arduino uno , 舵机和步进电机不能同时工作的问题。

解决方案 参见： 

http://www.cnblogs.com/sjsxk/p/5832406.html

Arduino学习经验(一)之解决舵机库和pwm输出冲突

官网资料： https://www.arduino.cc/en/Reference/Servo 

The Servo library supports up to 12 motors on most Arduino boards and 48 on the Arduino Mega. On boards other than the Mega, use of the library disables analogWrite() (PWM) functionality on pins 9 and 10,whether or not there is a Servo on those pins. 

舵机数量大于两个的时候要用外接电源（ not the +5V pin on your Arduino）：

Note that servos draw considerable power, so if you need to drive more than one or two, you'll probably need to power them from a separate supply (i.e. not the +5V pin on your Arduino).