Servo - 201306

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by

Dennis Clark

Q. I want to control my Bioloid Dynamixel servos with a Digilent UNO32 or Max32 controller on a new robot.

How can I talk to these servos with MPIDE? I read that it is a totally different type of servo than a hobby servo. Can you help me? Summer is here, and now instead of robots competing for time with the need to go skiing, robots are competing with the need to go biking, hiking, and other stuff. What I need to do is get involved with some outdoor robot activities. Perhaps Robo-Magellan or something like that. It could satisfy the need to be outdoors while scratching the robot itch. So many decisions to make! Anyway, time to get going on the question that I spent many hours solving this month. Onward!

— Kevin

A. That is a good question! You are correct when you say that he communications protocol is different from a hobby servo — way different from a hobby servo. My first step in answering this question is to find a document discussing exactly how one communicates to the Dynamixel servo. I found the most

thorough document discussing the AX12a at www.agaverobotics.com /products/servos/robotis/ax12/ docs/AX- 12.pdf.

Trossen Robotics has a similar but not as technical document at http:// support.robotis.com/en/tech support_eng.htm#product/dyna mixel/ax_series/dxl_ax_actuator. htm. Pointers to user open sources can be found at www.agaverobotics. com/products/servos/#?node =products.

I have a three year old Bioloid

Comprehensive kit, so I chose it to work with the AX12a servo for this article. The first thing we need to do is find out how to “talk” to the Dynamixel servo bus. The Dynamixel communications channel is a bus structure; by bus I mean that a single set of wires can talk to every device on the bus. Hobby servos — by comparison — have a set of wires for each servo individually attached to a controller. The bus configuration uses a LOT few wires.