I have made an attempt at a compound sling. Forewarning and spoiler alert, this attempt was pretty much a failure. But I am going to make some adjustments and try it again.
First things first. Here's a picture of the sling:
I'll try to explain the setup without being too confusing. There is a main retention cord permanently attached to a weight. In this case the weight is a red plastic ball filled with silicon. This is not ideal, but it's what I had available when building this prototype. Another permanent attachment on the weight is a secondary retention cord that connects to one side of the pouch.
The other side of the pouch is attached to primary and secondary release cords. The secondary release cord has a loop which is wrapped around a post on the weight. The primary release cord is made of two pieces of cord. The reason is so that it can come down on both sides of the secondary retention cord, and help to hold the projectile in place while the sling is rotating.
The basic idea is that when you let go of the primary release cord, the pouch is allowed to swing free on the secondary release cord. As the pouch extends out, the loop of the secondary release cord will slip off the post on the weight, releasing the projectile.
There are a couple adjustments I tried to apply that differ from the design by Sarosh. One is that I wanted to make the sling one handed, so a windup could be used without rotating your entire body. Second, I wanted the projectile to be in a rotating motion during the windup along with the weight. The hope is that less energy from the throw is needed to get the projectile moving when the sling is released.
Here is a video of this sling being used:
https://youtu.be/5oPGFPuNbwY. Sorry about the distance. I was trying to stay far away from my phone during the recording because I had no idea where the projectile was going to go.
There are a few problems with this sling and the attempt. One is that the weight and the projectile I'm using weigh the same. They are the exact same red plastic balls. Again, this was not ideal, but what I had available at the time of this test. Second, the cords on the sling came out shorter than I wanted. The sling needs to be spun around too quickly and it's difficult to see what's happening during the release. And related to that, because the sling is spinning so quickly, it makes it much more difficult to time the release. My first throw almost hit my phone (which I was using to record). You'll see that in the video.
I'm not sure when but I'm planning to remake this sling with longer cords. I also want to test with a projectile that is smaller and lighter than the weighted ball. But for the moment, this is my attempt. At this point I think the design by Sarosh is much more effective, but I'll report back after the next trial with my design.
Feel free to throw out any thoughts or ideas. This is by no means a completed design