Im building a dome

[Bassnut]

I am following Pmrids (Peter) ROR with interest and was thinking of doing the same thing. But then, because I dont actually have space for the roll off roof area required I had to think again. I have bought myself a WF rig for home (CEM40G, Askar 500, ASI2600mm, more on that later) I thought id make a Dome!. Round anything is hard, so I was expecting a nightmare, this could go so wrong. Im no mechanical expert so I tried to keep it simple. I drew the frame required in Fusion 360 to see if it was viable using 30mm plywood from bunnings and galvanised sheet over it. I printed a flattened frame template from Fusion360, scaled it up, and started cutting with a jigsaw. The dome is 1500mm in diameter. I extended the bottom past 180deg because that allows a single shutter to open far enough without a seperate fold out section, and it looks cool. Looks cool always matters :P. Im still apprehensive how it will pan out, but its going well so far. I will 3d print a rack and pinion for the base and slot cover (in sections) and use small DC geared motors and a PLC to automate it.

[h0ughy]

Wow that's extremely industrious and look forward to seeing the results of your hard work

[AdamJL]

That is incredible. I’m definitely following this one along. Good luck in your endeavours!

[Bassnut]

thanks David and Adam. The 3D drawing was only to see if I missed something geometry wise . It is actually not that hard, not required. Im winging the rest :D. Im guessing, once the slot position is right for the scope at the start of a session, the dome always just moves at rate RA?.

[AdamJL]

Yeah it should but syncing is going to be the fun part

[Bassnut]

OK, I thought so. Either I sync manually at the start of a session or sync by position sensors (encoders, hard) or optical transmitters on the OTA and sensors looking at these on the slit. far IR probably.

[multiweb]

Very cool Fred. :thumbsup: I thought you were building an ark with all the rain down there. :P

[strongmanmike]

Wow, awesome Fred, this is going to be a cool project to follow..so far so good. You're a pretty cluey bugger, so I have faith that it will be a great success :thumbsup:

Mike

[Startrek]

Fred,
Wow what a project, that’s really getting your hands dirty
Looking forward to seeing your progress
Cheers
Martin

[appiice]

Hello Fred

I built a 3m dome a few years ago, can I tell you some of my experience/s?

I think there are photos of the process here but if not I can put up a link.

I made mine from aluminum T section for the ribs and .6 and .4mm ally sheet for the covering.

I cut the covering segments and crimped and rolled the edges so they would sit flat on the ribs. Initially, I did the segment in one piece but then went to a join about half way up. I used a " non setting " mastic between the vertical joints and have no problems with leaks - at all.

If I was to build another one -I'm not! I would change the design from a rolled rib to a series of straight cuts, maybe 250mm or 300mm long, that would allow for the sheeting to be trapezoid shaped and because the rib was flat under the sheeting, the sheeting could be folded. Mine needed to be crimped to stop the covering from creasing. Overall it would be a much simpler way of building a dome.

Just be careful about the covering, I have seen lots of ply and or fiberglass covered domes and the all have one thing in common - they eventually ( or sooner ) leak. Silicone isn't your friend, good planning and building practices are.

I would look into the cost of gal sheet and aluminium sheet, the gal may be a little cheaper but you can cut he ally easily by hand or by circular saw.

Hare and Forbes have folder / guillotines that are fairly cheap as well that would handle both materials.

As for control, I'm using Levesdome http://www.dppobservatory.net/DomeAutomation/DomeDriver.php?msclkid=8059d488c210 11ec82b9b3b01fecee62 to control the dome, through ASCOM, it works well.

If you have any questions or want to talk to someone who has done what you are doing PM me.

Ed

[Bassnut]

Thanks for the encouragement guys, it's going to be an interesting exercise!.

Hey Ed, thanks very much for all the info and the link, very interesting read!.

This dome is only 1.5m dia and pretty light!. Ive already cut the ribs out of 30mm ply so ill go with that, although your idea of straight cuts is good.
Im thinking now of covering with 3mm Australian hoop ply rather than gal or al, its light and easy to work with for me. Im not worried about leaks. Ill go by my past experience and use gorilla or t-rex tape over the segment joins, its thick, flexible, waterproof, strong and uses very aggressive adhesive. Ive used it before on external joints incl roofs and found it amazingly effective. Remember the dome is only 1.5m.
For control, i used to be an industrial automation tech, so this part i want to do myself as part of the challenge. I will do the control entirely with a PLC. Not software and ASCOM on a PC. Im familiar with programming them and they are made for this kind of application. dome control (the way I will do it) is much simpler than some of the machine automation projects ive designed in the past . I noticed on your link it used switched motor control. This is very crude, i will use variable speed motor controllers, it will be smooth and quiet, not stop-start. The syncing math in the link looks frighting !. Instead, I will use a variety of sensors to sense scope and dome position and provide closed loop real time control.

[Startrek]

Fred,
I opted to make my own custom home made Dome control made up of electronic timers, switches and electromechanical relays , very primitive but works ok
However I do run into problems above 70deg in Altitude where the object is moving towards the Zenith , I have to override and manually rotate the Dome around to keep the motion of the object within the 600mm slot opening
Most objects I can track automatically for hours without manual intervention
Control box and gear cost me $450 and I just wired it into the existing NexDome motor control box
I adjust the timer for azimuthal rotation increments based on the predetermined path and movement of the object , I have a window of error as my slot is 600mm wide. If the slot was only 400mm wide it would restrict this system and probably wouldn’t work that well
I was thinking of using a old April PLC with handcontroller programmer but these things have no replacement parts anymore so I opted for a cheaper simple system. New PLC’s aren’t cheap

Cheers

Martin

[Bassnut]

Martin
Thats a very pro and neat job, well done !.
Ok, PLCs aren't cheap but it will be a small one ($300-400). Im determined to use one because I know how, they are opto isolated in and out, built in relays so no extra hardware and utterly reliable. Ive seen them last >20yrs going hard 24/7 in harsh conditions. The one I used at itelescopes ROR has been going 24/7 for 9 years now without a problem.

Partly what will make the control simple is i will mount a small long range ultrasonic proximity sensor (ok, not cheap, $300-400) on the OTA rings looking at the dome slot edge. If the slot disappears, ill just nudge the dome a bit more till it comes back (basic closed loop). Then i dont have to deal with fancy software, geometry, alignment and horrendous math. Ive heard horror stories getting that right, even on commercial domes. I may be able to do initial sync and flips with this, havent thought about it yet, but i can do this manually at the start of a session anyway, its at home, not remote. Ive realised dome tracking speed is so slow I may have to use stop-start tracking after all, but with gentle acc/dec on the drive.

[strongmanmike]

Clever approach, makes sense

Mike

[appiice]

Hello Fred

Sounds like you are on top of it! I was suggesting the metal covering as I can't remember seeing any wood / fiberglass domes ROF's that stayed waterproof.

Best of luck with your build.

Ed

[Bassnut]

Thanks Ed. You have made me think more about waterproofing. You're a builder so I have to consider.

[marc4darkskies]

An ambitious project Fred! Respect. Looking forward to watching your progress. Good luck!

Marcus

[Bassnut]

Thanks Marcus.

Today I assembled the ribs and a quick waterproof undercoat, pic attached.
Is it dodgy?, of course it is. You wouldn't want to get a ruler near it, you dont need that kind of negativity in your life.

[h0ughy]

The sphere of death defying acts

[Sunfish]

A thing of beauty and utility . Great work

[AdamJL]

Looking great, Fred!

[strongmanmike]

Ha! looks like an artwork sculpture, very cool :thumbsup:

A mini Barry Amstead structure in the making ;)

Mike

[xelasnave]

That's the spirit...you may have issues with your first one but after a few it becomes easier:D

I am in awe.:thumbsup:

So many times I have close to having a go which given the initial planning gives me some idea of the undertaking your have set upon.

And it is good creating an audience as hopefully our prescence will encourage you to put the time in a provide photos and progress reports.

Why shouldn't fibre glass be water proof? I think they sometimes use it for boat hulls.

Fantastic.

alex

[Bassnut]

Thanks for the encouragement guys.
Alex. Yes, the initial planning is frightening, but once you get started, winging on the fly reveals how much easier it can be.

It looks like small progress today but significant. After overthinking for hours I decided to go for 0.55 mm gal sheet covering instead of 3mm ply. On this test segment, It turns out its easier to work with, you can bend more. I nicked the edges folded them in level with the frame and screwed on. the edges look ugly, but ill cover the segment joins with wide flashing tape. Thick, sticky, waterproof and flexible, it will look fine and hide the nicks and screw heads.

Who ever dreamed up "measure twice cut once" obviously never built a dome. What if every-single-time you measure its different!!!. Spend all day measuring?, so silly.
Sometimes you have to use common sense, eyeball it and just get it done.

No measuring at all with the segment covers. Push gal against ribs, run round the inside against the ribs with a texta and start snipping, easier than I thought it would be, perfect!.

[strongmanmike]

Great work Fred, you are motoring along :thumbsup:

Mike

[Bassnut]

More al segment covers fitted today. I switched to a cheap Ozito jigsaw instead of tedious manual snipping. So fast, so loud (thin al is an efficient sound transmission device). What struck me was how stiff the whole structure became when the curved al was screwed on. It almost doesn't matter how stiff the ribs were.

[Hemi]

Brilliant and beautiful

[AstroViking]

Looks good, Fred, and progressing really quickly.

[appiice]

Hello Fred

Looking good! likely to late but as well as the tape over the joints I would look at one of the " non setting mastics " to seal between the sheets.

They are better than silicone as they skin where exposed to the air but other wise stay " wet " from memory they are about the same price as silicones. I brought a box from a local caravan repairer and they were cheaper than bunnings silicone.

And without meaning to rain on you, do you plan on being in the dome with your scope or will it be a remote setup?? I realised you said 1.5m in diameter when my brain was thinking 1.5m radius!🤦*♂️

Ed

[Bassnut]

I left a bit of a gap between the sheets, so yes ill look into mastic also, i was wondering what i would do with the gap, thanks for that!. Better than the middle of the tape hovering over the gap or silicone. I dont intend to be in the dome whilst imaging, although im pretty sure theres space enough to get in it if i have to, its only a small refractor.

[appiice]

Hello Fred

That would be, once you have one under your belt, a second bigger one won't seem like a problem at all.

What are you going to have the dome spin on and how are you thinking of driving the motion?

Ed

[Bassnut]

Ed
I think its one of those things you only built once, and do a ROR next time, its not a trivial task. :P

The dome will sit on a 1m odd high round pedestal (with an access hatch).

The driving, well thats a head spin. The last resort will be a 3D printed circular rack and pinion in sections but thats a monster print job, so im thinking of other rack like things like timing belt or chain stuck to the side, even bolts every 20cm or so as "teeth".

The latest learned thing (bit obvious really) is the waste in cut offs, some 30%. Round is a bietch.

[Bassnut]

A bit of unexpected success today.

Angle aluminum is very useful in building an obs, wheels can run on it, the angle part can be used to guide with more wheels say on a ROR. Its thin and strong.

But its straight, no use on a dome. I need to make a curved rolling slot cover with extra wheels also for guiding and some way to stop it falling off. Im thinking more tedious chunky circular bits in plywood from a large sheet.

BUT NO, you can bend angle aluminum into a circle without some fancy bending machine, I kid you not!. (I can hear mechanical experts saying duh, im not a mechanical expert).

Upon googling, turns out you can turn angle aluminum into butter and bend anywhich way by annealing it!.

Looses some strength but I dont care. to anneal, you heat up to a specific temp and let it cool naturally. How to know the temp?. its nuts, do some squiggly lines with a sharpy (a sort of texta, bunnings have them) and when you heat the al with a blow torch you know the temp is right when the sharpy lines disappear.

So off to bunnings, get a bunch of angle al, a blow torch, sharpys and start learning. The test went very very well!.

[Bassnut]

all the segment covers on now.
As a complete dome, it won't go through my workshop door, a real pain working outside (it can get windy cold in Torquay), so I separated the 2 halves and will work on rails etc separately in the workshop. What a difference!. Access to the slot is now soo easy and convenient. once rails are completed (and pretty much everything else), ill just screw the 2 halves together and install the fixed slot covers.
Now that I know how to bend angle al, no chunky ply for the rolling slot cover, hopefully, ittl be sleek and slim built with al and gal only.

[AdamJL]

Ha that looks amazing! :) Well done, Fred.

I notice you have a Ryobi drill press in the back there as well. Are they any good? I need to get a drill press at some point.

[Bassnut]

Thanks Adam.
The Ryobi is the best cheapest at bunnings IMO at $269 and suits my occasional use, cant be bothered spending more on this. Drills smooth and true and has good reviews. Although I like Ozito cordless tools, their drill press is rubbish (well, its $129!), wobbles all over the place, bad reviews. These 2 are the cheapest by far, not a big choice at bunnings.
you see, bunnings is 5 mins down the road, i live in bunnings, anything else is far away, im in regional victoria.

[multiweb]

:lol::lol::lol:

It looks awesome Fred. Quite a feat to match curved beams like that and get away with it. I agree with Ray. A thing of beauty.

[Bassnut]

Thanks Marc. Well, i didnt get away with it entirely. Had to get a ruler near it again and make some adjustments so the cover slot will roll over the hoop. It has to be the same diameter right round, damb it.

[Bassnut]

Actually, that part wasn't so hard. I Drew the dome in fusion360 (free version, any CAD software will do, like sketch up), captured jpegs of different views along with the background grid to give scale, printed them at A3 size, measured each item with a ruler, multiplied by the grid scale and got the height of each rib. The diameter curve of each rib is the same so I only needed the height and angle of the end cut for each rib. string and pencil on the ply sheet for diameter and cut to height/end angle. Printing scale is almost random, so the printed background grid made that irrelevant. If anyone wants the original captures, your wellcome, can be scaled to any size with the aid of the background grid on each pic.

[Bassnut]

After days of considering a 100 ways to drive the dome, ive decided to 3d print a circular rack afterall, because i know it will work. Custom made racks are crazy expensive.. To design this I thought would be a nightmare, but no, to my surprise a free plug in for fusion360 called Helical gear plus (also does straight) is super easy. Enter diameter, number of teeth, teeth pitch and your done. Ill split it up into printable segments and add mounting holes. The gear to match is easy. The attached pic shows a list of steps that were just me just mucking around with parameters. I have bought and tested a bunch of 12v geared motors off ebay at $24ea that albiet are small, but strong and robust (al case and brass gears), and given the price ill use 2 or 4 or them (or more) round the dome in parrellel. Less stress on the ABS rack that way too.

[Bassnut]

this might be a bit boring, unless your into DIY domes I guess :P.
A bit of a milestone today, finally got the slot door and its wheels sorted, along with making it rainproof, its been a bit of a challenge.

Turns out bending PVC angle with a heat gun is easier than al, it turns to putty, difficult to handle melted, but you can do anything with it.

So I used angle al for strength (wheel guides)and angle PVC to rainproof. Including U section (Yeah, bending U section, who would've thunk that was a thing :shrug:)
The pic is pretty rough, but will all will pan out in post. Ill use Topaz magic :D

I lost 2 days of stuffing around with adhesives thinking that would look cleaner than screws and pop rivets. What a disaster, slippery, al moved all over the place and what a mess, my hands will be black for weeks. Liters of turps to remove and back to trusty screws and pop rivets.

Round everything continues to be a painful headspin in every way possible (All structural materials are supplied flat, nothing is usable out of the shop).
But I must say, im OK with it, occupies the grey matter :thumbsup:

[strongmanmike]

Looks professional in that close up, nice :thumbsup:

Mike

[sheeny]

Well done Fred.


As an engineer I appreciate the challenges of your design, and I'm following with interest. Nice job on the bending.


Al.

[Bassnut]

Thanks Mike .Professional :lol:. I wont show a pic of the outside yet, its too embarrising, much adjusting was done, so many extra holes :P.


Thanks Al. As an engineer, you must groan at what hackers like me do :lol:. Everything is from bunnings and hand tools, its sooo time-consuming. I bet theres a 1000 better ways to do this but I DONT CARE. Im dodgy and proud :P

Today, guide rollers.

[Bassnut]

Today, drive for the slot door.
Rack and pinion is easy for a ROR, straight rack cut to length and a gear to match.
Curved rack for a dome is a bit of a problem, Id hate to think what a custom diameter curved rack would cost. I see flexible rack for sale but for huge money, and it seems to me the spec would change the more it was curved.
Anyways, i thought id post this update as its as it solved a problem unique to domes. And I havent seen this solution on the net.
ABS 3d printing is not suited to small engineering mechanical parts, so I made the rack and gear big and chunky. The gear goes onto a 6mm gearbox shaft with a flat. That would last 5 seconds before stripping the ABS and spinning. So I alradited a metal knob with a grub screw in it into the gear, so strong.
Ill use the same rack but a different diameter for the dome drive. The rack was printed in sections (size the printer can take)that can be easily be bolted together. Those segments BTW can be printed by many 3D shops in OZ in 5 days for about $10ea. I will use about $50 in ABS stock on rack and pinions for the whole project. The $20 motor/gearbox from ebay in the pic also has an encoder attached, so if something goes wrong whilst opening /closing the controller will know immediately and alarm.

[Joshua Bunn]

This is very cool, Fred. wonderful ingenuity and it looks great. :thumbsup:

[Bassnut]

Thanks Joshua :thumbsup:.
Small update.
I taped the segment joints up with Byute Flash. Got a bit worried with the wrinkly look, but with 2 coats of flat primer it's looking ok, ill use many flat white metal paint top coats. Flat paint hides imperfections.
The inside is painted with flat black Dulux Metal shield epoxy enamel. This is SERIOUS paint:lol:. The pic shows just one coat of this flat black enamel over white primer. Never before have i seen such coverage of black top coat over white!. One coat to my surprise will do!.
Ive always liked Dulux for pigment density, but this is nuts. It was very thick, possibly due to the temp being 10 deg :P and twice as much paint used over coverage stated on the can. Lesson learned, paint metal when its cold, half the work!.
The 3D printed rack fitted to the slot door worked a treat on test :thumbsup:.

[strongmanmike]

Wow looking good Fred, you're having fun, huh? ;) :thumbsup:

Mike

[LonelySpoon]

That sealant is a good way to go, Fred.

It's all coming along nicely.

N

[Bassnut]

Thanks Mike and Neville.
More challenging than fun id say :P.
Yes, the flashing appears to be a good guess, I couldn't think of any other way that wouldn't look worse, given my skill set ;).

[Bassnut]

Progress. Dome base built using mini ripple gal. Very light, flexible and stiff once screwed on. The rail for the dome concave rollers was easier than expected to fit. Rather than bent angle, flat 3mm al bar was much easier to bend
and fit with angle brackets, stiff as. Its true within a 1mm or so.

[Startrek]

Fred,
Brilliant design and clever use of ripple gal , really strong and easy to wrap and screw
Looks great !!
My only observation , being an Obs I’d be using stainless 302 or 316 fasteners and alum small angles etc… like I used in my NexDome. Plated and even gal screws and small brackets rust out after a couple of years , even quicker when your Obs is 200m from the beach like mine is. Salt air is a killer on cheap plated and gal fasteners etc… from China.

Cheers
Martin

[LonelySpoon]

Nice base, Fred!
Two observations:
1. Instead of brackets and the associated electrical differential causing breakdown /rust, I routed a groove in the base and dropped the ring into that.

2. A year later i ripped that out and replaced it with a hoop of rolled tube, with skateboard bearings. Almost no friction, can turn it with one hand.

Getting tube rolled for my 3m diameter dome cost only $158.

Neville
LSO

[Bassnut]

Thanks Martin and Neville

I hadn't thought of the corrosion or rust damn it, although im aware of electrical differential causing breakdown. It was hovering in the back of my mind for a little while but I barged on regardless.

Im not doing this all again, but i will bury everything in metal paint now. This should last until i leave this mortal coil.

I had thought of rolled tube, done by a local shop, but it sounded expensive, i didnt realise it would be that cheap!. I dont have a router or be able to make a slot accurate enough for the ring either.
Ive tested a concave roller on this rail, very smooth and friction free, better than i thought, so I bought a bunch, adjustable.

[Bassnut]

Put the dome on the base for the 1st time today (no wheels yet, or rain cover between the dome and base). Its looking a bit janky still, no top coat paint yet. Suddenly realised access might be a pain with the base door, so ill fit a hatch to the other side of the slot (not shown) to allow just stepping in
To give scale, its 1900mm high

[xelasnave]

That is brilliant Fred great effort.
Alex

[marc4darkskies]

Looking good Fred!!

Use a hose to simulate a rain storm to make sure you haven't overlooked any sneaky water ingress points!

[Bassnut]

Thanks Alex and Marcus.
Absolutely ill be rain testing, was always the plan. Why would you mention this?, no faith?, doubting my vast building skills? :eyepop:

Today I fitted the adjustable wheels (for sliding doors, from bunnings). Was totally surprised how well that went, the dome rolls very smoothly with a finger push.

The quick-release hatch allows very easy step-in access. I was concerned given the small size of the dome that access/standing inside would be a problem. its not.

[hrcoleman66]

Wow, That's progress!

Looks like the conversations standing around at ASOG have born fruit.

BTW, we missed you last week. I was all ready to offer you a seat as soon as you walked through the door.:lol:

Seriously though, Careful of those rollers. Exposed to UV, they get brittle and crack.

Cheers,

Hugh

[Bassnut]

Thanks Hugh, yes progress.
A rain skirt will go round the dome base. The wheels won't be exposed.

[Startrek]

Fred,
Great progress , looking good
Yes, one design fault with NexDome is they use 4 external nylon wheels to guide the shutter opening ( they should have weatherproof hoods or shrouds but it’s all $$$ )
Mines been up for 16months now and although they use UV stabilised plastic , I can envisage replacing them within a year or two.
The Dome itself is UV stabilised ABS and is guaranteed for 15 years ( still looks brand new )


Looks like your not to far off finishing it ( probably more satisfying building your own Obs from scratch)

Cheers
Martin

[strongmanmike]

Eeeeexcellent Smithers...eeeeexcellent :thumbsup:

Impressed with your ingenuity Fred, every post in this thread has put a smile on my face :)

Mike

[LonelySpoon]

Hi Fred,

Any ideas for the skirt?

I started with flexible garden edging, but found after a while it was too stiff and binding/dragging on the overlap I'd built in to the base ring.

Changed it to thin, flexible concrete jointing stuff, ("insertion rubber"?) which is working fine.

On my old 2m dome I used the tar-backed roof flashing, which could be flared out at the bottom as necessary. (I think that's what you used on your joints?)

Neville

[Bassnut]

Thanks Martin and Mike :thumbsup:

Neville. This pic is what im doing, pretty rough and not accurately to scale. The PVC angle and bar used are pretty thin and flexible, but stiffen up when bent with a heat gun. I used a rubber strip to pack out the dome ring diameter, I made the ring too small, it should have overhung the base ring, but most of this build design was on the fly as I went.
I cant really use rubber on anything that shows externally. Bunnings only has black, this whole thing needs to be white (to match house,daughters order). I tried to paint black rubber white, too flexible, didnt go well.

I haven't shown flashing tape on the pic, it and sealant will be applied where required.

I could have just made one large skirt over everything, but im trying to get the interface between the base and dome to look as slim and non-clunky as possible.

I thought about flared Buyte flashing tape, its used on the segment joins and the slot cover, but it does look a bit loosy goosy, I thought id try a bit harder on the base.

[marc4darkskies]

Not for one minute! ... 30 seconds or so maybe. 😁

Oh, and make sure you remember to put a telescope in it! ;)

[Bassnut]

A bit of a techy update.
The structure is finished and in the rain, no detection of leaks so far.
3D printed rack and pinions fitted and tested with motors.

I used 4 motor/gearbox/gears around the dome rack in parallel to spread the load because they were cheap and I had them. Very strong.

Spring loaded door hinges from bunnings worked a treat to mount the motors, covers dodgy alignments to keep gear/pinions nicely meshing.

The 2 motor drives (Pololu MAX14870 $28) are remarkably small but easily handle the small load allowing smooth accel/decel and current limiting.

The plan to use an ultrasonic proximity detector (Sensortechnik UPR-A 1500 CP TVPA 24 C $80 on ebay, more elsewhere) instead of fancy software to calculate dome rotation, on test works better than expected. Its a proper industrial sensor with a built in teach function and tracks the dome slot very well.

The dome top has no electrical connection at all with the base (no nasty slip ring). It will communicate with the base via a wireless link and the slot cover will be powered by a battery, charged by a small solar panel on the top.

Ive decided to build/program the dome control electronics myself using Picaxe 28X2, RF transceivers and custom PCBs instead of a PC or PLC, more fun, way cheaper.

[Bassnut]

Sorry, missed the gear part

[AdamJL]

Gosh I love this project!! Amazing work, Fred

[AstroApprentice]

Hi Fred,
Great project and an excellent build.
Could you please elaborate on:
"The plan to use an ultrasonic proximity detector (Sensortechnik UPR-A 1500 CP TVPA 24 C $80 on ebay, more elsewhere) instead of fancy software to calculate dome rotation."
Will you attach the sensor to the scope? If so, I can see how this would work perfectly for an Alt-Az mount, but GEM mounts can place the scope at odd angles resulting in even stranger dome slot positions for the scope to view through. I'm eager to see how you overcome this.

[Bassnut]

Thanks Adam!

Jason. Yes the sensor will go on the scope and it is EQ mounted.
Except for near meridian the tracking is simple, its a small refractor and the slot is big enough to view through just with the sensor tracking the slot edge.

I got a bit worried near the meridian when the sensor started detecting the top edge of the slot, what a mess i thought, but thats fine!, the dome just keeps rotating longer on this detection until this edge also disappears and the slot eventually flips right round!.

I do have some doubts about every orientation, i suspect (unless I can code this situation in, the dome motors have built in encoders) meridian flip and switching from north to south the dome will need to be set manually at the start, but since this is in my backyard and i tend to only image one object a night anyway, im fine with this. I manually operate flip on my remote rig too, its just easier, so im used to it.

Ill have a sensitive wifi video cam (baby monitor, can see in near dark, although i might turn a light on for this) in the dome so i can do all this remotely from inside.

[strongmanmike]

Ingenious approaches and skills Fred, nice work and good to hear you have no leaks, after a minor seal improvement, in one section of my entry door, neither does my 3M Scopedome, phew!

Mike

[AstroApprentice]

Hi Fred,
I wonder what will happen when the scope is on such an angle that the sensor detects the slot top and side simultaneously - could the system become ‘stuck’? This may be a very rare situation… anyhow, I hope your sensor works well as it will eliminate the laborious setup measurements needed for traditional dome slaving.

[Bassnut]

Thanks Mike. Im told every dome leaks at some time. I cant wait.

Jason. The sensor has a simple on/off output, it detects anything in its view. Simultaneous edges doesnt matter, will just cause rotation regardless.
Actually, I think this will make handling mount flips easy. On a flip it will just keep rotating untill the slot is clear.

[Bassnut]

A small update.
I designed and built a PCB for dome and shutter control.
It has a motor controller and radio transceiver on it. Given the dome top has no electrical connection with the base, radio control was required for the top.
Ill have 2 of these with different software. The base controller will drive rotation and the top shutter operation. You don't need all this really, but you know, i did this because I could, and it was interesting to do. The transceivers act as wired RS232 devices so I can do anything I want, like monitor battery voltage, shutter microswitches and any problem that might ensue on the top remotely. Base rotation and shutter motors are fully accel/decel/speed controlled too (not your crude relay hammering), so less stress on motors/gearboxes. I made the PCB a bit universal so I can turn lights on or make an alarm ect, its got lots in/outputs.

[oska]

That's awesome Fred, really impressive. Not many are brave enough to use the pic these days although they ruled in their day. Really tidy job :thumbsup:

[Bassnut]

Yes well, dated perhaps, im using the PICAXE version(Basic, a totally integrated and stable environment). I have found what you can do with a micro is more important than how flash it is. One line of code can do what an arduino needs many lines for, and faster. It allows fast and intuative coding. Also i must admit, im used to it, in my comfort zone. The Arduino ADI is powerfull to be sure, ive used it, but PICAXE kills it for fast reliable results for simple machine control. And you can just buy the PICAXE PIC chip for use with a custom PCB.

[oska]

I wouldn't say dated, I'd say old school (with reverence). I'm not at all implying you should have used arduino, in fact I'm more anti-arduino because you don't learn how to do thigs properly, kinda like getting a chauffer and thinking you've learned to drive. PIC's and HC0x were my faves in the day depending on the task. I've scoured too many datasheets to remember. Arduino makes it super easy in both supply (OMG quantity lead times of the past!) and coding if you can suffer it's limitations or just want to use it and don't care about the why & how stuff. I mean you can also easily sidestep the "arduino processing" stuff and use it properly and enjoy the swathes of hardware targeted at the environment. I use ESP32's or STM32's mostly, again coz they've made it too easy not because I can't otherwise.
Anyway, the result looks A1 you should be proud.

[Bassnut]

Update. So ive cranked up the automation design a bit and made/coded a wireless remote control box for it (no PC or wifi needed), the box is repurposed from an earlier timelapse project. Its old school, switches and buttons, no menus to surf through.
It continuously monitors conditions like weather and shutter status. If shutter to base comms is lost, or rain ensues whilst still open for some reason, and a few other operational failures, then an alarm goes off. Its a convenient device to have next to my bed (with display off) and alarm only when the situation is dire whilst imaging.

Its proving very useful for installing/diagnosing the dome drive system. It has manual and auto drive options (with limit switches) and OBS light dimmer functions. So i dont have to be in the OBs to test it comprehensively.

Ive been testing dome rotation automation using a Velleman board and Lesvedome ASCOM driver, as an interface to my motor controllers. ive lost a bit of confidence in the proximity sensor idea by itself, and given the ASCOM driver and interface board were so cheap (Maxim DL has scope position parameters built in) I gave it a shot.
And ASCOM control allows other scheduled/weather functions too (via DL maxim). I find ASCOM generally flaky though, I might revert.

Anyways, progress is slow, but I have the time and the weather will be **** for a few months yet. Ill be well prepared when it gets better.

[xelasnave]

You are a brilliant man.
Alex

[Bassnut]

haha thanks Alex. Not so good with the mechanicals though, but I can overcome deficiencies with electronics and coding. inefficient, but if it works it aint cheating I recon.

[Startrek]

Fred,
I agree with Alex, clever fella !!
Enjoyed the journey with your new Obs
I didn’t buy the proprietory Voyager Dome Control system for my NexDome instead I made my own “Startrek” signature vintage Dome rotation control kit made up of electronic timers relays and switches.
Suits my needs
I’m not one to go to bed whilst imaging with a fully automated robotic system and find all my data ready for me to process in the morning. I suspect in the future there maybe fully automated post processing too , so you wake up the morning and find your final image on your iPhone. Who knows what the future has in store for us ?
I’m a bit of a Stargazer and tinkerer , I like to get outside under the stars , in the cold and amongst all the moths and mosquitoes, keeps you on your toes and keeps the brain busy

Cheers
Martin

[Bassnut]

Martin,
Heavy duty electrical and neat , nice work :thumbsup:.
I like the clear top box, ill do that too.
Well, you say you like to be always up during imaging, but that's a tough call. When several nights in a row of clear skies for imaging are available you will suffer methinks. All you need as a minimum is a rain sensor with an alarm and sleep becomes normal. I understand the joy in being up the whole time, done it, but megadata is the last mile,and thats hard with no sleep.

[Bassnut]

update. ive been playing with the Lesvedome PCB/ASCOM board and too find it very usefull for synchronised dome rotation. Its a bit clunky, as im only using it as convenient USB/ASCOM interface to my own controller, but easy to do.
the pics show closed /nearly closed open/nearly open limit switches and the homemade rotation encoder. The limit switches are brilliant! ($35ea from Altronics), they are very robust and adjustable in every way possible, very easy to set up.
I went with closed /nearly closed, open/nearly open control because it allows very smooth operation with a speed controller and much better system monitoring. 10% of coding time was open-close operation, easy, and the other 90% for what if something goes wrong!. So many switches allows constant monitoring (and instant alarm/response) to switch sequencing errors, motor failure/overloads and automatic recovery proceedures.
Why bother. Well, given rain and still open is a bit catastrophic, being able to recover from that automatically, or alarm early before destruction is a bonus IMO
I can also just lean over in bed and push close at all costs on my radio remote control if needed on an alarm.