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How to attach Altitude encoders to dobsonians

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#1 Adun

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Posted 25 May 2021 - 01:33 PM

4 years ago I shared a DIY project for building an inexpensive DSC which used an encoder for Azimuth but an accelerometer for Altitude, mostly because of the difficulty of attaching an encoder to the altitude axis of my Z114 mini dob or my Skywatcher 10" dob.
 
Recently, while working on a dual encoder version of my DSC, I found a simple way to attach an Altitude encoder to my Z114 minidob. It seems almost obvious now, but 4 years ago I couldn't come up with it, so I want to share the Z114 fix, and invite others to share how they have managed to attach encoders to their dobs.
 
So here's the rule for this thread: Share your solution for attaching altitude encoders for your dobsonian, regardless of whether said dob is commercial or DIY, tabletop or gargantuan, truss or solid tube. Hopefully this will aid others in figuring out how to turn their starter dob into a push-to.
 
I'll start myself:
 
For the Zhumell Z114 tabletop mini-dob, the key is using a GT2 open belt:
 

Open GT2 belt


 
The Z114 OTA is held by a clam which connects to the wooden arm using a white nylon "bearing disc", of which you can see the edge in this picture:
 
IMG 20170118 210457

 
You can see that right next to the white nylon disc, the black cylinder has a little space where one could (using a silicone glue gun) attach a piece of GT2 open belt to turn the black cylindrical surface into a GT2 gear:
 
GT2 belt glued to Z114

 
Now we can use a regular closed GT2 belt (I used one of 488mm length):

A Gt2 timing belt (488mm)

 
And fix the Altitude encoder somewhere to the side:

Altitude Gt2 belt


At first I was going to use an acrylic Pelican ruler as an encoder bracket, drilling a hole in one side to fix the ruler in position using one of the Z114's existing screws, and 3 holes in the other side to affix the encoder to it, and let gravity provide the tension:

 

Ruler to attach encoder

 
However, 3 years ago, pgrunwald printed some brackets for the SignWise optical encoders:
 

In case anyone is 3-D printing,  I found a bracket for the encoder here: https://www.thingive...m/thing:2242951.
 
Specifically it is  "OH_Frame_SignWise.STL".   I was also able to easily raise the height of the mount using Autodesk Meshmixer by just selecting the top and extruding it 20mm.  The modified file is attached.

 
And he was kind enough to gift me a few (Thank you again!). It turned out one of them was perfect for fixing the alt encoder in a "click-in" removable way,  so that's what I used, although a drilled ruler + gravity would work too.
 
3d printed part used to attach it


side view

 

 

So, that's one way of attaching an Altitude encoder to a Z114. ¿What about your dob?


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#2 lphilpot

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Posted 25 May 2021 - 06:14 PM

I've had (Lumicon) encoders on only two scopes: My homebuilt 10" f/5.5 and my 14.5" TeleKit. Lumicon provided a screw on flange with a center hole and set screw, plus stay-arm, for the altitude encoder.

 

That worked fine on the 10" - I attached the flange to the center of the altitude bearing and mounted the encoder shaft in the flange. The stay-arm attached to the encoder housing. The recommended way of mounting to the TeleKit was the reverse - Foam double stick tape was used to stick the back of the encoder to the altitude bearing and the stay-arm was attached to the encoder shaft. Either way would've worked on either scope (just had to flip the altitude rotation direction in the computer), but mounting the encoder directly to the altitude bearing was slightly lower profile. However, it was more difficult (or at least, less margin for error) to center with the "first try is last try" nature of double stick tape.

 

No photos of the 10", here's the TeleKit

 

fik1rT5.jpg


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#3 Kunama

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Posted 25 May 2021 - 07:50 PM

I made the trunnions, drilled a 1/4" hole for the encoder, then made some tangent arms, attached the US Digital S6 encoder to them and ran the cables to the Nexus DSC....

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#4 pgrunwald

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Posted 25 May 2021 - 10:52 PM

I’m happy to print at cost. Shipping USPS priority is $7.  PM me to tell me what you might want.  


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#5 Speo

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Posted 26 May 2021 - 08:53 AM

Last year I built a similar project, using 2 encoders and ESP32 board. I installed one on a 10" Orion dobsonian, one on a 12" Meade Lightbridge dobsonian, and now I am installing one on a 12" Celestron Starhopper dobsonian.

 

Below are some pictures of my 12" Lightbridge installation. 

 

High resolution pictures available here: https://astrostuff.w...ic/tune-speaker

 

More details and few other installation ideas were posted here: https://www.cloudyni...ith-2-encoders/

 

Here is a neat installation that does not require drilling in the mount: https://www.cloudyni...2#entry11062230

 

Encoder brackets for 3d Printing: https://www.cloudyni...2#entry11066038

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Edited by Speo, 26 May 2021 - 01:32 PM.

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#6 Speo

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Posted 26 May 2021 - 12:21 PM

Encoders installation on 10" Orion base. I removed the intelliscope system and installed a SW OTA on rings

1 - OTA rings

2 - plywood trunnions (altitude bearings) with a strip of brass for friction

3 - 120 tooth gt2 3d printed

4 - altitude encoder  

 

For azimuth the only belt I had at the time was a bit too long so I 3d printed an idler to route the belt excess

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Edited by Speo, 26 May 2021 - 01:35 PM.

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#7 Speo

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Posted 26 May 2021 - 12:30 PM

My 12" Starhopper I am working on right now

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  • 11.jpg

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#8 Adun

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Posted 09 June 2021 - 11:06 AM

I'm quoting solutions for Skywatcher dobsonians from Ravi and stevo58:
 

Here are the construction details of my DSC:
1. I am using 600PPR/2400CPR optical encoders with 9:1 gearing; effectively 21600 counts per revolution.
2. I made the gears using 6mm thick plywood discs and glued 6mm wide GT2 timing belt on the periphery.
3. Altitude axis uses a 135 deg. sector of 360 teeth gear and a 40 teeth GT2 timing pulley fixed to the encoder. I have fixed the gear sector to the altitude bearing using three M4 bolts & nuts.
post-205061-0-12324700-1619785126.jpg
4. I fixed the encoder to a 50mm aluminium L angle and fixed it to the rocker box using a 75mm long SS door hinge. I can engage or disengage the encoder by just “opening” or “closing” the hinge.
 
post-205061-0-56179500-1619785142.jpgpost-205061-0-06055000-1619785152.jpg
5. Azimuth axis uses a 180 teeth gear (again made of 6mm thick plywood and GT2 timing belt) and a 20 teeth GT2 timing pulley. I replaced the azimuth axis bolt with a longer one and  fixed the gear to it. The encoder is fixed to a 50 mm aluminium bracket and is lightly tensioned against the gear using a tension spring.
6. The encoders are connected to Arduino via a cat6 cable (because I'm going to fix the circuit to the platform).


I just replaced the non-adjustable handle with a length of 10mm threaded rod on my SW.  I’m using a 60-tooth GT2 pulley, though, so I don’t have the same resolution (“only” 9000). I ground a flat on the rod at the right point, put a fender washer between the pulley and rocker, and tightened it down. This has worked fine for me, and it doesn’t take any longer to knock the scope down than it did before. If it starts to have a problem, a bit of non-permanent LocTite will take care of it.

 

It would also be simple to put a larger pulley or higher pulse encoders if I decide I ‘need’ insane resolutions like 50-75k.

sml_gallery_352638_16959_154734.jpeg



#9 Adun

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Posted 20 July 2021 - 10:57 AM

From OskiBear:
 

I was able to use 2 600 p/r encoders, installed on an AWB OneSky, and am very happy with the results. 
 
sml_gallery_257831_17248_298689.jpg
 
Fortunately there is just enough room on the OneSky's alt bracket to hang a belt (shamelessly stealing from Adun's idea in another forum). I worried originally about lining the belt up just so - but if you think about it, there's always going to be a point that doesn't need contact i.e. you'll never point the scope straight down. So you don't have to be exact when gluing a belt fragment tooth-side up to the alt bracket.
 
sml_gallery_257831_17248_339778.jpg
 
.
.
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I wanted to keep the handle grab accessible, so drilled a hole thru the other side of the mount upright and ran a coupler (as short as I could get it) thru from the encoder to the belt pulley. (see the little red barrel sticking out?). Drilled the hole a little oversize to allow for tensioning the belt (doesn't have to be much)
 

sml_gallery_257831_17248_67947.jpg




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