Backdrives on flatbottom S & C .

Discuss the prototype and how to model it.
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Re6/6
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Backdrives on flatbottom S & C .

Postby Re6/6 » Wed Dec 14, 2011 1:03 pm

A P-way question.

What would the minimum crossing angle be on flatbottom pointwork to have backdrive mechanisms fitted?

I'm building some BV9.25 and BV10.75 degree crossing angle pointwork and would like to build and add some cosmetic backdrives. Would these be of too sharp angle to warrant them on the real railway?

Perhaps I'm looking for 'modeller's licence' here! ;)

Advice and opinions would be very welcome. Thanks.
John

wally

Re: Backdrives on flatbottom S & C .

Postby wally » Wed Dec 14, 2011 10:16 pm

Back drives are subject to the geometry of the switch element of the S & C not the crossing angle ie. the "letter" portion of the turnout description not the numeric portion, the "BV" part of the reference in your case.

I suggest you may find the answer to the modern requirements at the following link.

http://www.rgsonline.co.uk/default.aspx

Happy searching

Wally

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Re6/6
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Re: Backdrives on flatbottom S & C .

Postby Re6/6 » Thu Dec 15, 2011 6:50 pm

Many thanks Wally. :D
John

doggeface

Re: Backdrives on flatbottom S & C .

Postby doggeface » Fri Dec 16, 2011 5:07 pm

A very interesting question! Pity that I have no idea what it is about -- what chance of a quick insight,

Regards


Peter

Jan
Posts: 80
Joined: Mon Aug 11, 2008 3:41 pm

Re: Backdrives on flatbottom S & C .

Postby Jan » Sat Dec 17, 2011 12:37 pm

doggeface wrote:A very interesting question! Pity that I have no idea what it is about -- what chance of a quick insight,

Regards


Peter


Hi Pete,

Me neither, but a quick keyword earch in Google (other search Engines are available..) came up with this:
The backdrive is a mechanism which distributes force throughout the length of the switch in order to move the rails more smoothly. It is a system of levers which are bolted together, with fulcrums mounted on the sleepers.


Cheers

Jan

wally

Re: Backdrives on flatbottom S & C .

Postby wally » Sat Dec 17, 2011 8:00 pm

In anticipation of this query, whilst en route to Plymouth Station this afternoon I took these two pictures as an attempt at an explanation.

Firstly as stated the backdrive is an arrangemet of "traditional tiebars" in a modern turnout, which are coupled together either mechanically from a single drive source (think point motor in modeling terms) or a series of electrical / hydraulic / pneumatic (as appropriate) actuators all working to a single controll signal, which allows the longer switch blades of a modern shallow angled high speed turnout to move throughout their length without flexng or deviating from constant gauge

DSCF1748.JPG

This shows the general layout with only a single backdrve on the relatively short switch rail, on a longer switch there will be additional units with the spacing reduced to just a few sleepers between them; hence the original question.


DSCF1749.JPG

A detail close up showing the mechanical arangements of the auxillary drives, all other operated systems will just look like a series of clamp lock actuators.


H T H

Wally
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craig_whilding

Re: Backdrives on flatbottom S & C .

Postby craig_whilding » Sat Dec 17, 2011 9:52 pm

Any idea what the wire clipped along the stock and switch rails is for? Something to do with track circuiting or a type of tell tale in event of failure? Looks like it'd be about the same to model as the mechanical lubrication pipework on a steam loco..

wally

Re: Backdrives on flatbottom S & C .

Postby wally » Sat Dec 17, 2011 11:25 pm

Thats the point heater cable for frost prevention, it's just a heavy duty piece of resistance wire inside an electrical insulator; well thats the simple way of describing it!

Wally

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Re6/6
Posts: 492
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Re: Backdrives on flatbottom S & C .

Postby Re6/6 » Sun Dec 18, 2011 9:44 am

Thank you Wally for answering Peter's question and the very useful snaps. Just what I've been looking for! :D
John


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