Why does "sin(frame)" where frame is "1" set a shape key to 0.841 and not 0.017? 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:


And at frame 1:


Thank you for your help!
-Ben
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):


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