Hi, everyone! Welcome to my first instructable! I hope it will be helpful to anyone who wants to make an automatic door closer with this design, using sheaves and internal counterweight. I'd like to apologize for any grammar or english errors, because i'm brazilian and i am also trying to learn english while publishing some few ideas that i was able to put in practice!

Well, let's go to the instructable:

Bill of Materials:

Well, I didn't take any picture of all the material that I used in this instructable, but here is a list of the most important that were used:

-> 0,5m of " U" Beam (35x10mm) for office divider panels;
-> Two 50A1 sheaves (Diameter 50, A1 channel);
-> One 60A1 sheave (Diameter 60, A1 channel);
-> 2 pieces of M8x50 DIN933 screws;
-> 14 pieces of M8 DIN934 nuts;
-> 2 pieces of M8 DIN125A washers;
-> 1 piece of M8x95mm cut of threaded rod;
-> 2m of wire/rope. I used clothes line rope, here;
-> 6 sets of 6mm steel screws for concrete fixturing;
-> One bottle for counterweight.
-> 6 pieces of aluminium rivets 3,2x12,7mm

Materials left to get other level of finishing:
-> 700mm of sewer PVC pipe of 75mm diameter;
-> One cap of 75mm PVC sewer pipe.

Tooling:

Tools that I needed to make this instructable:

-> Power Drill
-> 8mm concrete drill bit
-> 3,5mm HSS drill bit
-> Angle grinder for cutting the "U" beams;
-> Hand riveter for 3,2mm rivets;

Step 1: Making the Sheave Supports

Cut two U beams with 120mm length and one U beam with 195mm length with the angle grinder.

For the two "L" supports, cut only the beam laps at 60mm of the border. This will allow you to bend the "U" channel easily, and precisely, using your hands. The drawing will give you the dimensions of this part that I made. Do the same for the "U" support with the 195mm piece of "U" channel. Forget about the 45º cut that the drawing represents, i just messed up one part when I made that because i didn't realize that the beam was so easy to bend!

Before bending the parts, make sure you've drilled the fixture holes of 6 and 8mm of diameter.

After bending, you will need to place two rivets on the laps of the "U" channel, to make sure it will not unbend with the counterweight and the forces involved on the operation of the assembly.

Step 2: Placing the Sheave on the Supports

For the "L" supports, it will be easy to place the sheave. Just place the M8x50 screw in the 8mm hole with the washer, and fasten the nut on the other side. Then, place the 50A1 sheave on the screw. At last, fasten two nuts against each other on the end of the screw, keeping the sheave not too loose but not too tight that it will not spin easily! You will need two wrenches to do that!

The "U" support is not so easy, and will need to be done "in field", while installing the assembly. There will be the same need to place two nuts in each side of the sheave, to keep it "not too loose, not too tight".
This assembly needs to be done while installing because the two fixture holes are behind of the sheave, making it impossible to place the concrete fixture screws while the sheave is assembled. There are two images with 3d views of the assembly of this support.

Step 3: Installing the Supports

After all that work has been done, here comes the easy part!

Drill holes on the wall to place the sheave supports on the right places. It will depend on the context of your installation, the images have some measurements that I took and may guide you while installing yours.

Place the rope tied securely on the door, and on the other tip there comes the counterweight!

Step 4: Attach the Counterweight and Enjoy!

Here comes the final step: Attaching the counterweight. For my case, I used a 600ml bottle of gatorade, filled with 1,0 kilograms of steel nails and water to fill the empties.

With a total course of 210mm, it is 2,05 Joules of potential energy stored each door opening!

Finally, a video to show the thing working: