6-cylinder
Radial Lego Pneumatic Engine
by
Paul Krieg |
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Overview |
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This is a working model of an airplane engine. The real ones always had
an odd number of cylinders but with Lego I am not sure that is possible
above 3 nor is it necessary. Actually this engine is just 3 engines of
the 2 cylinder opposed type sharing the same crank shaft. Timing this
type of engine is trickier and I have not tried it with your valve gear
which I like very much because it is small and simple. This engine is
very powerful and runs very fast. It can easily be made double acting
but then it will run slower and is so powerful that you can damage some
Legos. These engines are hungry for air so I use a quart size soda bottle. The engine you see here was built in 1994 and is part of an
airplane. Some parts (mostly the valve gear) have been rebuilt since then. |
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Construction
I had to find books that had a good illustration of the construction of
this type of engine to figure out how to connect all the piston rods at
the same place on the crank shaft. This picture shows the front removed
to show this connection. Really one of the piston rods should be connected solidly to the ring to which the other five piston rods are
connected, but I have no way of doing this. What you see does work. |
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| Valve gear |
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This is the valve gear on the rear side of the engine. As you can see one valve controls two cylinders. A
valve can control any two cylinders as long as they are opposed 180 degrees from each other.
The rest is
timing and I start by choosing one valve and I set it so it is beginning to supply air to one of its cylinders at
the beginning of its power stroke. Then I will do the same to the other two valves making sure I am
choosing the appropriate cylinder so that it will push at the right time and not work against the other
cylinders just to get the timing kind of where it will be. |
| Next I will find the position that is best by trial and
error and make sure that when it is done all of them are in exactly the same position. This will take time
and patience. When you are done your engine will run very fast with impressive power. I find advice one
timing this engine difficult to make simple. I would recommend building a simpler engine first. |
6 cylinder crank
Here is a view of the crank shaft from the back side. One of the valves
is moved out of the way to improve the view. You can see that I used
the piece that is actually meant to be used as a crank shaft. It fits
and works inside the rim of the Model Team wheel hub that connects all 6
piston rods to the crank shaft. |
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| It was meant to look like this |
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I recently purchased 2 more 48 mm single acting cylinders. Now I
have built the engine to look the way it is supposed to look. The
difference is with the top and bottom cylinders. In the previous photos
you received I had to extend the engine frame to accommodate the longer
cylinders. Now the engine has 6 even sides. I'll worry about having
all the same color later. |
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Valve Gear Detail |
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Here is a picture of the valve gear showing the connection of the
hoses and the timing of the gears to give counter-clockwise rotation
of the engine. |
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The blue 1x2 plate represents the position of the crank. The spoke of the outer gears that is closet to
the mounting of the eccentric rod (green on the left gear) is my point
of reference. The pink teeth show where they would mesh as it is rotated. The numbers on the valve ports correspond with the numbers on
the cylinders.
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Congratulations!
Paul's 6-Cylinder Radial Engine has won the Hall Of Fame contest by Lego Mindstorms Monthly,
Jan/Feb 2003 Issue 7, an internet publication of the Lego Mindstorms Forum
Group.
- CS |
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Radial
Engine Building Instructions |
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What
you can do with the Radial Engine
Air Powered Air Propelled Vehicle |
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