How to select stepper motor for a Z-axis application with Ballscrew

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Discussion Overview

The discussion revolves around selecting an appropriate stepper motor for a Z-axis application using a ballscrew in a 3D printer setup. Participants explore the necessary torque requirements for lifting a build platform, considering factors such as weight, friction, and motor specifications.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes the weight of the build platform and the need to account for additional resistive forces when detaching printed models, leading to a requirement for a stepper motor capable of lifting at least 6.6kg.
  • Another participant suggests checking the inputs regarding the lead of the ballscrew and emphasizes the importance of including friction in calculations when moving upwards, while assuming zero friction when holding or moving down.
  • A participant questions whether a stepper motor with 1.8Nm holding torque is excessive, suggesting that calculations indicate a need for only 0.04Nm holding torque.
  • There is a mention of considering Detent Torque in addition to Holding Torque, with a note that not all stepper designs have Detent Torque, which may affect load stability when the motor is not energized.

Areas of Agreement / Disagreement

Participants express differing views on the adequacy of the 1.8Nm motor, with some suggesting it may be over-engineered while others emphasize the importance of considering various torque types. The discussion remains unresolved regarding the optimal torque requirements and the implications of different torque types.

Contextual Notes

Participants note the need for accurate calculations that account for friction and the specific characteristics of the stepper motor, highlighting potential limitations in assumptions made during the discussion.

Vatech
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TL;DR
it is needed to select stepper motor for a Z-axis application with Ballscrew.
we suppose as knowing data that the z axis is verstical and the load is 6.6kg.
I build a Z-axis (not the one displayed on image). The weight of the Buildplatform is 2.29kg and is going to be used on a MSLA printer, so the weight might get increased 1kg additionally, so 3.29kg. The problem is that when detached from the printed model from Fep film there is a resistive force, this needs tools and test to be calculated so this is unknown data for the time.
That’s why i would like to be able to lift double the weight , meaning 6.6kg.
The ball screw is a SFU1204 , meaning 4mm travel per full rotation. Friction

1632326628795.png


I sourced experimental a stepper that has 1.8N holding torque, but how could i calculated the minimum Holding torque of the stepper motor needed to lift up the platform?

1632326436058.png
 
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Better check your inputs. I have seen ball screws with 4 mm lead, but never one with 0.4 mm lead.

When sizing a stepper motor for a slow speed drive, such as a 3D printer build stage, you can ignore acceleration. With a ball screw drive, include friction when moving up. Sources of friction include the ball screw bearings, the ball nut, and the stage bearings.

Assume zero friction when holding and when moving down. This will be somewhat conservative, but is good practice with the low friction of a ball screw drive.
 
jrmichler said:
Better check your inputs. I have seen ball screws with 4 mm lead, but never one with 0.4 mm lead.

When sizing a stepper motor for a slow speed drive, such as a 3D printer build stage, you can ignore acceleration. With a ball screw drive, include friction when moving up. Sources of friction include the ball screw bearings, the ball nut, and the stage bearings.

Assume zero friction when holding and when moving down. This will be somewhat conservative, but is good practice with the low friction of a ball screw drive.
Sorry for misstyping the 4mm
1632374462003.png

and this are the specs of my motor
1632374540108.png

By the above calculation is needed a Stepper with at least 0.04Nm Holding Torque? So in my case the 1.8Nm is a bit too much? OverEngineered?
 
Vatech said:
So in my case the 1.8Nm is a bit too much?
Maybe.
You have calculated the Running Torque to move the load.
You should also consider the Detent Torque, if any (not all stepper designs have any), and the Holding Torque.

Unless you plan to keep the motor energized to hold the load, it is the Detent Torque that will keep the load where you put it.

A quick explanation is at:
https://www.motioncontroltips.com/faq-whats-the-difference-between-detent-torque-and-holding-torque/

(above found with:
https://www.google.com/search?&q=stepper+motor+holding+torque)

Cheers,
Tom
 

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