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DIY motor focuser

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#1 sebo

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Posted 29 August 2019 - 05:41 PM

Hey,

 

I would like to share with you my recent open-source project of motor focuser. It has quite sleek design, is easy to make and doesn't cost a fortune. It currently works with INDI platform (sorry ASCOM users). 

 

Details available here:

https://2.71astro.co...les/ticfocuser/

https://github.com/s...b/TicFocuser-ng

 

It works great and that's how it looks:

 

ticfocuser_final.png

 

 

 


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#2 rkinnett

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Posted 29 August 2019 - 08:35 PM

Looks great!

 

Does Ekos focus reliably with this?

 

You may find the step size of that ungeared NEMA17 to be too coarse.  The MyFocuserPro project provides a good tutorial for selecting stepper motors for focuser in this manual.  You might consider putting a smaller pulley on the motor shaft and a larger one on the focuser shaft to improve step size and torque.


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#3 sebo

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Posted 30 August 2019 - 05:21 AM

Looks great!

 

Does Ekos focus reliably with this?

 

You may find the step size of that ungeared NEMA17 to be too coarse.  The MyFocuserPro project provides a good tutorial for selecting stepper motors for focuser in this manual.  You might consider putting a smaller pulley on the motor shaft and a larger one on the focuser shaft to improve step size and torque.

Thanks!

 

Yes, Ekos focuses good with it. I'm using 1/2 microsteps, so with 1:10 fine-focus on Stelltrack it gives me 4000 steps / focuser revolution.

 

The motor indeed would be too coarse if used at the rated currency. It is rated at 1.7A, since Stelltrack focuser doesn't require much of the force, I use the step motor on ~200-300mA (don't remember the exact number now). With that setting it is really smooth and silent.

 

PS: the manual you've attached is great. Thank you.


Edited by sebo, 30 August 2019 - 05:37 AM.


#4 rkinnett

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Posted 30 August 2019 - 08:55 AM

Oh I see, you’re driving the fine focuser knob.  People say not to do that but I’m not sure why.  My guess is that it wears the focuser gearing instead of external gearing, but I’m sure it won’t wear the focuser down anytime soon.  That 10:1 gearing in the focuser probably gets you fine enough resolution even without microstepping.  If you can avoid microstepping then you can disable the driver when you’re not actively focusing and save that 300mA, which isn’t much, but it will help if you run on batteries.

 

Do you hear or feel any hum or vibration or occasional ticks when you’re not focusing?  I had that problem when microstepping a NEMA17 at about 500mA, so I generally avoid microstepping to avoid vibration, in addition to saving power.

 

Thanks for sharing your design and code, by the way.  That Pololu T825 looks pretty convenient, much less wiring compared to Arduino-based projects with separate motor drivers.  The packaging looks great.  You noted on your project page that you’re considering using the smaller profile NEMA17s. With your 10:1 gear ratio those should produce twice the recommended minimum torque, so they should work fine at slightly higher current.

 

If someone were to borrow your code and write an ASCOM wrapper for it, then this could become a very popular approach.


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#5 Garyth64

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Posted 30 August 2019 - 12:39 PM

I made a fine adjustment focuser control on my 5" Apogee using 2 cheap servo motors.

It worked pretty good.

 

 

Attached Thumbnails

  • Servo focuser.jpg


#6 janame

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Posted 03 September 2019 - 09:57 AM

What focuser is that?  Did it already have a pulley for the belt or did you add it?



#7 darkcloud

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Posted 03 September 2019 - 04:06 PM

This looks great.  I am contemplating doing something similar with my Steeltrack.  Can you share the source of your mechanical parts (mounting bracket, drive belt pulley, belt, etc.)  Thanks!

 

 

Hey,

 

I would like to share with you my recent open-source project of motor focuser. It has quite sleek design, is easy to make and doesn't cost a fortune. It currently works with INDI platform (sorry ASCOM users). 

 

Details available here:

https://2.71astro.co...les/ticfocuser/

https://github.com/s...b/TicFocuser-ng

 

It works great and that's how it looks:

 

ticfocuser_final.png



#8 sebo

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Posted 03 September 2019 - 04:18 PM

This looks great.  I am contemplating doing something similar with my Steeltrack.  Can you share the source of your mechanical parts (mounting bracket, drive belt pulley, belt, etc.)  Thanks!

Hey,

 

unfortunately I just order these pieces for couple of $ from a guy producing focusers by himself (Dreamfocuser - site in Polish), so I don't have technical drawing for it.

 

Nevertheless it is a very simple bracket. Dimension of holes on the focuser you can find in Steeltrack manual. Belt is 168-3M-06 and then you need 3mm pitch pulley. I was considering building it by myself - but as said, found a local source of a ready product.



#9 sebo

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Posted 12 September 2019 - 12:24 PM

What focuser is that?  Did it already have a pulley for the belt or did you add it?

Sorry for late answer (somehow I missed the question). The focuser is 2" BDS-NT Baader Diamond Steeltrack® Focuser, pulley is not included but the focuser is prepared to attach 168-3M-06 belt. It is pretty simple to be done.



#10 sebo

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Posted 12 September 2019 - 12:32 PM

Slowly TicFocuser-ng is moving towards 1.0 version. Source code is still on a feature-branch, but in general, should work. To check it out:

git clone -b 1.0-feature_branch --depth 1 https://github.com/sebo-b/TicFocuser-ng.git

Main changes:
- added "general info" tab, showing current parameters (VIN, current limit, etc.) and errors of Tic controller
- added new ways to connect the focuser (see below)

 

Connections:
- LibUSB - USB connection but not dependent on Pololu Tic library.
- Bluetooth - if you add a cheap BT module ( e.g., HC-06) to Tic controller, you can control it wirelessly.
- Serial - UART connection.

 

If there is enough demand, I can write i2c connector.

 

In the near future I'm planning:
- add Bluetooth Low Energy connection
- design a new 3d printed case for Tic with connected BT module

 

Enjoy and clear skies!


Edited by sebo, 12 September 2019 - 12:33 PM.

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#11 tkottary

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Posted 15 October 2019 - 10:19 AM

Could you attach stl for the other side of case too ?



#12 Lacquerhead

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Posted 21 October 2019 - 10:31 AM

I like the small footprint!  I may need to take this idea and merge it with ArduFocus.  I need to read Joao Brazio's code to see if it can be easily refactored to use I2C.  I would think it should be pretty straight forward since he's sending Dir/Step directly to the DRV8825 carrier.



#13 tkottary

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Posted 29 October 2019 - 04:13 AM

I was able to write ascom driver based on Sebos code . I will upload to github once I  test it fully. 




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