The next piece to be machined was the right ascension box top, bottom and sides. I haven't purchased the metal yet to machine the bearing blocks(which go at the north and south sides of the RA box), so those will come later. We started with the RA sides, which are two of the strangest shaped pieces on the mount.
The first part we machined was the top of the pier. The pier top has 16 counter-bored 1/4-20 clearance holes to mount it to the pier(to be designed), 3 slots to allow limited rotation(about 20 degrees) for polar alignment, and a post for a screw to push against to allow rotation. The three slots each have a 1/2-20 bolt in them, which lock the mount in place once azimuth is adjusted.
Today almost two years of design work began to take shape; the first pieces were rough cut out of 3/8" thick aluminum. We cut the sides and top for the right ascension and declination boxes, and the bottom and sides of the polar fork. I had a local print shop print these pieces at 1:1 scale so we could lay them out beforehand and make sure we maximized our use of the aluminum sheet.
Last month I wrote about a design I had been working on for a large German Equatorial Mount for astrophotography, to be machined this summer. After I finished the design I called Ed Byers to order the right ascension gear, and we ended up discussing the design. He gave me an amazing amount of advice, and I decided to redesign the mount to fully take into account what I learned from speaking with him.
Pictured above is a Solidworks render of the mount with an 80mm APO telescope pictured for scale. During operation it will (hopefully) carry a much larger instrument. Below is a summary of the features of the mount.
To augment the knowledge we gained through building mount control electronics and software last summer, and to (hopefully) construct a respectable imaging mount, we designed and plan to machine a large German equatorial mount this summer. I have been working on the design since September 2012, and should finish the design this weekend. After I complete it I'll post more pictures, the Soldworks files, and some more explanations of some design choices. Our goal is to image with a 12-14" reflector. Finite Element Analysis was used in some key places, but my version of Solidworks is relatively limiting in that regard. The only major change that will happen between now and the final design is an increase in strength of the polar fork, and the addition of a plate on declination to mount a telescope to. Here is a brief list of some design highlights:
In order to learn more about how telescope mounts work, and to save a significant amount of money, Izak McGieson and I set out to design and program our own mount control electronics. We started this in June of 2011, after adding steppers to a very cheap Chinese mount carrying a 4.5" Newtonian. We completed the majority of the electronics and software on that mount, but after realizing the following December that the accuracy of our electronics was outdoing the accuracy of the mount, we decided to upgrade. We upgraded to a Japanese made Vixen GP-2, and also replaced the 4.5" Newtonian with an 80mm apochromatic refractor(Astro-Tech AT80EDT) with hopes of widefield astrophotography. Our mount and software are capable of closed loop GOTOs using plate solving to accurately place the telescope, and guided tracking for astrophotography. This post is about the mount electronics, you can find the post about mounting the motors here. A post about the software will be written soon. With the exception of Astrometry for plate solving and Xephem as an object database, we wrote all of the software.
This is my third of four flashlight builds, but the first one to be usable The first one was more an act of desperation for lathe projects than a real build, and the second, while technically bright enough to be useful, was aesthetically disappointing. Regardless, the third build is both bright enough to be usable(almost too bright), and something I'm proud to carry around.
I've always wanted to try terrestrial night photography with an actively cooled CCD imager and a regular SLR lens. The combination of a regular(wide to an astrophotographer) field of view with the incredible noise characteristics of a professional imager seems quite appealing. I recently acquired an SBIG ST-2000XCM CCD Imager for astrophotography, so this dream is only one adapter away from reality. At only 2 megapixels, the resolution might be a tad low, but the light collection and low dark current are way beyond any dSLR, even the low noise Pentax K-5. SBIG makes an adapter for their ST-2000 taper to fit Nikon and Canon lenses, but not for Pentax. I could purchase the SBIG to Canon adapter and use a Canon to Pentax bayonet adapter, but that would increase the flange distance and prevent me from focusing on infinity; rendering the setup totally useless for outdoor photography. Instead I machined my own adapter to go directly from the SBIG Taper to the Pentax K-Mount, properly spacing the lens according to Pentax's flange distance specification.
Front and back views of the completed adapter. The first step was a rough Solidworks design.
To fit a Vixen GP-2 mount with GOTO electronics from Vixen directly costs $999, twice what the mount itself costs. To buy just the motors with no control electronics is $430, only slightly less than what the mount costs. This was partially the motivation for adding our own off the shelf stepper motors, as well as the opportunity to design all control electronics and software to gain a deeper understand of how GOTO, tracking and autoguiding systems work.