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Here are the photos of my new Rail Crane with Power Functions:
http://www.brickshelf.com/cgi-bin/gallery.cgi?f=287011
It’s an 8mm scale model of a Cowans Sheldon 76T crane. Some details still to
finish - I want to make sure it passes the scale load lifting test first. The
scale load will be 6 full battery boxes, equivalent to 76 tonnes in 8mm scale.
The first few pictures show an early prototype:
This has 3 medium motors and 2 IR receivers. It provided a good test of where
everything might fit (or not!), as well as the jib lifting mechanism.
The next few pictures show the second prototype, including the match wagon and
relieving bogies. This prototype has the same quantities of electrical parts as
the first one.
Showing this to some children provided a good durability test, as well as
showing how the jib will rest on the match wagon. It was at this stage that I
determined that the turntable needs to be able to rotate freely when the jib is
stowed, so that the train can go round corners.
The final version of the crane
contains just 2 medium motors (behind the yellow 1x2x3 panels) and one IR
receiver. I decided that adding a fourth motor for the second winch would not
be possible in the space envelope, so I opted for a gearbox approach. One motor
selects the function in the gearbox via a worm drive
http://www.brickshelf.com/cgi-bin/gallery.cgi?i=2840361 . The four functions
are turntable, jib raise/lower and two hooks. The other motor moves the
selected function. I designed the gearbox so that it is possible to select two
functions at once, in certain useful combinations, such as either hook together
with jib raise/lower. The four functions are fully remote-controlled.
The three string-driven functions use worms to prevent slippage when not
selected. The turntable deliberately has no worm drive, despite ending up a bit
too quick, because I need it to turn freely when the train goes round corners.
The roof lies flat quite nicely when the jib is lowered:
http://www.brickshelf.com/cgi-bin/gallery.cgi?i=2840364 and the crane just
fits within the loading gauge of my layout. Like the real thing, it is a little
taller than most wagons.
Power for the IR receiver and motors comes in from a 9V wire, which will go
through one of the relieving bogies and connect to a battery box in a brake
coach (like this one http://www.brickshelf.com/cgi-bin/gallery.cgi?i=1953717 ).
I will probably use another IR receiver and an interlocking circuit in the coach
so that two IR signals are required to move the crane, reducing interference
from members of the audience at shows - especially when the crane is approaching
a tunnel!
I used small BBB wheels because wheelsets would not fit underneath and using 12V
wheelsets made the bogies weak. With BBB wheels I can use Technic beams for
strong bogies. The stabilisers operate in pairs by hand, using the white half
bushes in the frames.
Mark
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