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Jessun

My personal Sky Crane

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I am stuck with the limits of my balcony measuring a bit under 3*3" so waiting for the AP1600 mount I quickly realized that it wouldn't even fit out there without any OTA hitting the wall or doors...

A few solutions:

Build a bigger balcony.

Move the wall.

Don't bother with the mount.

Something else.

So I decided on Something else and set out to build my own mobile pier/tripod. Armed with a welder, some stuff from the local DIY store, a few cans of spray paint and a roll of very deer Kapton tape I designed this thing, that I just had to call Sky Crane inspired by the success of the Curiosity team. I even gave it a suitable space look :grin:.

The most tricky aspect of the build was that it had to be done on that same balcony - so the welding proved difficult on the limited space but I got there in the end. The frame weighs 52 kgs, fully equipped it's at 80kgs and it also carries up to 50kgs ballast at the back totalling 130kgs. The bars that will extend over the rail of the balcony to give me those vital extra 10 inches have a cross section metal content corresponding to a quarter of what is used to mount a B747 RR Trent engine to the wing - and that thing delivers 68000lbs of thrust too... Clearly they use far superior metal in their bolts but this design is just designed to carry a 52kg mount plus up to a 50kg (400mm) telescope plus CW, so I am convinced they won't snap.

Such a big telescope load would be tricky to polar align being a moving setup, hanging over the edge of a balcony so I built in three half tonne actuators that jack up the whole thing using the switch box mounted on the left. I can easily move each jack half a millimetre at a time. There's a fourth switch not yet in use dedicated to a future powered AZ adjustment meaning that I'll be able to polar align to an acceptable accuracy using just the switches. To aid this the top box features an LED screen connected to a sensitive camera that fits onto the polar scope so I won't even have to lean over the edge to have a look.

It has a 220V power supply with a 26AH battery backup with the goal to move towards a UPS system for any eventuality. When finished it will also incoporate an industrial USB hub - that uses 12V as a source to power whatever needs powering. On the right you'll see a clever zippered sleeve riveted to the frame that will hold all the cables for a tangle free setup. Best solution I've seen for cable management maintaining instant access to each cable.

The business end has a 10mm aluminium mounting plate seen in the picture with the Astro Physics 1600 10" mounting ring. Depending on scope/camere setup I may have to put a section in between there to lift it to the right height.

When looking at this design you have to bear in mind that since I can't flip it's in this configuration only suited to image east or west. Pointing at Polaris the counter weights will extend below the balcony rail, but with limits preset they should never crash into it hopefully!

post-16323-0-73288700-1345208529_thumb.j

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The ingenuity of Astronomers never fails to impress me!! "Respect"!!

Perhaps, at some stage, a photo of the completed setup??

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Sure Nibor, when it all comes together... I'm just preparing for the future with this build.

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Here it is seen with an iOptron mount and an Orion 8" RC. The design allows me even with this load to sit on the mount plate adding another 80kgs still lifting and tilting it by the flick of a switch. It is naturally far from ideal in terms of pier design but it's the best I could come up with for my particular problem - limited balcony space.

gallery_16323_1997_205349.jpg

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I'm well impressed with the ingenuity and engineering - looking forward to first light report!!

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looking forward to first light report!!

So do I! Sadly the iOptron threw all the toys out of the pram last time I used it so I need to make sure the mount actually works before putting any blame on the actual pier...

I know the pier fits on the balcony and clears the rail by a fraction of an inch - the rest is speculation so far... fingers crossed :-)

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I'm curious as to the structure and stability of your balcony ?

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At a maximum it will be Pier 130, Mount 50, Scope 50, CW and accessories 30 so about 280kgs. That really only equates to perhaps 4 quite slim people out there. I don't think it's at risk of collapsing even with 10 or 15 people on it - it would make everyone rather nervous about balconies if building regulations were that marginal... The balcony has a sturdy concrete filled metal frame.

I worry a bit more about the old wooden floor inside...

All will be secured with Dyneema slings, such as OTA, CW,s etc. Belt and braces all around!

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Pity anyone who is underneath if a counterweight accidentally slips off the end of the counterweight arm :)

Very ingenious solution though and particularly impressive given the difficulty of construction.

James

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My main focus is safety. I am not a welder so I had to work on the assumtion that any - or all - welded joints can break. As it is designed now gravity holds everytning in place apart from the top support for the jacks. If they fail catastrophically the rest of the structure will slide down the bolts - only half an inch - and land on rubber dampeners and the bottom support will lake the load - again held in place by gravity alone - the rubber is there to lessen the impact mainly with the mirrors in mind.

The two main top bars would still balance on the four middle legs even if all welds snapped - the scope and the ballast at the back will keep them from tipping anywhere. The ballast sits in place by gravity, but as a good measure an M20 rod holds them in place. (The 4 inner ones that is - the outer ones could in theory fall off if the M20 bolt snaps - but they are additional really and not needed to balance the thing.) These main bars consist of two full length angle profile that were heated and bent to form the knee. Again - no critical welds.

The OTA's have recessed safety stop bolts, plus an outer extra saddle that keeps it in place should it want to slip due temperature changes etc.

The CW's attach with an allen key, and the bar as a screw on safety stop. The Dyneema slings will be fitted in the event that the bar snaps or comes loose. I'm working under the assumption that if anything can happen in theory it will - so prevent it. Cameras and focusers will get the same safety sling.

All in all it's a design I worked on with one target only - nothing can ever be allowed to drop.

Looking up at what people stick out from their windows and balconies I can tell you that there are a lot of seriously heavy pottery looking far more dangerous to me...

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Looking up at what people stick out from their windows and balconies I can tell you that there are a lot of seriously heavy pottery looking far more dangerous to me...

You may have a very valid point there :)

James

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Thanks Steve! Looking at my maths a few posts up here, I think I need some luck too :grin: ... Let's just call it a typo....

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Here's an example of a common local design.... Not too heavy but from 10m up it would probably knock you to the ground should you have one land on your head :grin:

post-16323-0-21869100-1345814193_thumb.j

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Yes. No. Prayers are for some other kind of forum :p And the welds are redundant - just makes assembly easier.

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Hi Jesper, nice job. Do you know how much total lift length your actuators have ?

I have a telescopic steel pier which at the moment I jack up with a built in car scissor jack but could do with powering it.

Need something thats around 500mm closed with about 300mm lift.

Dave

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Cheers Dave!

Sounds like you need one of the same I have but the 300mm stroke lenght version (I use the 150mm ones). I belive the larger ones are 475 mm in the retracted position measured between the mounting holes.

http://www.gimsonrobotics.co.uk/GLA4000_12V-linear-actuator.html

They are not very fast so would take you 37 seconds to go end to end.

They work a charm, and are very quiet too.

Good luck with the build! Sounds interesting!

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wow, that so admirable :) Anyway, do you intend to reveal the process of creating it? I eager to know :)

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Hello elly12 and welcome to the forum!

The process of creation was one of improvisation. I have no scetches, just a paper with a few basic measurements. I started with the base. I made it T shaped so I could stand next to it on the limited space on the balcony. Then I put four bars to make the central 'pier'. It was made hollow for cable management. Next came the two main bent bars that extend over the edge. I made two rather than one beefy with the idea that the camera could go between the bars in a telescope park position - making a potentially large setup compact enough to clear the door frame.

At this stage the actuators were ordered, but I had no idea how to incorporate them. In the end I went for simplicity and I came up with a design that would be allowed to break without any major disasters - break due to dodgy craftmanship. The actuator frames on the sides also came to serve as stabilizers for the inner pier.

Improvisation then continued with the wiring and placement of control boxes.

So I wish there was a clever blueprint somewhere but I'm not good with that kind of stuff.

Thanks for looking and again welcome to SGL.

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Cheers Dave!

They are not very fast so would take you 37 seconds to go end to end.

Thanks Jesper, it takes be longer than that to wind it up by hand

Dave

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