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iam trying to control the rotation speed of a propeller in Blender using a custom property for RPM (Revolutions Per Minute), and i want the propeller to gradually increase from zero to a high speed value, and then be able to gradually decrease back to zero. However, iam encountering an issue where the propeller changes its rotation direction and speeds up before stopping

I can see why it is not working, because my custom property is driving the y value, so when i tell it to go from 100 to 0 it is understanding that it should just take the value back down, by going back to where it came from I can see where the problem is but i dont know how to fix it , here is a link for a video which explain what i meant : https://drive.google.com/drive/folders/1IpwCiy_OLw9J0TmcA-i3oD1CgmwBu1yH?usp=drive_link enter image description here

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  • $\begingroup$ Have you verified the direction change, by stepping frame by frame, and looking at the actual angle in the rotation property? Depending on the speed and the frame rate, you may get the illusion of rotation in the wrong direction. This is basically a generalization of the Nyquist frequecy in signal processing. $\endgroup$
    – user143855
    Commented Oct 26, 2023 at 22:52
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    $\begingroup$ thanks @TitaniusAnglesmith but its actually change the direction of the rotation and not illusion of rotating , I can see why it is not working, because my custom property is driving the y value, so when i tell it to go from 100 to 0 it is understanding that it should just take the value back down, by going back to where it came from , I can see where the problem is but I cannot solve it $\endgroup$
    – Yahya Tarek
    Commented Oct 26, 2023 at 23:25
  • $\begingroup$ In that case, you'll need to keep track of the absolute rotation for the previous frame, define the difference, and add the difference to the previous frame. The simplest way to achieve this would be to use a function that gradually increases upto a maximum, then gradually decreases. A Parabola with prioperly tweaked coefficients is probably a reasonable starting point. $\endgroup$
    – user143855
    Commented Oct 26, 2023 at 23:32
  • $\begingroup$ To clarify my previous comment. A parabola would be a reasonable function for the angular velocity. The actual angle could then be calculated from the integral, which would be a cubic polynomial. However, I'm not convinced you actually need a driver. You may be able to achieve this by using keyframes and setting the easing to quadratic. $\endgroup$
    – user143855
    Commented Oct 26, 2023 at 23:45
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    $\begingroup$ many thanks @TitaniusAnglesmith $\endgroup$
    – Yahya Tarek
    Commented Oct 27, 2023 at 19:24

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