7Wells Observatory Build

[Gina]

I certainly enjoyed building mine and in fact I'm still adding refinements.  My comment was rather "tongue in cheek" as I didn't really care what the total cost has been - it's a hobby and as long as I have enough money to feed myself, keep myself warm and pay the bills, the expenditure doesn't matter.  Life is to be enjoyed.

[old_eyes]

So amidst all the messing around trying to get the observatory working and then the mount behaving itself and waiting for the few gaps between the rain storms, I managed to take my first image with the full set up.

09/12/2019 50 x 120 sec frames NGC7000 Equinox ED80 QHY168C OSC camera

Processed using Pixinsight. After calibration, alignment and stacking I could not seem to be able to correct the background without bleaching all the colour away, so I just did some non-linear stretches followed by a little bit of Local Histogram Equalisation to bring out the structure in the nebula. Quite pleased with that.

Lots still to fix. sensor is not at the right distance, and is not orthogonal. But not bad considering it was more or less a full moon and a stiff breeze.

So I am officially declaring first 'real' light 🥳

[old_eyes]

Yesterday and today managed to get the rolling roof powered with a gate opener.

Beacuase of earlier design decisions when I was not thinking about automating the roof in any way, the motor had to go inside hte warm room with the gear and limit switch poking through to the outside.

This is the outside view:

And this the inside:

I plan a box inside the warm room to cover the motor. Tidier and warmer.

The good thing is it works. Open:

And close:

Those remote control key-fobs are quite useful!

The next step on the journey is to power the south flap. Then I would be able to fully automate the observatory at some point in the future.

 

[Gina]

I have my flap mechanically connected to the ROR using rope and pulleys.  Delightfully "Heath-Robinson" 😄

Can you close the roof if there's a power cut?

Edited December 15, 2019 by Gina

[old_eyes]

26 minutes ago, Gina said:

I have my flap mechanically connected to the ROR using rope and pulleys.  Delightfully "Heath-Robinson" 😄

Can you close the roof if there's a power cut?

I saw your nautical approach to the problem and considered it. I think a linear actuator is simpler with my configuration, but it is as yet an untested idea!

I can close the roof manually if I am in attendance. The key you can see in the gate motor in the interior shot unlocks the drive mechanism. In the unlock position the roof slides easily with a gentle push. I made sure that bit worked!

For automation it is a different problem as in a power cut there is no automation 😮. Has anyone designed a weighted pully system where if there is a power cut the motor clutch releases and the roof is drawn smoothly closed? It can't be done with the usual cheap gate motors, but some of the more exotic self-buiold systems could do it I suppose.

[Gina]

My roof drive motor runs off the main observatory supply of 13.8v which has battery backup.  But in the event of motor failure or whatever my motor unit has a manual clutch which disengages the sprocket.  I can then push the roof closed by hand.

[old_eyes]

14 hours ago, Gina said:

My roof drive motor runs off the main observatory supply of 13.8v which has battery backup.  But in the event of motor failure or whatever my motor unit has a manual clutch which disengages the sprocket.  I can then push the roof closed by hand.

Yes I thought about making everything low voltage in the observatory, but it made everything more complex and bespoke. It was simpler and cheaper for me to use off the shelf mains components.

I may install a UPS to drive computer, power supplies and roof automation in the event of a power cut. All it would need to do is to keep everything going whilst I shut down. A couple of minutes max. But that is for the automated future (if it ever arrives). 

In another thread you mentioned using a leisure battery with a permanently connected charger istead of a UPS. How to you configure that? Is there any isolation between the charger and the equipment to stop noise or transients breaking through, or do you just connect charger to battery and battery to everything else? What sort of charger do you use?

[Gina]

The "charger" is a standard 13.8v PSU, connected directly to the battery and to the power distribution box which includes fuses and switches for individual circuits - mount, imaging rig, ASC and roof control - plus digital ammeters for each circuit and an overall digital voltmeter/ammeter for the battery.  Imaging rigs have a 470µF electrolytic plus 0.1µF ceramic capacitor across the power input to remove spikes or interference.

[old_eyes]

Got some time today to fix the linear actuator south flap opener.

Here it is in position using my usual bodging approach of random blocks of wood and brute force.

It is operating on one side of the flap, but so far the hinges on the flap seem up to it. As a trial I have added 5kg of counterweight on each side of the flap to help the motor, but I am not sure if it is needed. These things pull 300kg.

The actuator has internal stops so I just set up the geometry so that when the actuator is fully retracted (position shown) the flap is in the closed, upright position, and when the actuator is fully extended the flap is down ready for use.

This is the flap closing:

It is not quick but it seems to work smoothly.

Currently operated off the main 12V supply by a DPDT switch in the warm-room. Could be automated in future.

Quite pleased with that.

Lessons learned? Don't operate the actuator whilst your safety locking bolts are in place! I think if I had not turned off the power quickly it would have broken the south flap frame. It is strong and did not like being thwarted!

 

[Davey-T]

Good job, I made a telescopic pier for my obs'y that raises it 300mm using a similar actuator.

Can't see from the video but might be a good idea to have a hinge in the centre if not got one already.

Dave

[old_eyes]

6 minutes ago, Davey-T said:

Good job, I made a telescopic pier for my obs'y that raises it 300mm using a similar actuator.

Can't see from the video but might be a good idea to have a hinge in the centre if not got one already.

Dave

Yes, there are three substantial hinges across the width of the flap. No evidence of any twisting or strain yet, but I will keep an eye on it.

[SamAndrew]

Using 4 of these in my build, good for the money but a little noisy! was accutely aware when I was closing up at 1am and the neighbours bedroom window is only a few m away.

[old_eyes]

1 hour ago, SamAndrew said:

Using 4 of these in my build, good for the money but a little noisy! was accutely aware when I was closing up at 1am and the neighbours bedroom window is only a few m away.

Yes. I have been watching your progress with interest. It is a neat design. Did you sort out whether there would be any excess wind loading with the ‘wings’ partially open?

the actuators do make an irritating whine, but at least it is over fairly soon. Mine take about 45 sec fir the full travel.

[SamAndrew]

Only real way to find out is to test it in action; so far so good, it survived storm Brendan last week while closed. Last night wasn't windy so no issues. Will just keep an eye on it.

[old_eyes]

I have now learned enough about using my observatory to start making small improvements. More will follow in the summer fallow months.

The first thing I have done is to add the iOptron Minipier. This gives me an additional 200mm of height that I can use to get better horizons. I still have plenty of roof height for a larger scope if I want. It also gives me better azimuth adjustment for polar aligning the mount as the adapter plate I was using to connect the altair astro pier to the mount does not have a centre pin.

The second change was to change the brute of a 9.5kg counterweight supplied with the mount to a 5kg weight. This is plenty for the rig weight, makes counterweight poistioning less critical for balancing and moves the centre of mass further away from the axis. All should help performance.

Edited April 10, 2020 by old_eyes

[michael8554]

The moment of inertia is proportional to the square of the distance from the axis to the weight. 

Some say it's better to have the heavy weight close to the axis. 

Michael 

[old_eyes]

13 hours ago, michael8554 said:

The moment of inertia is proportional to the square of the distance from the axis to the weight. 

Some say it's better to have the heavy weight close to the axis. 

Michael 

Yes, You are right. My thinking was that a weight further away would help damping, but the majority opinion seems to be heavier/closer (eg https://www.cloudynights.com/topic/475458-is-there-some-tips-for-counterweight-placement/ and http://www.robincasady.com/Astro/WeightCalc.html).

A lot of the argument seems to be based on reduced stress to axis and motor, but the rate of movement while guiding is extermely small and I would have thought differneces in moment of intertia would be irrelevant. A different story when you are slewing at maximum speed I suppose.

What I did find is that balancing was easier because you move the lighter weight further.

I also found in the first trial that guiding was tighter. However, I had just redone the drift alignment, seeing was different, and hte trial wa only over a couple of hours. I will leave things the way they are at the moment and see what I get with further runs.

One of the frustrations with this hobby is that it takes a long time to work out whether the changes you have made are improvements or not!