LondonNeil

20 minutes isn't bad at all I reckon.  I am guessing it'll be heavy, but being able to dismantle and easily fit inside a car will be such a boon

Nice clamps, nice build. 

How long do you think the scope will take you to set up when all finished?

For some the fun is the complexity of the problem and finding your own solution!

Just on your 4 points though,  a chaon driven solution could still separate (the chain would just be resting/running around the segment and the pin by which it pulls could be just that,  a pin that sits in a link)   reset still easy,  just flick a switch and motor back to the start (the chain needs to be a loop to facilitate this and allow it to pull in both directions). Maintenance just as simple as chains are very durable and robust.  Design and build yes. I'm not sure it's really any harder but the friction design had been done already so use it,  unless you need to change because you've hit a problem. 

I agree,  simple is beautiful, so if the friction drive works that's great.  If you're struggling with it and a 12" or bigger dob is going to test it, a second motor or 3 freewheeling cogs and a foot or two of bike chain are probably pretty simple alterations. 

I've read the other thread and just for interest pondered on the drive and inherent risk of slip with a friction drive. I came up with an idea,  it is entirely untested though.  I thought of a chain drive.  If you built a loop of chain that ran around the segment where it were pinned to it at the end,  then round a driven cog, then 3 free wheeling cogs, there works be no possibility of slip.

Bicycle chain cogs are cheap,  it would add a bit of added complexity though.

I thought I'd update this to provide a record of some stuff that isn't easy to find about the st120 but my own Google efforts found a few questions that are asked frequently!

St120 dew shield removal

Yes it is just a friction fit, a very tight one though.  The technique I found works for me is to sit in a chair (one without arms) and rest the ota, across my thighs. Have the primary lens cell at the point of resting on my left thigh,  hold the focuser end of the tube down with my right hand,  grasp the end of the dew shield in my left hand and push downward, quite hard,  as if trying to bend the ota over your leg. Watch carefully and you'll see the faintest movement of the shield vs the primary lens cell. Then turn/rotate the ota 180 degrees and repeat so the push would be 'trying to straighten' or bend the ota other way. Keep doing this and for the first 5 or 10 pushes it'll seem the shield isn't going anywhere even though you'll see the faintest of movements each push.  Eventually you'll see it's moved a mm then 2.  Once it's moved about 10mm it does get easier and is soon off. Don't worry about getting close to the end and push/ pulling it right off when pushing hard and damaging the lens or yourself,  the collar is 30mm deep and the lens is slightly recessed. 

Primary lens cell removal.

  As described above the lens cell is easily removed to clean it or access the tube,  it's the same way you access the cell om a Mak127 and probably many sky watcher telescopes .  The 2 glass elements are held in by a plastic collar that has 2 small holes in it.  Something like a large paper clip will fit in these and with something in the 2 holes and the tube gripped between your knees the collar can be unscrewed allowing a rubber seal and the glass to simply fall out. 

Weights

Exact weights of the skywatcher star travel st120 are hard to find, so with it like this I weighed it on my new kitchen scales.

Ota minus dew shield but with my skywatcher electric focuser fitted  3185g 

So without the electric focuser it's going to be 3kg ish

Dew shield 460g

Rings bolted to a 9.5" dovetail 578g 

Red dot finder 40g

My Bresser 2" star diagonal 490g

A typical cheap 1.25" diagonal is more like 180g

2 to 1.25" adapter 80g

Then a typical decent EP such as a Baader Hyperion  I weighed at 370g and a Morpheus a bit less at 310g (just the ones I happened to pick up, I would think different FLs would be a bit different weight)

My2" barlow  (errr...stellalyra?) 240g

So taking the whole set up with a heavy ep, Barlow, 2" diagonal,  adapter, red dot and the chunky steel dew shield, rings and dovetail,  the total weight is

5443g

But,  if you use a 1.25" diagonal and no barlow you reduce that by 550g to 4893g and a lighter EP could reduce that anther 200g

If you ditch the chunky dew shield and make up an astrozap like flexible one (I'm using 1mm polypropylene sheet) you can save 300-350g.  I've made up a 200mm long dew shield, so longer than the 160mm steel one,  and it's about 150g (about,  as I've not quite finished,  I'm making a guess at the weight of some press studs I intend to add).

So tube, finder, electricfocuser, rings, 2" diagonal,  (no adapter as using a 2" ep), Hyperion ep, and new flexible dewshield, rings and dovetail  totals 4813g

Ie, changing the dew shield...... could be worth it as it brings the weight below the spec max for an az gti mount (5kg) and well below the max for one side of the gtix (6kg). It's also weight right at the front that is saved,  so reducing the moment quite a bit. 

Doing the maths, the CofG moves backwards about 20mm so the scope should still balance very easily.  Again I say 'should ' cloud and 3 kids keeping me occupied,  plus summer,  I've yet to test the new ds!

Without the dew shield also makes the ota 130mm shorter, so easier to pack.

I bought a large sheet of polypropylene for not very much... about 11 quid I think it was.   I've used about a fifth of it.  I'll use some more to make up a solar filter with the film I've just bought (should be more durable than cardboard), I might also make a bahtinov mask.... and I'll still have ⅔ left. 

 I'll likely be making flexible and light weight dewshields for more scopes having bought an Altair starwave 102ed.... ever so slightly heavier and longer at f7 so 2-300g saved from the end could be the difference between joy and frustration on my gtiX!

I hope those tips and weights may be of use to someone!

Yes.  I won't pretend to know all the consequences but it does seem to me that the distance uncertainty is a pretty big issue!

https://www.scientificamerican.com/article/how-old-is-the-north-star-the-answer-could-change-our-maps-of-the-cosmos/

Intriguing!

2 hours ago, Mr Spock said:

I'm comparing the CC with one of the best apos made. It isn't a fair comparison!

Exactly, I see that,  but it was interesting to try and see how extra aperture might make up for it's comparative failings, especially in the areas you wanted due to light pollution. 

Interesting and honest review.  I

It does seem counter intuitive for 7" of aperture to turn out worse than 4" but then again, very intuitive that £439 can't match £3k.  

How would the CC compare to a similar priced frac?  Is there a refractor in that price range?  A large achromat or a small ED I guess.

I've been big before,  I started there stupidly buying a classic 300 dob.  As I drove home with it I thought,  that was a mistake!  Ì gave it to my brother and nephew who live in much darker skies (4-5 ish) and have decent views from their garden. 

I've now got,  I think,  a pretty sensible set up. St120 and mak127,  plus an ed102 which is waiting at my MIL for me to collect. If I prefer that to the st120 then the 120 goes. 

I'm just slightly lusting after the celestron 8inch in the classifieds.   I could manage the scope but the bigger tripod and the large eq mount would be such a faff compared to the az gtix I use.  Plus no matter how many times I read that fuzzy hunting from bortle 8-9 is fruitless I still want bigger.   It's just to wave it about isn't it?  Stupid....but why do I keep thinking about it!?

😅

Ahh yes! Long periods of cloud find me camped in the classifieds! Because we all know that expensive tv ep or Thai 8" tube can burn through cloud don't we?

A trolley was part of my thinking Dirk!  I already use a little one I made up from an old Pram and it works quite well.   So well it does eat away at the objections a bit! 😅

Why am I never content ?  Am I trying to compensate for..well...uhhhmmm 😲

I have poor views from my garden so I need something small enough to carry to the nearby park.  I still look longingly at big aperture scopes on solid mounts....35 or 40kg of kit by the time I've added a power bank and a selection of eps...more with packing cases....I guess I could drag it to the park.... where there's a will there's a way.... maybe! 

This is normal behaviour isn't it?  Stupid.....but normal?

Aha, yes ic4587 is in synscan's db. Excellent, thank you. 

I can 'find' it by star hopping in the app...start from epsilon,  find the 3 almost in a line to the south, hop on and yes I see it.... but it's not in the database,  can't click on it. 

Hmm, yes that's different to me. 

Ahh, I just tried something,  I searched on 'Cr B' and get  a long list. 

Alpha,  beta, constellation,  R, gamma,   theta, epsilon, zeta², delta,  tau, iota, kappa xi, eta,  eta (again?), mu, nu¹, sigma,  sigma¹, rho, nu², lamda, omicron,  pi, upsilon, zeta¹, rs,  uv, rr, and u.

Great.... but no T....grrr!

Is there a way to find it in the synscan app?

What thorough reviews,  thank you.   It seems worth considering unless you are chasing the very very best!  

BTW, I've read the hercules wedge is designed for imaging and unless modified to change the filter its not suitable for visual 

I take it that's the full version Elp?  Because I can find the constellation but none of the various searches suggested find T for the free version on my phone.   It's a bit frustrating I can't put the paid version on the phone,  but it's locked down by work. 

Thanks!  Stellaryium on my phone doesn't seem to find it but sky tonight does! Hip 78322, hr5958, hd143454, tyc2037-1144-1.

Thanks for ID ing it,  I tried to find it in Stellaryium but couldn't.  Possibly because I've only got the free version (work phone and it's locked down preventing the full version being purchased).

That scope was advertised here by mrzuiko. I've said I want it for a local scout pack. Although I've yet to manage to fetch it so if I'm beaten too it it's my own fault. 

Hoping to be able to fetch it next week but life keeps getting in the way!

Great,  i think I'll try it.  It's in aliexpress for £24 delivered (although I think there are probably taxes to add)  and that is marked as the celestron 

How did you find the holder to work for you? Well and easily or tricky?  End result looks good. 

BTW, with the skywatcher at least,  the fine focus issue that remains is the target moving in the fov as focus is shifted the other way, as a result of the way the mirror is moved.  So I've bought a baader t2 diagonal with a focusing ep holder. Yet to try it but expect it to solve that issue but it feels a bit stiff so I may end up preferring the peg.