Cool info about the Surrurer truss Ken, great to know for future builds. I wasn't trying to do anything special with the truss design on this scope, I have just been making up everything as I go along and having fun.
Amazing to hear about what you had to do with the Isaac Newton telescope construction!
And Alistair, don't worry about hijacking the thread, I'm keen to hear new ideas or gain a better understanding about stuff.
Any finite analysis structural program given the correct inputs will quickly give you the deflections.
It's structurally a simple arrangement...much easier than building a bridge!!
(Having said that....I saw the calc sheets - logarithms/ slide rule in those days. And in the end they actually measured the end deflections under various loads and machined a bit more of the diameter of the stubs!!!! until they got to spec.)
Thanks. I don't have access to any programs so any data you have on just how much it deflected would be great to know.
talk of deflection, the Space Shuttle's "Twang" comes to mind, although not quite the same.
So they machined more of the central stub so it'd deflect more? I'm guessing to match the other half??
For us with a non structural background, its hard to imagine how the steel joints would act as a hinge and deflect, but I guess once you go big like the Hale and VLT, the deflection is to be expected.
From an amateur perspective, our pseudo serruriers just work off balance with the hub at the midpoint, in my case, I've used woven Carbon Fibre Truss nodes that are quite rigid and that's why I was keen on understanding the hinge concept as I don't know where there'd be scope for deflection due to compression and tension given our tiny load.
Being hand built with rudimentary tools, its nowhere near rigid as I'd like. I took inspiration from the Officina Stellar RC trusses.
we're all learning I guess. that's part of the fun.
Brent, et al,
I'm sure that Mark Serrurier is turning in his grave.
His revolutionary design concept was a "truss" design where the deflections of the top and bottom sections were balanced - this maintained the alignment of the optical axis.
The "hinged" attachments also allow for the parallel deflection of the top and bottom rings to maintain their parallel alignment.
Not many (if any) of the amateur truss designs should be called "Serrurier Truss" designs.....
(Notwithstanding all the great design work he did, he had to "compromise" his final design for the 200" due to the Coude access. I have copies of his original design paper etc. etc. Ask me about Sir Barnes Wallis' "rigid dick" telescope tube design - now that IS an original!!)
The 'design' I copied was Rolfs (SkyViking) and his build principles were for the parallel deflection you mention. I agree my build is not a perfect and pure example of Serrurier Truss engineering but the rigid centre cage mounting and the inherent traingular elements made it extremely rigid and was able to support my weight (85kg) standing on end. Hence it is an extremely light & stable OTA requiring minimum counterbalance and retaining alignment extremely well.
Purity of Serrurier design may be of value for big scopes but in a 10" f5 probably not so critical. It acheives better than my requirements are for sure.
Also easy to modify as I did when adapting for DSLR focus.
And it was fun to build and looks cool !! ...
The 'design' I copied was Rolfs (SkyViking) and his build principles were for the parallel deflection you mention. I agree my build is not a perfect and pure example of Serrurier Truss engineering but the rigid centre cage mounting and the inherent traingular elements made it extremely rigid and was able to support my weight (85kg) standing on end. Hence it is an extremely light & stable OTA requiring minimum counterbalance and retaining alignment extremely well.
Purity of Serrurier design may be of value for big scopes but in a 10" f5 probably not so critical. It acheives better than my requirements are for sure.
Also easy to modify as I did when adapting for DSLR focus.
And it was fun to build and looks cool !! ...
Do you have any pics I could see? or a link a contraction thread?
I was originally going to copy Rolf as well, but changed it to make it attach to my horse shoe mount better.
About the horseshoe mount, does it have motor drive and tracking? how are you driving it? I'd be very interested to see that. pics would be great.
if you don't have autoguiding yet, let me know if you're interested in adding it with microcontrollers and quadrature encoders from wheels found in deskjet printers.
I built a wooden forkmount with steppers and finally added ST4 autoguiding in RA but haven't tested it out fully, happy to share plans and ideas..
About the horseshoe mount, does it have motor drive and tracking? how are you driving it? I'd be very interested to see that. pics would be great.
if you don't have autoguiding yet, let me know if you're interested in adding it with microcontrollers and quadrature encoders from wheels found in deskjet printers.
I built a wooden forkmount with steppers and finally added ST4 autoguiding in RA but haven't tested it out fully, happy to share plans and ideas..
Cheers
Alistair
Yes the mount is driven (using roller drives) with a modified dual axis stepper motor drive upgrade kit for the old synta EQ mounts, I have added an ST4 port the the hand piece for guiding but haven't tried it yet.
It has been out of action for a few months but I will be giving it some upgrades ready for the new scope. I will certainly post some pics.
Your mount sounds sounds great! I would love to see it and find out how you’ve made it. Swapping ideas and plans sound good .
An update on the scope progress, I got some aluminium plate, 160x250x6mm (flat pack focuser ) and have cut out some bits, I’m planing on building something similar to the focuser on my refractor, but I guess we’ll see.
Adding up how much the scope has cost so far:
$22 Aluminium
$16 MDF
$49 70mm Secondary mirror
Total: $87
Not to bad, should finish it off under a hundred I hope, (already have a dodgy primary mirror)
That Focuser looks good. Did you build that?
$100 for an 8 inch is a testament to your diy skills.
This is my fork mount, started with the idea of keeping it under $200, 2 years later, I'd rather not count what I've spent, but have learnt so much along the way.
Full frame sensors have a diagonal of 43mm, and your 1100d has a diagonal of 26.6mm. I would always oversize the secondary a little bit, (my 6 inch f5 has a 63mm secondary) beware though that the corrector will probably be your limiting factor when it comes to larger sensors.
Do you have any pics I could see? or a link a contraction thread?
I was originally going to copy Rolf as well, but changed it to make it attach to my horse shoe mount better.
Jo
Pic as below when I completed the OTA build and first mounted it up. Differs from yours and Rolfs of course. I used a ply diaphragm to maintain stability at the cage. My Primary cell is inside the OTA rather than as Rolfs which is external.
That Focuser looks good. Did you build that?
$100 for an 8 inch is a testament to your diy skills.
This is my fork mount, started with the idea of keeping it under $200, 2 years later, I'd rather not count what I've spent, but have learnt so much along the way.
Pic as below when I completed the OTA build and first mounted it up. Differs from yours and Rolfs of course. I used a ply diaphragm to maintain stability at the cage. My Primary cell is inside the OTA rather than as Rolfs which is external.
Full frame sensors have a diagonal of 43mm, and your 1100d has a diagonal of 26.6mm. I would always oversize the secondary a little bit, (my 6 inch f5 has a 63mm secondary) beware though that the corrector will probably be your limiting factor when it comes to larger sensors.
Thanks for the info Peter, I have received the 70mm secondary so that should be good.
What do you reckon would be a good Coma corrector? I like the idea of the Sky Watcher CC as it's actually a 0.9x reducer as well which would bring my scope down o F4.5, they seem hard to find though. The other option would be a baader MPCC I suppose.
Have been able to do some more work on the focuser, it looks like it will do the job.
It is 100mm in diameter and 55mm high, the tube is from an old rack and pinion and has an ID of 60mm, am yet to cut it to the correct length. Not sure if I have gone a bit overboard with the number of bearings but I want it to be able to solidly carry my super cooled 350D which it quite heavy.
Tomorrow I will start working on the Crayford roller system.
I am starting to have a few thoughts of motorising it, what do you reckon? I have seen some neat setups driven by Arduinos and stepper motors and am keen to give it a go but am not sure were to start.
That focusser is a serious bit of engineering. You obviously have the facilities (and skills) to build any thing you need. The accuracy and alignment of that many bearings is a big ask.
Excellent and inspiring work. I always like to see someone else's ideas about problems I have considered.
I've been following this myself .... All I can say is ... this guy's got serious talent when making ' home grown ' parts ... imagine how much he is ' saving ' in $$$$$'s from buying readily manufactured components.....
The holidays have given me a bit more time to work on this so hopefully have first light at the end of the week.
Got the roller drive mechanism working on the focuser today, need to find some proper bolts for screwing on the top plate and yet to drill and tap a thread for the compression bolt but on trying it out this arvo it has nice smooth movement and can lift 7.5kg's (probably more) strait up without braking a sweat, not sure if this is that good but as my camera setup it only around 3 kg's it should work alright.
Here are a few pics of it in it's rough form, will clean it up and hopefully finish it off (make nobs ect.) tomorrow.
.
) and have cut out some bits, I’m planing on building something similar to the focuser on my refractor, but I guess we’ll see.
