Publish low level data on ROS in C++ on Aliengo without sending commands

[mcamurri]

Dear unitree developers,

I am trying to obtain telemetry from the robot at a constant rate on our Aliengo robot.

Based on this example: https://github.com/unitreerobotics/unitree_ros_to_real/blob/Aliengo/unitree_legged_real/src/exe/ros_udp.cpp
I've made a modified version that publishes at constant rate rather than waiting for a command to be sent to the robot, eg. by moving the following lines:

unitree_ros_to_real/unitree_legged_real/src/exe/ros_udp.cpp

Lines 106 to 108 in b6227b8

	low_state_ros = state2rosMsg(custom.low_state);
	pub_low.publish(low_state_ros);

after the data is received from the robot, here:

unitree_ros_to_real/unitree_legged_real/src/exe/ros_udp.cpp

Lines 57 to 60 in b6227b8

	low_udp.Recv();
	low_udp.GetRecv(low_state);
	}

However, the returned values are always empty and it is hard for me to understand how to fix this.

I initially tried to send an empty command at the beginning of the program and that seemed to have worked, but the next day I tried again and only one valid piece of data is sent, then all subsequent messages are identical to the first one.