Observatory automation first step - motorised roof

[RobertM]

This is the first step on a road that will, hopefully, allow the observatory to run through the night unattended.  Also I'll (hopefully) be able to take advantage of those clear slots that we often wake up to when the weather forecast says cloud the whole night   Well of course all this is theory but it should work - others do so why not !

The first purchase is one of these Ducati belt drive Garage door openers http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=251238092989.  I've been looking around for a cheaper belt model for a while now but most of them are chain drive and are likely to be too noisy at 3am - must think of the neighbours !  This one seems just the ticket and has some really neat features and more importantly lots of documetation on the electronics.  It's almost the same as the one from Screwfix but has an uprated load capacity of 100kg.

The next step is fitting it followed by building an ASCOM controller with interlocks to prevent any expensive mistakes.  I have quite a few ideas in my head and also a collection of notes with various sensors and designs and the like which I'll share as the project comes together (or doesn't) over the course of time.

Got to do something between clear spells, I was thinking of building a Chieftain tank 1:1 out of lego but then I thought the automation would be more of a challenge and give the weather gods something to mull over

Robert

[Carole]

Also I'll (hopefully) be able to take advantage of those clear slots that we often wake up to when the weather forecast says cloud the whole night   

So how is the roof going to know when it's clear Robert if you're in bed asleep?   

Carole

[MarkS]

I have no plans for a motorised roof (at least not yet).  However, I reckon my roof will weigh 300-350kg so I'm using proper roller bearing wheels to overcome friction - each pair has a load capacity of 270kg .

Next week the wood arrives for my Easter project - a 4m x 3m shed for Dee.  The basic construction will be identical to my observatory plans (except no roll-off roof) so this will give me a chance to iron out any design problems before the real thing!

Dee mentioned something about being treated like a Guinea Pig but I swear I've never shut her in a cage 

Mark

[RobertM]

Also I'll (hopefully) be able to take advantage of those clear slots that we often wake up to when the weather forecast says cloud the whole night   

So how is the roof going to know when it's clear Robert if you're in bed asleep?   

Carole

Carole, that's a silly question !  Roofs can't think

But seriously, there will be monitors for clear skies as well as for rain plus a few others.  I've yet to do the process flow chart but it won't be complex.

Robert

[Fay]

as long as you don't rely on the forecasts Robert!

[MarkS]

I've yet to do the process flow chart but it won't be complex.

Maybe this will help:

System State     Action to perform
------------     -----------------
Raining             Close the Roof
Clear               Open the Roof
Clear&Raining    System Error - Windows must shut down

[Carole]

Carole, that's a silly question !  Roofs can't think
But seriously, there will be monitors for clear skies as well as for rain plus a few others.  I've yet to do the process flow chart but it won't be complex.

Was trying to be funny, but I'm not very good at cracking jokes.

But as you say seriously, I wondered whether you had some sort of automation planned that might detect clear skies and it automatically opened, or some sort of alarm to wake you if the skies cleared.  I know others are working on this. 

Carole

[MarkS]

System State     Action to perform
------------     -----------------
Raining             Close the Roof
Clear               Open the Roof
Clear&Raining    System Error - Windows must shut down

I've just thought, that last case can be caused by your neighbour switching on the night-time garden sprinklers ...

[RobertM]

as long as you don't rely on the forecasts Robert!

I'd thought of a weather feed direct from the met office and inverted so it did the opposite but then I thought, sometimes they get it right

Carole, yes I hoped that was a joke

Robert

[Mike]

It's a fairly easy process to create a cloud sensor with an MCU and a couple of temperature sensors.

[RobertM]

Thanks Mike I been thinking about that and also whether to use an Arduino or RaspberyPi for the project.  Cost wise there probably isn't that much difference.

I'm thinking the Pi might be better in the long run but I can think of more applications for the Arduino like control of the cooling on my 550D that's in bits at the moment.  Also there are starter kits that come with lots of different IO modules for testing plus the Ard can be very had in a very small package with low power consumption.  There is a bridge kit for the Pi to take the shield boards but I'm not sure how good library support would be.  I'll decide once I know all the interfaces relays and sensor types.

Robert

[MarkS]

... my 550D that's in bits at the moment. 

That makes two of us!

[RobertM]

... my 550D that's in bits at the moment. 

That makes two of us!

Looks nude with it's clothes off, a bit like C3PO did in the original film.

[Mike]

The Pi would be complete overkill. You could use the Arduino just as a chip programmer. The extra components required to get the chip working on its own are minimal and you can embed them into other circuits whereas the Pi has an SMD chip.

[RobertM]

Thanks Mike, That's interesting about the SMD chip I'll research a bit more.

[Ivor]

Robert,

I'm looking into the same project at the moment how did you get on with this?

[RobertM]

Hi Ivor,

Been a bit lazy... I've got to change the wheels first - rolling resistance is about 20kg at the moment !  The originals are too small (40mm) so I'm going to put 100mm nylon castors on before I motorise.  That's the most tricky bit as I'm going to have to jack the roof up a fair bit to be able to get screwdriver access.  The motorised garage door opener is ready for fitting so once that's adjusted and working then I'll finish the logic diagram and start coding.

So many other things to do ... Sigh

Robert

[MarkS]

I've got to change the wheels first - rolling resistance is about 20kg at the moment ! 

20kg?  I wish I could reduce my rolling resistance that far!

[Ivor]

Well you're a few steps further along than me, I'm still working out the best design for the dome. Someone gave me a tour of their observatory at the weekend and they had upgraded the wheels to inline skate wheels (ebay specials from China) which have sealed bearings. This worked really well he was rotating the dome with little effort.

[RobertM]

That's interesting.  If I did that then I wouldn't need to rework any of the cladding for extra height 

I'll take a look into that...

[The Thing]

That's interesting.  If I did that then I wouldn't need to rework any of the cladding for extra height 

I'll take a look into that...

Just get a couple of pairs of inline skates off ebay and screw the wheel assemblies/soles to the truss. Simples.

[MarkH]

Mmmmm Duncan, you've just prompted a thought.......... ptfe: lowest coeficient of friction known to man. Might be worth considering Mark.