Using rosserial to communicate with MX-64 DYNAMIXEL motor - arduino

Question

When I try to use rosserial to communicate with an Arduino to control the MX-64 motor, every time I use rostopic pub to send a message, it will give me this error:
"Mismatched protocol version in packet: lost sync or rosserial_python is from different ros release than the rosserial client "
If I remove the Dynamixel.move(X_SERVO_ID,rollint); function in the code or don't send any information though ROS, there will be no error. I tried all the rosserial examples, all of them are working just fine without any error.
The weird thing is even if it gives me an error, the program is still working. Every time I send a message, the DYNAMIXEL motor will start moving.
#if (ARDUINO >= 100)
#include <Arduino.h>
#else
#include <WProgram.h>
#endif
#include <ros.h>
#include <std_msgs/Int8.h>
ros::NodeHandle nh;
#include <Dynamixel_Serial.h> // Library needed to control Dynamixal servo
#include <sensor_msgs/Imu.h>
#define X_SERVO_ID 0x01 // ID which we will be set in Dynamixel too
int rollint = 0;
void motor_cb(const std_msgs::Int8& cmd_msg) {
rollint = ((1.00*(90-cmd_msg.data))/360)*4095;
Dynamixel.move(X_SERVO_ID,rollint);
}
ros::Subscriber<std_msgs::Int8> sub("MX_Motor", motor_cb);
void setup() {
delay(100); // Give time for Dynamixel to start on power-up
nh.initNode();
nh.subscribe(sub);
}
void loop(){
nh.spinOnce();
delay(1);
}

Answer 1

It looks like your Dynamixel servo is hooked up to the same serial port that you use to communicate with the rosserial server. In many Arduino boards like the Uno the hardware serial port (where your Dynamixel is hooked up) is connected to a USB serial converter (which connects ROS via USB).
You need to connect your Dynamixel to a different hardware (or software) serial on your Arduino and initialize it with Dynamixel.begin(Stream&) (Dynamixel_Serial.h#L162), where Stream& is that hardware / software serial.