Reproducing the Velador Experiment
Camera and Laser Mounting Cells
The mounts for both the camera and laser must provide for mechanical adjustment rather than manual aiming, in order to repeatedly attain the necessary precision for aiming. The camera and laser mounts should be such that the camera and laser can be rigidly clamped to the mount, and then adjustments made to the mounts rather than the camera and screws.
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Lance Osadchey has recommended use of a Bogen 410 camera pointing device, which is adequate given slight modifications to the support beam design. However, this device was relatively expensive for the budget I laid out (US $177 vs. my $100 budget), with a greater range of motion than required for internal mounting. A three point spring loaded mount with screw adjustment at each support will be used instead.
The spring force at each mounting point should keep the mount rigid against small loads when the screws remain fixed. Screws should be long enough to reach from a metal bracket at the support beam end, through a small compression spring, through the camera or laser mount, and out the end of the support beam assembly to accept a nut for tension and adjustment. This arrangement is similar to that of a typical telescope mirror cell, and can allow for fine adjustment of only a few seconds of arc. As with a telescope mirror cell, the mounts form the ends of the support beam.
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Most of the cost of these hand built mounts is in the fittings. No single fitting more expensive than $1.50 was used. However, each mount has 25 to 28 components including a cut and bored backboard. Total cost for both was approximately $20.
For each mounting cell backboard, I cut a piece of 1x6" yellow pine lumber large enough to extend across the end of the support beam. The lumber used was a piece of yellow pine that was too warped for use as part of the support beam, but not too much curvature to allow a maximum 1/8" gap for this small piece.
The backboard is held on the support beam by three 1" steel corner brackets. A 2.5" #6 machine screw is secured to each bracket with a washer and nut in order to act as a spindle for a 5 lb/in spring. The spring is slid over the screw after it is bolted in place in the bracket and capped with a washer. The screw is then inserted through the backboard at the appropriate position and a third washer and a nut are placed on the screw on the other side in order to hold it in place. The final nut is used for adjustment. Right now, I'm using hex nuts, but wing nuts would be easier to work with. The adjusting nut shuld be tightened until the springs are set solid to hold everything in place for installation, but must be loosened to allow the springs to expand for calibration. (The mount will not move along the spindle while the spring is fully compressed.) The bore holes in the backboard must also be at least 1/8" wider diameter than the spindle screw, to allow the backboard to tilt back and forth.
The laser mounting cell is shown below. The laser holder is made from a set of steel and brass gas pipe fittings, hand threaded into a hole bored with a 1" wood bit. The fitting on the end is a 1/2" brass pipe gas compression fitting whose internal diameter is a close enough match to the laser pen that padding the laser with a single strip of 20# paper will hold it in place. (The laser is not shown.) The pipe fittings can be drilled and tapped for a mounting screw for further reducting of sagging, but this setup is expected to be adequate for trials at small elevations.
The two springs and spindles which are visible are in the open/adjusted condition (top of image) and set solid/installation condition (bottom of image).
Below is a picture of both the laser and camera mounting cells, ready for installation. The laser is not shown. The camera is shown installed using a flat bracket. Note that the backboards are axially symmetric, and the camera lens and laser are approximately at the geometric center of their mounting cell backboard. The USB cable and power cord for the camera will be secured with a staple and then threaded through the adjusting gap between the support beam and backboard, requiring a 1/8" gap between the installed cell backboard and the support beam at installation. Note that the screw bore holes have been aligned so that the brackets can be installed on the inside surface of the assembled support beam.
