I'm working on an obstacle avoiding wheels. When I try the code (with usb port/cable connected to the arduino) the dc motor works fast, and the servo motor and ultrasonic were working just fine. When the arduino board is connected to the laptop thru a port, it functions just fine. However, when I removed the port/cable, and the only source of power is 4 li-ion battery, the dc motor's speed lessened and the servo and ultrasonic didn't work at all. How do I fix this problem??
Hello @anlalala
Post a picture of your project, a drawing showing how it should be connected, show devices and their information/datasheet, including type of batteries, and if you are having trouble with your code, post that, too.
Your battery power supply must be high enough voltage and current to support the motors, motor drivers, sensor and the arduino.
Hi, @anlalala
Welcome to the forum.
Thanks.. Tom... 
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