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  #21  
Old 30-10-2018, 04:48 AM
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Quote:
Originally Posted by Wavytone View Post
...complete with period errors arising from such a small pinion.

Would have been much better if the teeth had been helical, or use a toothed belt between the two.

Yes, I know.. but I had only this one in my drawer....
If ever I stumble on the suitable helical gear, I will print the new matching sector - it is easy enough to do.

And it can't be belt (in conventional configuration) because I keep the OTA and mount separate when not in use (when put together they are too heavy to handle)... and I do not want to complicate assembly - this way, I simply put the OTA in place and encoder (and drive) is automatically engaged.



BTW, period of PE (due to teeth engagement) is a bit less than 1°, not sure about amplitude...

Since encoder inputs are used to calculate the tracking rates for EL and AZ motors, even 1° accuracy is good enough for visual.

If I need any better, I simply sync the system with observed (or photographed) object from data base (which is a bit fiddly process, not wanted when in dark and people around waiting for next object to have a look at).
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  #22  
Old 30-10-2018, 02:05 PM
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Quote:
Originally Posted by Wavytone View Post
... Would have been much better if the teeth had been helical...
Prompted by your comment, I went to have a look at Banggood... and found there metal helical gear, of apparently right size.
Being a metal part, I will be able to "lap" the gear sector (printed with ABS filament) in boiling water, to improve gear matching even further.

And, on Thingiverse this contributor made available designs suitable for helical sector (and much much more).

Thank you for suggestion!

Last edited by bojan; 30-10-2018 at 03:46 PM.
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  #23  
Old 30-10-2018, 09:04 PM
sharpiel
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Bojan, I really like the things you do.
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  #24  
Old 31-10-2018, 08:01 AM
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great. Bojan !
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  #25  
Old 02-11-2018, 06:59 AM
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Banggood has suitable pinion gear as well.
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  #26  
Old 21-11-2018, 11:30 AM
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After 20 days of waiting, gears arrived.
I am pleased with smooth match with previously printed test gear sector.
Now I have to print the whole sector (110°)... and remove a bit of material from the neck of the small gear (where the hole for grab screw is now).

As the gears are modulo 0.6, I will have up-gearing ratio of 365/10 = 36.5, and with 40 ppr (and quad decoder implemented in Ek' box) I will have 5840 tics/rev which results in 3.7arcmin resolution.
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  #27  
Old 21-11-2018, 04:02 PM
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Gear cut to size...
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  #28  
Old 27-11-2018, 05:58 AM
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Yesterday afternoon I experimented a bit with two other options - both gears printed, and cheap 360ppr encoders (~$13 at ebay).
Final decision depends on preliminary assemby, maybe this coming weekend.
I am looking forward to holidays... I really need a week or two away from work to sort out all that I started recently...
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Last edited by bojan; 27-11-2018 at 06:38 AM.
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  #29  
Old 09-12-2018, 05:59 PM
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Encoders transmission in place...
(rusty spring goes on first occasion..)
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Last edited by bojan; 09-12-2018 at 06:24 PM.
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  #30  
Old 25-02-2019, 10:01 AM
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This is the final solution for elevation encoder.
The load is now on ball miniature bearing (ø3mm), and encoder shaft is parallel to horizontal shapt of th etelescope (not that it really mattered for good functionality...)
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  #31  
Old 21-02-2022, 06:04 PM
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After many years of use, I decided to "modernize" this scope.
OnStep (v4.24 running on MEGA2560 + ESP8266 + HC06) h/w is installed and working ok, functionality is very similar to Mel Bartels' software.
However, I had mechanical issue - vertical shaft (ø25mm) is still not stiff enough so the dob frame swings significantly which is quite annoying when windy and when un-intentionally touching the scope while observing.

I tried to use large lazy Susan (ø440 mm, purchased on ebay for that purpose couple of years ago), I tried it over the weekend and the improvement was dramatic, but I am also trying to find and implement the solution with lower resistance.

Small rubber wheels (3~4 riding on (rusty) ring welded on the tripod - I will have to flatten it and polish with angle grinder to make it aligned with vertical shaft), or ball bearings with rubber tubing is coming to mind.. I will try to put together something, but just in case there is some off-the-shelf solution.. I would try that first.

Does anybody knows about something suitable? maybe something like this?
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Last edited by bojan; 21-02-2022 at 08:33 PM.
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  #32  
Old 22-02-2022, 06:34 AM
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Maybe this solution could be OK ?... ø22 mm bearing with silicone rubber around ø6 mm shaft as dumping ..
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Last edited by bojan; 22-02-2022 at 06:50 AM.
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  #33  
Old 22-02-2022, 07:02 AM
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Hi Bojan

Would ball transfer units do the job:

https://www.statewidebearings.com.au...transfer-unit/

Rod
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  #34  
Old 22-02-2022, 07:34 AM
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Hi Rod, this could be OK.

I fund this on ebay, it looks similar.. worth a try. No need to alignment in direction.
Or this..
What I need is vibration dumping.. load is secondary.
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  #35  
Old 22-02-2022, 08:00 AM
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I will try this silicone tubing and bearings first (I have them in my stash).

Last edited by bojan; 22-02-2022 at 08:10 AM.
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  #36  
Old 25-02-2022, 11:03 AM
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Tube arrived today... I hoped it would have a tad thicker wall, but this should be OK as well.
I can try to glue the tube with silicone rubber...which will fill the gap (~0.1 mm) Or.. I can try with cone spacers (that will force rubber tighter into bearing)

Anyway, I think 1 mm layer of silicone rubber may be OK for damping and also to accommodate tolerances of the metal ring.. (which I intend to grind flat and perpendicular to shaft by mounting angle grinder on the frame. I started this couple of years ago but stopped.. because I needed scope for something. Now it's the time to finish this idea.
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Last edited by bojan; 25-02-2022 at 11:57 AM.
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  #37  
Old 28-02-2022, 07:55 AM
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Shown below is the jig for grinding the rail for damping casters, to be flat & perpendicular to vertical shaft...
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  #38  
Old 28-02-2022, 11:28 AM
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And.. I found that the timing belt for AZ encoder became sticky and some teeth are now missing.. the rubber deteriorated and soon it will turn into a paste-like goo.. so it's time to change timing belt (420 mm, pitch 2.5 mm, 168 teeth).

I found it on AliExpress (10 pcs for ~$35, free delivery) and RS-components (1 pcs for ~$35, belt + postage).
Also on MBA for 7.66 AUD (+ postage and GST)
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Last edited by bojan; 28-02-2022 at 03:33 PM.
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  #39  
Old 03-03-2022, 09:47 AM
Maberly1959 (Amanda)
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thats really very inventive, i hadn't thought of a mechanical intervention to prevent my dobsonian from moving
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  #40  
Old 03-03-2022, 06:05 PM
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Quote:
Originally Posted by Maberly1959 View Post
thats really very inventive, i hadn't thought of a mechanical intervention to prevent my dobsonian from moving
Thank you..
I build this dob mount from available parts, in hope it will be strong and stiff enough (as it was for the original purpose - front loader washing machine drum). It is.. sort of, but this way it will be much better.
Stability to wind blow and touch varies from case to case.. and here the obvious problem was vertical shaft - too "springy".

It is also pretty loud when stepper motors are working ( I have them mounted on rubber brackets). But, the tube resonates like the cavity of the acoustic guitar. When I remove the OTA from the mount, motors can't be heard at all.

Luckily, those vibrations are not visible even at high magnification (~400x).

Last edited by bojan; 17-03-2022 at 09:42 AM.
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