Fitting the SkyWatcher Auto Focuser onto a Starwave 70ED

[Marky1973]

A little while ago a post of mine developed into a discussion around auto focusers and whether the Skywatcher AutoFocuser would fit my Starwave 70ED. I had a play with the motors from my EQ3-2 which did work, but was a bit fiddly as the motors are always running and you need to turn them off when focussed - and it is easy to forget or over-shoot the sweet spot!

So I just thought I'd give the SWAF a go and ordered one a few days ago. It arrived yesterday and, out of the box, I can say it doesn't really fit. However, I did manage to make Heath Robinson proud and fix it up without having to mod it in any way - other than a trip to Tesco for some extra nuts and a battery (it doesn't come with one annoyingly) it was fairly easy. It isn't fixed perfectly, but it is solid and the focuser moves the focus tube and holds it solidly, so I think it must be working.

Anyway, I didn't take a video or pictures of every stage, as I thought I would get it fixed, then re-do with photos... but it wasn't quite that easy so, when it was done, I didn't feel the need to dismantle and re-do!  But I thought I'd post some info anyway, just in case anyone else is thinking about the AF - it is possible, if you aren't desperate for perfection! I suspect the Starwave range have similar focusers...of course, if anyone has a better way to do it - let me know! 

I set the scope up in my EQ3-2 so I could hold it steady and removed the single focus knob on the right and the central focus lock nut. The plan was to use that hole, or one of the other screw holes on the underside of the focuser to fix the AF bracket.

I tried to add the AF as it was, using the flexible coupler between the AF and the focus axle with the knob removed, but the distance between the focus lock hole and the AF motor unit was too great to fix to the bracket and the scope, so that wasn't going to work. The motor unit come with an adapter on it that looks like it would fit a variety of bars, but is also removable.

I loosened the grub screws and pulled it off. It is flippin' tight, so I wouldn't pull it off unless you are sure you can fix the unit as I suspect it will be tricky to get back on - it has a small rubber ring inside the shaft so will take a lot of pressure to get back on.

Anyway, without that, the motor unit was much closer to the scope and the bracket met in all the right places. However, all the nuts that I had would require the bracket to be drilled to allow them to fit through and into the focuser on the scope. I didn't want to do that (just yet) in case none of this worked and I needed to sell on! So I moved it so I could use a large hole on the bracket, close to the center of bracket - but this meant the gap between bracket and motor housing increased.

The bracket was also very close to the coupler, and I didn't want it rubbing/resisting when using the AF in case it affected the motor. So I added 3 split rings under the bracket to raise it from the scope and give clearance.

I then connected the motor unit to the bracket with a couple of bolts and used a couple of nuts to tighten/lock the bolts and stop them "undoing" themselves... so it all looked a bit like this....

And that's probably not quite the order I did it all in as I had to make a few bits up as I went along and there was a bit of trial and error when getting the bracket in place. I also had to loosen and adjust a few times to make sure the brackets were level, the coupler was central and there wasn't too much movement or play in the motor when it starts up.

But, with the battery pack attached it all worked and I focused really easily on a wall through the window as a test. Of course there is no clear night forecast in Gloucester until 2016 now, typically, but I feel confident it will help focusing. Looking forward to trying it out proper!

Took me a while but, knowing what I am doing, I reckon I could do it all in about half-an-hour - so fairly easy. With plenty of nuts and bolts and holes, I reckon it should fit plenty of models.

Sorry for the lack of pictures and rambling commentary, but hope it helps someone! At the very least it will remind me what I did in 6 months time when I take it off for some reason, lose some nuts and can't remember how to put it back together....

[JamesF]

Well done.  I've done quite a few mods for these now.  I don't think I have any actually on a scope that they fitted out of the box  I decided in the end that it was easiest to find a piece of scrap steel or aluminium sheet to make a new bracket from, bending it as required and drilling mounting holes to fit whatever focuser I needed it to.

James

[Marky1973]

Yeah, I can see the attraction of making the bracket yourself. I was determined it wasn't going to beat me though! I just wanted to get the thing fitted without having to drill anything - I haven't had the scope for even a year yet, so didn't want to try doing something that would end in tears!

Hopefully I won't pop downstairs later to find it has just fallen off....

[JamesF]

Ah, I didn't drill anything on the actual OTAs or focusers.  Just drilled my own mounting holes in the plates I'd made so they matched up with suitable mounting holes in the focuser.  So for example in this one I made a plate that matched the existing focuser spindle assembly mounting holes and used the existing mounting screws to fit it:

This one was a bit more tricky.  I ended up using existing holes, but I needed longer screws and spacers to make it all fit:

Making your own bracket also means it's possible to leave all the adjustment screws and locks easily accessible.

The first time I did one was a far more "suck it and see" approach though.  It still works fine, but it's nowhere near as neat as the two above.  You can make them fit pretty much anything if you're suitably determined

James

[Marky1973]

Nicely done - the problem with the STARWAVE is the focuser doesn't have similarly useful screws at each corner, so you do have to get a bit more creative! Just wish the clouds would beggar off! 

[JamesF]

Yes, you have to start getting quite creative when you don't have any particularly viable mounting points

James

[Marky1973]

Well, I've not had much time to use the scope recently because of these light summer nights/clouds/apathy, but I have been out a couple of times to play and just thought I had to come back to say the focuser works a treat - both visually and with the focus assist on APT. Much easier than trying to get focused by hand - and I thought i had quite nimble, steady hands....clearly I was actually a sausage-fingered oaf....FWHM readings were usually around 1.6 at best in APT after 20 minutes of playing around - first time with auto-focuser and I was at 0.7 in seconds - so onwards and upwards - I think they can be recommended and are pretty cheap considering the price of other astro stuff!

The only problem I have encountered is that is sometimes struggles on inwards focus at the slowest speed, but a tiny twist on the speed control sorted it out - I will have a play and check the fixings though to make sure nothing is catching anywhere....