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Point Motor Position


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All the information is see / read implies that the point motor should be installed under the baseboard directly under the turnout / crossover. This means the tracklaying operation has to be 'interrupted' to drill the necessary holes through the baseboard for the point motor operating 'pin'. And you need to get it all lined up properly.

 

A more logical position for the point motor would be to the 'side' of the turnout, at the switch toe and offset laterally by (say) 15mm to 20mm from the track centreline. The advantages I see are:

 

  1. the location of the point motor is less critical
  2. installation can be done 'after' tracklaying
  3. can be installed either side of the turnout (space permitting)
  4. operation of the switches can be by a simple 1mm steel rod between the turnout and the point motor
  5. it's actually where there are installed in real life anyway

Despite the above, I don't see anyone using this method as the 'default 'installation method, only when it's impossible to install the point motor directly under the turnout (baseboard frame, turnout on a bridge, etc.).

 

What am I missing?

 

Ian

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Probably nothing, other than perhaps that:-

 

1. At one time 'point motors' were a rarity on the prototype, and so for a model they have to be hidden away under something, and...

2. Model point motors look nothing like the prototype anyway, and would be far too big in most scales.

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In 4mm scale, model point motors are huge, and difficult to hide under buildings and scenery. For example, the point this one operates has track either side of it, so it has to be some distance away, and the flat area where the tube runs was intended to be a level area of the goods yard where something big enough to hide the building would have been out of place. The point motor was fitted under what was planned to be an embankment leading up to a road overbridge.

 

post-7091-0-87401600-1445328499.jpg

 

Getting access for maintenance can be difficult too, without unsightly joins around removable buildings and sections of landscape. All but two of the motors are underneath on this layout, for these reasons, and the two on top are because the baseboard framing was in the way.

 

 

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Most people prefer to have the motor under the layout for ease of maintenance and wiring rather than buried in the scenery with a complex linkage. Drilling a simple 10mm hole through the baseboard when laying a point is a very quick operation.

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There seemed to be some rather odd bits of sprue with a PL10 point motor and adaptor base I bought a while back. One piece was definitely crank shaped and has been used as such as there wasn't room to mount the point motor in line. Nothing in any instructions says that is what it's there for but it is handy.

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I think that the OP is saying keep them under the baseboard but have the hole for the arm come up to the side of the track instead of straight underneath it. Then the motor is still hidden out of the way and means that you don't need to worry about how it's going to fit at the same time as laying the track. I've put in several myself this way. The downside is having to arrange a linkage instead of just coming up through a moving sleeper or similar (see the second picture in http://www.rmweb.co.uk/community/index.php?/topic/90326-another-kirkby-stephen/ for my attempt, sorry that it's not easy to see).

Wonder when we'll get to scale functioning point motors? Might happen some day.

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Actually, I was more thinking that the point motor should be offset from the turnout switches, but still mounted under the baseboard (with the usual hole).

 

That way tracklaying can progress without have to stop and sort out the point motor hole under the turnout. The hole could be drilled 'later' and the point motor fitted in the usual way, but the exact position wasn't so important..

 

All it would need is a short 'drive rod' (bent to length) to the side of the turnout switches, something that could be disguised as a real life switch machine. The 'drive rod' can be kept short or made longer if required.

 

Why don't I see anyone doing this? I must be missing something 'critical'.

 

Ian

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All it would need is a short 'drive rod' (bent to length) to the side of the turnout switches, something that could be disguised as a real life switch machine. The 'drive rod' can be kept short or made longer if required.

 

Why don't I see anyone doing this? I must be missing something 'critical'.

 

Ian

I think appearance is the biggest problem. Not as difficult to disguise as mounting the motor above the baseboard, but still an unrealistic object in a place where it would be quite visible. It would be difficult to ballast around, and keep the operating slot clear. The slot is under the tiebar when it's below the point, in an area ballast and adhesive needs to avoid anyway.

 

I agree it can be a pain to cut the slots while track laying, especially as I'm not very good at switching from one task to another, and it's likely to encourage more tea breaks, but I think it's worth the bit of extra effort.

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The main obstacle to a more prototypical arrangement is the very non-prototypical stretcher bars (aka tie bars) used in commercially produced pointwork.

 

If you are prepared to replace the stretcher bar then something like this can be done:

 

post-5673-0-16348900-1445350341.jpg

 

You should just be able to see the operating wire from underneath at one end of the first stretcher bar.  The stretcher bars are copperclad strip on edge with Ambis etched brackets for attachment to the blades.  The track is 7mm scale, 32mm gauge built with ply timbering and Exactoscale chairs.

 

Regards.

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It's good to hear all your views on this subject. Now I understand the pros and cons of the two options (under the turnout, or beside the turnout) for the under baseboard position.

 

I still like the flexibility the 'beside' option gives, although I can appreciate that in most layouts this is probably not necessary, or can be avoided by good layout planning (baseboard support positions, allowing space for the point motor). 

 

Ian

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