Getting back into imaging after a long break

[carastro]

You are so clever with this stuff Gina.  I can only manage a bit of Blue Peter and  perhaps a little bit of woodwork  

carole

[Skipper Billy]

I would gladly come round and assist you if I was nearer but sadly I am well over 700 miles away.

Best wishes for a full and speedy return to rude health.

[Gina]

That's very nice of you - thank you.

[DaveS]

1 hour ago, Gina said:

My automation won't cost more than a fraction of that.

Somehow I thought you'd come up with something a lot more cost-effective .

Being a cack-handed nerk I'll probably end up buying something off-the-shelf 😆.

[Gina]

As recommended by the late Per Frejval who obtained the motor for me I bought a proper H-Bridge motor driver.

I decided on the Arduino shield version, Pololu Dual VNH5019 Motor Driver Shield, as that seemed an easy way to control it.  That was 4½ years ago and I'm now using the RPi for remote control.  The H-Bridge motor control has inputs for speed (by PWM) and direction and an analogue output for the motor current (each amp of output current gives 140mv of signal).  Arduino has analogue inputs, RPi doesn't.

This means a number of options.

1. RPi linked to Arduino
2. RPi direct - ignoring motor current reading
3. RPi plus my own interface including an ADC

Ideally, I would produce my own INDI driver and have controls for Open Roof, Close Roof and display lights for Open, Closed, Opening, Closing plus possible a light showing motor current very roughly. viz. Off, Normal, High and Limiting represented by Grey, Green, Amber, Red.  Or I could have a linear display in amps.

Edited July 16, 2019 by Gina

[Gina]

Until I get the drive chain attached to the roof and run the motor, I don't know how much current will be needed and whether full speed would be too fast or not.  I now have a rain sensor and could easily connect that into the control system which would close the roof and report back to KStars/Ekos.  With the widefield rig I don't need to park the mount before closing the roof but if I get to use the big MN190 it will definitely have to be parked before closing the roof.  I have no imaging plans for the MN190 ATM.

[Gina]

This is my main thread on controlling the roof :-  Gina's Observatory Roll-Off-Roof Automation (from Page 7) but there's a lot of currently irrelevant information in it and I am about to write a Blog.

Edited July 16, 2019 by Gina

[Gina]

On 07/07/2019 at 12:40, Skipper Billy said:

These work REALLY well - mine sets off a flashing blue light in the indoors office.

https://www.reichelt.com/gb/en/rain-sensor-12-v-dc-m-152-p118916.html?PROVID=2788&wt_guka=54951089435_263550074609&PROVID=2788&gclid=CjwKCAjwsIbpBRBNEiwAZF8-zyeetSC6-sBQe7HbOXJ8ZlIHj0cs_mxpFmbIff0kmP8jJgbx7C-EixoCurMQAvD_BwE&&r=1

The instructions say they need a 12v stabilised supply but mine is 13.8v.  Is this really true - how accurate a 12v supply does it really need?  If it really is 12v exactly I'll have to see if a buck converter will handle that small volt drop.  I think a regulator chip might just.  Another way would be to use two buck converters back to back, one high-low and the other low-high.

Edited July 16, 2019 by Gina

[Skipper Billy]

I always take it as a guide - a fully charged 12v battery puts out nearly 14v - never had an issue.

My sensor runs off 13.7v - 14.1v and has done for many years without issue.

[Gina]

Great!  Thought that might be the case.  Thank you.

[Gina]

Been doing a bit on the observatory roll-off-roof.  There was an aluminium peg that engaged in a hole in the wood frame of the roof at the east end to stop it lifting in a severe storm that was binding.  I'm replacing that with a better arrangement so cut the pin off with a hacksaw.  Also, with some newly arrived PTFE spray, I lubricated the wheels.  The result was a very free moving roof.  A light push and it continues going for several feet or until at the end of travel. 

On to the motor drive.  I released the clutch on the motor to free the chain, pulled the chain through and connected it temporarily to the east end of the roof with a clamp.  The weight of the chain was enough to pull the roof open.  Decided to see if freeing the chain from the worm gear motor drive would allow my to close the roof by hand in the event of motor failure (the reason for choosing this special type of garage roof opener motor unit).  I opened the roof about half-way, pulled the chain through to take up the slack and then (with the clutch free) pushed the roof closed with the chain going through the motor unit.  Found I could do this quite easily.   RESULT!

Next is to try power on the motor and see how well it opens the roof.  After that I shall design brackets to attach the chain ends to the roof framework.

[Gina]

Test successful!   Connected motor to bench PSU set to 13.8v and applied power and (once connected the right way round) the motor opened the roof effortlessly!  Maximum current was about 2A and generally around just 1.4A.

[DaveS]

Great progress Gina!

Can't offer more than interest and support, as your knowledge of automation is way beyond mine. 

[Gina]

I worked on remote control systems in my career (amongst other things).  Technology was very different then though.  (60's & 70's)

[Gina]

I've designed a specially shaped bracket to attach the chain to the open end of the roof.

[Stub Mandrel]

21 hours ago, Gina said:

I worked on remote control systems in my career (amongst other things).  Technology was very different then though.  (60's & 70's)

🙂

 

Sorry Gina...

[Gina]

Not quite that far back!

[Gina]

Wet today so nothing doing outdoors but design is always possible if I feel like it.

[Gina]

I've composed a Blog on my observatory roof automation so will be posting further progress there.  This thread will return to imaging.

Observatory Roll-Off-Roof Automation

[Gina]

Seems unlikely that there will be any progress on astro imaging for a few weeks but who knows...

[Gina]

With the rain stopped I donned my Wellies and went out to the observatory intent on taking some photos of where certain roof parts might go but I was thwarted by a flat camera battery!

It was a worthwhile trip though as I discovered a problem with the ROR guttering.  Luckily, I noticed some drips from the guttering at the stop end having opened the drop down window.  So I reached up and felt in the guttering - water at the supposed high end - gutter full.  Felt at the downpipe end - no water.  Felt along the guttering and the water didn't reach much further than half-way!!  This is in spite of the downpipe end being seemingly lower on the roof end beam.  So something has changed since I built the observatory.  I can't believe the woodwork could have shrunk or expanded by that much so the foundations on the south side must have subsided.  Guess the floor is no longer level.  I'll take a spirit level out tomorrow and check - not going out again tonight (still need to take it easy).

This is the roof and guttering after the roof repairs and before the downpipe was added. 

This would seem to show that guttering slopes considerably to the right (north).  Compared with the roof, it does.  Compared with the wide world, it doesn't - the left-hand end is actually a couple of inches lower.  The only way to deal with the problem will be to turn the guttering round and have the downpipe on the right (south).  It will need a fine day to do this but the sooner the better as raianwater is running out of the guttering at the south end and onto the observatory structure.

Edited July 19, 2019 by Gina

[Stub Mandrel]

16 hours ago, Gina said:

This thread will return to imaging.

 

13 hours ago, Gina said:

imaging... gutters 🙂

[Gina]

I wanted to post about that somewhere - this is where it landed 😄

[Gina]

Been out to observatory.  Opened east drop down window, rolled roof back a bit and the forward hitting the end with some force which shook half the water out of the gutter.  Opened the roof fully, undid the downpipe end and unclipped the guttering far enough back to be able to get it free and lowered guttering and downpipe to empty the guttering.  After that was able to free most of the guttering, unscrew some brackets and get the rest down.  Closed up the roof and came back indoors.  At least the rainwater runoff will now be spread out.  Now having a coffee break.

[Chriske]

2 minutes ago, Gina said:

Now having a coffee break.

Coffee...?😳