Beat the 40 challenges in about an hour, used the same strategy from around 20-36 and then started having big problems.
I continued with the same strat tho (similar one you can find on youtube), and just made everything extra carefully making every bar equally long on both sides, going for balance, etc and it worked!
Probably could go on for 20 levels or so, but it's not as fun after getting the achievement ^^
 "Defend your Honor!"){kind=icon}
 "CycloManiacs"){kind=icon}
 "Cargo Bridge"){kind=icon}