Skywatcher Autofocuser advice

[cuivenion]

Hi, I'm thinking of getting the Skywatcher Autofocuser for my imaging rig. I just wanted to check. The auto focuser motor holds the focuser in place while in use, I don't have to use the lock screw while using the autofocuser do I?

[Tomatobro]

no you don't have to lock the screw. The gearbox has enough reduction to make it lock when the motor is not turning.

If however you have a Crayford focuser then the holding limit is governed by the spindle friction.

[cuivenion]

Got it, thanks for the info.

[tooth_dr]

If it's the same as both my SW focusers, the actual grip of the motor shaft by the motor coupling is governed by a thick O ring.  I was having slippage when the scope was pointing upwards, and thought it was the spindle slipping on the focuser.  However closer inspection revealed that it the motor shaft slipping inside the coupling of the motor.  Presumably this prevents damage and allows some sort of slip should you exceed the focuser travel.  But it meant I was losing focus.  Like you I didn't want to have to use the locking screw, so I drilled and added a small grub screw to the autofocuser coupling, to directly grip the focus spindle, and this solved the problem.  It now moves and holds 2kg of imaging kit.

Edited June 19, 2020 by tooth_dr
Edited to correct mistake with regards to position of slippage

[cuivenion]

1 hour ago, tooth_dr said:

If it's the same as both my SW focusers, the actually grip of the focuser shaft by the motor coupling is governed by a thick O ring.  I was having slippage when the scope was pointing upwards, and thought it was the spindle slipping on the focuser.  However closer inspection revealed that it the focuser shaft slipping inside the coupling of the motor.  Presumably this prevents damage and allows some sort of slip should you exceed the focuser travel.  But it meant I was losing focus.  Like you I didn't want to have to use the locking screw, so I drilled and added a small grub screw to the autofocuser coupling, to directly grip the focuser spindle, and this solved the problem.  It now moves and holds 2kg of imaging kit.

Thanks, I watched this video as it is essentialy is the same focuser as mine (130pds):

From your description you seem to be saying you had to drill and tap another hole in the motor coupling for a grub screw, but this video shows that a grub screw to connect the motor to the spindle already seems to be there?

 

 

[tooth_dr]

1 hour ago, cuivenion said:

From your description you seem to be saying you had to drill and tap another hole in the motor coupling for a grub screw, but this video shows that a grub screw to connect the motor to the spindle already seems to be there?

 

 

I had a look back at my photos and my description wasn't quite right!

Slippage occurs between the motor shaft and the coupling.  Not between the coupling and the focuser shaft.  The grub screw on the larger part of the coupling doesn't tighten on the motor shaft - seems to be friction by a rubber o ring when it's screwed together.  This wasn't sufficient for my kit.  I added a grub screw here.  The existing grub screw is 180 degrees around on the back.

[cuivenion]

1 hour ago, tooth_dr said:

I had a look back at my photos and my description wasn't quite right!

Slippage occurs between the motor shaft and the coupling.  Not between the coupling and the focuser shaft.  The grub screw on the larger part of the coupling doesn't tighten on the motor shaft - seems to be friction by a rubber o ring when it's screwed together.  This wasn't sufficient for my kit.  I added a grub screw here.  The existing grub screw is 180 degrees around on the back.

I think I know what you're getting at. Couldn't you use a longer grubscrew in the existing hole rather than drilling/tapping a new hole though?

[tooth_dr]

2 hours ago, cuivenion said:

I think I know what you're getting at. Couldn't you use a longer grubscrew in the existing hole rather than drilling/tapping a new hole though?

I dont think so, that hole for grub screw A doesnt go through C to the shaft, it just goes against the other threaded part B.

Even when all grub screws are tightened, ABC can be removed in one unit (albeit stiff due to rubber O-ring and pressure/friction fit onto motor shaft)

You could drill right though and rethread the hole for A, but it's six of one what way you go about it.

Anyway mightnt be an issue for you, just thought it was worth mentioning as a potential source of movement.

 

  

 

 

 

 

Edited June 19, 2020 by tooth_dr

[cuivenion]

No probs thanks for the info.

[Merlin66]

I also use the SW focus motor on all my scopes.

I decided to use a geared belt drive to the 10:1 focus knob for finer control of focusing.

 

[cuivenion]

30 minutes ago, Merlin66 said:

I also use the SW focus motor on all my scopes.

I decided to use a geared belt drive to the 10:1 focus knob for finer control of focusing.

Interesting way of doing it, do you find the focuser is still held in place as well using that method?

[Merlin66]

Yes, so far....

I only do spectroscopy and solar imaging. No issues with a Baader Cool wedge, Powermate and ASI 1600MM camera.

 

[cuivenion]

I'll add one more question has anyone tried rechargable 9v batteries in these. I thought I'd better check as astro gear can be quite sensitive to voltage, and rechargables tend to run a little lower in voltage than alkalines.

[Merlin66]

The use a 9V block battery....I use mine everyday it's clear for solar imaging, the battery must be a couple of years old and still work OK.

 

[cuivenion]

Cool, I'll get a few durecells in that case then. I was thinking rechargables might be good if they only lasted a couple of nights.

[callisto]

On 20/06/2020 at 05:10, Merlin66 said:

I also use the SW focus motor on all my scopes.

I decided to use a geared belt drive to the 10:1 focus knob for finer control of focusing.

 

Hi there,

Where did you get your geared belt fittings if you don't mind me asking,

Cheers,

Mark

[Merlin66]

The one's I use today came from Small Parts in Australia.

https://www.smallparts.com.au/store/categories/timing+belt+lengths+categories/

While in the UK I got them from MotionCo

https://www.motionco.co.uk/timing-belts-timing-belts-c-25_38_27.html

I use the 6mm bore 30 tooth pulley and length of XML belt to suit, usually 100 XML.

 

[JamesF]

Looks like the design for the Skywatcher motor focuser must have changed?  None of mine have come with that sort of coupling.  All three of mine have come with a flexible coupling and there's no kind of O ring or anything.

James

[tooth_dr]

1 minute ago, JamesF said:

Looks like the design for the Skywatcher motor focuser must have changed?  None of mine have come with that sort of coupling.  All three of mine have come with a flexible coupling and there's no kind of O ring or anything.

James

My most recent one came with a black flexible coupling as well as the silver ones above. 

[Merlin66]

In the previous diagram....

Part B screws into Part C, and compresses an internal O ring onto the motor shaft, then Screw A "locks" it in place.

I think this is designed to give a "flexible joint" between the motor shaft and the focuser spindle.

All the kits I have, contained both the silver and black flexible connectors, as mentioned above.

 

Edited June 21, 2020 by Merlin66

[callisto]

9 hours ago, Merlin66 said:

The one's I use today came from Small Parts in Australia.

https://www.smallparts.com.au/store/categories/timing+belt+lengths+categories/

While in the UK I got them from MotionCo

https://www.motionco.co.uk/timing-belts-timing-belts-c-25_38_27.html

I use the 6mm bore 30 tooth pulley and length of XML belt to suit, usually 100 XML.

 

Cheers 👍

Mark

[cuivenion]

I'm not really set up for drilling and tapping, so I bought a 6mm to 4mm flexible coupler, hopefully that will do the job. The o ring coupler probably would have worked, but I'm more comfortable with a bolted connection.

https://www.ebay.co.uk/itm/Flexible-shaft-coupling-joint-Stepper-Motor-Coupler-Connector-VARIOUS-SIZES/262814471837?ssPageName=STRK%3AMEBIDX%3AIT&var=561957397165&_trksid=p2060353.m2749.l2649

[StarManFlorida]

I have the Skywatcher 400 Imaging Newtonian reflector that I want to automated via software (NINA). Has anyone automated this focuser at this time ?  It seems that these newtonian reflectors have different focusers and attaching something to the focuser can be a problem.