Gina's Observatory Roll-Off-Roof Automation

[Gina]

Thank you Per    Yes, you're right, the flap doesn't need to go further down than horizontal.  But I think it will need something to pull it out of the weatherproofing seals.  Or perhaps the seals need rethinking.  I guess counter balancing could be arranged to open the flap as well as balancing out some (but not all) of the weight.

I can't quite see how Peter's mechanism works, unfortunately  

[Gina]

This should work

[Gina]

Roof partly open.  Flap fully open.

[Davey-T]

If only you had a giant 3D printer then you could print the whole obs'y 

I see the Chinese are printing houses.

Dave

[Gina]

Could be a possibility for my mini widefield observatory when I've got my Giant 3D Printer done   But it's amazing how useful even a fairly small 3D printer is   Mine gets lots and lots of use

[Davey-T]

Peters looks like it's using the weight of the roof to counterbalance the flap, both driven by the same thing.?

Dave

[Gina]

I searched for Peter's original thread and found it HERE   You can see how it works better in his thread with explanation and another video.  It uses pulleys and string as well as a counter balanced lever system.

[Gina]

I've been having further thoughts about the wall flap (window).  I may go for string/cord to close the flap when the main roof closes.  This works out simpler and the rainwater down pipe doesn't get in the way which I discovered it would with the wooden pushing system.  Also, the mechanism will be inside rather than outside.

Here is a screenshot of a SketchUp model showing the design.  I have omitted the roof ATM but it would pull the cord and when nearly closed, pull the flap up to the end of the roof.  I may need to add some small weights and pullies to hold the cord taught to stop it coming off the pullies or getting tangled up with something.

[Gina]

I checked my chain drive motor today on a 13.8v supply and was surprised how quiet it was on no load.  It also drew only 1.2A.  A bit different from the 12v winch

[Gina]

Design for the brackets to support the wall flap on a 25.4mm diameter aluminium tube.

[Gina]

Having serviced the UP 3D printer I'm now printing the first bracket. 

I had to fix the printer as it was losing hot end heating after about 6 layers.  The repair I made to the hot end heater connections broke down and I had to remove the stranded connecting wire, clean that and the heater connection, wrap the connecting wire back round the heater wire and bind the the lot together with Kapton tape.  Then it started getting too hot so I gave it a good going over and recalibrate.  That seems to have fixed it

[Gina]

Large pulley turned to shape for chain and ball bearing.

[Gina]

I now have the large chain pulley finished and equipped with ball bearing with spacers and hub to fit between the sides of the cover.

Some photos...

Pulley, chain and cover with the bearing just visible.

Fitted into the observatory and bolted to the framework with rubber seals fitted above and below chain cover.

Outside view of the chain cover.  The brush type weather excluder could do with moving over to the right a bit to reduce the bristle bending.  Might leave that until it's a bit warmer.  A mere 2C here this afternoon and windy with it

[redtail]

Very nice,i now have my roof working by remote.Just need to wire up the rain sensor.

[Gina]

A bit more progress with photos.

The large pulley and chain.

This shows whee the chain emerges from the large pulley.  Used to work out alignment of drive motor.

Drive motor placed on mounting board with chain placed in approxinate position.

[Gina]

Motor unit and small pulley now mounted on base.  Designed and printed inner pieces to go inside the ball bearing to space the pulley away from the wood and provide a larger area to take the pressure and the size of a 70mm x 5mm wood screw, used to fasten the pulley to the 50mm thick wooden base.  A penny washer was used under the screw head to spread the load and avoid possibility of splitting the ABS plastic.

Here is a screenshot of the SketchUp model of the two bearing inners.

Here is the small pulley mounted on the wooden base.

To fasten the motor unit to the base I drilled holes through the plastic casing and attached it with wood screws, again 70mm x 5mm diameter.

[Gina]

Gradually getting there   Motor assembly now mounted in the observatory.  I have also coupled up the chain in the motor with the chain in the observatory making a total of three lengths of bicycle chain.  It is too long and I shall be taking off nearly a metre once I've confirmed the exact length required.

Here are a couple of photos.  The chain runs well with good alignment round the large (black) pulley, through the motor unit and round the small (green) pulley.  I have yet to screw a spacing block to the ROR carriage and the chain is just parked over a bolt and hence out of alignment from the small pulley.  However, in spite of that I was able to check that the chain ran through the motor unit freely enough to manually open or close the roof without power, with the clutch disengaged - something I was a bit unsure about.

Edited February 4, 2015 by Gina

[Davey-T]

Looking good Gina, do you think it will need some sort of "soft start" to take up the load ?

Dave

[Gina]

Looking good Gina, do you think it will need some sort of "soft start" to take up the load ?

Dave

Thank you

Yes, I'm planning to provide a "soft start".  I shall be running the motor off an H bridge driver run from an Arduino and varying the power is no problem using PWM.  The driver also provides current sensing so it can be protected by removing power if the current gets too high, indicating a jam up.  A "soft start" would also be provided by having the chain a bit slack.  In both directions the chain being pulled would be a length of 2.4m hanging down slightly.  On starting the first thing to happen would probably be to take up of most of the slack.  This would depend on the weight of chain versus the starting pull required.

Edited February 4, 2015 by Gina

[perfrej]

You're getting there! You don't really need soft start when you run the motor off of 12V supply. But then again, it is cool to fiddle the acceleration software!

/per

[Gina]

Thank you Per

[Gina]

Schematic showing the roof open and motor drive parts.

[Gina]

Managed a short time out in the observatory this afternoon sorting out the chain drive for the roof.  Couldn't stay out there very long as it was bitterly cold with a strong NE wind.  Couldn't stand the east wall flap and roof open for too long

Sorted out the western end chain mounting block and checked clearance on that.  Just about alright I think but I'll check again when it's not so cold.  Found the large chain pulley cover tended to rotate as the pulley turned under load so I need to stop that.  May need a bit more clearance with a new cover.

No chance of doing anything to the wall flap while we have this bitterly cold wind   Might be lovely sunshine but any job outdoors would have to be sheltered from the wind.  You sit indoors and think with all that lovely sunshine I ought to be outdoors enjoying it but there's 20 odd degrees C difference in the temperature

Edited February 6, 2015 by Gina

[Gina]

Changed the design of the chain cover to give a bit more clearance and to provide holes for wood screws to prevent rotation, and printed it out.

[Gina]

With warm sunshine and slightly higher overall temperatures with a lighter breeze, I was able to do some work in the observatory this afternoon.  Found the reason for problem with the large pulley and cover - the spring links joining the chains are a smidgen wider than the main chain and didn't sit down properly in the groove in the pulley so I'll have to put the pulley back in the lathe and widen the groove.

I removed the fixing bolt and large pulley, chain and cover with a bit of a struggle - shortage of room.  Then I was able to check that the new cover was the right size and shape.  It should be fine and will be better than the old one

There are still a couple of things I want to improve on the roll off roof before it is entirely suitable for unattended operation.  The current bout of cold weather makes for very slow progress but progress there is

Edited February 8, 2015 by Gina