In order to achieve enough reduction (mech. advantage) from the chain slack to the sled, I had to reduce by 4x. The chain slack is attached to a double pulley with some non-elastic paracord. Then, elastic 3/16 cord is anchored on the frame, then passes through the double pulley, back to a pulley mounted to the frame, then back to the double pulley, then finally through the corner pulleys and onto the sled.
I bought 25ft of paracord and 50ft of elastic cord. The pulleys need to run smoothly for the system to begin to work. I haven’t really been using the system recently though, since my cuts aren’t in the corners right now.
Hope that helps!