| << Back a page |
Steve's 'BarnDoor' - manual drive
Clock timer
All that is necessary is to turn the Drive Nut at the same rate as the clock (1 rpm). A simple quartz controlled clock mechanism was used with the seconds hand only fitted.
 |
To assist in turning the Drive Nut at the correct rate, a card guide was fitted to the clock, dividing the rotation into 10 second segments. Clock 'ticks' can thus be counted in sets of 10 and the wheel moved 'by touch', especially if the segments of similar guide on the BarnDoor arm can be felt. |
| To make it easy to turn the Nut, an old pulley**
wheel was used.
Generally, the larger the wheel the better. The greater the movement needed to make one turn, the easier it will be to judge the angular position (and hence the accuracy achieved) and the smoother the motion of the 'nut' will be. The Drive Nut is epoxied to the centre of the wheel. A bolt (with washers) is fitted for use as a turn ('index') pointer (this was removed when the motor drive was fitted). **using a pulley wheel allows a drive belt to be fitted later, for a motor drive (a belt is better than gears, since this minimises / eliminates any vibration from the motor). |
 |
Whilst the initial plan called for a touch sensitive guide on the BarnDoor lower (fixed) arm, problems with leg 'wobble' soon put paid to this idea.
It was thus decided to fit a lamp (red light, to avoid loss of your night vision**) and move the wheel 'by eye'.
** note that whilst red light preserves your night vision, it will still ruin your photos. To minimise any chance of reflections getting into the lens, the base and fixed arm should be painted black .. and the camera mount (seen below offset towards the top edge) should be moved to a position directly opposite the lamp.
 |
 |
| Complete, with finderscope | Detail showing illumination (red) light and 10second 'hex' posn. guide |
| << Back a page |