How to Choose the Right NEMA 17 Motor for an Electric Focuser?

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Patricia202

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Hello everyone, I plan to build an electric focuser using a NEMA 17 stepper motor from Skysmotor. I have some questions during the selection process and would like to ask for your advice:

1. What is a suitable holding torque for a focuser? Is around 40 N·cm sufficient, or is a higher recommended?

2. Is it necessary to choose a NEMA 17 with a gearbox, or can microstepping drive meet the accuracy requirements?

3. Is there a significant difference in focusing accuracy between a step angle of 1.8° and 0.9°?

4. How can I reduce the impact of vibration and resonance on image quality when operating at low speeds?

5. Are there any special recommendations regarding motor current and heat dissipation in astrophotography environments (low temperature, long-term operation)?

I welcome experienced builders to share their model selections and troubleshooting experiences. Thank you very much!
 
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Hellion

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Let’s address these questions. I will give my expert answers.

Patricia202 said:
Hello everyone, I plan to build an electric focuser using a NEMA 17 stepper motor from Skysmotor. I have some questions during the selection process and would like to ask for your advice:

1. What is a suitable holding torque for a focuser? Is around 40 N·cm sufficient, or is a higher recommended?
Click to expand...
40 N·cm is perfectly sufficient. Using more is often excessive and dangerous to long term efficacy of the unit, causing fasteners to oftentimes fail.
Patricia202 said:
2. Is it necessary to choose a NEMA 17 with a gearbox, or can microstepping drive meet the accuracy requirements?
Click to expand...
Yes, the gearbox is a game changer as it permits a much wider range of accuracy. The gears provide a mechanical advantage to the drive and allow it to work less but with greater precision.
Patricia202 said:
3. Is there a significant difference in focusing accuracy between a step angle of 1.8° and 0.9°?
Click to expand...
Perhaps that is best left to the end user and personal taste. Decide what is best for you and go with it.
Patricia202 said:
4. How can I reduce the impact of vibration and resonance on image quality when operating at low speeds?
Click to expand...
The importance of rubber or silicone mount dampeners cannot be understated. They allow the resonance to be soaked up to a large degree but it can only be mitigated and not eliminated entirely. Use discretion.
Patricia202 said:
5. Are there any special recommendations regarding motor current and heat dissipation in astrophotography environments (low temperature, long-term operation)?
Click to expand...
Make sure there are ample avenues for proper heat dissipation. This can be a crucial concern even in the cold vacuum of space. Heat can build up in any enclosed space and in any ambient environment, so make certain that high heat generating devices have a proper heat sink and/or some space inside the housing, in effect “a place for the heat to go” making sure not to let it exceed the factory heat specification during the duty cycle. I would highly recommend a refrigerating unit to keep the focuser cool and within operating specs. Further study of your personal specifications is warranted. Can you describe the application in minute excruciating detail?
 
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