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Super-Simple Servomotor Controller

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#1 rlw1138

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Posted 28 November 2021 - 08:51 PM

I don't "astro-photo" -- strictly visual -- and I wanted a way to turn my focuser knobs without touching them.

 

I didn't need it to remember any focus positions, or compensate for temperature, or to interface with k-stars or stellarium or whatever.

 

I just wanted it to "feel" just like using the normal focuser knob.

 

I also wanted an easy Arduino project.

 

I wanted it all to be fairly cheap, too.

 

I've come up with a very workable combo: the software's only a little over 3K of memory so it runs in most any Arduino MCU board, even the tiniest ones.

 

It uses cheap servo-motors and minimal components (but yes, some soldering is needed).

 

The most difficult part -- for me, anyway -- was the physical mounting for the motors and the drivetrains.

 

On my Maksutov, the motor is driving toothed timing-belt pulleys. The motor is screwed directly to the side of my Newtonian with a small wood pulley driving the larger focuser knob with a 3mm thick round urethame drive belt. My Lunt Solar 50mm uses a little homemade aluminum pulley with the same 3mm round urethane wrapped almost all the way around the helical focuser body -- the motor is fixed to the side with Velcro!

 

Of course, you'll need a personal computer that can run the Arduino IDE software (to program your electronics). And you'll need to be able to solder.
......

 

Full details -- including wiring diagram and the program -- are on my Wordpress blog: https://s4rc4sm.word...tor-controller/

 

There's a (very) short video demo, and also a link to github for the latest software. (I tweak, I can't help it)

 

What do you think?

 


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#2 cmooney91

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Posted 29 November 2021 - 10:43 AM

Very nice. 

For others who are not as savvy with soldering and flashing, they could use a ready made "RC servo tester" with an extension cable to have a proportional control knob for the servo. 


Edited by cmooney91, 29 November 2021 - 10:43 AM.

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#3 rlw1138

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Posted 29 November 2021 - 03:12 PM

I wanted to do that -- to avoid having to do what I ended up doing! -- but I could only get it to work with a "normal" 0 to 180 servo. For some reason, none of my 'continuous' servos would turn. And I needed more than 180 degrees of travel.



#4 Josepm

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Posted 30 November 2021 - 09:20 AM

Interesting... As I already have all the parts, I will try it. 

As I wish to have the focuser control away from the scope, I assume that using a shielded cable to the rotary encoder will be fine.

Thanks for your post!


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#5 rlw1138

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Posted 30 November 2021 - 11:04 AM

Shielding the control cable won't be necessary.

 

The "read_rotary_encoder()" subroutine I used should ignore any spurious 'blips' on the wires.

 

Pro-Tip: Mount the encoder and the Arduino in the same enclosure, and you'll be all set. If your enclosure is transparent (I used a plastic pill bottle) the red LEDs help you locate the control in the dark.




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