Jovets Observatory build

[Carole]

Are you having a round slotted dome or a 6 faced roof which you were considering at an earlier stage? 
Since you have created a circular ring for the top of the walls, I am guessing a slotted dome which would be better since you will be able to reach the Zenith.   

Carole

[Mike]

Why would you need a stepper motor? Is the dome going to rotate with the scope? If so what method are you using to ascertain which direction the dome is pointing in?

[Ivor]

Are you having a round slotted dome or a 6 faced roof which you were considering at an earlier stage? 
Since you have created a circular ring for the top of the walls, I am guessing a slotted dome which would be better since you will be able to reach the Zenith.

It's going to be a mixture of both, imagine an eight sided squash bottle top with a slotted roof through the middle. Being so close to the boundary line I've got to keep the 2.5m limit and the walls needed to be high to get over the fence. It's hard to describe hopefully I'll start to building it up this coming weekend.

Why would you need a stepper motor? Is the dome going to rotate with the scope? If so what method are you using to ascertain which direction the dome is pointing in?

Initially I plan to count the steps of the motor and have the Arduino keep track of position. ASCOM sends the target degree to the dome driver and once I know the maximum speed the dome can go without slippage, I should be able to keep it accurate enough. Later I will look at using a magnetometer for more accuracy.

[Canadian Roger]

So an octagonal cylinder with a flat top?  The slit to go up one side and right across the top?

How wide will the slit be?  The roof could have to move very quickly if a satellite you want to track goes through, or near, the zenith. The wider you make it, the better.

I'm intrigued by this, as my Chief Financial Office recently approved freeing up some funds for a springtime renovation.  I've often wondered about modifying a cylindrical polyethylene water tank, or a calf nursery like this one:


These can be had for about $300, or (where's the Pound Sterling symbol on this keyboard?  Ahhh...cut and paste from somewhere else) in the region of £150. 

[Ivor]

You are close, the hatch will be in two parts with the vertical bit will hinge at the bottom and the top section will slide back. The automation of these part will be in  phase 3 as it's more a nice to have and I can delegate this responsibility if I'm not at home when starting the session.

The slot will be 1m wide so plenty wide enough for any scope I'm likely to have.

I love your idea but I'd be weary of the thermal coefficient of polyethylene. I looked into using HDPE as an alternative material to wood but I was discouraged when I discovered a sheet 2.4m x 1.2m sheet would expand/contract 6mm in a temperature range of -10c to 30c which would lead to no end of leaks. I imagine it would be even worse for you.

[Mike]

I would not count on the steps of the motor for position at all. There are many reasons why a pulse would not cause a step or why the dome would move on it's own for other reasons. If I were you I would use some kind of encoder technology or magnets for getting precise positioning.

[Canadian Roger]

Will the top of the octagonal cylinder (the roof) be sloped to allow the rain to run off?

I'm now very intrigued to see this roof.  My observatory is 8 foot by 6 foot, and an octagonal cylinder with a sloped end sounds like it might be something that could be retro-fitted on to my existing sctructure.

[Ivor]

I would not count on the steps of the motor for position at all. There are many reasons why a pulse would not cause a step or why the dome would move on it's own for other reasons. If I were you I would use some kind of encoder technology or magnets for getting precise positioning.

OK thanks Mike, I bought a couple of bluetooth boards and a GY-273 HMC5883L magnetometer, I'll run this off a seperate Arduino.

Will the top of the octagonal cylinder (the roof) be sloped to allow the rain to run off?

I'm now very intrigued to see this roof.  My observatory is 8 foot by 6 foot, and an octagonal cylinder with a sloped end sounds like it might be something that could be retro-fitted on to my existing sctructure.

Yes either side of the opening will be sloped, I'm keen to be careful with any angle though having seen Mark's misfortune I don't want to create a wing.

My design has been driven by the standard size of sheet plywood 2.44m X 1.22m (8ft x 4ft). In the UK you can get a larger sheet 10ft x 5ft I've used this to make the roof oversized on the ring so the roof doesn't hit the walls when it rotates.

I have a new question I can't see north as the house in the way who have other determined north for the pier plate alignment? I have a GPS compass I thought this might be the best approach rather a map compass. Also how accurate does this really need to be, if I think about my current manual approach with a tripod, surely placement of the peg needs to be somewhere between true north and magnetic north.

[MarkH]

Ivor, when you say you can't see north, do you mean you can't see Polaris? If so how about using a ra calculator at a precise time and triangulating of of other known stars.

[Ivor]

I can see Polaris for my imaging (see first page of the thread) but to align the pier plate prior to concreting it in I need to align it to north. See Mark's pier plate as an example.

http://forum.orpington-astronomy.org.uk/index.php?topic=9071.90

[MarkH]

What would you be trying to see north had the house not been there?

[Ivor]

I could choose a reference point due north of the pier from an OS map and use that as well as a compass to reconcile any inaccuracies. In the current situation all I have is a compass, which might be enough I'm not sure how precise I have to be.

[MarkH]

If you find no alternative I have a polar mate, which used with my tripod gives an observatory recognized standard for alignment I'm  happy to help out if need be.

[Canadian Roger]

The Sun will be due south at noon, plus or minus any offset for being east or west of the meridian for your time zone (should be easy for you!).  You could use the door jamb at the right time and mark where the shadows fall.

Of course, the requisite sunny day may be an issue...

[Carole]

I don't think the pier orientation needs to be "spot on" as you can adjust the mount head, but obviously it's best to get close.

Suggestions:
a) Can you not find a way to put a marker on something when you can see polaris at night, and use the marker during the day.  Obviously if you don't get clear skies then this is not an option.

b) The plates on the top of my pier can be rotated (see the bolt underneath the top plates) and as there is a double plate with bolts in between, the level can also be adjusted.  If you do a similar top plate then hopefully if you get it slightly wrong it could be adjusted afterwards.  (see the photo of my mount b= post 12).

Carole