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After reasonable feedback about the complexity of my first reversible pneumatic
engine, I realized there was a very simple mechanical solution that would give
reversability *and* variable speed.
http://www.brickshelf.com/gallery/kclague/Computing/p6010044.jpg
http://www.brickshelf.com/gallery/kclague/Computing/p6010045.jpg
The difference between going forward vs. backwards is the phase relationship
(difference in angles) between the pistons and the timing switches. In one
direction the switches are 45 degrees clockwise relative to the pistons, and in
the other direction the switches are 45 degrees counter clockwise relative to
the pistons. So I needed a mechanism to be able to change the phase, to make a
reversible engine.
When trying to add two rotational rates, I always think of a differential.
While the differential subtracts (takes the difference), this is easily turned
into addition by reversing rotations where necessary.
In this case, once the engine is running, the switch rotation rate is the same
as the pistons rotation rate, so the differential is subtracting the piston
rotation rate from 0 to get the switch rotation rate (I'm not sure this is
exactly right, but you get the idea.)
What the differential does allow us to do though is change the phase
relationship between the pistons and the switches. The pistons come in one
axle, the switch rotation comes out the other axle, and the rotational position
of the differential case adjusts the phase between the pistons and the switches.
The transparent 24T/worm gear box controls the rotational position of the
differential case. The worm gear provides a locking mechanism so that once
changed, the case cannot move. Turning the axle that goes through the worm gear
turns the 24T gear, which meshes with the differential case. Turning the case
changes the phase between the pistons and the switches.
When the switches have a phase of 0 relative to the pistons, the engine cannot
run. As you change the phase from 0 to either -45 degrees, or 45 degrees,
eventually the engine is able to run, but not at peak efficiency until the phase
gets to -45 or +45.
This makes it reversible and variable speed.
Please correct me if I've got anything wrong above.
PLMKWYT
Kevin
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