Welcome to Router Forums. This is a bit off topic, but we frequently get off topic here.
As a teen, my friend and I put a salvaged tow truck cable from our tree house to a tree about 250' away. It had about a 14' drop from beginning to end. To avoid hitting the tree at the far end we placed several long springs on the cable, followed by a cable clamp. The springs totaled a length of about 6' and if the springs completely compressed, the cable car (platform) would not hit the tree. Since the platform was oak and quite heavy, we used a rope to pull it back to the tree house. At the low end, the platform was about 4' above the ground, so it was easy to get down from it. With two of us riding at the same time, the pulley would completely compress the springs, but the stop was well cushioned. We enjoyed that ride for over three years before losing interest in it.
Not sure if any of this will be of any help to you, but it does show that there are others out there with similar ideas, although our experience took place over 60 years ago..
Central North Carolina
Last edited by CharleyL; 07-28-2018 at 02:26 PM.