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I am trying to animate a shape key oscillating between -1 and 1 by driving it with the expression "sin(frame)".

I would expect that to result in the shape key value being "0" at frame 0 and 180, a value of "1" at frame 90, and a value of "-1" at frame 270.

Instead, I am getting a very rapid oscillation which never becomes negative, and has bizarre values that I wouldn't expect. The sin of 1° is 0.017, so I would think the sin of 1 frame is 0.017, but instead it is resulting in 0.841.

Here's a screenshot of this simple setup at frame 0: At frame 0, the result of the expression "sin(frame)" drives the Shape key to be a value of "0"

And at frame 1: At frame 1, Shape key is driven to a value of "0.841" instead of "0.017" like I would expect.

Thank you for your help! -Ben

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    $\begingroup$ Use this expression: sin(radians(frame)) The sin function expects angles in radians apparently $\endgroup$
    – TLousky
    Dec 30, 2015 at 16:03
  • $\begingroup$ that seems to be it, however it seems shape keys can't be negative. Do you want to post that as the answer so I can accept it? $\endgroup$
    – Ben Mora
    Dec 30, 2015 at 16:15
  • $\begingroup$ Just did, cheers. You're right about shapekey min and max values. $\endgroup$
    – TLousky
    Dec 30, 2015 at 16:28

1 Answer 1

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The sin function expects angles in radians, rather than in degrees, which is why the correct driver expression will be:

sin(radians(frame))

Here's an example of this expression driving the Z value of a cube (you can see that it does indeed get negative values as well, and oscillates between -1 to 1): enter image description here

Though as you pointed out, shapekeys have a min value of 0 and a max value of 1.

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