This is a Parts list to get you pointed in the right direction to build a motorized zoom machine that can be used for spiral star trails or zooming your lens in and out. Some of the gear sizes and the lens gear will have to be modified to fit your cameras zoom lens. For this instructions guide I used a Nikon D800 with a 14-24mm zoom lens as an example.
Servo City Parts List:
1. 0.5 RPM Gear Motor (RZ12-3000-05RPM). For faster rotation try a more powerful motor.
2. Aluminum Clamping Motor Mount
3. 12 Inch Aluminum Channel
4. 9 Inch Aluminum Channel
5. 1 Large Square Screw plates
6. .3125 inch L x 6-32 Zinc-Plated Alloy Steel Socket Head Cap Screw (25pk)
7. ¼ inch Collar
8. ¼ inch Bore Set Screw Hub .770 inch
9.1/4 inch Shafting & Tubing Spacers (12pk)
10. (2) .250 inch ID x .500 Inch OD Flanged ball Bearing (Stainless Steel)
11. DC Power Cable
12. Digital Manual Speed Controller
13. 8 Cell 12v Battery Tray (plug end)
14. 7/64 Female Crimp Terminals for 14-16 awg (6pk)
15. ¼ inch x 2 ½ inch D-Shaft
16. 32 Tooth, 32 Pitch, 6mm Bore Pinion Gear
17. 64 tooth or 84 tooth 32 Pitch ½ inch Bore Aluminum Gear
7/64 inch Hex Key
Redrock Micro Lens Gear .8 Film Pitch Mod. (Make sure to get the right size for your lens)
Sunwayfoto MP Rail DMP - 200 and Sunwayfoto L Bracket
Dynamic Perceptions MX3 motion control for more movement options.
Step 1: Attach The Aluminum Channels
Attach the 9" aluminum channel to the 12" aluminum channel using 1 large square screw plate and (4) Zinc-Plated Alloy Steel Socket Head Cap Screws. The positioning height of the 9" channel may vary depending on your camera model and lens.
Step 2: Insert Ball Bearings, spacers, D-Shaft and Large Gear
1) Put a (.250" ID x .500" OD) Flanged ball bearing in the larger holes at the top of the 9" aluminum channel.
2) Insert the .25" x 2.5" D-Shaft into the 2 holes where the ball bearings are. Use the appropriate number of .25" shafting/tubing spaces needed to help assist in the alignment of the gears. (For this project I used 6 spacers)
3) Attach the 64 or 84 tooth gear to the D-Shaft. (The size of the gear will vary depending on circumference of the lens you are using)
1) Attach the 32 tooth 6mm Pinion gear to the motor. For this project I used a very slow .5 RPM Motor to rotate the lens extremely slow. Experiment with different RPM motors to find the speed you need for your desired effect.
2) Next attach the Aluminum clamping motor mount to the 9" channel next to the large gear. Insert the motor and line up the smaller 32 tooth gear with the larger 84 tooth gear. Once they are meshing correctly clamp the motor securely.
Step 4: Attach a motion control box and power supply
1) Attach the female crimp terminal s to the motor and hook up the digital manual speed controller. (You also can use a motion controller like Dynamic Perceptions MX3 for even more controlling options.) The MX3 will give you the ability to use a time lapse method call "Shoot - Move - Shoot". When doing a vortex star trail you need to take a long exposure, let the gear turn the lens slightly, then the camera will take another exposure. This slow rotation gives you the spiral effect when photographing the north star and using this technique.
2) Attach a power supply to the control box. A 8 Cell 12v battery tray was used to power this device.
Step 5: Attach a gear to your lens and the motor to your tripod
1) Next we need a gear around the lens to rotate it. I found a product called Redrock Micro Lens Gear with a matching pitch. They make different size models that match the lens you are using.
2) Attach the 12" aluminum channel to a tripod. The easiest way Iíve found so far was to screw a Sunwayfoto (or similar) rail to the channel. Then the rail would be able to get attached to my tripod. The rail has a sliding and locking point for an L Bracket that goes on the camera. This allows you to attach the camera and slide it into position so the gear on the camera will mesh with the motorized gears.
3) For a constant zoom in and zoom out I recommend using a motion control box by servocity.com. If you need more capabilities I recommend using MX3 by Dynamic Perceptions.