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You did not mention whether you configured the servos, so I thought it'd be worth mentioning.

Each servo stores a set of parameters internally. You must configure (or at least check the configuration of) every servo separately before you attempt to communicate with them.

There are 2 key parameters you must ensure are correct in order to communicate with the servos.

The first parameter is the baud rate. You are trying to connect to the servos at 57600 bps, and you said you also tried 1000000 bps. You must ensure all servos are configured to use the same baud rate, and use that value when you load the node.

The second parameter is the servo ID (which should be unique to each servo). You are attempting to communicate with servos which IDs range from 1 to 25. It could be that your servos were configured with IDs out of this range.

Configuring the servos:

You may use RoboPlus (on Windows), which is the official software from Robotis.

Alternatively (if you know the parameter values currently configured), you can also change the servos IDs, as well as set the desired parameter values using these ROS nodes.

Related question: ClamArm using Dynamixel Motors: No Motors Found

I hope it helps!