When the Buz 71 goes ON. The volt over D -- S is only 0,05 volt. A transistor has about 1,5 volt and 2 transistors have 3 volt. This give 3 volt losses to the motor. Not good.
A Buz 71 need over 4 volt up to 8 volt on the gate to go on. Therefor the lithium lipo cell. The current to the gate is only 0,007 mAmp. Means nothing. Now the motor can run with only 1,2 volt , like the ORBO. Now I still have to much losses in the core. (less info)