Geoscience and Environment

Camera Rig

The Mark I model of my rig was exactly as designed by Brooks Leffler. The rig shown below was my Mark II model. This rig has a few modifications. A thin plywood plate has been added to the top to make the rig detachable from the supporting Picavet. A boom has been added at the bottom left to support a spar to indicate the direction the camera is pointing in the vertical plane. A small plastic card was glued to the back of the radio receiver to provide additional support. Click on the image to see the details.

Note especially the servo at the top of the rig. This servo was modified to permit 360-degree rotation according to instructions provided by Brooks Lefler. The instructions are easy to understand and if performed correctly will result in reliable operation. Unfortunately, my hands and eyes were not up to the task of drilling the plastic precisely and I knew it. So I felt uneasy about the strength of the assembly. The photos below describe a further modifiation to provide a safety device.

Camera Rig (JPG 60K)

The shutter control mechanism must be carefully positioned.

Shutter release (JPG 19K)
The Mark III model is shown below with a safety device in case of failure of the upper servo assembly. The red wire (from a coat-hanger) is tied to a post attached to the under-carriage. As the servo causes the under-carriage to rotate, the red wire tracks the movement. If the servo assembly fails, the red wire supports the under-carriage. The second image shows construction details. A thin-walled metal tube is fastened to the top plate and to a dowel glued to the bottom plate. A hole was drilled in the dowel to allow a nut and a lock-nut to be fitted to the bolt from the servo. The additional weight of the Mark III compared with the Mark I is about 300 grams. Possibly, this extra weight caused the failure of the servo assembly during the first flight of Mark II. If so, the margin of safety was not great enough for safe flying. However, I am reasonably certain the cause was my lack of skill in modifying the servo. I removed too much plastic while drilling. (Click on the photos to see larger images.)

Mark III Rig (JPG 26K) Modification Detail (JPG 21K)
On the first flight after modifying the rig, the servo assembly failed. But the safety device worked. Replacing the servo took about an hour. To fasten the servo to the plywood plate, a bolt must be inserted through the geared rotation post at the top of the servo. This post is the component that causes the entire rig to rotate. I removed the plastic cover from the body of the servo and extracted the geared post. When drilling a hole through the post to accommodate the bolt, I used a different drilling method to avoid removing so much plastic as before. I used a drill-bit just big enough so that I had to thread the bolt into the plastic post. Then I drilled the larger bore for the head of the bolt by hand. With a gloved hand I held the drill-bit using it to ream out the plastic only a little.

Clearance is needed for the bolt head at the bottom of the post so that it does not touch the brass feedback post in the servo body. I used a fine hack-saw to cut down the brass post protruding from the body of the server. This operation allowed me to remove less plastic from the geared post, thus preserving its strength.

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