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Hi, i am making a robot which would be having a weight of not more than 10Kg.it is a four wheeled robot with chained differential drive and has two motors in all.i want it to have a good speed and a good torque.can any one tell me which motor will be best for it,and y that motor is best??

Please help me out to understand how this H-brigde is working? i tried but i couldn't make any sense. i mean i know the general working of the circuit...but i don't know the reasons why one transistor goes to Saturation and other goes to cuttoff... i found it through google.it is attached in the form of image.. thanks