joy_node outputs on the topic joy. throttle reads that topic and outputs on a topic joy_throttle (which is default, it just uses <input_topic>_throttle unless otherwise specified). I've noticed that sometimes the nodes don't seem to connect, when inspecting the node graph with rqt_graph. Should check if this is still a problem, and if it is, fix it.
joystick_interface/launch/joystick_interface.launchlaunches three nodes:joy_nodethrottlejoystick_interfacejoy_nodeoutputs on the topicjoy.throttlereads that topic and outputs on a topicjoy_throttle(which is default, it just uses<input_topic>_throttleunless otherwise specified). I've noticed that sometimes the nodes don't seem to connect, when inspecting the node graph withrqt_graph. Should check if this is still a problem, and if it is, fix it.