I designed this in college, partly because I finished my CAD class curriculum early, and partially because I needed a cable cam for a job I was doing as a photographer. I ended up having to change the design because I couldn't wait for parts to ship to me, but the concept was the same.
This model is designed to take small gimbals and camera systems across either a metal cable or a small diameter rope of some kind and is capable of withstanding quite a bit. Depending on how you source your parts, you can make this model either very light or very strong. This was before carbon fiber was readily available to me, but I am sure if you used carbon for some of these parts, particularly anything that can be cut easily lying flat, you could get the weight down considerably.

The mates aren't perfect, but It stays together and allows simulations to run correctly, so It works!!