Stop motion string pendulum

This is my first attempt at doing the pendulum exercise, it lacks a sense of weight, which I determined was because the spacing was too equal. The coin moved at a regular pace both ways without a sense of real life forces acting on it, such as gravity. One issue in particular was that the coin stopped very abruptly at the end/start of the motion, giving the animation the effect that a sudden force was making the coin move in the other direction, which for this exercise I didn't want, I wanted a more natural motion. However I did note the affect the spacing had on the motion as I felt it could be used in the second stop motion pendulum exercise.

This is my second attempt after doing a few practice takes, taking into account what I learnt from my first attempt. I made the spacing more varied in an attempt to portray a sense of weight in the animation, with the coin slowing down at the end of the movement and speeding up at the start. This is more succesful than my first attempt but the movement is still quite uncanny and doesn't really look real. This is because I have still have regular spacing, just with one fairing in the middle of the movement further away from the end/start movements. This made it look like the coin was travelling through some kind of thick liquid, even moving by its own accord, rather than in response to gravity. 

After a few more practice takes I produced what is currently my most recent attempt. From my last attempt I think I gained an understanding of the importance of having spacing which indicates reaction to realistic forces, so I came up with a more formulaic way of doing the spacing. I would have the first frame being the peak of the motion, so the coin would be in an only slightly different position, then I had the start of the motion where I moved the coin about 3 times the distance as the tiny distance in the first frame. I then moved the coin so on onion skin half of it was still in the ghost coin. In the next frame I had the coin so the edge was touching the last frame using onion skin. Then I would move it a considerable distance before reaching the frame on the bottom of the curve, after that point I would repeat the process going back up. This is a method I used after several takes to try to get a more consistent movement, I also think the spacing is more effective as the motion is quite smooth and it doesn't look uncanny.