Gina's Mini Dome Observatory for Widefield Imaging Rig

[Gina]

I might not go for the conventional dome design for my final micro observatory as I think the mechanics of the rotation system are going to be complicated and awkward, but we'll see.  Building the dome has been very interesting and quite enjoyable which is the main purpose of life

An alternative design I've been thinking about is a variation on the clamshell using spherical sections.  The ability to print shallow overhangs makes all sorts of things a practical proposition.  The advantage of a clamshell design is that it only needs one motor to open and close and nothing to rotate as it doesn't The same idea of linking sections so that only one needs driving that I've used in the conventional dome, can be applied to a clamshell.

Edited June 28, 2017 by Gina

[Gina]

9 minutes ago, Stu said:

Does that mean completely reprinting the whole lot Gina? 

Not necessarily, a darker green bottom part with lighter green top would look alright I think.  Alternatively, I have 2 reels of the current green colour on order which I might use.

Edited June 28, 2017 by Gina

[Dr_Ju_ju]

you only live once.....   I've used the Deep Purple on my D-Bot printer ....

[Gina]

Ah, another D-Bot builder   I have a few ideas for another 3D printer a bit bigger than my Titan but just ideas ATM.  No project in view as yet but I have quite a lot of V-slot extrusion and a few wheels to go with it.   The experience I have had building and modifying the Titan could be employed to build an improved printer.  A new printer would not be anything as large as my Giant printer design but could be slightly larger that the Titan and have other extra features. 

Advances in filament and the Marlin firmware have made a number of improvements available and I would like to include these.  Also, one or two of the deficiencies I have found with the Titan could only be solved by a new build - modification would not be a practical option.

Edited June 28, 2017 by Gina

[Dr_Ju_ju]

I used to have a large Mendel variant but found it was too wobbly, and the D-Bot ticked all the right boxes for strength & rigidity, so I'm re-using the 300x300 bed, motors, Rumba control etc.

 

One thing I'm still not too sure on though, is the slope back to front of the bed & the reliance of the Z lead screws to keep things level (I'm using auto bed levelling, so I want it to start off level).

[Gina]

I noticed that problem with the D-Bot design.  I too would be unhappy with the way the print bed is supported.  In fact the Z rail system is something I would like to improve on my printer and which I think may need a new build to fix.  I think it's already better than the D-Bot though.

Edited June 28, 2017 by Gina

[Gina]

Providing print bed support and precise linear motion is quite a problem and I haven't yet found the perfect solution.  Wide V-slot rail with well spaced wheels on a rigid frame has gone a long way towards it but I am still getting slight rotational vibration in the XY plane about the Z rail.  This is causing a rough surface on the print.

[Dr_Ju_ju]

I've managed to get the bed level, running on the v-rail smoothly, helped by the anti-backlash lead screw nuts (http://ooznest.co.uk/3D-Printer-Mechanical-Parts/Hardware/ACME-Anti-Backlash-Nut), but the proof of the pudding is yet to come..

[Gina]

I've looked at the way the bed support is held horizontally on the D-Bot and IMO the wheels that run on the back rails are not sufficiently far apart.  Any speck of dust or filament particle on a wheel or rail will cause noticeable variation in table angle.  My wheels are 140mm apart.  Anti-backlash nuts shouldn't be needed on the Z drive screw rods as the weight should ensure that the nuts sit cleanly on the rod thread.  Another possible problem I foresee is debris getting into the nuts.  In my design I took care that no debris could get into critical parts.

I don't wish to criticise the D-Bot design too much as I believe it to be very much better than most RepRap printers out there.  Rigidity of the frame is paramount and so many printers are poor in this respect.  Also, the use of V-slot rails and wheels is a vast improvement on round rods and linear bearings.  There are many good things about this design.

Edited June 28, 2017 by Gina

[Gina]

Overnight my brain has been working in the background on the conventional dome rotation drive and support system and has come up with a rough design   The support will be a number of rubber tyred ball bearing wheels at 45° running in a track made of ABS sections glued together.  This system provides weight support, will hold it on an imaginary vertical axis and also prevent wind lifting it off.  The drive system will consist of a ring gear on the rotating part with internal teeth.  This will be driven by a small spur gear on a stepper motor.  To allow for a certain amount of clearance on the wheels, I will use large teeth, probably at least mod 4.

[Gina]

Here is a sketch of the arrangement.

[Gina]

Here is a cross-section showing the dome with its support and drive system followed by a 3D model of the ring gear (orange in the cross-section).  I tried mod 4 at first then decided on mod 3 for the teeth.  The ring gear can be printed in one piece on my Titan printer being 280mm OD and with a pitch circle of 126mm radius (252mm diameter).  The green parts below the dome will be printed as 4 sections and fitted round the ring gear and onto the dome bottom face with solvent welding with acetone.  All these parts will be in ABS.

[Gina]

Pinion for stepper motor for rotation drive.  6t mod 3 to match the ring gear with 64t giving a ratio of 64:6 or 10.67:1.  If this ratio is any problem I could change the ring gear to 60 or 66 teeth for 10:1 or 11:1.

[Gina]

I have 3D printed the dome drive ring gear in PETG filament on my GinaRep Titan printer.  Since this filament is not solvent weldable (AFAIK) I have added lugs with holes to bolt it to the bottom of the dome.  This is the first virtually perfect ring gear I have printed of this size (nearly a foot diameter).

[Gina]

I was planning to print the casing for the micro observatory with this same filament but being a rather dark green, although it will match in with its surroundings, I think it will get very hot in the sun and make the camera and other gear inside also very hot which would not be good.  I am therefore thinking I might be better off using white.  The dome itself and mount cover is a light green and should be alright I think.

[Gina]

I now have ABS printing fine on my  "GinaRep Titan" 3D printer and printing the ring that supports the dome - in three parts - photos to follow.  So if I want to I could print the casing in ABS    The opaque white PETG from rigid.ink is out of stock, unfortunately.   Mind you, the ABS is cheaper

[Gina]

A couple of photos.  Top view and underside view showing two of the three running ring sections and the ring gear place with the holes lined up.  Looks like the brim wants removing.

[Gina]

With the greater strength and stability of PETG filament compared with ABS or PLA I think I'm going to try 3D printing the fork to save a lot of work with aluminium.  This diagram shows the new design (in orange).

[Gina]

Some photos.

[Gina]

Dome now glued onto support and rotation part.  I'll post photos tomorrow.

[Gina]

This applies here too :-

Being particularly interested in printing items that can be used for observatories and other outdoor astro stuff I've been looking further into available types of filament (there's a lot of them) and come across ASA which is similar to ABS but specially UV and weather  resistant.  Review here.

Want to Use ABS in Hot Sun? We Compare ABS vs ASA Filaments

[Gina]

As promised, here are some photos of the dome with the support and rotation ring added.

[Stu]

You must be very pleased with that Gina, it looks fab  

[Stub Mandrel]

You could use it as a space helmet

Would make an excellent Avatar pic...

[Gina]

It is going quite well, yes    Bit big for a space helmet    Avatar pic... that's an idea

Edited July 9, 2017 by Gina