What do Sky-watcher Dobs use?

[emadmoussa]

For the base, do they use roller bearings similar to that of Revelation or GSO? Or anything else?

[Avocette]

The 150p, 200p and 250px don't have roller bearings as new, just three Teflon 'friction' pads so that why a number of us modify with a lazy Susan (LS) bearing which is a large circular ball race (see my posting yesterday in DIY). The 300p has a roller bearing (plastic frame with many roller needles held sandwiched between two large galvanised steel discs). This is not quite as good as the LS (IMHO) since the circular rotation is defined by the central bolt so there can be a little side to side slop. This is no particular issue until you fit a setting circle then it can cause an error in reading of a couple of degrees whereas otherwise you can 'push to' to about 0.5 degree accuracy. I think the SW roller bearing is also fitted as standard to other Dobs. I'm busy contemplating whether to remove the roller bearing on my 300p and replace it with a LS when I add Teflon friction control pads which are sorely needed to stop 'over-nudging'.

[emadmoussa]

The 150p, 200p and 250px don't have roller bearings as new, just three Teflon 'friction' pads so that why a number of us modify with a lazy Susan (LS) bearing which is a large circular ball race (see my posting yesterday in DIY). The 300p has a roller bearing (plastic frame with many roller needles held sandwiched between two large galvanised steel discs). This is not quite as good as the LS (IMHO) since the circular rotation is defined by the central bolt so there can be a little side to side slop. This is no particular issue until you fit a setting circle then it can cause an error in reading of a couple of degrees whereas otherwise you can 'push to' to about 0.5 degree accuracy. I think the SW roller bearing is also fitted as standard to other Dobs. I'm busy contemplating whether to remove the roller bearing on my 300p and replace it with a LS when I add Teflon friction control pads which are sorely needed to stop 'over-nudging'.

Humm. Interesting. Speaking of which,  does the Flextube goto move as smoothly as the manual version? Or the motor causes some friction?

[Avocette]

Can't help with the GoTo version personally. I'm a confirmed PushTo nudger myself! Off topic I have heard that the GoTo Dobs must be levelled well to locate and track accurately, and this may need some thought (no tripod legs to shorten) and the manual 300p Flextube is about at the limit of my capability for manhandling in two pieces. So factor in the extra weight of the motors for the GoTo.

[emadmoussa]

Yep, same here. If it only track at high mag, push/nudge would've been the ultimate solution

[mitchelln]

Humm. Interesting. Speaking of which,  does the Flextube goto move as smoothly as the manual version? Or the motor causes some friction?

Hi.

No, it is much stiffer as you are working against the clutches. Up and down is not too bad, but the base rotation is pretty tight. You would struggle to nudge.

[emadmoussa]

Hi.

No, it is much stiffer as you are working against the clutches. Up and down is not too bad, but the base rotation is pretty tight. You would struggle to nudge.

And in practical terms this will negate the simplicity of a Dob.

[mitchelln]

And in practical terms this will negate the simplicity of a Dob.

Well, it negates the simplicity of a manual dob I guess the GOTO ones are aimed at people who want to do tracking without spending a fortune on an equatorial mount.

[emadmoussa]

In mind my mind I was thinking tracking without compromising the smoothness of manual pushing/nudging. A difficult combination to perfect it seems.

[mitchelln]

In mind my mind I was thinking tracking without compromising the smoothness of manual pushing/nudging. A difficult combination to perfect it seems.

Indeed. It is a pity there is not a way to disengage the clutches, but I guess that would have added to the cost. BTW I'm pretty sure my 300P does not have needle bearings in the base. I think it just has telfon pads like its smaller cousins.

[emadmoussa]

Indeed. It is a pity there is not a way to disengage the clutches, but I guess that would have added to the cost. BTW I'm pretty sure my 300P does not have needle bearings in the base. I think it just has telfon pads like its smaller cousins.

Is it because it's a goto perhaps?

[mitchelln]

Is it because it's a goto perhaps?

Possibly.  It is very stiff to rotate the base. It could probably be improved, but it means taking the whole thing to bits which I can't face. I'm told setting up the clutch again is a right royal pain.

It is annoying that SW did not make the bottom plate of the base removable so you could get at the bearing material without deconstructing the entire mount.

[emadmoussa]

indeed.

[Tinker1947]

Axminster Tools do some roller bearing there normally placed in a row for timber ect to roll over them, on the base of a dob they (6 would do ) make for a very smooth push........this is the link....they could be mounted under a board so the bearing just show through the top...

http://www.axminster.co.uk/universal-transfer-ball

[brantuk]

My 300P Synscan goto flextube may not be as smooth to push as manual dobs - but it's certainly not a struggle. The clutches stay engaged cos there's no way to disengage them - but more importantly so you can move the scope manually whilst the encoders monitor it's position. I usually move it manually to known objects and it just carries on tracking merrily.

For unknown object positions I just use the goto and let it do the slewing. In practise I actually move it manually to the target neighbourhood - then use "goto" to the object using a short slew to save the battery. The only problem with it really is the amount of backlash - but even that can be compensated for. Hth

[emadmoussa]

I'm assuming a goto will add a noticeable extra weight to the base?

[Tinker1947]

My 300P Synscan goto flextube may not be as smooth to push as manual dobs - but it's certainly not a struggle. The clutches stay engaged cos there's no way to disengage them - but more importantly so you can move the scope manually whilst the encoders monitor it's position. I usually move it manually to known objects and it just carries on tracking merrily.

For unknown object positions I just use the goto and let it do the slewing. In practise I actually move it manually to the target neighbourhood - then use "goto" to the object using a short slew to save the battery. The only problem with it really is the amount of backlash - but even that can be compensated for. Hth

I'm planning on 16" with GoTo what you have just type is a very helpfull, does it need aligning pointing north ect so it know where it is......

[emadmoussa]

I'm planning on 16" with GoTo what you have just type is a very helpfull, does it need aligning pointing north ect so it know where it is......

I wonder how manageable the 16" will be. I'm wondering about the 14" and might end up upgrading to 12"....Not sure yet.

[mitchelln]

The 14" is barely portable. You have to take the base to bits to get it through a standard door. It is also really heavy. Beyond a single person to more than shuffle it really. 

A guy turned up at a local astro event recently with a new 14" and by the end of the evening he was convinced the 12" was a better bet. It took two of us to get it in and out of his car and move it. He was a fit young guy as well. He put his 14" up for sale the next day.

The 16" must be for static use only I would have thought!

[emadmoussa]

The 14" is barely portable. You have to take the base to bits to get it through a standard door. It is also really heavy. Beyond a single person to more than shuffle it really. 

A guy turned up at a local astro event recently with a new 14" and by the end of the evening he was convinced the 12" was a better bet. It took two of us to get it in and out of his car and move it. He was a fit young guy as well. He put his 14" up for sale the next day.

The 16" must be for static use only I would have thought!

How about the actual tube? Is it as awkward?? Also, difference in views...worth the extra weight and size?

[Tinker1947]

i plan a extra door and space on the back of me Obby, plus a sack barrow would need moving a couple of metres....Emad the bigger the better...

[emadmoussa]

i plan a extra door and space on the back of me Obby, plus a sack barrow would need moving a couple of metres....Emad the bigger the better...

I know - I'm just concerned the base my get me divorced I lean towards the 14" though...Just wanted to know first hand how manageable it is.

[mitchelln]

How about the actual tube? Is it as awkward?? Also, difference in views...worth the extra weight and size?

The 14" tube needs 2 people really. It weighs 30 odd kilos and only just squeezes through a door. I have knocked my 12" a number of times against door frames. Sheared a focuser screw off once!

When the guy turned up with the 14" I was surprised how much bigger it was. It made my 12" look small! However, it was the considered opinion of a number of us that the views were no better and this was in a dark spot in the middle of the New Forest on a clear night. The guy was disappointed and as I say, put it up for sale the very next day.

To be honest, I find setting up my 12" a chore sometimes and at least my base can be kept in one piece to move it.  Life is easier at meetings where there are people to help me lug it I've got pretty adept at setting it up in my garden, but then I'm only moving it a few metres. I would imagine if I had the 14" it would get a lot less use. You have to see one to believe how unwieldy it is. I nearly went there, but glad I didn't now. I wouldn't have seen half what I have.

As is often said here, the best scope is one you actually use. I don't think the weather in the UK is good enough to really make use of these very large scopes unless it's under a dome.

[brantuk]

Brilliant - get a big dob and a divorce at the same time - solves two problems in one go - I like your thinking lol :grin:

The views in the twelve inch are a pivot point in dobs imho - it's the last of the small dobs before "going large" and you need a good 4" extra aperture for an appreciable difference. I've always thought 14" a bit of a wishy washy size - but of course it's a huge step up from 8" so I do see it's relevance in the market. My 16" lives in the garage cos it won't go through normal doors - and it needs wheelbarrow handles and ramps to move it or put it in the car boot - but it's manageable (just).

The 300P goto just needs aligning with two or three stars to get it working. It starts off inaccurate but as you go through a session using pointing accuracy corrections on different objects across the sky it gradually becomes spot on - I find the first half dozen adjustments make a huge difference. Leveling is important for accuracy so I fitted leveling feet - as you would for manual setting circles (and in which case north alignment is essential).

Polar aligning is only needed with the "Auto" version of these scopes. It's not really polar alignment - bit misleading really - but it's "setting your latitude" from level using the pole star - much better description. My 12" is actually an "Auto" converted to a "Synscan Goto" (which is just a handset switch). And no longer requires latitude setting via pole star cos it's typed in at setup time. Hth

[emadmoussa]

The 14" tube needs 2 people really. It weighs 30 odd kilos and only just squeezes through a door. I have knocked my 12" a number of times against door frames. Sheared a focuser screw off once!

When the guy turned up with the 14" I was surprised how much bigger it was. It made my 12" look small! However, it was the considered opinion of a number of us that the views were no better and this was in a dark spot in the middle of the New Forest on a clear night. The guy was disappointed and as I say, put it up for sale the very next day.

To be honest, I find setting up my 12" a chore sometimes and at least my base can be kept in one piece to move it.  Life is easier at meetings where there are people to help me lug it I've got pretty adept at setting it up in my garden, but then I'm only moving it a few metres. I would imagine if I had the 14" it would get a lot less use. You have to see one to believe how unwieldy it is. I nearly went there, but glad I didn't now. I wouldn't have seen half what I have.

As is often said here, the best scope is one you actually use. I don't think the weather in the UK is good enough to really make use of these very large scopes unless it's under a dome.

Do you know the diameter and weight of your 12" base? And do you guys use coma corrector with such a scope?