If you have been reading my blog you will know that I love building things. I almost like it more than using things. So, after my recent experiment with a tracking mount I decided to start again, from scratch, to try and make a more robust, heavy weight mount that will not complain when I load it up with cameras and scopes. I also use the iOptron SkyTracker a lot but you cannot load it up too much.
The previous tracking mount is shown in one of my previous posts, Look at https://starsinphotos.wordpress.com/2014/09/23/diy-autoguider-for-long-exposure-astrophotography-part-2/ . This mounts works surprisingly well but it looks like a dogs breakfast, it’s sensitive to bumps and it is too bulky to transport easily.
My new design will be more solid with a steel based design rather than aluminium. Its harder to machine but the design is relatively simple so it is quite easy to make. I have decided on a few design parameters that will make the design robust and will not require any skilled machining capability (apart from the worm wheel and gear). I will also make a new worm gear combination (130mm diameter with approximately 270 teeth. The previous one I made was not very accurate and it only tracked smoothly for about 3 hours at a time, then I had to “rewind” the RA axis to get to the start of the good section on the work gear. My stepper controller design have buttons for a fast forward and rewind on the RA drive.
The new tracker design is based on a square section of 125mm mild steel U-channel with two pillow block bearings that holds the 20mm steel RA shaft.
It should be possible to get the steel supplier to cut the U-channel to the correct length when you buy it but I got an offcut cheap and had to spend a few hours to get it nice and square. The U channel and the 20mm rod cost me $10. The two pillow block bearings was a bit more expensive, the two of them cost about $60.
So now I have the RA shaft mounted and it feels VERY solid. I am thinking that I might be able to load my 8″ SCT OTA on to the mount if all goes well. The new 140mm worm gear will fit onto the 20mm shaft on the left (or bottom) side and the camera / scope mount will be on the right (top) side. The stepper motor and worm will be below the U-channel on the bottom.
I am going to try and build the tracker without any ability to adjust for altitude polar alignment. In my opinion, its too hard to get a very solid mount if you add the adjustment elements to the design. This mount will be mounted on a fixed altitude block that is centred on Adelaide (35 degrees south). I will use the Meade tripod legs to make large changes to that and small changes will be made by an adjustable tripod foot consisting of an adjustable pipe flange that can be rotated to make small adjustments on the tripod leg facing south. Azimuth will be adjustable with the Meade tripod head bolt. I may go so far as to include a method for making small adjustments to the azimuth as I have battled with that in the past.
For accurate polar aligment I will keep on using my green laser pointer on a small aluminium bracket that attaches to the RA shaft itself. This implies that I can achieve very good polar alignment with a mount that may not be perfectly square and with bearings that are not fitted very accurately on the mount. It’s legal to use a green laser pointer in South Australia if you have the correct documentation with you.
My existing stepper controller and autoguider works well and I will use it again for this mount.
Update 22 January 2015:
I have now got two new 130mm diameter aluminium “blanks” for the new worm gear. This time I had them professionally machined so that they will be 100% square on the 20mm shaft, unlike last time…..
Over the next few days I will cut the worm gear and a new worm. I will post some photos when it is done.
Update 27 January 2015:
Yesterday, I cut the worm gear and it turned out much better than before. I have 279 teeth on this disk and hopefully they will be quite smooth after I have polished them.
The new tracker is slowly coming together now…
Now for the worm….
I will update this post as the mount gets built over the next few weeks.
Comments and questions are welcome…