I have been re-building my 12 inch F5 Bartels Dob and thought I would share my progress. The first photo below shows the original. I have been using it for about 4 years. It had epoxy gears and nylon allthread for worm drives. The system worked well but I felt I could improve upon it.
The next photos show my rebuild. I hope they are self explanatory but the main features are:
- Professionally made worm wheels and gears by Lenord Stage
- An aluminium flex rocker made of 'connect it' parts from Bunnings
- A square single 'ring' secondary cage again made from connect it parts avalable at Bunnings
- Friction clutches on both axes. The flex rocker sits on top of a thin aluminium base with three teflon pads supporting it. The base of the flex rocker is covered with laminate.
- A wire spider. A lot of people think they are hard to make. They are not. I show it in the jig so you can see how it is set up.
- One piece truss assembly. Ken Beard at the ASV's Instrument Making section uses a similar system which I copied.
- Fast slews. Too fast really. I have run it at 6 degrees per second but I actually find that unmanageably fast. I set it to run at around 3.5 degrees per second instead.
- Home made mirror
I still have a lot of work to do on it but it is usable now. I get good tracking after a 2 star alignment but some sloppiness in the motor mounts is causing backlash and making the gotots less accurate than I would like.
I will also be adding encoders. These will help address any slip in the clutches.
I would like to lay out the electronics more neatly. At the moment I have just bolted on the original circuit board and laptop mount. I hope to come up with something neater. Any suggestions appreciated!
In the field I control the scope via a serial to wifi adapter. I use skysafari on my iphone to send goto commands. Works great! I also have the DOS version of Guide installed. It is a handy back up and I often use it for the two start alignment.
Rod.