I just completed a version of the focuser for use on a Celestron CGE 1400. I used a NEMA 14, .9 degree stepper, direct coupled to the existing optical tube focuser. The stock focuser only moves approx. .78mm per revolution (35 full turns, stop to stop), giving a whopping 133 steps in the CFZ (at 400 steps per rev.) at F11, and 54 steps in the CFZ when using a focal reducer at F7. I 3D printed a mount to attach the motor to the focuser, clamping around the existing boss on the OTA. Backlash and mirror shift isn't really an issue as long as final focus is performed moving the mirror out toward the corrector. A NEMA 17 would have also worked with plenty of steps in the CFZ.
Overall it has been an excellent, satisfying, and fun project. 3D print files for the focuser mount for both NEMA 14 and 17 motors, and the coupling for attaching them to the focuser shaft can be found at Thingiverse at: https://www.thingiverse.com/thing:2996764 for anyone that may be interested.
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Robert,
When I started the project the plan was to build the focuser for use with my Moonlite Crayford style focuser. But using the NEMA 14 would have required either a belt drive or 1/8 or 1/16 stepping. Then I realized the SCT focuser had such very fine movement that the motor set to full steps would only change the focus by 1.95microns per step. So now I use it either with the Windows app, or as an Ascom focuser in BackYard Nikon and usually just use the 10 steps button for fine focusing, resulting in the equivalent of 13 steps in the CFZ at F11 and a combination of 10 steps and single steps at F7. It works great and I really appreciate all of your hard work in its developement.
Don
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Lee,
The motor I used has a holding torque of 11.0 N cm (15 oz./in.). Draws 0.4 Amps per phase. It's a 0.9 degree per step motor. It runs hot, but within the motor specs of 80deg. C temperatur rise.
I purchased it on Amazon, https://www.amazon.com/gp/product/B00PNEPZQC/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1 for about $20 U.S. It has been very reliable so far.
Also, if you're going to use the flexible coupling, I ended up driving 2 small screws through it into the motor coupling hub due to slippage. The telescope side has never slipped with just a zip tie holding it.
Don
Last edit: Don Beatty 2018-09-01
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
I just completed a version of the focuser for use on a Celestron CGE 1400. I used a NEMA 14, .9 degree stepper, direct coupled to the existing optical tube focuser. The stock focuser only moves approx. .78mm per revolution (35 full turns, stop to stop), giving a whopping 133 steps in the CFZ (at 400 steps per rev.) at F11, and 54 steps in the CFZ when using a focal reducer at F7. I 3D printed a mount to attach the motor to the focuser, clamping around the existing boss on the OTA. Backlash and mirror shift isn't really an issue as long as final focus is performed moving the mirror out toward the corrector. A NEMA 17 would have also worked with plenty of steps in the CFZ.
Overall it has been an excellent, satisfying, and fun project. 3D print files for the focuser mount for both NEMA 14 and 17 motors, and the coupling for attaching them to the focuser shaft can be found at Thingiverse at: https://www.thingiverse.com/thing:2996764 for anyone that may be interested.
Hi Don
Thanks for sharing the bracket, it looks great! Wow, that sure is some number of steps within the cfz though.,
Cheers
Robert
Robert,
When I started the project the plan was to build the focuser for use with my Moonlite Crayford style focuser. But using the NEMA 14 would have required either a belt drive or 1/8 or 1/16 stepping. Then I realized the SCT focuser had such very fine movement that the motor set to full steps would only change the focus by 1.95microns per step. So now I use it either with the Windows app, or as an Ascom focuser in BackYard Nikon and usually just use the 10 steps button for fine focusing, resulting in the equivalent of 13 steps in the CFZ at F11 and a combination of 10 steps and single steps at F7. It works great and I really appreciate all of your hard work in its developement.
Don
Hi Don
You are most welcome, glad you figured a way that works.
Regards
Robert
Don,
good work.. I plan use your focuser attachment idea for my C8.
Can you tell me any more details about the NEMA14 stepper you used? torque, amps?
thanks,
lee
Lee,
The motor I used has a holding torque of 11.0 N cm (15 oz./in.). Draws 0.4 Amps per phase. It's a 0.9 degree per step motor. It runs hot, but within the motor specs of 80deg. C temperatur rise.
I purchased it on Amazon, https://www.amazon.com/gp/product/B00PNEPZQC/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1 for about $20 U.S. It has been very reliable so far.
Also, if you're going to use the flexible coupling, I ended up driving 2 small screws through it into the motor coupling hub due to slippage. The telescope side has never slipped with just a zip tie holding it.
Don
Last edit: Don Beatty 2018-09-01