| I tried without success to find a true parabolic
mirror. What you see on the right is a 4 inch spherical makeup mirror on loan from
my wife. Note the horizontal (azimuth) turntable and the vertical (elevation)
turntable, each driven by its own motor. The wheels and tires do not turn;
they are supposed to be non-slip feet. |
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In the rear view you can see the complete
elevation drive-train. As the angle increases the resolution must become
finer; therefore there is a double worm and wheel drive. The first is next to
the universal joint. The second worm engages the vertical turntable. A
criterion of the design is that there is no shuddering as it turns through tiny
increments. Also, the mirror is overhung or cantilevered and extra support is
required for rigidity. See in this picture and the one above that each drive has its
own rotation counter. Finally, the pulley at the end of the elevation drive is for
visual indication of the rotation of each increment. |
| The extra rigidity for the cantilevered mirror
load is provided by the second worm. There is an acceptable cost in additional
friction. See the white friction clutch to protect from high torque. |
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Note from the image on the left that there are
three #2 shafts providing point contact on the front of the mirror, and from the
picture above it there are four #2 shafts on the back. These provide a secure bedding
for a curved mirror without risk of breakage. |
