Animate a ballista firing I created a tower with ballista on top and I want to animate it firing and reloading etc. My idea for the animation is to create a cylinder as the ballista bow string as in this image  




I found several tutorial about adding keyframes to record the movement of an object as a whole. But in this case I need to record the movement of the middle part of the string only, drag it backward to stimulate the movement of a bow, like this




Maybe my idea here is dump af since I just started Blender for a few month, so any recommendation is much appreciated :D
Thank you in advance!
You could use shape keys.
In Object mode select your object and in Object Data Properties give your object two shape keys. They will be named Basis and Key 1.

Select Key 1 and toggle to Edit mode. Select the middle vertices of your object. Make sure proportional editing is on (o key) and the mode is set to linear. Press g and adjust the white circle so that is covers the string (Mouse scroll wheel). Move the vertices until it looks good.

Toggle to object mode and change Key 1 Value. This value can be keyframed to create animation.

PS. If you use only a little bit geometry in your bow string then you don't even need proportional editing. You can just grab and move the vertices where you want. If you want to edit the actual bow to move while firing then proportional editing is handy.