12th July 2019 "Skywatcher" DC Motor Focuser update Pt.1:

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I am having to return the Skywatcher [clone] focuser motor to the dealer. [I had ordered a Skywatcher, as per their website, but this is Denmark and there is no consumer protection here.]

The two control paddle buttons stopped working almost immediately. Meaning that the focuser would continue to move in one direction even when the button was released!

While the other button was completely dead to any prodding or pressing. Because one button was in constant contact the 9V battery was rapidly drained. Hopefully without burning the motor coils! Now costing £50 equivalent for the complete kit and still advertised on the dealer's website as a "Skywatcher" product.

https://fullerscopes.blogspot.com/2019/03/260319.html

Update: I decided not to return the motor focuser kit to the dealer and bought a HiTec-Astro DC motor, focuser control box instead. This will provide software controlled focusing from the laptop screen and will still use the existing gearbox motor. The HitecAstro box is provided with a downloadable driver to be used under the ASCOM umbrella. So it should be accessible without much effort thanks to the ASCOM[AWR] set-up already controlling the mounting.

I have ordered a 14T GT2 pulley and a 200mm drive belt. Calculating belt length was a bit of an unknown even using online calculators. I have had to ignore the number of V-shaped teeth on the 31mm Ø Feather Touch, slow motion knob. So I just used the overall diameter in the end.


Faced with a simple drawing I realised that calculating belt length was actually very simple: 2CD + [Pi x PCD1/2 + PCD2/2] My motor's Center Distances are fully adjustable between 50 and 60mm. So, 100 + 73mm = 174mm. Or, 120 + 73 = 193 mm. As the belt will have to ride over the FT's slow motion knob, a 200mm belt should be fine. If not, there are hundreds of outlets for ordering slightly shorter belts.

The FT's gold anodized, slow motion knob is 31mm in diameter and has 35 conical teeth. Giving it a pitch of ~2.8mm. Quite close to 3mm. Which suggests I should have gone with GT3 instead of GT2 toothed hardware. I shall just have to see how the belt reacts with the odd "teeth". There is no question that the drive will be continuous. Simply due to friction over slightly more than a semi-circumference. The 14T was the smallest pulley I could find for the motor shaft. I anticipated obtaining the maximum possible gear reduction. I can't very well make the FT slow motion knob any bigger. Well I could, with a press-on arrangement but it seems rather unnecessary.

The original O-ring drive, with home turned, brass motor pulley, was too difficult to remove for rapid focusing over longer distances. Hopefully the new drive will be quick enough not to strain my patience.

The "Skywatcher" drive was incredibly slow and crawled even at "full speed." Though being driven by 12V. Or [more typically] 13.8V, instead of 9V, should provide a little extra oomph. I might have to move the drive belt over to the direct focuser knob but the Lacerta 2" solar prism + camera is a bit of a lump to bodily lift against gravity. Particularly at high solar altitudes around mid day in midsummer.

It is often very difficult to use the eyepiece with the oddly angled, 67° Lacerta wedge without acrobatics. Using the binoviewer is often impossible around the middle of the day. A 90° Herschel prism would have worked better at this time of year. Though at all other times the Brewster angle is a bonus for comfortable [upright] viewing. Rather like a spotting scope with angled eyepiece. 

I have also ordered a 5 meter RJ10, straight, black, telephone cable to connect the HiTec control box to the focuser motor. The supplied, coiled cable with the DC focuser motor kit was a real pain. Stretching, as it did, between the focuser and my laptop desk on such a long instrument as my 7" f/12. Particularly on such a big mounting. I kept fearing a plug would detach under the tension! Hanging the motor control paddle from the focuser was difficult because of the weight of the coiled cable and the sheer range of movement of the focuser in practice.

[See Pt.2 in the next post.]

Click on any image for an enlargement.

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