Arduino Mega,HG7881, RF 433 RF transmitter power supply problem!

Hi everyone! I need some help. I build a robot. The transmitter side i have an UNO, joystick, 433Mhz receiver and liquidcrystal display. The reciver side i have arduino Mega,Dual DC Motor Driver Controller Board HG7881, 433Mhz receiver module and two dc motor. This system suppose to do when i claim the joystick the motor is moveing. Its simple. But when i connect the receiver side an external battery (4 X 1,5V battery to the motor conroller and 9V to te arduino) after different time the receiver part is always reboot and and the dc motor is stuck.I measuring the voltage but every where is higher then 4,7V. If i don't connect the dc motor controller to the board the tansmit is fine and succes. whats the problem?