Here I am adding the hinge after cutting two 1x4" boards. Each board is 12 inches long. Not too much to it at this point.
After the hinges are on, I measure 11.4" inches (11 3/8) from the center of the hinge to a spot where I drill a 1/4" hole for the 3" 1/4-20 carriage bolt to go through. This is the top board. Place a nut on the bottom side of the board.
The wood ball is normally used by crafters as a toy doll head. It's sold at craft stores like Michael's. I think it's actually 1 7/8" diameter. This makes it fit inside the plumbing fixture (I'll look up the name for it soon), which has a rubber compression ring inside. When tightened, it compresses against the ball and holds it quite snugly. There are no lock screws or anything else used.
I coated the ball with polyurethane finish to keep moisture out. The balls I used have a slight flat spot with a hole already drilled in it. I found a 1/4 threaded screw went in with a little work, so I didn't drill for a nut. I threaded it in as tight as I could and then dunked the entire ball in the polyurethane, so that helps 'glue' it in. Hung it out to dry by the threaded rod.
The hinge is at the right side. Keep the camera close to the hinge, so the screw turns easily. This helps especially if you decide a motor like I did. Also, the tripod mount hole should be fairly close ( a few inches) from the hinge so that the entire unit balances well on the tripod. You can actually wait to the last to drill this hole and balance the unit with the camera in place.
Here is a view from straight down. You can see how the tripod is to the left of the center of the board. Balancing will help ensure your tracker does not get tipped over if it gets bumped in the dark.
The prototype board shown consists of a 555 timer and a SAA1027 stepper driver chip, with a few additional support components. It's powered by a 12volt supply, such as a car battery. For details on the circuit schematic, click here.
At some point I will be making a printed circuit of the design, which will be available with all parts for a nominal charge TBD for anyone interested.