Problem subscribing to ax12_controller_core topic

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Hi, I am new to ros and I have a dynamixel ax12 driver publishing position information and I want to access that info and put into a variable that I can use for a transform. I have done the publisher and listener tutorial successfully, but I am having trouble getting it to work with the dynamixel. Specifically I am unsure of how to change the paramaters in void since the motor doesnt seem to use std_msgs. Any suggestions? Below are the topic data and what I have for my listener.cpp program so far.

rostopic list= /motor_states/ttyUSB0

/motor_states/ttyUSB0 [ax12_driver_core/MotorStateList] 1 publisher

rosmsg show ax12_driver_core/MotorStateList

ax12_driver_core/MotorState[] motor_states

float64 timestamp

int32 id

int32 goal

int32 position

int32 error

int32 speed

float64 load

float64 voltage

int32 temperature

bool moving

============Begin Listener.cpp=================

#include "ros/ros.h"

#include "std_msgs/String"

void motorCallback(const std_msgs::String::ConstPtr& msg)

{ ROS_INFO("I heard: [%s]", msg->data.c_str()); }

int main(int argc, char **argv) {

ros::init(argc, argv, "listener");

ros::NodeHandle n;

ros::Subscriber sub = n.subscribe("motor_states/ttyUSB0", 1000, motorCallback);

ros::spin();

return 0; }