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 . 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.
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 . 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?.
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.
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
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.
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.
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
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.
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).
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.
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.
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.
. 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.
. 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?.
I thought you were building an ark with all the rain down there. 
