[As Lactose! observed, this attempt is very wrong anyway... so no need for spoiler]
Place any 6, 3 weigh on each balance ---- you can either eliminate that 6 or its one of them. either way 6 remains ---- observation 1
Of the remaining 6, ....
case 1:
Place any 4, 2 weigh on each balance ---- if it balances, the odd ball is in the remaining 2 ---- observation 2
by now you know the weight of each of the 11 as you can divide the total weight on one side by 2
place each of the remaining 2 one either side, the side which weigh less or more than the average weight in observation 2 is the weigh ------- observation 3
case 2:
Place any 4, 2 weigh on each balance ---- if it does not balance, the odd ball is among this 4 ---- observation 2
One side weighs less than the other, note the weigh on each side, i.e ... divide each side's weight by 2, ex. say... you get 2.5 for one side and 3 for the other
case 2a
remove the top 2, if it balances, the odd ball, the odd ball is the remaining 2, note the weight on the scale ---- observation 3
One of the 2 removed is the odd ball. The one removed from the side less or more than the average weight observed during observation 3 is the odd ball
Or if it does not balance after removing the top 2, then the side that is equals to one of the calculated averages (say 2.5) in case 2 is among the 11, while the other is also now known to be more or less through the observation of the balance ---- observation 3
case 2b
Place the remaining 2 on the scale the one that weighs more or less than the average weigh from observation 2 is the odd ball ---- observation 3
****Not sure if this mis-mash is correct... whatever****