Simple motorized Dobsonian mount for short 12" tube
I recently bought a Newton 300 (Quattro 300P, F/4 ) for astrophoto. Once mounted it on my EQ6R-Pro, after some first-light photo sessions I realized that instrument is good, and the mount even holds it, but I'd rather not host it on it permanently, its a bit wobbling on the wind. Let's this tube wait for heavy load mount (my other big project).
However, I currently have no visual instrument and missed the dark sky a lot. Since the short 300/F4 tube is the maximum that can fit in my car (not considering collapsible Dobsonian tubes which can't be adopted to photo easily), I decided to build a stool for trips under the dark sky with this 300/F4 as main portable visual instrument.
This was naively conceived as a project for a couple of weekends. Of course it turned out differently, it's now three and it's not over yet. Then I thought, how can I be without photos? At least for a planetary photo I wanted need to add simple tracking, so I decided to make a motorised one.
So, the history of this case of furniture building began with drawing in FreeCAD and searching for laser cutting services capable to work with 12 mm plywood. In short, the plan with the laser did not work out (some of them quoted the price of a helicopter, others were strange or weird, others disappeared in the middle of correspondence, one more said 'I will calculate everything ASAP and reply tomorrow' then two weeks of silence). Anyway, I didn't find a laser guys (PM me please If you know some for future projects), But I found my old electric jigsaw, so I printed out everything on A4 sheets, glued them on with alignment on the crosses in the corners and go ahead.
1. Photo in the process of work. The plywood was glued with epoxy resin and covered with it from all sides for stabilization and protection from moisture.
2. Pulley on the axis Alt, 2GT on 320 teeth printed at once, on the second attempt. The first attempt I printed it laying on the hot bed, but the shape was slightly distorted (the ‘elephant foot’ at its worst), so second time I reprinted with high supports. The Az pulley, 480 teeth was printed from 6 segments and glued together. It will be screwed to the lower, fixed base of the mount.
(Everything was printed with PETG on my Ender3V2 upgraded, with Sprite direct extruder and touch sensor.)
3. Printed and purchased parts assorted, OnStep controller from Terrans with remote handle. The bearing is 220mm, a bit small, but I couldn't find a larger one for a reasonable price, if the stiffness is not enough, I may add some rollers (?) later.
Due to the small diameter of the AZ axis bearing, there was noticeable wobbling on that point. I made 6 PTFE support pads, installed them in 3D printed holders, they slide on the surface of plywood pre-coated in epoxy and sanded with 400-grit sandpaper. That supports were leveled with spacers to aligned them in the plane.
Most of the weight still applied to support roller bearing, but the PTFE sliding items take the load in case of any inclination, so the wobbling feels eliminated completely, while the motor spins everything without problems and the timing belt does not slip.
About the motors, I added 1:10 planetary gearboxes, so no anymore torque issues in case of tube imbalance, the torque is plenty.
Put it on legs for more comfortable access to the eyepiece. The legs are removable and made of 4 layers of 12mm plywood glued with epoxy. This is temporary solution, someday I will replace this tube with a longer one, something like 300 F1:6.5, more suitable for visual observations, especially for planets, and no legs will be necessary for that tube length. There are also thoughts of replacing the 2GT 6mm belt on ALT axis with a GT3 10mm, and reprinting the vertical axis pulley, making it a bit bigger and with a 3GT profile. This will improve rigidity in ALT direction.
But these are plans for future refinements.
In general the telescope is ready for first light!
That's looking very nice Igor and while laser cutting the ply would have probably been nice I think you have done an amazing job with the jigsaw and saved a considerable amount of money and time being stuffed around in the process. That thrust bearing looks like a decent unit too.
It's all coming together very nicely.
