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  #61  
Old 07-05-2012, 10:38 PM
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wow I wouldn't want to fall thought that you would be diced up like jullien carrots

Ide hate to have to remove the secondary hub for any reason!

Good work in any case
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  #62  
Old 07-05-2012, 11:44 PM
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Thanks Rolf, yep it still is sort of a test as I have to redo the bottom part of the UTA due to that incorrect slot I made for the focuser.
So will square it up once assembled. I was thinking of using butter paper and light through the focuser to do a basic alignment and will then use star tests.

Brendan, the secondary assembly comes off easily by just removing the 3 wing nuts because its actually 2 parts, the mirror with the holder comes off. So I have access to the secondary if needed without disturbing the wires.
Only bits left now are to measure the upper and lower truss lengths.
Trevor here has kindly offered to machine the carbon fibre truss ends for me. still in 2 minds of whether to use 16mm pultruded or 20mm woven CF tubes.
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  #63  
Old 08-05-2012, 12:15 AM
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that question is easy to answer protruded, as woven is better at bending.

carbon strands have the most strength when pulled aka put into tension they are incredibly strong. but normal to the grain they are flimsy. Hence why woven twill is used on "cf plates" because it allows far more strength when loads that act normal to the face are applied.

the loads that your telescope will see the protruded rods will work just fine in tension and compression
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  #64  
Old 08-05-2012, 12:22 AM
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I guess that's inherent to trusses in that all members are under tension or compression and no radial loads.
only problem with the pultruded rods is the diameter. the max dia available is 16mm with a 2mm wall.
correct me if I'm wrong, but I think even a 1.5mm wall but 20mm diam would be better than the 16mm as wider pipes tend to be more stiff.
I've got a sample 16mm, so will test.
I wonder why most professional scopes like planewave, officina stellare and other RC's use woven tubes.
I've seen some ATM builds with roll wrapped tubes that are actually bad at axial loads.
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  #65  
Old 08-05-2012, 01:40 PM
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Quote:
Originally Posted by alistairsam View Post
I guess that's inherent to trusses in that all members are under tension or compression and no radial loads.
only problem with the pultruded rods is the diameter. the max dia available is 16mm with a 2mm wall.
correct me if I'm wrong, but I think even a 1.5mm wall but 20mm diam would be better than the 16mm as wider pipes tend to be more stiff.
I've got a sample 16mm, so will test.
I wonder why most professional scopes like planewave, officina stellare and other RC's use woven tubes.
I've seen some ATM builds with roll wrapped tubes that are actually bad at axial loads.
you nailed the issue there mate. ATM Roll Wrapped! This is why im hesitant to construct my own CF tube as the CF actually reinforces the epoxy resin. get the mixture right and its pretty damn good. get it wrong they are woeful... your basically using a Resin tube.

Planewave and the like use Woven tubes for one reason.... they look damn good, couple that with extruded rods they are just grey/black

I would say a 16mm rod depending on your length between cages is possibly a bit to thin. Ide be looking more like 20mm x 2mm as you cannot get protruded rod then woven rod will be fine.
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  #66  
Old 07-01-2013, 03:50 PM
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Its been a few months, but I finally finished my 10" F4 serrurrier truss with CF tubes. I went with woven 1mm x 16mm CF tubes rather than pultruded as they were half the weight of the pultruded, 72g for a 1metre x 16mm OD tube.

I've tested collimation with a cats eye AC and its holding well at different orientations, there still is some flex but very minor.

The guitar string spider is working a treat, hardly any spikes and very rigid.
I need to get a proper shroud done though.

All up, the OTA weighs 11.5Kg with a QHY8 ccd and the guidescope/guidecamera and my dew heater box.
I plan to replace the wooden dowels in the UTA with CF as well, so should end up at 11kg.

The truss nodes are terminated on Aluminium elbow joints which is basically two U channels inserted into each other so they are free to swivel to the required angle.
The Octagonal shape causes the trusses to form a cone which is what I wanted as that has better rigidity than the cylindrical truss configuration.

I used a 1inch long 16mm wooden dowel as the CF tube insert to connect to the Aluminium elbow joint, but since the standard size is 16mm OD, and the CF tube ID is 14mm, I had to convert my drill press to a wood lathe to turn it down to 13.5mm. I then used the 6minute Epoxy glue available from hobby shops to glue it inside the CF tube. They're only 1 inch long so doesn't add up too much weight.

I also got a belkin 4 port powered hub which supports the qhy8, qhy5 and canon1000d. I finally have no more USB issues after changing about 3 different hubs.

My HEQ5 pro seems to handle it okay, but i'm guessing its borderline for this mount.

still, I'm happy with the way its turned out. comments, suggestions, welcome.
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  #67  
Old 07-01-2013, 04:33 PM
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A lot of work in that ...well done ..!!

Flash ..!!
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  #68  
Old 07-01-2013, 05:51 PM
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A beautiful job Alistair. You mentioned CF tubing at the SVAA camp in November, and that spider is a work of art. Glad to see it all coming together.
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  #69  
Old 07-01-2013, 06:48 PM
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That's one nice looking telescope!
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  #70  
Old 08-01-2013, 12:01 AM
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Quote:
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A lot of work in that ...well done ..!!

Flash ..!!
Thanks Roland, Larry.
yes Flash, it was quite a bit of work, sometimes I wondered if I over complicated it, but being F4, I was set on improving rigidity as much as possible, and it just added on. Moreover, I had no access to Al milling, so had to work with wood.

A CF rolled tube would have been perfect if I could afford it, but since I couldn't, I had to make my own and Rolf and Brent's trusses provided the inspiration.

I'm currently doing a PEC train on the HEQ5 as the PE is around 45arc sec and with the weight of the OTA being borderline for the mount, I need to use PEC to smooth out the guiding as much as possible.

I wanted to fix a cylindrical shield on the inside rather than cover the trusses, just for aesthetics, but not sure where I can get plastic sheets.
Else I might have to use a shroud with velcro.

At snake valley, the primary was completely dewed up when I had no shroud.
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  #71  
Old 08-01-2013, 06:08 AM
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That looks absolutely gorgeous Alistair, congratulations on completing your build!

I'm in the process of building a 12.5" version of my Serrurier truss design, over here: http://www.iceinspace.com.au/forum/s...ad.php?t=98823
I'm trying to optimise every piece of it in terms of weight savings, and at this stage overall it looks like I will end up with a 12.5" OTA weighing only the same as my current 10"
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  #72  
Old 08-01-2013, 10:36 AM
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Thanks Rolf, I had to do the same to save every gram.

I wanted to mention that the UTA might need reinforcement. I found that the four supports aren't sufficient to keep the secondary rigid at different orientations.
the weight of the secondary mirror actually warps the 18mm ply by a few microns, and that's sufficient to throw a laser off the primary at different orientations, and this is even though I terminated the strings very close to the 4 supports.

what is the weight of your 10inch truss?
with the new 3inch focuser and stepper motor, along with a bigger mirror, won't the weight be quite a bit more than the 10inch?
what stage are you at?
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  #73  
Old 08-01-2013, 11:12 AM
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Hi Alistair,

The total weight for the old 10", including optics is 11.85 kg, without optics it's 7.85 kg.

For the new 12.5" so far I've calculated the expected weight based on the exact volume and density of the different materials (birch plywood, aluminium, steel nuts & bolts). OTA alone excl. optics should be around 6 kg, and with optics ~11 kg.
I'll be using a conical mirror which will save quite a bit of weight. The weight of the conical 12.5" primary is pretty much the same as that of my current traditional shaped 10" primary. The conical is also mounted using a single bolt through the back plate of the mirror cell, so that saves some hardware too.
I'm also using lighter birch ply this time (the old one is made from pine). Also, the 3 long steel bolts that hold my mirror cell are now only 10mm thick this time, the old ones were 12mm but that is unnecessary.
I've done various other tweaks here and there (the anchors with the guitar tuners are now as slim as possible etc).

I have excluded my whopping 1.3 kg 80mm finderscope from these calculations because this time I intend to make it detachable. I only use it initially to locate the target, so it's silly to have that extra weight sitting the OTA while imaging. Instead I want to create some sort of clip-on holder for it. Alternatively I'll just put a Telrad (~300g) on the OTA, but I really prefer using the big finderscope.

Cheers,
Rolf
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  #74  
Old 08-01-2013, 12:09 PM
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Hi Rolf,

That is very light. What about using pine instead of ply? once they're varnished, they shouldn't warp. they're softer, but lighter.
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  #75  
Old 08-01-2013, 12:21 PM
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BLOODY GORGEOUS!

Alistair, marvelous work, my friend. I am in awe of this project of yours. I've been following in it quietly, but closely. I am so impressed.

Alex.
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  #76  
Old 08-01-2013, 12:31 PM
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Hi Rolf,

That is very light. What about using pine instead of ply? once they're varnished, they shouldn't warp. they're softer, but lighter.
Hi Alistair, I found that the pine ply I used for the old 10" was a tad too soft for my taste and also the finish of the beech ply is much finer.
With all the various bits and pieces that end up being attached to the ply rings I preferred using beech this time. The beech rings also appear very stiff compared with the pine.
I think the weight difference all up is about 200 grams, so I'll live with that.
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  #77  
Old 08-01-2013, 12:43 PM
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BLOODY GORGEOUS!

Alistair, marvelous work, my friend. I am in awe of this project of yours. I've been following in it quietly, but closely. I am so impressed.

Alex.
Thanks Alex, it has been quite a journey. your work has been an inspiration as well.
This is why DIY is so rewarding. you learn so much and see the fruits of your labour.

I built this 10inch as this will stay with me for a long time. I don't see myself splurging on a new mount anytime soon, especially with a new baby en route, so I tinkered away as much as I could to get close to what I wanted.
I've added some build pics here and will keep adding more.
http://alistairsam.wix.com/astronomy...ild-pics/c1hpx

Cheers
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