Hi,

I recently mounted a cheap stepper motor like belt drive to my Baader steeldrive focuser. It's the BYJ28-48 motor that comes with a driver board and can be bought at many places for a few dollars. Whith the driver board I can run it nicely with a python script directly from 4 of the the Raspberry Pi 2's GPIO pins.
My plan is to drive the motor via indi drectly from the Raspberry 2, in addition to the other astro hardware. It means some software will have to be written and my plan is to make this my little contribution to INDI astronomy.

As I see it there are some ways to achieve what I want:

• I could write an indi driver from scratch that directly manages the GPIO pins to drive the motor
• I could run a separate (C/python) process that talks to indi via a FIFO and emulates some existing focuser that has a simple to understand protocol
• I could do something inbetween

At first site the second option seems to be the easiest to implement, however I'm not sure which focuser would be the easiest to emulate. Also I don't know what the implications of this approach will be on the performance of the raspberry.

However I may also be totally on the wrong path here and as I am not very experienced in software writing I would greatly appreciate any comments before I delve deeper into this project.

Hi,
look at this page indiduino.wordpress.com/category/devices/
I hope, it will be useful for you.

Check Astroberry Focuser driver. Info is available on the forum - indilib.org/forum/general/699-astroberry-initial-release.html

So it seems somebody had the same idea before me ...
Thank you!

Hi, I am also very interested building a focuser for my Skywatcher Newton. My new Raspberry Pi 2 arrived yesterday . I am ready to order the stepper / driver. Now I speculate how to realize a motor focus, what stepper would be sufficient for a focuser.Should it be bipolar, 1.8°/step, 5/12V, what holding torque?
I did some calculations please tell me if this is total crap! :
My current cheap skywatcher focuser needs for full pull out:
3,8cm or 3turns or 1080°
that is:
0,0063cm = 0,06mm for 1,8°

My critical focus zone is
58um for blue light = 0,06mm

Its also very unclear to me how to do the mechanics, how to mount the motor, directly or with cogwheels or toothbelt.
Any thoughts on this?

The 28BJY-48 motor that I am using has a 1:64 reduction gear which means that is has 3072 steps/turn and more than enough torque and resolution. But it is also slow and there's also quite a lot of slack. I haven't figured out the exact amount slack yet but it's more than a few steps. But at $3 including driver circuit you can't complain.

My telescope is a skywatcher Maksutov-Newtonian that I bought with the Baader steeltrack focuser. The steeldtrack has a 2,5 mm belt drive groove so I bought a drive belt and sprocket at conrad. I mounted the motor with a piece of bent aluminium strip and some screws and spacers. See also the picture in my original question.
I don't know the skywatcher focuser but my guess is that you could do something similar with the skywatcher focuser. You will have to make some slotted holes in the strip so that you can influence the tension of the belt. If the focuser doesn't have a belt drive groove I would try an o-ring or elastic band.

ok thanks, my image of the focuser becomes clearer. I think I will also bend a piece of aluminium. Do you control your focuser in indi or outside indi?

Currently outside of INDI. However user Kaczorek kindly pointed me to the astroberry sources, and i'm trying to incorporate a driver for my motor in that software. But there's a lot to learn so the process is slow, but interesting...

I needed a focuser for my SCT. I decided to use builtin focuser knob which moves the main mirror. This results in inherent field of view shift when changing direction of focusing, but I can leave with this. For Crayford focuser the solution suggested by mrpraline looks very nice. I used 2 gears instead transmission belt. This way I minimized backlash of the system.
All you need is Raspberry Pi + stepper motor + stepper controller + astroberry driver (major update is coming soon).
To keep it simple I decided to power a stepper motor from RPi with 5V. Therefore I used low voltage motor (PG2528-0502U 5V 0.2A 0,5Nm) and controller ( DRV8834 10,8V 2A). I use USB type B port (4 pins for 4 wires of bipolar stepper motor) on focuser side and standard USB port on RPi side. This way I use standard USB type B cable to connect the devices. If you decide to use this solution make sure you don't connect any other usb devices to the focuser port on your RPi. It tramsmits 5V impulses to your stepper motor which could be not good for anything else, including your CCD (!).
I use KStars for remote controling of my mount, ccd and focuser, including precise autofocus with Ekos. This is really cool!
Mechanical design is documented in attached simple FreeCAD files (also available on the project site ). It would be just perfect to have files ready for 3d printing but I will leave it to an expert. In the meantime I used copper laminate as the main building material.

@Kaczorek very nice! My parts list will be complete soon.
I think I will go with the DRV8834 too. I will try a belt drive and try to re-use the original focuser knob since
these are screwed on an strange small shaft that would make require extra money to buy an shaft adapter.
I will buy an aluminium angle with 100x100x1000mm and 1mm thickness and then cut into parts. Its quite cheap and should match between this white plate and the four screws. For the stepper I think I will try this one: Bipolar, 200 Steps, 28×32mm, 3.8V, 0.67A . I borrowed my old pair of EQ5 Motors, IF I will get them back I can maybe use one of these instead. For the motor shaft I will try such a OpenBuilds GT2 (2mm) Aluminium Timing Pulle y

Are the black ribbed grip sections rubber rings? If they are, why don you just remove one and use a rubber band straight on the motor axes? Then you will have a free 'manual override' function too...

I have just uploaded new version of Astroberry drivers. Check this out