DH and I had the same trouble last year, TT. For some reason it just didn't make sense until I started putting it together, and even then there was a LOT of fiddling to get the proportions all right.
Given your materials, try this website for guidance: http://www.geocities.com/hillbilly_n...LOWEENfcg.html
. It helped me understand what went where as well as or better than any other I found.
Here are some quick pointers that we learned last year:
1) The crank arm needn't be really long. Ours was only 8".
2) The distance between the hand/arm pulleys and the head/body pulley doesn't have to be really far. Ours is perhaps 18-20".
3) Make sure your crank arm rotates below your pulleys and that it won't tangle in the lines. Learned that one the hard way
4) We used a replacement patio door roller (Lowes or HD will have them) instead of a washer assembly on the end of the crank arm. It has ball bearings, so it rotates smoothly. We drilled holes in the perimeter for the lines to connect to it, and used swivel connectors for fishing line to actually attach the lines to the roller.
Anyway, I hope that helps. I don't have pics of my platform handy, but if I find some, I'll post them.