Introduction: Manual Setting Circle for Dobsonian Telescope

Picture of Manual Setting Circle for Dobsonian Telescope

As a long time viewer of instructables.com, I am happy to present my FIRST instructable. This shows how I made manual setting circle for my dobsonian telescope. A setting circle is used to set the azimuth coordinates to help locate objects. I got the idea from a very long thread on cloudynights.com. And from products like the Halo.

The degree circle can be rotated independently from the base. The idea is that I can point the telescope at a known object such as the north star (Polaris) and rotate the circle so that the marker is at 0. I can then use a mobile app such as SkEye to get the ALT/AZ coordinates of another object and turn the telescope so the marker is at the AZ coordinates. I will use a digital level to set the ALT coordinate.

Step 1: Concept and Design (3D Model)

Picture of Concept and Design (3D Model)

As a 3D artist, I like to prototype my concepts in 3DS Max so I started by making a quick model of the telescope and base. Then I "opened" up the base and added a circle with a slightly larger diameter than the base. The circle has a hole cut out in the middle just slightly larger than the ball bearing turntable. The top half of the base will go over this.

Step 2: Physical Prototype - Part 1: the Degree Circle

Picture of Physical Prototype - Part 1: the Degree Circle

The next step was to create a printable degree circle. There are a few floating around on the internet, but I decided to use Adobe Illustrator to create my own. I created it to be 21" in diameter and it has a small dash for every 1°, a long dash for every 10°, and a number every 5°.

I printed it out onto 4 sheets of paper, spray mounted them to a piece of poster board and cut it out. Then I "laminated" it with packing tape.

Step 3: Physical Prototype - Part 2: Red LED Pointer.

Picture of Physical Prototype - Part 2: Red LED Pointer.

To act as a pointer, I took a red LED from an old computer mouse, a switch from an old toy, some wires, a battery pack from a flashlight, and a random mounting bracket from an old bicycle. I wired the LED to the switch and battery, taped the switch to the handle of the base.

Step 4: Finalizing the Prototype

Picture of Finalizing the Prototype

Next I needed a more durable, but lightweight surface that I could mount a final printout to. My original idea was plexiglass, but I couldn't find the right size. I saw someone was throwing out a table and that the top was thin enough and could be separated.

I had my degree circle printed and laminated at Stapes. I used a heavy duty spray adhesive and mounted it to the tabletop. I then used household tools (scissors and a box cutter) to cut it out.

I got a battery pack free from http://www.keyelco.com/

- Go to product and click “Add to Sample Cart” to order. No registration is required. You fill out a sample request form. No corporate email address was required. It ships UPS Ground. You do not have to pay the shipping.)

The degree circle rotates by hand. I thought I would need some kind of "locking mechanism", but surprisingly it
doesn't really move when I just spin the base.

How to use it:

1. Locate a known stellar object (i.e. Polaris)

2. Spin the degree circle until the pointer (Red LED) matches the coordinate of the object (roughly 0 for Polaris)

3. Use an app such as SkyEye to find the Alt/Az o

Many thanks go to everyone who posted their designs on cloudynights.com. I wouldn't have been able to make this without them!

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