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Two Cylinder Pneumatic Engine |
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| This is a model of a steam engine built using
Lego pneumatic parts. I've always been fascinated by steam engines and thought it would be
a challenge to model one in Lego. The model was inspired by pictures of the steam engines
of a bygone era. I'm intrigued by the valve gear mechanisms designed by the Victorian
engineers to ensure that the steam enters the cylinders at the right time to push the
pistons of their engines. |
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| In particular, I don't think that the reciprocating to rotary action motion concept has ever been used with the Lego pneumatic cylinders in the official instruction manuals. The working principle of the model is based on the pneumatic control circuit which is explained at Eric Brok's website. | |||||||||||||
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| The model uses relatively few parts including the pneumatic elements. I'm a sort of *minimalist* when it comes to Lego building. That's partly because I don't have too many sets myself and also so that it could be easily built by others if they're inclined to do so. | |||||||||||||
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| The two cams are offset
by a right angle (90° phase difference). |
The tubings from one
air switch are cross-coupled to provide negative feedback to the opposite pneumatic
cylinder. |
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| The most tricky part in building this model is getting the linkages to the pneumatic valve switches correct so that the air is fed to the appropriate cylinder at precisely the right time. | |||||||||||||
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| Timing of the switching over of the air valves is critical. This is set by the alignment of the slide bar and pulley in relation to the cam. | Note that Lego geometry requires an intervening 1/3 height plate to get the slide bar to line up with the centre of the pulley. | ||||||||||||
| Now, I'm not sure whether TLG ever envisaged that
the pneumatic cylinders could be used in this manner. However, when I found the correct
position for the linkages, they fitted precisely within the existing Lego geometry, as if
they had been pre-planned. What amazes me is that you never know what you can do with
the Lego parts until you try it! |
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More pneumatic engines |
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