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Author Topic: New coupler development (was Coupling survey)  (Read 24453 times)

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Online Chris in Prague

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Re: Coupling survey
« Reply #165 on: July 10, 2015, 07:23:22 am »
That's excellent news.

Offline belstone

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Re: Coupling survey
« Reply #166 on: July 10, 2015, 12:07:16 pm »
One (and hopefully only one) last round of fiddling still to do:

1. It occurs to me that the central buffer might make the vertical post above the delay bar redundant.  Its purpose is/was to provide something for the drawbars to push against when propelling vehicles, and to stop the drawbar from dropping down behind the delay bar and locking the whole thing solid.  I'm going to build up a few with the vertical post snipped off and see if that works.  If so it will make the coupler look neater and save a bit of space on the etched fret.

2. The drawing needs to be reworked again to extend the support channel for the shank forwards a bit, making the coupler stronger and easier to assemble.  It will also make for a much stronger short shank hook-only version, for locos with NEM pockets that stick out further than they should (e.g. Dapol Class 26). I'll also put another half-etch line at the back end to make it easier to cut the assembly to length for the NEM version.

3. I need to find a source of flexible steel tube, internal diameter around 0.8mm to stick on the end of the drop arm.  The stuff I am using was bought at an exhibition about 30 years ago and was intended for wire-in-tube point operation, but I'm struggling to find anything similar.

Then I need to either knock "Belstone" into exhibitable shape or build a small demo layout and take it to a couple of shows so people can see that the coupler actually works.

Offline busbar

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Re: Coupling survey
« Reply #167 on: July 10, 2015, 02:12:11 pm »
I have followed your progress reports with great interest and very much look forward to the finished product being available: from your reports it is obvious that it will be very well researched and developed item.
Good luck with the search for the tube.

Dave

Offline belstone

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Re: Coupling survey
« Reply #168 on: July 12, 2015, 11:52:41 pm »
I got a bit sidetracked resurrecting old Poole relics this weekend, but still found time to test my idea of removing the vertical bar.  It works fine- call it Mk 3c. Here's the current state of play, unpainted, on a Farish 16 tonner, showing just how neatly I can bend the drawbar loop with my simple jig. I'm starting to think this might just be a viable product.


Offline belstone

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Re: Coupling survey
« Reply #169 on: July 12, 2015, 11:59:58 pm »
The "thirty quid special" - Farish 4F (bought as non-runner, 20) with a couple of wagons picked up unboxed for a fiver each.  Loco has the Mk 3c plain hook (no loop).

Offline Newportnobby

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Re: Coupling survey
« Reply #170 on: July 13, 2015, 10:33:04 am »
Can I ask if it would be possible to post a pic of a couple of items of stock coupled with standard couplings and one with your Mk3 couplings for comparison of closeness please?
 :thankyousign:

Offline belstone

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Re: Coupling survey
« Reply #171 on: July 13, 2015, 11:59:15 pm »
Can I ask if it would be possible to post a pic of a couple of items of stock coupled with standard couplings and one with your Mk3 couplings for comparison of closeness please?
 :thankyousign:


It depends how they are mounted, and what spec the original coupler pockets are.  If you do away with the pockets and mount the couplers direct to the chassis you can close the distance right up until the buffers are almost touching, but that isn't great on curves.  From the left: Mk3c in NEM pockets (but the upper vehicle with a longer shank than it actually needs): standard Rapidos: body-mounted Mk2 couplers (same basic dimensions as Mk3)



These three wagons are all on body-mount Mk2s, about the same distance between them as Peco Elsies:



Standard N gauge on the left, Mk2 / 3c combination on the right:


Offline Newportnobby

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Re: Coupling survey
« Reply #172 on: July 14, 2015, 10:22:26 am »
Thanks very much for taking time out to do the pics :thumbsup:

Offline belstone

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Re: Coupling survey
« Reply #173 on: July 14, 2015, 11:20:51 am »
Had another test session last night, still getting about 90% reliability (three failures in thirty shunting operations) which isn't bad considering I have a mixture of unmodified Mk2s with three different loop designs, reworked Mk2s with new loops, Mk3b and Mk3c, and three different designs of magnetic drop arm. That tells me these things aren't especially fussy about being assembled accurately. One derailment (early Mk2 with incorrectly shaped loop fouling a buffer), one failure to couple (Mk3b in floppy NEM pocket pushing the hook off-centre) and one failure to uncouple (loop on an early Mk2 dropping over the back of the delay bar on a Mk3c).  If one of these couplers doesn't work, there is always a reason.  I'm no longer getting unexplained failures.  Should get the Mk4 drawings done this week and provided I don't screw them up (again) that will be the version that goes into production. Stronger shank attachment, no vertical bar and the back end of the delay bar slimmed down slightly to improve buffer beam clearance on close-coupled installations.

Still need to investigate alternative plastics for the 3D printed NEM adapters - the first batch have a slightly greasy finish and don't seem to take cyano very well even when "keyed" with abrasive paper. I also want to try slightly shorter bar magnets as I think they will work better with the straight drop arm and make the positioning of vehicles over the magnets less critical.  At the moment they have to be placed within 5mm either side of the magnet centre point, which is no problem with locos that run 100% at very slow speeds.  But not every N gauge loco is as good as the 4F and Class 26 that I was using for last night's test.


Offline belstone

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Re: Coupling survey
« Reply #174 on: April 28, 2016, 02:27:00 pm »
Whatever happened to my coupler project? Well... I started increasing train lengths and ran into problems.  Unexplained derailments, especially on curves, and couplers locking up and refusing to uncouple.  Then I had to put modelling on one side for a while due to other commitments, and I pretty much gave up on the coupler project.  But at the club last night I was talking to a few people about my attempts to design my own coupler system, and found myself thinking it would be a shame to abandon the whole idea when I had got so close to a coupler design that worked.

So I had a very close look at what was going on with the derailments.  I found three causes.  One is that the delay bars on the last batch were fractionally too long, and in certain circumstances the raised loop of one coupler was getting snagged under the delay bar of the other.  That's easy to fix.

Second cause is trickier, being a fundamental design flaw.  The pivot for the loop sits slightly lower than the hook, so the loops are pulling at a slight angle.  Only a few degrees, but with enough load on them they try to straighten up and lift the front wheels of the first or second wagon off the rails. I have sketched out a revised hook design that allows for a straight pull, need to try and remember how the CAD drawing package works so I can draw it out properly and check that all the other bits still fit. I might be able to shorten the distance between vehicles slightly as well which would be a nice bonus.

Third cause - my idea of extending the shank to form a central buffer is a bad idea.  When propelling vehicles round curves with the loops in the "delay" position the shank-buffers tend to slide sideways against each other and override.  When the track straightens again they lock up and force the vehicles sideways off the track. I can't make the buffers any bigger or they will interfere with the ends of the hooks.  So I am going to try a bar on each hook, extending downwards and at a 45 degree angle sideways.  The idea is that the bars on each vehicle meet in an "X", allowing sideways and vertical movement. Not sure that will work propelling 30 wagons round a 9 inch Setrack curve, but it's worth a try.

So I still haven't given up on the design, not least because it should work with under-track electromagnets, which would be far better in many ways than permanent magnets between the rails - no need to get rid of steel wagon weights for starters.

Richard

Offline busbar

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Re: Coupling survey
« Reply #175 on: April 28, 2016, 03:37:00 pm »
Richard

I followed your earlier efforts with interest so am very pleased to hear that you have not abandoned the project. I look forward to further progress reports.

Dave

Offline Newportnobby

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Re: Coupling survey
« Reply #176 on: April 28, 2016, 04:24:15 pm »
I have been holding off progressing my small end to end layout as your project was sounding better than the Dapol easi-shunts and....................sorry, Richard, I'm lying through my teeth there but it struck me as a good excuse for me not making any headway :-X
I have followed things with interest and will continue to do so so please keep us informed.

Offline belstone

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Re: Coupling survey
« Reply #177 on: April 28, 2016, 04:29:02 pm »
I have been holding off progressing my small end to end layout as your project was sounding better than the Dapol easi-shunts and....................sorry, Richard, I'm lying through my teeth there but it struck me as a good excuse for me not making any headway :-X
I have followed things with interest and will continue to do so so please keep us informed.

Oi! That's MY excuse for not building a layout.  :D

Offline Newportnobby

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Re: Coupling survey
« Reply #178 on: April 28, 2016, 04:30:09 pm »
I have been holding off progressing my small end to end layout as your project was sounding better than the Dapol easi-shunts and....................sorry, Richard, I'm lying through my teeth there but it struck me as a good excuse for me not making any headway :-X
I have followed things with interest and will continue to do so so please keep us informed.

Oi! That's MY excuse for not building a layout.  :D

A plagiarist am I :angel:

Offline 25901JFM

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Re: Coupling survey
« Reply #179 on: May 01, 2016, 04:21:24 pm »
This is something that interests me and would love to hear more on this project.
John

 

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