TOU 3 of 4

Next I moved on to the construction of the tie-bar mounts.  These are simply two cubes of the larger size plastic tube mounted on top of each other.  Two things to consider:

-          if you are cutting the tube, as I did, with a piercing saw do clean off the edges of the tube earlier to remove any plastic swarf still attached that may interfere with the smooth sliding of the tie-bar.

-          the height of the mount should be dictated by the height at with the point motor provides drive.  In the case of the Conrad motors that I am using, this is quite high and I wanted to make the connection at the same height.

These really are just one piece glued on top of the other.

After this, it was time to try the functional tie-bar out for size, to ensure that it slid freely.  I actually found that the fit was a little looser than I had expected from two adjacent sizes of tube.  However the amount of slack was not so great as to cause problems, and it gave me a bit of wiggle room for fitting them in place.

The pictures do show a slightly different order of fitting the mounts as some pictures were taken during the build of the initial TOU, and some during the batch-build of the balance of them.  The differences aren’t critical though, and just show that there are many ways to go modelling in P4.

This is the completed unit, with the functional tie-bar fitted in place.

Two points to remember, thankfully neither of which I fell foul of, but I’m sure that I came close:

-          The copper-clad strip should face the outside of the unit, so that the dropper tubes extend out over the edge.  This is probably the only critical bit of the entire process, as there needs to be clearance for the dropper wires to come down from the point-blades past the edge of the TOU, and then go through the dropper tubes.

-          If you fit both the mounts to the base first, without including the functional tie-bar, you won’t be able to slide it in to the mounts afterwards.  There simply isn’t the free room to do this.  So it does all need to come together in one go.

So that completes the building of the TOU.

(to be continued...)

TOU - 2 of 4

The first thing that I did was to make the functional tie-bars.  These will sit below the baseboard and have the task of holding the dropper wires that come down from the pointblades. 

Much is made of the torsional stresses that are put in dropper wires when they are soldered in place on turnouts.  I’m not sure how much I buy into this idea, unless the section under load is particularly short.  However I saw advantages in keeping the TOU and the pointblades physically separate:

To do this, I used some small bore brass tubing.  This needs to be just a little larger in bore than the wire that you choose to use for dropper wires.  In this size, brass tube is more easily cut by rolling it back and forth under a sharp scalpel blade to create a score mark than by trying to saw it.  Using cutters will, of course, simply close up the ends of the tube, which is no good at all.

The length of the dropper tube isn’t actually critical.  I used the length shown in this picture to make both tubes for this tie-bar.

The dropper wires are very flexible, and I didn’t need to rely on the accuracy of the functional tie-bar to keep the pointblades the correct distance apart.  Nevertheless, to ease the stresses and strains of holding the pointblades in place, I made the two dropper tubes 16.5mm apart.  This was measured on the copper-clad strip, and as you can see two saw cuts made for the tube to sit in before it is soldered.  This just helped keep it located correctly and at right-angles.

As you can see in the next picture, I later cut a further gap in the copper clad to insulate the dropper tubes from each other.

In this picture you can see that all of the tie-bars have been made.  I have four turnouts on the board that I am building, so four was the number that I made.

You can also see that the first functional tie-bar has been glued to a section of plasticard square tube.  This is the smaller section – in my case ¼” in size.  This was done simply with some two-part epoxy. Again, the alignment isn’t critical, but it should be roughly central, and roughly square, to the plastic strip.

The next, rather dark, picture shows the production of the mounting plates.  These are approximately 70mm by 30mm.  You could make them larger if you wished, but I wanted to be able to fit them reasonably easily underneath the baseboard.

The small squares of plasticard that are being fitted are an extra that may not be necessary for other modellers.  The smallest woodscrews that I have available to fix the completed units to the baseboard are still too long to go through the TOU, and then into the baseboard that is made out of 6mm ply without the ends of the screw bursting through the top surface.  Therefore by putting spacing plates, the screw goes fully in but the tip will not come out of the other side.  If you used thicker baseboard, or glued the TOU down rather than screwing it, these would not be necessary.

I made provision for three mounting points for the screws.  In practice only two, at either end, have proved to be necessary.  After the spacing plates were glued in place and dry, they were drilled with 2mm holes to take the screws.  Given that plasticard is fairly soft, this was just done with a drill in a pin-chuck.  There was no need for any machine tools or suchlike.

(to be continued...)

Turnout Operating Units - 1 of 4

I’ve been asked to do a write-up of the Turnout Operating Units that I am using on my P4 demo board.  I wasn’t going to do this until they had been installed and satisfactorily operating, although I had done a “finger-driven” test of how effectively they work.

These are certainly not an original idea.  I believe that the original Protofour TOU was produced on a similar concept, using sliding plastic curtain rail to provide the base.  The main criteria that I wanted to meet were:

• Mounted below the baseboard
• Cheap and easy to produce
• Robust but not necessary to be “engineered”
• Did not need to be relied on for gauging the switch rails

Turning to the last point, my philosophy was that these TOUs would drive the switch rails with an approximation of the correct gap between them.  However for the precise gauging I am using a “semi-cosmetic” tie-bar.  I use the term semi-cosmetic, as primarily the role is to look authentic, but it will also provide the exactness of the distance between the rails that cannot be produced from a flexible drive mechanism three or four centimetres below the railhead.

The materials used are all very commonplace.  You may have them already.  If not, all of them are readily available from Derek Russan at Eileen’s Emporium, and no doubt other suppliers.  I just know that Derek definitely does have everything available as that’s where I got most of my components from!  Usual disclaimer, no connection, etc.  The list is:

• Copper-clad sleeper strip. I had offcuts from track-building to use.
• Fine bore brass tube.  By fine, I mean something that will take a 0.45mm brass wire down the inside and be a sliding fit.  My tube came from some left-over from a High Level Models kit.
• Straight 0.45mm brass or nickel silver wire.  The sort that comes in 12” lengths from various sources.
• Thick plasticard.  I used some 60 thou that I had in the drawer, but the thickness is not critical as it is used to provide a robust mounting base.
• Two sizes of square Plastruct tube.  One that is a loose sliding fit inside the other.  The dimensions, again, are  not critical, and I believe that I used 5/16” and ¼” for my TOU. 

This is the tube that I used.  As they always say, other makes and flavours are available.  The TOU’s themselves are roughly seven centimetres in width, so you can make a number of the units from the two strips in each packet.

(to be continued...)

Tie-bars fitted

And in a burst of competent soldering, all of the remaining tie-bars went easily into place :-)

That's one of them.  Tomorrow I hope to fit the dropper wires to the point blades and connect it all up...

Flymo

Lesson for today...

Retro-fitting tie-bars (or stretcher bars to give them the proper name) is *never* easy when you've already laid the track, and ballasted up to a height that interferes with fitting them under the rail.

Oh, and as you tidy up the soldering on the first one, the joint breaks.

Argh!  Enough is enough, for tonight...

Wiring

A short preamble - I really don't like doing wiring.  It scares me.  Which is daft, as I've a Physics A-level, and I've re-wired an entire house before, so I should be comfortable about where the pluses and the minuses have to go.  But for some reason whenever it comes to wiring for models I have a mental block...

You may recall that it was quite a while ago that I finished track-laying on my "demo board" - this will be both a test track for my own use, and also a way of showing those interested in P4 modelling the different types of track that are available.  A while ago I fitted the power feeds to the tracks, and was able to get something running.  The next step is to fit the point motors and the uncoupling magnets.

First of all, an overview of the track-plan, drawn out in permanent marker on the top surface of the board.   Push-button switches have been fitted through drilled holes to provide the ability to just press switches along a route.  I thought that this would be easier, particularly for others that may have a play with it, than a more prototypical lever frame.  The rotary switch in the top corner is for selecting the power supply for each of the three roads.

And this is what it looks like underneath.  There are two separate power inputs - I wanted to keep the ones for the "trains" and the "track" separate.  At the moment the intention is to run this as DC, but I suppose that there is no reason why it wouldn't work equally well for DCC train control in future, if I decide to change.

At the bottom, the rotary switch feeds the three lines of track.  And at the top, the new wiring that I am now putting in.  The bus-bar has the feeds to the positive side of all of the switches soldered to it already.  The red wires are to the point motor switches; the pink ones to the uncoupling magnets.  It's probably an unnecessary distinction, but I can do it, so I did...

 

The track plan drawn on the underneath of the board helps me identify what is what - a tip picked up from somewhere on RMWeb I think, where it was used for a 2FS layout.  It's better if you use Templot to make it look smarter, but I ain't  that clever :-(

The next step is to install the point motors themselves.  For these, I'll be using functional tie-bars beneath the baseboard, and operating the point blades by means of wire running up through small holes.  This is the batch of  tie-bars being made out of copperclad strip.

So maybe I'll try fitting one of these tonight...

Flymo

Bl**dy computers...

Just a quick apology if I've missed anyone's vital news...

I rely on an RSS feed to tell me when a new post has been made on a blog.  It seems that at some point in the last couple of months, one of the automatic updates to Blogspot/Windows/Antivirus/whatever turned off all the alerts for me :-(

And I was just thinking that it was because everyone was busy, and quiet...

Flymo