I wanted a simple way to automatically close my backyard gate so
the dogs would not wander out if the gate was left unlatched.
Video in step 6 shows actual operation.
Step 1: Weight Driven Gate Closer
Sketch shows basic logic, gate opens outward, clothes line brings pulley 1 to the left and raise 8lb weight.
Step 2: Weight Driven Gate Closer
Parts came from Lowes Home Improvement store, clothes line and rope section in Vancouver, WA, USA. Window sash weight (~ 5$) from Northwest Salvage in Vancouver, WA.
Step 3: Secure Clothes Line to Gate Hook.
Above is the inside view of the gate, latch on left, and gates swings outward. Large hook screwed into 2x4" scrap that was secured to the gate with 4 screws.
Step 4: Secure Sheave to Inside Gate Post
Sheave mounted on inside gate post so line will not bind on post when gate is opened.
Clothes line pulley is tied to line.
Step 5: Weight at Top
Tie weight to length of clothes line, loop over top pulley 2, thru the center pulley 1 and tie it to hook at bottom of post.
I selected weight by using plastic bag filled with rocks until I found the right weight. 8 lb window sash weight worked for me.
May need to oil hinges so gate operates smoothly. That's it!