Goraplx,
I would not do smaller- (6) motors with 30a esc?
From the photo, it appears that you need to use flux and more heat to get the solder to "run". It looks as though your solder was too cold and without flux.
A proper solder joint should be smooth & shiny until set (dull).
Check the web for videos.
Also, a proper solder connection should never break off.
I hope this helps.