▁and ▁they ▁are ▁character ized ▁by ▁low ▁noise ▁and ▁the ▁cap ability ▁to ▁charge ▁the ▁battery ▁during ▁bra king ▁or ▁down hill ▁r iding ▁. ▁ ▁Mot ors ▁ ▁The ▁B ion X ▁electric ▁b icy cle ▁wheel ▁hub ▁mot ors ▁have ▁certain ▁innov ative ▁characteristics , ▁often ▁not ▁found ▁on ▁similar ▁hub ▁motor ▁products , ▁including ▁having ▁the ▁motor ▁controller ▁embedded ▁within ▁the ▁hub ▁itself ▁and ▁integrated ▁reg ener ative ▁bra king ▁ab ilities ▁that ▁allow ▁the ▁batter ies ▁to ▁be ▁partially ▁re charg ed ▁when ▁r iding ▁down hill . ▁ ▁The ▁D ▁series ▁of ▁mot ors ▁was ▁the ▁most ▁recent ▁and ▁strong est ▁B ion X ▁technology ▁with ▁a ▁tor que ▁of ▁ 2 5 / 5 0 ▁N m . ▁The ▁motor ▁cyl inder ▁is ▁much ▁larger ▁but ▁th inner ▁than ▁in ▁previous ▁versions ▁and ▁we igh s ▁ 4 . 0   kg ▁( 8 . 8   lb ). ▁Before ▁that ▁was ▁the ▁S ▁series ▁which ▁with ▁ 3 . 5   kg ▁( 7 . 7   lb ) ▁was ▁l ighter ▁than ▁the ▁P ▁series ▁at ▁the ▁same ▁strength . ▁The ▁P ▁series ▁mot ors ▁were ▁the ▁first ▁produced ▁by ▁B ion x . ▁They ▁have ▁a ▁tor que ▁of ▁ 9 / 4 0 ▁N m ▁at ▁a ▁weight ▁of ▁ 4 . 7   kg ▁( 1 0 . 4   lb ). ▁ ▁* Since ▁the ▁maximum ▁legal ▁power ▁specific ations ▁in ▁W att s ▁are ▁different ▁for ▁the ▁same ▁motor ▁in