Basic needs: don’t put to much wear on the string; energy efficient; able to hold onto the string, duh; good for completely vertical to horizontal, more of a strong traverser than straight climber.
My current thoughts involve one motor continuously spinning. The spinning turns two wheels at opposite iterations. Each wheel had a half on half of cycle where they have two wheels on the edge flipping position. I’ll need to draw this out.
This is why I need to start modeling stuff in Blender. First I need to learn how to use Blender.