Hobbies And Interests
Things You'll Need
Instructions
Designing the Equatorial Platform
Determine the exact latitude from which the equatorial platform will be used. The virtual RA axis of the EP must match the angle of the poles at the user̵7;s specific latitude.
Cut a 3-by-5-foot sheet of Kraft paper, using the scissors.
Draw a 4-foot line in the center of this sheet of Kraft paper, using the straight-edge ruler; then draw an overhead view of the triangular top platform section of the EP that is centered on this line such that the line bisects the north side of the overall triangle, thus creating two adjacent right triangles. The overall triangle must be large enough to accommodate the footprint of the Dob̵7;s ground board. This drawing will serve as the template for both the base and the top sections of the EP.
Cut a second 3-by-5-foot sheet of Kraft paper.
Draw a 4-foot horizon line three inches from the bottom of the sheet of Kraft paper, and then draw a 4-foot line from one end of that horizon line at an angle equal to the latitude, using the protractor.
Construct a scale side-view drawing of the EP on the second Kraft paper sheet, using the latitude-angle line as its virtual RA axis, including plywood mounting bases for the southern axle, the northern roller bearing and drive roller. Draw a vertical line from the point along the RA axis line that is equal in height from the top of the platform as the altitude axis of the Dob is from the ground. The point where this line intersects with the platform̵7;s top represents the center of the Dob̵7;s base when placed upon the platform. Draw another line that is perpendicular to the RA axis and that intersects the center-top of the north bearing roller. This line represents the radius of the virtual northern bearing circle.
Cut a third 3-by-5-foot sheet of Kraft paper.
Cut a 4-foot length of string.
Tie one end of the string around the pencil and tie a knot in the string at a distance from the pencil that is equal to the radius of the northern bearing circle recorded in Step 6.
Hold the string knot at a point near the center of one of the 3-foot ends of the third sheet of Kraft paper and, keeping the string between the knot and pencil taut, trace an arc across the paper with the string-bound pencil. This arc represents the radius section of the northern bearing circle. Mark a point near one end of that arc to represent the location of the bearing drive roller. Mark a second point along the arc that is equal in distance from the first mark to the spacing between the two rollers shown in your scale drawing. This second mark represents the location of the free-spinning bearing roller.
Calculate the circumference of the virtual northern bearing circle using the electronic calculator, by multiplying the length of the radius recorded in Step 6 by 2 and by Pi (3.1416).
Divide that circumference by 24 and mark a third point along the northern bearing arc that is that distance from the mark made for the location of the free-spinning bearing roller. Draw a straight line from a point one inch beyond this third point mark to a point one inch on the other side of the first point mark, to define the total northern bearing circle section that will support the top platform.
Building the Equatorial Platform
Transfer the component drawing of the overhead view of the top platform twice to the plywood, using the pencil. That template will form the profiles for both the EP̵7;s base section and its top platform section. Transfer the drawing of the northern bearing circle section to the plywood. Transfer the various bearing mount pieces to the plywood as well. A single 4-foot-by-8-foot sheet is sufficient to provide all elements needed for an EP to support a Dobsonian of up to 18 inches in aperture.
Cut all curved lines with the jigsaw blade angle set at 90 degrees.
Cut the straight line of the northern bearing circle section and the straight lines of the attachment points of the bearing mounts with the table saw blade angle set at the angle of the virtual RA axis (the latitude angle).
Cut all other straight lines with the table saw blade angle set at 90 degrees.
Sand the radius edge of the northern bearing circle section smooth, using the sanding block and sandpaper, and attach it to the underside of the northern end of the top platform using wood screws and wood glue, orienting it at the location shown on the side-view plan and so that the angle cut of its straight edge tilts the section toward the northern end of the platform.
Attach the northern bearing roller mount pieces to the top side of the EP base, using wood screws and wood glue, at the positions shown on your scale drawings of that assembly.
Attach the southern axle mount pieces to the EP base and to the underside of the top platform, using wood screws and wood glue at the positions shown on your scale drawing of that assembly.
Attach one free-spinning skate wheel to one of the roller mount assemblies, using the standard hardware that came with the wheel.
Attach the second skate wheel to the drive shaft of the 50:1 spur-gear equipped 12-volt stepper gear motor, omitting the bearing from the wheel. This may require a custom bushing, depending on the specific motor and skate wheels you have selected.
Attach the drive motor/skate wheel assembly to the other roller mount assembly, following the manufacturer̵7;s instructions.
Place the upper platform section on the lower base and clamp the southern axle mount pieces in their working positions, using the C-clamp. Drill a hole through both at the point of the RA axis, using the drill and a 1/2-inch bit. Insert the southern axle bolt into these holes in the sequence: metal washer, PTFE washer, plywood mount half, PTFE washer, plywood mount half, PTFE washer, metal washer and nut, followed by the second nut to lock the first.
Connect the motor wires to the Stepper Motor Driver and to the 12-volt power source, following the manufacturers' instructions.
Position the northern bearing circle section so that the excess arc is behind the drive roller.
Center the Dob on the platform and start the drive motor using the Stepper Motor Driver.
Center a bright star in the telescope̵7;s field of view and adjust the motor speed until the star appears stationary.