After making my first star tracker, I immediately started to wonder about making a goto mount. The tracker took me a year and a half with several drivetrain configurations and lots of lessons learned. This Big Ballhead GoTo Mount took less than half that time to make. It was only possible due to the availability of control boards like the OnStep MiniPCB offered by Chad Gray, and the huge repository of information in the OnStep io group—thanks!
Pics: https://www.flickr.com/photos/clockworkbikes/albums/72177720327324828
I carried over some features from the tracker: ball/socket joint for precision adjustments, fine-thread X/Y adjustment screws, smallish NEMA 14 stepper motor, helical planetary gear reducer, and LiPo 21700 cells.
Some features that I believe to be unique are: ball/socket course adjustment, ball/socket fine adjustment, each removable tripod leg contains (10) parallel batteries that join in series when attached (3S10P), image train mounting that supports two points and allow full rotation, lens/scope can be changed with camera in situ, camera-to-filter wheel mount allows full rotation (replaces 5mm thick tilt plate).
Not unique but nice: internal mini router, only phone with ASIAIR needed, mount baseline angle is 33* (as opposed to 90*), one big cable for all wires (power and data), internal heat-sink connected to external heat dissipater, relocating focuser PCB to minimize focuser body, external USB receptacle to OnStep Teensy, 45 Ah 12V internal battery, alternate ZWO camera body, 19 lbs. w/o image train.
I finished this juuuuust in time for my annual trip to the west for solo astrophotography. Of the 6 nights, the first 4 had many interruptions due to my mistakes and learning on-the-fly. The last 2 night were 5 hours of shooting 5-min. exposures. Things that need fixing or redesigning are: tripod leg tip angle is too acute to get a good purchase, no home sensor was used so a marking on the course adjustable section is needed (at a min.), guiding with a 40mm lens is dumb, 5mm between the DSLR lens and camera sensor needs to be removed (the rotating camera-to-filter wheel mount was removed in the field to achieve), bring short DC extension cables so the batteries can charge while the legs are off, plastic spherical bearings that the micrometer heads are mounted to allow for too much play (brass should be used), and probably more stuff I haven’t realized yet.
This was a really fun project that was a big stretch for me. I’m looking forward to getting more sleep now that I can just let a plan run all night. Next… learn PixInsight.
P.S. The ammo box is extra power. It has an off-the-shelf 100 Ah 12V battery connected to 5.5mm barrel outlets and step-down 5V USB outlets.
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BIG BALLHEAD ASSEMBLY 7000630-B all.pdf
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