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Need help in how to build an electronic focuser

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#1 DeepBloo

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Posted 22 October 2021 - 09:09 PM

Hello everyone. I have a Nikkor 180 ED that I'd like to build an electronic focuser with. I'd like the design to be self sufficient (if that is the right word to it) like a ZWO EAF. I've seen designs where steppers are used and is plugged to a stepper driver + Arduino which is then controlled by the main computer. I would like a design that doesn't have to have another microcontroller before being connected to the main computer (I'm thinking of Servos instead of steppers?). Although I'm not sure if this is even possible.


This is for the sake of being compact and having less cables. Are there focuser designs out there that can run on 5v USB? I'd like to connect and control it via Raspberry Pi.

Sorry if my thoughts are all over the place. English is not my first language.

#2 DJL

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Posted 22 October 2021 - 09:46 PM

Martin's Astrophotography had a video about something like this recently, maybe it will help: https://youtu.be/-P5RCB1L32c



#3 TelescopeGreg

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Posted 22 October 2021 - 09:47 PM

I believe there is some support for an autofocuser in the Astroberry distro, but do not know the specifics in terms of supported motors and driver electronics.  I'd love to find out.



#4 gregj888

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Posted 23 October 2021 - 12:55 AM

Here's a good place to start.  Well documented with options for wireless and temperature compensation.

 

https://sourceforge....focuserpro2diy/

 

There are several videos on it... poke around on Youtube-

https://www.youtube....h?v=pf-vaF5jWOk

 

There are also a couple of other including at least one here on CN.  Good news, they can all use pretty much the same hardware.

 

Greg



#5 TelescopeGreg

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Posted 23 October 2021 - 07:46 PM

Here's a good place to start.  Well documented with options for wireless and temperature compensation.

 

https://sourceforge....focuserpro2diy/

 

There are several videos on it... poke around on Youtube-

https://www.youtube....h?v=pf-vaF5jWOk

 

There are also a couple of other including at least one here on CN.  Good news, they can all use pretty much the same hardware.

 

Greg

Thanks for the links; very informative. 

 

Without hijacking the thread, but wondering...  If one is already using a Raspberry Pi 4B / Astroberry to drive the mount, would this Hat and a NEMA-14 stepper work?  What INDI software is needed to drive it, or is there something else missing from the puzzle? 

 

https://www.amazon.c...g/dp/B08CCWDDQR


Edited by TelescopeGreg, 23 October 2021 - 07:47 PM.


#6 DeepBloo

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Posted 24 October 2021 - 01:42 AM

Here's a good place to start.  Well documented with options for wireless and temperature compensation.

 

https://sourceforge....focuserpro2diy/

 

There are several videos on it... poke around on Youtube-

https://www.youtube....h?v=pf-vaF5jWOk

 

There are also a couple of other including at least one here on CN.  Good news, they can all use pretty much the same hardware.

 

Greg

Thanks for the headstart, I'll look it up.


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#7 gregj888

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Posted 24 October 2021 - 09:47 AM

Telescope,

 

Not sure it will drive a NEMA-14 check the current capacity, but it should. 

 

There may be Pi focusers out there, you'll have to look.  You can use myfocuser as a code model if you do need to write your own.

 

The Pi is probably fast enough that not being real time isn't an issue if using it to control mount motors, but IMHO it's better to hand that to OnStep.  Use the Pi as a mount computer talking to the cameras, FW, focuser and mount/OnStep.   Guessing that's what you are doing, but a side note.

 

I've come to like smart devices.  FW and Focusers with their own small processors, connected with USB/RS-232/Ether/BL especially if I build them.  Easier to build/program and debug on the bench and little worry about too many wires on the mount.

 

Lots of ways to skin this cat, YMMV...



#8 TelescopeGreg

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Posted 25 October 2021 - 05:40 PM

Telescope,

 

Not sure it will drive a NEMA-14 check the current capacity, but it should. 

 

There may be Pi focusers out there, you'll have to look.  You can use myfocuser as a code model if you do need to write your own.

 

The Pi is probably fast enough that not being real time isn't an issue if using it to control mount motors, but IMHO it's better to hand that to OnStep.  Use the Pi as a mount computer talking to the cameras, FW, focuser and mount/OnStep.   Guessing that's what you are doing, but a side note.

 

I've come to like smart devices.  FW and Focusers with their own small processors, connected with USB/RS-232/Ether/BL especially if I build them.  Easier to build/program and debug on the bench and little worry about too many wires on the mount.

 

Lots of ways to skin this cat, YMMV...

It says 2.5 amps, vs the required 0.4 amps for the motor, if I am understanding the specs correctly. 

 

It would be perhaps better to make a separate controller box, connecting it to the Pi over USB.  I agree with you that separating functions into their own boxes has advantages, but on the other hand, the Pi is just sitting there with its GPIO pins waving "Hey, what about us?".  

 

I remembered a thread and conversation from over a year ago.  It's beyond time to dust it off, so I'm going with the design from Kevin Ross: 

 

https://www.cloudyni...up-sv80-access/

https://github.com/k...ndi-wmh-focuser


Edited by TelescopeGreg, 25 October 2021 - 05:57 PM.


#9 Pinbout

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Posted 25 October 2021 - 08:20 PM

Just for a different perspective - using a motor to drive a motor - no batteries

 

https://youtu.be/2qVNxvnkGug



#10 gregj888

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Posted 28 October 2021 - 02:35 PM

TelescopeGreg,  I don't see a problem and you have a lot of current capacity in the driver....

 

The issue on separate boxes is wires, nothing more really.  Separate micro-controllers helps during development and can help with power distribution (long wires to motors isn't really good, but less than 1m isn't usually an issue. 

 

The nice thing about a USB (Ether, WIFI or BT) is you can move the device to another telescope without pulling a controller out of the middle of 4 other devices... That may or may not hold up as a decision point for a given setup.  After all a couple of companies are completely integrated and making hay with it.

 

Get it done and let us know how it worked.

 

I ordered a PCB for my focuser last night.  Will have to see if I did it right :-)...  XIAO and 8825 or silent stepper...

 

Xiao-w-TMC2208.jpg

 

 



#11 TelescopeGreg

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Posted 28 October 2021 - 05:05 PM

TelescopeGreg,  I don't see a problem and you have a lot of current capacity in the driver....

 

The issue on separate boxes is wires, nothing more really.  Separate micro-controllers helps during development and can help with power distribution (long wires to motors isn't really good, but less than 1m isn't usually an issue. 

 

The nice thing about a USB (Ether, WIFI or BT) is you can move the device to another telescope without pulling a controller out of the middle of 4 other devices... That may or may not hold up as a decision point for a given setup.  After all a couple of companies are completely integrated and making hay with it.

 

Get it done and let us know how it worked.

 

I ordered a PCB for my focuser last night.  Will have to see if I did it right :-)...  XIAO and 8825 or silent stepper...

 

attachicon.gifXiao-w-TMC2208.jpg

Thanks for the perspective, and yeah, using the Pi Hat does lock the Pi into the setup.  But I currently have no plans to retire it, and the hat is cheap enough that I figure it's worth the learning if nothing else.  Never built anything that moved on its own before, at least not to this level of precision. 

 

Hat and motor are on order; should be hear early next week.  I've got Kevin's WMH INDI driver compiled and loaded (super easy!  Well done, Kevin).  CCDciel configured, at least as far as I can go without the physical board installed.

 

Remaining to do besides the wiring is making an expansion ring for the Pi's case to account for the extra board, and figuring out the drive gear and belt.  The thought is to put a gear on the motor, and wrap a toothed belt around it and the fine focus adjustment knob.  Should make for easy removal when the scope is being transported or used for visual.  I figure I can 3D print a small attachment block to mount the motor in the finder shoe, which is directly above the focus knobs.
 


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#12 Bob4BVM

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Posted 29 October 2021 - 04:09 PM

Just for a different perspective - using a motor to drive a motor - no batteries

 

https://youtu.be/2qVNxvnkGug

Yup, simple as it gets.

Takes me back to my Navy days, our radar azimuth sweep cursors were driven in sync with the rotating antenna via a pair of selsyn mots, reliable, rugged, very precise, no electronics involved.  


Edited by Bob4BVM, 30 October 2021 - 03:04 AM.

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#13 gregj888

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Posted 30 October 2021 - 12:45 AM

TelescopeGreg,

 

Here's mine.  I need to fold up a new box for the motor that's big enough to also take the control board but that's pretty easy.  I did the mechanics a couple of years ago, but never found a controller I was happy with.  The new board should do the trick

 

 

focuser.jpg




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