a trick i thought up for voltage with feigao XL motors.

[BL_RV0]

ok.
what you do to find the optimal voltage for a decent speed setup is.... you look at the rating...? of the motor like the rating of a 7xl would be 7. for a 14xl it would be 14. ok? now divide that voltage by 2 and you get the number of cells you should use. ill make a table for ya. for all the odd-rated feigao's, 7xl, 9xl, 11xl, and 13xl just divide by 2 and, since you cant have 1/2 of a lipo cell, round down. heres the table. all setups are based on en emaxx in 2nd gear with 20/72 gearing.

rating voltage rpm speed
6xl: 3s 30846.9 32mph
7xl: 3s 26440.2 28mph
8xl: 4s 30843.2 32mph
9xl: 4s 27424.4 29mph
10xl: 5s 30858.0 32mph
11xl: 5s 20846.0 30mph
12xl: 6s 30858.0 32mph

its a bit slow, but its a cool, good setup.