Quantity   Component name
1 × RC Toy Whatever you find at the thrift store, your choice here determines the layout of your robot
1 × "Robot Controller" Your choice, could be a Arduino, PIC, ARM, SBC, whatever
1 × RC Electronic Speed Control (brushed motor application) PWM-controlled high-current motor driver, standardized and cheaply available
1 × RC Servo (as needed) PWM-controlled high-torque/speed positioning servo
1 × Bluetooth HC-05 or HC-06 Radio-serial interface to controller logic from smartphone or tablet.
1 × Arduino Motor Sheild / RC Skid-steer ESC Skid-steer electronic speed control
1 × Hobby Battery (LiPo or NiMH) MOAR POWAA!!!
1 × Voltage Regulator So that awesome hobby battery doesn't let the magic smoke out of anything.
1 × RC Hobby Radio Receiver/Transmitter (optional) If you're inclined to go that route instead of bluetooth.