A lighthouse mechanism

Outside the fence.
BrockleyAndrew
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Re: A lighthouse mechanism

Postby BrockleyAndrew » Fri Jan 07, 2022 8:30 pm

Thanks Terry. Yes, that all sounds perfectly beyond me!

I took my son on the RH&D when he was at peak Thomas TTE phase but that was 15years ago.

Now that things are opening up again I'm keen to do a Bluebell trip while the kids are at school. If schools stay open....

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Julian Roberts
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Re: A lighthouse mechanism

Postby Julian Roberts » Sat Jan 08, 2022 8:52 am

Actually Andrew it was on your other general Dungeness thread I was hoping for an RHDR reference, sorry to go off piste on this one. You could surely model the track? - most of the time there's no train there after all. Here is a pic at New Romney showing the relatively overscale height and width rails - you might be able to work out if the smallest rail available would work?

20180801_133206.jpg


Just to correct the impression the trains are rather slow, here is a brief video from the observation car -

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BrockleyAndrew
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Re: A lighthouse mechanism

Postby BrockleyAndrew » Sun Jan 09, 2022 10:48 pm

Ah, thanks Julian, I'd forgotten the other thread! The way I envisage a trackplan is very much plank, to have a narrow strip (the line was dead straight and finished just before the lighthouse) with the lighhouse on the left so that the platform and station are behind the track. Depending on the depth of the plank, that would have a gentle curve of the RHDR loop entering the left front and departing the right front with no operational point/opportunity even if I had the skill to build or get my head around the scale conversions of the locos. The other thing that nearly curbed my enthusiasm for the layout idea was the realisation that the run around loop for a terminus with a tiny station still works out as a loooong plank. Trying to imagine the layout as a diagonal with more scenic space, more interesting for viewing, makes it so much bigger.

But you do have a point, one could just model the track of the smaller gauge to acknowledge it was there. Or keep the depth narrow and omit the light gauge.

On the lighthouse light front I have some cheap small Fresnel lenses for 3d game viewfinders on order, will see how suitable they might be. I've also measured up my paper lighthouse model (unbuilt) to do the dimension conversions. The model is 1/250. I intend to build it soon and make a mini diorama to test out layout ideas and calculate scalefour dimensions.

BrockleyAndrew
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Re: A lighthouse mechanism

Postby BrockleyAndrew » Wed Feb 09, 2022 7:49 pm

My family think I'm mad..... caught in the hallway trying to focus beams in the mirror using my smartphone light and cheap plastic lenses. I am very much not an expert in lenses and the physics around their use. I have calculated that the Lighthouse floorplan diameter at the top is 94 mm which means that my lens has to be a lot less than half (47mm) to be workable. My Fresnel lenses for 3D glasses arrived and are lovely and flat and thin but are focused for their 3D application and therefore would need to be the 3-5,inches away from the light source. I have scoured the internet for information but of course can't really find an answer to the question - does stacking Fresnel lenses in a small model reduce the lense distance. However, practical experiments seem to show that using multiple lenses reduces the physical length for focussing a beam. The current experimental set up has two thin Fresnel lenses being fed by a cheap small magnifying glass (plastic) which reduces the overall lens set up to around 32mm radius. Theoretically I am tortured about using magnifying lense plus two Fresnel lenses to achieve spotlight but it seems to work so I will probably go with that!

BrockleyAndrew
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Re: A lighthouse mechanism

Postby BrockleyAndrew » Thu Mar 24, 2022 8:00 pm

More cheap Fresnel lenses purchased and I can achieve a long focused beam with the lens stack 27-30mm roughly from the light source (my mobile phone torch feature which I have found from all this mucking about to be two square LEDs (?) side by side rather than one light) which works well if not quite scale accurately within the radius of the Lighthouse floorplan. The lense assembly will be around 40mm tall and I agree with the earlier suggestion on this thread that the rotation could come from below the floor and the light source drop down from the ceiling.

Given that I will have to distance the stacked lenses from the light source and knowing it will not be a dot centre point of a circle but a physical thing in the middle I think I have to make that the basis of the design and design the focus distance from it when bought.

So it needs to be a white light that can be placed centrally from above dropping 20mm from ceiling and be as small as possible so as not to add too much to the 28-30mm focal length of the lense assembly radius.

I'm working on an 8 sided design which is not the ten sided of the prototype but enough to look more multi beamed than 4 or 6 and the "flash" timing (10 seconds) can be worked out with rotation speed.

Hope that all makes sense.

Any suggestions most welcome.

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Neil Smith
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Re: A lighthouse mechanism

Postby Neil Smith » Fri Mar 25, 2022 11:34 am

Just a thought - but whilst my studying of physics was more than 3 decades ago, I am not sure you need the source of the light to be "central". As long as the axle about which it rotates is central, if you off set the light source via a crank type arrangement, then that will buy you more space to fit in your focal length. And you will still achieve the light beam going out in the directions you wish, and so achieve the blinking effect etc., whilst also not making the head of the lighthouse too large.

I cannot see a reason why this would not work, albeit with a slightly more complex arrangement for mounting the LED(s)?

All the best

Neil

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Guy Rixon
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Re: A lighthouse mechanism

Postby Guy Rixon » Sat Mar 26, 2022 4:37 pm

If the light source is moving fast enough, then you only need one lens to work optically and the rest can be opaque dummies. It just needs to go round fast enough to produce the right flash-pattern. In fact, that can also be done with a static lamp and rotating optics.

BrockleyAndrew
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Re: A lighthouse mechanism

Postby BrockleyAndrew » Sun Mar 27, 2022 5:58 pm

Thanks Neil and Guy,

Food for thought and I definitely hadn't thought using just one panel with dummies for the rest....

I've ordered a few mini LEDs to experiment with. They should arrive later this week.

Andrew

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Jol Wilkinson
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Re: A lighthouse mechanism

Postby Jol Wilkinson » Mon Mar 28, 2022 8:31 am

As I recall from my sailing days, the rotation of the lamp gives the impression of an increasing and decreasing brightness of flash when seen from a distance.

Flashing lights, such as on buoys, beacons , etc. are rather different with a "sharper" flash.


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