Parts List
2 x base plates 1
4 x long frames 2
4 x short frames 3
8 x short rods 4
4 x long rods 5
4 x large gear wheels 6
4 x medium gear wheels 7 9 x small gear wheels 8
3 x small sprockets 9
1 x medium sprocket 10
2 x large sprockets 11
1 x medium pulley wheel 13
5 x long axle shafts 16
2 x medium axle shafts 17
1 x short axle shaft 18
1 x engine shaft 19
1 x black cable 20
1 x red cable 21
1 x battery holder 22
1 x solar module 23
1 x solar engine 24
4 x shaft plugs 25
20 x anchor pins 26
90 x chain links 29
1 x attachment plate 27
1 x crane hook with spool and cord 28
Large Drawbridge
Tall Bridge with Roadway
Drawbridges aren’t just something found on medieval
castles — they are still used today for roads that go
over rivers and canals. When a large ship comes, the
roadway can be raised up to let the ship pass through.
Then, the bridge is lowered again so pedestrians and
vehicles can cross over the river.
For our next project, we will be building this kind of
drawbridge. The actual bridge is located at the front,
and it can be raised and lowered with the help of
the crane hook, spool, and cord. The cable is guided
over a pulley wheel mounted high up the bridge. The
bridge is just as wide as the roadway running through
the lift machinery structure. This lift structure is built
high in order to allow tall vehicles to use the road as
well. The framework at the rear is needed to let you
anchor the lift machinery securely to the base plate.
The engine turns the cord pulley by way of a combina-
tion chain and gear drive.
The direction of the solar engine’s rotation deter-
mines whether the bridge is raised or lowered. The
simplest way to change the direction of flow of the
current is to reverse the position of the solar module
in the holder.
When operating the bridge, be careful not to let the
cord jiggle up and down too much. You can stop
the bridge anytime by holding your hand over the
solar module. The shadow of your hand will prevent
enough light from getting to the solar cells. But the
engine doesn’t just wind and unwind the cord. At
the front of the model, there is a medium gear wheel
which is rotated by a reverse gear drive when the
bridge is raised or lowered. It signals to ship traffic
that the bridge is in movement. The large gear wheels
at the top don’t turn at all, however. They just serve to
make the model look nicer.
The model is actually easy to build. You first as-
semble the bridge itself and then you construct the lift
machinery. Make sure that the sprocket wheels that
are linked to each other are positioned in a straight
line. Also, the chains should not sit too tightly or too
loosely. Check periodically to see whether everything
is moving smoothly and easily.
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