Crab Comet conversion

Julian Roberts
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Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Mon Apr 01, 2019 8:58 am

Hi Allan! The Crab chassis is being painted but I hope to be able to arrange a test on Grayrigg before long with you. What I mean about modelling weight is the way a train stops and starts. It's got to be able to go slowly to before there is even a possibility it can start and stop realistically. DCC control can help of course but I haven't gone down that route. As can various types of controller even with straight DC .

I did make a video with my Q1 on Dubbieside of exactly what I mean but it is somewhere inaccessible on my pc. Here is what I think is a realistic minimum speed but it doesn't show a start and stop. This is the third loco I made in P4. There is no flywheel - there's no room!



Here is my fourth loco (just a new chassis under a 2nd hand body). It can run just as slowly but it is up to the operator to create the illusion by the quality of the start and stop....or not as in this case! :( This one does have a flywheel.



Both these locos have 1:108 gearing.

If the second video doesn't work it's at https://youtu.be/ApsQA44XqaE

Julian Roberts
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Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Thu Apr 04, 2019 9:00 am

Jol Wilkinson wrote:.... does anyone else find that the loose fit of the crankpin bush on a AGW (or even Sharman Wheels if you still have any) can cause a problem.

Loco "chassis" that will can be propelled or run smoothly when the crankpin nuts are loose sometimes develop a tight spot when the nuts are tightened. Loosened off, wheels rotated a quarter turn or so, or rocked back and forth and re-tightened and the problem may be cured. I should add that I use a GW quartering jig and LRM alignment jigs for setting up, having assembled the rods and broached them for a close fit on the crankpin bushes. However, there is more play between the crankpin and the bush than the crankpin and the rod. Opening up the coupling rod crankpin holes is usually the solution, but not an ideal solution. I wonder also if the bush holes are sufficiently concentric, especially on the brass Sharman ones.

I can always get over the problem but it usually takes a little time even with four coupled locos. So getting a consistent and close "fit" of the rods, pins and bushes seems a bit of pot luck. A threaded, concentric, bush which fits on the pin accurately would seem to be the answer.
.


I wrote to Colin at AGW to ask if he'd ever considered producing the bushes in a threaded version, though I described my reasons for wanting one (a long threaded bush would be useful if soldered to the return crank) rather than for the reasons Jol has described above. He replied (perfectly understandably) that this is a bit specialist, and that he could make a thousand and have them hanging about for years. (Perhaps if I'd quoted Jol's post above he might have been more interested...)

But if anyone else thinks this is a good idea, and is going there, maybe Scalefour North this weekend is a good time to have a chat about it with Colin, whether for my reason or Jol's - or any other for that matter.

Julian Roberts
Posts: 715
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Thu Apr 04, 2019 12:31 pm

Having disassembled the chassis I ascertained the middle wheel crankpins were not going to be removed without ruining them. So I got on with making my own equivalent of the Ultrascale recessed crankpin as previously described. Otherwise the chassis is ready to paint. The gears are now 1:120 and I have used another motor, abandoning efforts to remove the 1:90 worm from the previous one.

As well as reading it in the books, I have noticed for myself on today's trains vividly that a black underframe is anything but black and is covered with a film of yellowy/reddish dust that highlights all of the shapes. Yet I subconsciously still think it's "black" - I think it's the transparency of this film of dirt that mixes up my perception.

20190404_125755.jpg


Anyway I sprayed the chassis with primer and then satin black. After a couple of days I mixed up about four different enamels till I had roughly what I wanted and sloshed it everywhere, thinned down with white spirit, and a thinner still slosh over the loco body, with a brush, blowing to recreate the effect of the train moving through the air and the dust swirling around. I was aiming for something reminiscent of the dust from the red earth of Ayrshire, and rust.

Really my aim isn't so much realism as an excuse to make all the various bits I've patiently attached stand out - or at least be visible. All those sandboxes and sandpipes that took such hours - no point if you don't see them. Of course it's difficult to know whether I've overdone it or not done it enough. The great thing is that it can always be modified, especially if you're lucky enough to be in Allan Goodwillie's orbit!

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With trepidation I soldered the "Roberts Retainer" to the return crank and managed not to unsolder the rivet holding the eccentric crank. I then modified the second return crank to have the same arrangement. I was lucky that the return crank was just big enough to accommodate the retainer I had made.

20190403_110834.jpg


So now I am back to where I was several days ago, determining how many shims are needed to get the return crank to screw down to the correct orientation. Now however the return crank serves as a bush for all the rods too and winds on around 20 times.

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Julian Roberts
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Re: Crab Comet conversion

Postby Julian Roberts » Fri Apr 05, 2019 5:57 pm

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I'm pleased to say the screw-on return cranks that incorporate a bush for all the rods have proved their worth (in terms of the time and effort to make them) and, with nail varnish applied as a glue for the last two or three turns, are staying screwed down and in position through three or four hours running on my auto-reversing test plank. Thus I can say that, subject to them staying put, the loco is now a goer and ready testing in service... :!: :D The running is smooth enough that I feel reasonably sure if they come loose it is not because of a fault, and that some 243 Loctite Retainer will do the job more durably and they shouldn't loosen off again till I need them to.

20190405_174338-1.jpg


The gearing gives a more than reasonable top speed on my home layout controls, though strangely the same voltage gives less speed on club layouts. Yes there is motor whine at top speed, inaudible at an exhibition, but the loco seldom goes at that speed on the layouts for which it is intended. The slow speed is much better now with the higher ratio, improved yet further probably by the total clean up involved in stripping it all down for painting.

The videos are pretty duff I know but are there to prove something at least. Radio 4 was on at an ordinary listening level underneath the board to give some idea of noise level.


Regarding the weathering, I don't know if I'm in a hole but I'm definitely not digging any more till I next meet up with Allan who has promised a weathering session for our WS4Group mutual improvement classes. Sometime I'll get Rountuit and renumber the loco and give it a local shedplate; and finish final details like coal and coal rails, and some some further blackening.

Very many thanks to you Forum people especially Philip Hall, Davids Holt and Bradwell, and Allan Goodwillie, for your encouragement and many useful tips. Especially the tip re the Ultrascale recessed crankpin. Although I had to make my own (to be compatible with the AGW 1M thread) I don't know if I'd have thought up how to solve the problem of the return crank in that way otherwise. Next time I know to use the (Ultrascale) 14BA screw for any wheel that has a return crank, and their recessed crankpin.

Attached below a few more shots below taken at the same time. In ordinary light and at a distance the weathering doesn't seem extreme to me and does what I intended. Still to do is to somehow highlight the moving valve motion in a similar manner.
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Allan Goodwillie
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Re: Crab Comet conversion

Postby Allan Goodwillie » Fri Apr 26, 2019 7:59 pm

Hi Julian, :)

First time I have been on the forum for a while - just been trying to catch up on my own project. My goodness the crab is fairly coming on! I will be at Bonnybridge show tomorrow (Saturday) just to enjoy the show. :D

I notice Jol mentioned a few postings back about how sometimes when you tighten up the nuts the coupling rods sometimes bind, and most people open out the holes in the coupling rods a little more assuming that will cure it , and sometimes it does, but this is something I brought up in my loco building thread for beginners and the thing to check is the thickness of the connecting rod boss compared to the depth of the bush around the crankpin. What you want to make sure of is that the nut when tightened comes into contact with the end of the bush before there is any chance of it contacting the connecting rod boss. There has to be a working clearance/tolerance between the two otherwise they will bind. Opening out the holes increases the amount of slop and will lead to earlier wear and tear than is necessary. I know this is a very simple piece of advice, considering the complexity of what you have been building, which has been very absorbing, but worth mentioning as there will be others who have only built maybe an engine or two and have not even thought of this as being something to check as in most descriptions of how to get free running coupling rods nearly always concentrates on opening out the holes.

Grayrigg will be out of commission until next year I am afraid after the problems with the garage roof and the damage done. It is still leaking and some of the baseboards will have to be scrapped and started again, however all the scenery lifts off and I will take off the wiring looms before lifting the boards and seeing what can be salvaged - I think it may be next spring, if you can wait that long, sorry. :cry:

Allan :)

Julian Roberts
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Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Sun Apr 28, 2019 8:20 pm

Hi Allan thank you for getting back to me. I'm really sorry to hear of the damage to Grayrigg. Especially when you're wanting to concentrate on your new layout. Anyway the Crab performed its first goods test services very satisfactorily on Kettlewell and was passed for running there. I was pleased that propelling forwards (as well as backwards) while shunting there were no buffer locking issues. But the trackwork is kind to stock on that layout. Calderside will present a stiffer test. I won't post a video owing to the banter in the background - not for family viewing...

I fully see what you mean regarding tightening down the retaining bushes. I find as a normal experience the short AG bush is not long enough. I use a long one and file it down so it's just a little proud of the rod. So I have to buy extra supplies of the long ones and have lots of surplus short ones! I think the Crab is finished apart from the coal, weathering and changing the number to a Scottish one. Apparently this one was shedded at Fleetwood during the early BR emblem time. Now I've started completing the LMS Compound (some way to go...)

Couldn't come to Bonnybridge as I was cycling this weekend including along part of the Fort Augustus line.
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Last edited by Julian Roberts on Sun Apr 28, 2019 9:16 pm, edited 1 time in total.

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Allan Goodwillie
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Re: Crab Comet conversion

Postby Allan Goodwillie » Sun Apr 28, 2019 9:07 pm

Hi Julian, :)

The Fort Augustus line - that must have been lovely this weekend - Dave and I were planting out the back garden today and I did go along to the exhibition at Bonnybridge. I think the lads put on a good show and it was well attended on Saturday and with the AMRSS meeting being on on the Sunday I am sure they will have done alright financially. Not to worry about Grayrigg It will be repaired in time, but just not this year I still have water coming in from my neighbour's garage, but Davy has promised to get his roof done as well, so I will not be doing anything until after then anyway.

A discussion I had with the exhibition manager at Bonnybridge was that he was finding that he was being offered more and more small layouts and less bigger ones as the years are moving on. I am trying to make Scott's Road be compact, yet have lots of movement as it did in real life. This time it is the exchange yard that is central to the operation, but the length will be around 24/30 feet which makes it medium size and as big as I think I can manage in the car. :)

Taking Jean for a meal and attending the annual musical follies at Fingask Castle on Saturday, should be fun. ;) NO trains however, but beautiful views out over the river Tay from high up on the north shore. Been there twice before-the castle and gardens are stunning, would make a nice model.

Allan :)

Julian Roberts
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Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Sat May 18, 2019 3:43 pm

This is to (somewhat belatedly) acknowledge the mention in the Snooze from Will. My main reason for doing this thread was because I became known for the thread on gauge widening, where it was justifiably said "Why don't you do some modelling". This was to correct the impression that I never did any. I did a warts and all blog kind of thing, to encourage others to persist too. Hope I didn't have the reverse effect. Sorry that I'm no engineer and it all looks so crude compared with most modellers. And again many thanks for so many helpful hints.

The natural successor to this project is a 2-6-2 wheel arrangement. This will be a V1/3 from a well known kit designer where all the wheels will be individually sprung.

Julian Roberts
Posts: 715
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Sat Jul 27, 2019 3:33 am

To more or less wrap up this thread here is a video of the Crab stretching its legs at a certain iconic location that some may recognize. 7 coaches were handled with no slipping on the 1:100 gradient. I wasn't running at max speed just in case of any mishap (which did not occur) while I was distant from the controller - this was about 3/4 regulator.

Our group were guests of Chris Pendlenton for the day. The layout runs on DCC so the Crab couldn't run except on its own with the layout switched to DC. As well as preventing the realistically high speed running desirable on a big layout such as this, I can well see why my high gearing is unnecessary for low speeds with the sophisticated DCC control on this layout, and the motor whine counterproductive to the soundscape DCC enables, as in the next video, a 9 coach boat train leaving Collingwood Yard for the dock, top and tailed by big pugs. (Unfortunately I didn't record the completely believable start and stop which is the whole reason I want good low speed control).

We had many hours of faultless running. Big trains of wagons were propelled over the complex pointwork.
20190718_174920-1.jpg

I could forget this was P4 and I was as though 'really there'. Such a standard comes through attention to detail. For example, every one of the 200+ wagons has spring suspension and sprung buffers. Chris has written plenty over the years in MRJ about how he gets such running. But he doesn't write on this Forum and his methods are to some extent below my radar, relying as I do on material easily accessed on my phone while travelling about. His locos have individually sprung wheels, not the AG type of very light buffer coil spring where just the end stop is adjustable, but more near in design principle to those in Dave Bradwell's kits. Fiddly to build perhaps, but each wheel is therefore adjustable, just as the real thing was, to get correct weight distribution, as well as ride height. If there's anything I'm sure about after this build it's that the weight borne by ideally each wheel needs to be adjustable, particularly in the case of the front pony wheel which needs to have plenty of weight on it, to attain fully reliable track holding.




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Horsetan
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Re: Crab Comet conversion

Postby Horsetan » Sat Jul 27, 2019 1:30 pm

Julian Roberts wrote:.... a V1/3 from a well known kit designer where all the wheels will be individually sprung.


Not Worsley Works? (That's the only one I can think of....)

Julian Roberts wrote:.....His locos have individually sprung wheels, not the AG type of very light buffer coil spring where just the end stop is adjustable, but more near in design principle to those in Dave Bradwell's kits. ....


That's because Dave more or less productionised the Pendlenton ideas. The tail of the leaf spring is supposed to fit into the hollow Exactoscale grub screw, but sometimes it falls out of the bottom when you're picking the model up.....
That would be an ecumenical matter.

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PeteT
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Re: Crab Comet conversion

Postby PeteT » Fri Aug 02, 2019 9:58 am

Horsetan wrote:Not Worsley Works? (That's the only one I can think of....)


I would think it will be the Dave Bradwell kit - as aluded to with the springing - as seen at Scalefour North earlier in the year.


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