  • 1 month later...
  • RMweb Gold

Hi Al, having now spent some time fine-tuning my own version of this, I've realised there may be issues with memory wire actuators if you try to operate a number at the same time. Can I ask what ampage your 5v bus is? How many TOUs do you think you can operate simultaneously?

I'm currently using batteries to power two TOUs (for an Inglenook) but I'd prefer to build a power supply for them, and in the future I hope to build a somewhat more complex layout!

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