Oh,
I posted the results just before leaving work and come home to find a debate raging. I didn't initially notice anything force related in hermunch's solution. I'll take another look now to see what NickyNick is talking about.
Scratch that, my girlfriend just walked in the door. Maybe later.
Okay I found some time. This is going to be difficult to explain unless you have a very good knowledge of physics but I can still see no problem with Hermunch's solution.
What you need to remember about force around a pivot is distance multiplied by mass = weight. An object of 4kg that is 2metre from the pivot will perfectly balance an object of 2kg that is 4metres on the other side of the pivot.
Nahuelgq's solution left a big hole in the right hand side and then placed a big chunk of weight out to the right. Further than Hermunch did. Hermunch was also very careful to thin out the weight on the right the further it extended away from the pivot. Hermunch also didn't leave a big hole and balanced all the central weight on both sides.
Hermunch's solution also rolls left at the start giving even more weight to the left of the structure. Nahuelgq shifts right giving extra weight to the right of his structure.
To my eye everything seems fine.
Not to mention my knowledge of physics gives no reason to believe that the welding in Hermunch's solution could possibly create extra rotational force. It is not a closed circuit so the energy can disipate properly. I see no bugs in the energy being abused.
I used exactly the same technique in the 670 solution I submitted. I didn't use welding to create force I used it to cheaply hang the metal bars as far from the pivot as a possibly could. Remember Distance x Mass = Weight.
I know physics, that's why I am a duck to water with this game.
Further opinions are obviously welcomed.