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Celestron focus motor

1 month 2 weeks ago 1 month 2 weeks ago by Bart.
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Celestron focus motor #63599
Edit: that photo was way to big,...

I'll post the finished board later.

15 cm wavefront condensor | Earth rotation undo-er | Few photon discriminator plates | Photons to electrons transmogrifier | Stellarmate
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1 month 2 weeks ago
mhammady
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Celestron focus motor #63610
Hi Bart

Is it possible to share the 3D print design for the C8 attachment? it will help me design my own or just use your design

- Mohamed

Celestron 8SE, Sky-Watcher HEQ5 Pro mount, Raspberry Pi 4 Kstars-Ekos-Indi server, MyFocuserPro2
ZWO OAG with ASI120MM Mini (mono) guide, ZWO ASI183MM Pro, Canon 600D T3i, ZWO EFW (LRGBHaS2O3), Celestron f/6.3 reducer

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1 month 2 weeks ago 1 month 2 weeks ago by Bart.
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Celestron focus motor #63618
I've uploaded it to Thingiverse, so anyone can download it:

www.thingiverse.com/thing:4670151

The controller with the code will be uploaded later on, for now it looks like the Arduino code below...
It's still 'quick and DIRTY', but everything works already, even a cheap infrared remote controller (and the position is updated to EKOS as well!)
If someone has any remarks on the code or suggestions on how to make it faster/ more interactive, please let me know!

I feed the motor + controller purely from USB now, which works OK. this is nice, since it removes -another- cable from the system!

I use a motor similar to this one:
www.omc-stepperonline.com/nema-17-steppe...ngth-mm%5B20%2C21%5D
there exists also a version with 400 steps per revolution.
For my Newton telescope (with Crayford style focuser) I use a little bit larger stepper motor with 400 steps/rev, but it doesn't have to be -big- still. Both can be controlled with this driver with ease.

Cheers!

Warning: Spoiler! [ Click to expand ]

15 cm wavefront condensor | Earth rotation undo-er | Few photon discriminator plates | Photons to electrons transmogrifier | Stellarmate
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1 month 2 weeks ago 1 month 2 weeks ago by mhammady.
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Celestron focus motor #63654

Bart wrote: I use a motor similar to this one:
www.omc-stepperonline.com/nema-17-steppe...ngth-mm%5B20%2C21%5D
there exists also a version with 400 steps per revolution.


Thanks Bart for the code and the design. I have a question regarding the accuracy of the motor you are using. AFAIK it is capable of 200 steps/rev, but I'm seeing many videos using the NEMA17 with planetary gearbox as this one:

www.amazon.com/gp/product/B00PNER7JA/ref...01_s01?ie=UTF8&psc=1

My question to you is how are you satisfied with 200 steps rather than 5000+? and Jo advised that the DRV8825 s capable of producing 1/32 steps order, but can it e used and convert a 1.8 degree motor to 0.05 degree one, or the hardware SHOULD support the micro-stepping as well?

- Mohamed

Celestron 8SE, Sky-Watcher HEQ5 Pro mount, Raspberry Pi 4 Kstars-Ekos-Indi server, MyFocuserPro2
ZWO OAG with ASI120MM Mini (mono) guide, ZWO ASI183MM Pro, Canon 600D T3i, ZWO EFW (LRGBHaS2O3), Celestron f/6.3 reducer

telescopius.com/profile/mhammady

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1 month 2 weeks ago
El Corazon
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Celestron focus motor #63659
Bart, when you say you power the controller and the motor through 5V USB, how do you connect the power to the stepper control board and the motor? You can't route 600 mA through an Arduino, can you? Output there is limited to 40 mA, isn't it.

Do you have a wiring diagram?

I like the one cable, everything through USB option,

Jo

Atlas Pro AZ-EQ, ASI1600MM-Pro, ASI120MM-S, ES102ED, WO-Z61, Nikon D3300, ASI-EFW, ZWO LRGB,Ha,O3,S2 filter set

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1 month 2 weeks ago
Bart
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Celestron focus motor #63662
Hi Mohamed,

You don't need all that resolution on a Celestron. it is already 'geared' by the focuser thread inside. 200 steps/rev is plenty. 400 would also be fine.
I use 400 steps/rev on my Maksutov Newton telescope with a Crayford style focuser. This is a much more sensitive focuser, because the translation per rotation of the focus shaft is more. Diameter of shaft: 4 mm, and so: 4 * Pi / 400 = 0.0314 mm/step (full step!) This is a faster system ( f / 4.8 ) which is more critical to focusing than the Celestron ( f / 6.3 ) and even then it -just works- with no problem.

I think I used 16x microstepping with that system. What this is, is that the stepper driver interpolates the electrical current through the phases of the stepper motor, so the magnetic angle can be 'anywhere' within the normal full (native) step angle.

Don't use all that heavy gearboxes and just direct-drive that stuff :-)
The beauty of the Trinamic drivers is that they can be controlled over SPI protocol, so digital communication with the focus controller (arduino like) and can quickly change settings such as stepper current and microstepping. So you could, if you like, change the microstepping value dynamically. This is almost useless for a focuser, because it's a slow system anyway (but fast enough!).
The change in current, however, is exceptionally useful in this regard, because you don't want to heat up everything by holding the stepper at a certain angle with high current. You want the 'hold current' for that, just enough to lock the position.
When you are changing the position, the current is first increased, enabling higher torque, and next a move is initiated. Then it goes back to hold current again. Very strong but minimal use of electricity.

Jo,
I feed the stepper driver directly from the USB (Vcc pin on the Seeeduino Xiao). it is buffered by a 100 uF capacitor. I'm not routing 600 mA -yet- but 300 mA works fine. There is one downside of powering the Trinamic with only 5 V, which is the reduced speed the steppers can get to while keeping high torque.
Luckily, focusers which require a bit more rotational speed (SCT telescopes) need only low torque and vice versa, a focuser which requires more torque (Crayford/ rack & pinion), the speed can be very low.

I intend to design a few PCBs within a month. I may make a few 'kits'.

Cheers,
Bart

15 cm wavefront condensor | Earth rotation undo-er | Few photon discriminator plates | Photons to electrons transmogrifier | Stellarmate

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1 month 2 weeks ago 1 month 2 weeks ago by mhammady.
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Celestron focus motor #63668

Bart wrote: You don't need all that resolution on a Celestron. it is already 'geared' by the focuser thread inside. 200 steps/rev is plenty. 400 would also be fine.
I use 400 steps/rev on my Maksutov Newton telescope with a Crayford style focuser. This is a much more sensitive focuser, because the translation per rotation of the focus shaft is more. Diameter of shaft: 4 mm, and so: 4 * Pi / 400 = 0.0314 mm/step (full step!) This is a faster system ( f / 4.8 ) which is more critical to focusing than the Celestron ( f / 6.3 ) and even then it -just works- with no problem.


Hi Bart,

Thank you for taking the time to explain this to me, but I still confused about SCT C8. According to the equation, the C8 shaft is 13mm, so, 13*Pi/200 = 0.20 mm/step. Would you please explain how this is ok with SCT compared to 0.0314 for the Crayford focuser?

- Mohamed

Celestron 8SE, Sky-Watcher HEQ5 Pro mount, Raspberry Pi 4 Kstars-Ekos-Indi server, MyFocuserPro2
ZWO OAG with ASI120MM Mini (mono) guide, ZWO ASI183MM Pro, Canon 600D T3i, ZWO EFW (LRGBHaS2O3), Celestron f/6.3 reducer

telescopius.com/profile/mhammady

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1 month 2 weeks ago 1 month 2 weeks ago by dmsummers.
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Celestron focus motor #63699
@mhammady: The 8SE appears to have a thread pitch of 24 threads/inch or 0.94488 threads/mm (1.0583mm/thread(or 1 rev)). You're at F10, so your CFZ is on the order of 2.44*10^2 (244um). If you were to use the Celestron (1k cnts/rev), the math works out to 1.058um / count or 230 counts "length" for the CFZ. The ASI has 5760 cnts/rev, which works out to 0.1837um/count (1328 counts CFZ length). That's overkill unless you know you'll be adding a focal reducer. As Bart indirectly points out, at F10 and 200 counts/rev, you'd have a CFZ length of 45 counts. That seems "skinny" to me. 400 counts/rev would give you 90 counts CFZ length. 1000 would give you room for that focal reducer you're going to want ;-) . My 2 cents. Cheers, Doug.

RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.

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1 month 1 week ago 1 month 1 week ago by mhammady.
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Celestron focus motor #63812

dmsummers wrote: @mhammady: The 8SE appears to have a thread pitch of 24 threads/inch or 0.94488 threads/mm (1.0583mm/thread(or 1 rev)). You're at F10, so your CFZ is on the order of 2.44*10^2 (244um). If you were to use the Celestron (1k cnts/rev), the math works out to 1.058um / count or 230 counts "length" for the CFZ. The ASI has 5760 cnts/rev, which works out to 0.1837um/count (1328 counts CFZ length). That's overkill unless you know you'll be adding a focal reducer. As Bart indirectly points out, at F10 and 200 counts/rev, you'd have a CFZ length of 45 counts. That seems "skinny" to me. 400 counts/rev would give you 90 counts CFZ length. 1000 would give you room for that focal reducer you're going to want ;-) . My 2 cents. Cheers, Doug.


Thank you Doug for your math explanation. I must ask you from where did you get the 8SE detailed specs. I've searched for a long time for it and could not get any :(

I almost always use focal reducer F/6.3 which brings my focal ratio down from 10 to 6.3 (ideally), and my CFZ should be around 97um (92 for shorter blue & O3, and up to 126 for higher Red & Ha).

For the 1.0583 mm/rev (1058 um/rev), the 200/rev stepper motor should give 1058/200= 5.29 um / step. This should be ok for the CFZ, the 400 would e 1028um/400=2.64 um/step, also should be better in my case...

It seems that I'm missing something with my calculations on why the 200 stepper motor would be an overkill. According to my calculations, a 200 stepper motor with ~1mm thread focus shaft would give about 18 steps within 97 CFZ(f6.3) and about 47 steps within 244 CFZ (f10), so please rectify me if I'm wrong...

Thank you...

- Mohamed

Celestron 8SE, Sky-Watcher HEQ5 Pro mount, Raspberry Pi 4 Kstars-Ekos-Indi server, MyFocuserPro2
ZWO OAG with ASI120MM Mini (mono) guide, ZWO ASI183MM Pro, Canon 600D T3i, ZWO EFW (LRGBHaS2O3), Celestron f/6.3 reducer

telescopius.com/profile/mhammady

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1 month 1 week ago
dmsummers
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Celestron focus motor #63815
Hi Mohamed, I got the thread pitch info from these sources (not authoritative, but the info seems trustworthy):
agenaastro.com/articles/guides/miscellan...reads-explained.html
agenaastro.com/articles/guides/focusers/...ser-on-your-sct.html
Cheers, Doug

RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.

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1 month 1 week ago
mhammady
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Celestron focus motor #63818

dmsummers wrote: Hi Mohamed, I got the thread pitch info from these sources (not authoritative, but the info seems trustworthy):
agenaastro.com/articles/guides/miscellan...reads-explained.html
agenaastro.com/articles/guides/focusers/...ser-on-your-sct.html
Cheers, Doug


Hi Doug,

I read those articles before, and the 2" 24TPI standard mentioned in this article referring to the mounting thread on the OAT backside. I don't think they meant the thread size of the focuser shaft connected to the back main mirror. I still think it is much coarser than ~1mm because of the long-distance it can travel.

- Mohamed

Celestron 8SE, Sky-Watcher HEQ5 Pro mount, Raspberry Pi 4 Kstars-Ekos-Indi server, MyFocuserPro2
ZWO OAG with ASI120MM Mini (mono) guide, ZWO ASI183MM Pro, Canon 600D T3i, ZWO EFW (LRGBHaS2O3), Celestron f/6.3 reducer

telescopius.com/profile/mhammady

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1 month 1 week ago
dmsummers
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Celestron focus motor #63819
Yea....you're probably right. I had a similar question for Celestron Tech support when I fit my ASI EAF motorized focuser to my RASA 11. They told me it was 0.75mm. It's entirely possible that they've used the same pitch on most of their scope sizes, but I wouldn't bet my life on it. I suspect if you use 0.75mm for your calcs, you're not going to be very far off....

RASA11, Celestron CGX-L, ASI183mc Pro, 60mm guider + ASI290mm mini, ASI EAF focuser, PPB, Rpi4-4Gb+SSD, Powered USB3 hub, hardwire Ethernet.

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