Subject:
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Re: New MOC: 4-8-4 Northern
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Newsgroups:
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lugnet.trains
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Date:
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Tue, 13 Jan 2004 07:54:26 GMT
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Viewed:
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2492 times
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In lugnet.trains, Shaun Sullivan wrote:
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In lugnet.trains, Mark Bellis wrote:
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In lugnet.trains, Shaun Sullivan wrote:
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(1) Working pistons; as with the Hudson, there are two per side - the drive
piston and the valve piston. The pistons here actually have the least
friction of any of my designs to date - on straightaways they work
brilliantly! On the curves, the drive wheels do not ride on the rails of
the track, so the pistons do not move.
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Could you try adding Walschaert’s valve gear, as I did with my British Class
9F 2-10-0 and LMS Garratt 2-6-0+0-6-2? You can use the ++ pieces for the
valve gear cranks and a dark grey 3+stud pin for the main rod crank with
model team wheels.
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Hi Mark,
Thanks for the feedback!
I finally tracked down some photos of your trains. With respect to the
Walchaert’s gear, are you referring to the following?
http://www.brickshelf.com/cgi-bin/gallery.cgi?i=334094
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That’s the one! I used the cam behind because it has 3 + holes. I tried making
expansion links but they weren’t strong enough, so I reverted to what you see
and fixed the motion in forward gear.
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I’m having a tough time pictureing your description ... do you have a link to
a clear image?
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I wish I had a digital camera to make explaining this easier!
I haven’t put cranks on my Northern chassis yet, so the picture was just from my
head! For the Northern I’ve used model team wheels with single 24mm pulleys
behind them as the means of attaching them to axles. A dark grey 3-axle+stud
piece is the main crank pin, with the stud in the pulley and the axle through
the MT wheel. The ++ pieces will sit on the end of these - the angle can be
tweaked as the stud of the pin with fix it in the pulley.
The frame is 2 studs wide at the bottom, using triangular brackets and double
right angle joints with 2-stud axles holdign them together. Dark grey axle pins
then hold the RA joints into technic plates on top, where conventional studded
parts take over.
The gears are as follows: 20:20:20 all at right angles between 2x 71427 motors
facing each other on top of a 4-wide studdd beam frame. The middle 20 tooth cog
is meshed with a 12-tooth cog underneath, and this has an 8 tooth cog on its
axle. The 8-tooth cog meshes with a 24t and then an 8t on the wheel axle, both
vertically downwards, supported by the triangular bracket frame.
The motors are higher up on the Northern chassis than on the 9F and Hogwarts
Express (Hall). They’ll be int he middle of the boiler - hopefully for you not
too close to the dry ice!
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I’ve not had tilt problems with my engines, but I usually suspend the wheels
off the rails altogether and use two technic 71427 motors to power them -
gear ratio 8-24c-8-24c-8 at motor level, with 20-12 from the middle 8 tooth
cog down to the driving axle with the valve gear on it. The engine has a
4-wide frame of technic beams, giving holes for gear axles and a strong
inner structure.
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I’ve thought about using motors as you described to turn the drive wheels, so
that they wouldn’t not have to drag along the tracks. The last time I truly
looked at this was with my 0-4-0 in an attempt to attain some working
linkages in very limited space, but I didn’t meet with any success. I should
look at it again here, since I have plenty of room.
You know, it might be that simply adding a motor could solve my problem here;
if the drive wheels are *always* moving, I think they could climb themselves
back up onto the rails quite easily when coming out of curves. The only
major challenge, as I see it, is trying to match the train motor speed with
the technic motor reduced drive wheel speed, so that most of the time
(except, presumably, on the curves) the two don’t have to fight each other at
all. Hmmmmm ...
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I always put the wheel centres where they should be on the prototype - given
that most suitable Lego wheels are a little too small for the prototype wheels,
the driving wheels are naturally off the rails, so the whole engine is a 2-bogie
loco with the wheels as extras. This gets ri of the tilt problem too. So far,
all my big steam engines have had the drive motors under the tender, so there’s
no wobble of the loco itself. I use 2x2 turntables to support the front bogie
of the 9F and Hall (the 9F has a tiny pair of wheels under its turntable to make
a bogie of 4 - but it’s hardly visible!). The tilt or wobble will only occur if
both bogies are motors supported only on their pins. If you raise the Technic
plate, through which the motor pin goes, up by 1 plate and make a 2x2 hole in
the bottom layer of plates, the motor will support the frame on a 2x2 hole,
eliminating tilt and wobble. Notice that bogie plates do not suffer like this -
there is no bezel at the base of the pin - you could always file it off on the
motor if nothing else works. I deliberately kept the wobble on diesels - it
makes them more dynamic for exhibitions!
The load on the driving wheels is only from the wheels and the valve gear - no
traction - so 2x technic 71427 motor is enough for 4-5 sets of coupled driving
wheels + valve gear. A gear ratio of 20:12 (speeding up the motors) is about
right for an engine running at around 50mph (3rd notch on a Lego controller is
56mph to 8mm:1ft scale, for a single train motor).
The Garratt was different, as it is designed to crawl at 20mph with 100 coal
trucks! This has 1 train motor and 1 technic motor at each end, with a
micromotor turning the rotating coal bunker!
When the 9F goes over a large enough hump, the cogs can rub on the track. This
was noisy on 12V track before I converted to 9V! T wheels will be quieter
though.
You might need these modified parts for steam engine valve gear:
Quarter bushes, made by cutting a small pulley in half on a sacrificial axle
driven by a fast technic motor. The motor is my lathe! Pins with 1 stud of axle
and bezel, made by cutting off the connector peg part of a connector peg/axle
piece. I wish Lego made these parts as they are so useful - I’ve used at least
50 of each!
Mark
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Message is in Reply To:
 | | Re: New MOC: 4-8-4 Northern
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| (...) Hi Mark, Thanks for the feedback! I finally tracked down some photos of your trains. With respect to the Walchaert's gear, are you referring to the following? (URL) having a tough time pictureing your description ... do you have a link to a (...) (21 years ago, 9-Jan-04, to lugnet.trains, FTX)
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