Behavior Control
This control is developed by:
AvatarDJ Sures
Created October 15 2015
Updated February 1
Help Index


How To Download and Use This Control

  1. Make sure you have the latest version of EZ-Builder installed.
  2. Select Download This Control button below to download the file.
  3. Double click the downloaded file to open it.
  4. The installer will automatically add this control to EZ-Builder.
Download This Control

Connect and control Robotis Dynamixel servos to the EZ-B v4. This open-source plugin converts the Virtual servo ports on the EZ-B v4 (v0-v99) to control Robotis Dynamixel servos. The servos supported are XL-320, AX-12, and XL430 models. Dynamixel servos are very different than regular hobby PWM servos. Firstly, they are considered much more professional due to their design which is specific for the use in robotics. Each Dynamixel servo contains a microprocessor. The microprocessor is told what position to move the servo into over TTL at the configured baud rate. 

Cable Accessory
This plugin requires a cable accessory to easily connect your servo to the EZ-B v4 or IoTiny. You can find the cable accessory in EZ-Robot's store by clicking here. If you desire to READ servo positions, the cable will need to be modified. There are instructions below for connecting the servo to READ positioning.
User-inserted image

Wiring For Read Positioning
While we recommend using the Dynamixel servo Cable, you can optionally manually wire the servo yourself to the ez-b v4 or IoTiny using this diagram. If you wish to read servo data with bi-directional communication, you can also connect port D5 and D6 together. On the EZ-B, D5 is TX and D6 is RX. This means if you connect D5 to D6, the EZ-B will be able to read the servo positions.
User-inserted image

There are two options for connecting the Dynamixel servos. The default option for the EZ-B v4 (not IoTiny) is UART 1 (port D5). The second option is low speed serial of any digital port for both EZ-B v4 and IoTiny. To reference the pins of the EZ-B, consult the tutorial for the EZ-B by clicking here.

*Note: we highly recommend using Hardware UART on the EZ-B v4 only. Do not use software UART on the EZ-B v4 for dynamixel servos. Only use software UART when using an IoTiny. You will also require the hardware UART of the EZ-B v4 when reading servo positions. Read Electrical Wiring further down in this document for bi-directional communication with EZ-B v4 for reading servo positions.

Most Dynamixel servo documentation states the operating voltage in the manual. Check the documentation for your dynamixel servo model to ensure your power source is sufficient. If you experience unusual behavior of Dynamixel servos, the first common issue is insufficient power. 

Servo ID
The Dynamixel servos each have a unique ID. Because they are chained together through one cable, each servo must be given a unique ID. servos with the same ID will respond to the same commands, and therefore mirror their behaviour. New Dynamixel servos come pre-configured with the ID of 01. servo V0 relates to dynamixel ID:0, V1 is dynamixel ID:1, v2 is dynamixel ID:2, and so on...

Using this configuration utility, you can assign new ID's to servos. You may also test the servo to ensure the ID was successful.

Servo LEDs
The LEDs on the dynamixel servo can be controlled using the EZ-Script ControlCommand(). View the Cheat Sheet when editing a script to see the available ControlCommand syntax for the Dynamixel plugin.

Source Code

EZ-Script Commands
There are a number of EZ-Script commands added with this control. The commands are as follows...


Returns the temp of the specified servo

Returns the direction of load on the specified servo

Returns the load of the specified servo

Returns a ping response if the servo exists. Otherwise, returns false

Step by Step Instructions
Once you have the servo wired, and sufficient power is provided, you can use any control in EZ-Builder that uses servos. This means it will work with Auto Position, Camera, WiiMote, Joystick, and more. In this example, we'll show you how to move a dynamixel servo with a generic servo control. Before following these steps, ensure you have this plugin installed.

Step 1
Load EZ-Builder

User-inserted image

Step 2

Connect to your EZ-B v4 or IoTiny controller

User-inserted image

Step 3

Add the control by selecting the Project tab and Add Control

User-inserted image

Step 4

Navigate to the servo tab and select Dynamixel. If the plugin has been successfully installed, you will see the Dynamixel plugin in the list.

User-inserted image

Step 5

The Dyamixel control will be added to your project. Press the Config gear icon to load the configuration screen.

User-inserted image

Step 6

Enter the baudrate that matches your servo configuration. The servos have a baud rate that can be specified, or a default baudrate shipped from factory. If you need to change the baudrate of the servo, use the Dyanmixel utility. You cannot change the baudrate of the servo in EZ-Builder. This value is the baud rate that the EZ-B will use to communicate with the dynamixel servo. This must match the baudrate of the servo.

User-inserted image

Step 6a

Specify what port the servo is connected to the EZ-B v4 or IoTiny. On an EZ-B, it is highly recommended to use a hardware UART. On the IoTiny, any digital port can be specified for use. It is important to follow this recommendation. There are blue question boxes in the plugin (and throughout the EZ-Builder software) to assist you robot development. It is recommended to use the blue question marks and read the content to understand what options do.

User-inserted image

Step 7

Each dynamixel servo will have a unique ID. Enable each ID for the servos by checking the respective box. When an ID is checked, the EZ-Builder software will use the Vx (virtual servos) corresponding with that ID. For example, if you enable Dynamixel servo ID #2, the EZ-Builder V2 servo will control it. Also, specify the protocol version of the servo. Different dynamixel models will use one of the two protocols. Consult the datasheet of the dynamixel servo to know what protocol it uses -or- contact Robotis for more information on using their product. To get full resolution of the servo, also ensure you have entered the MAX resolution for that servo model. Each model has different resolutions, or it can be configured using the Dyanmixel utilities.

User-inserted image

Step 8

After you have enabled your servos, press Save

User-inserted image

Step 9

Now we will show you an example of how the servo can be moved. We will do this by using a generic horizontal servo control. Press Project -> Add Control to return to the add control menu. Navigate to servo and select Horizontal servo. Remember, any control in EZ-Builder that uses servos can now control dynamixel servos by the respective Vx (virtual) servo ID.

User-inserted image

Step 10

Press the GEAR icon to configure the horizontal servo control.

User-inserted image

Step 11

To configure this control to use a virtual servo, select the servo to bring up the port dialog. This applies to all controls in EZ-Builder that use servos.

User-inserted image

Step 12

Select the Virtual servo ID for your dynamixel servo from the list and press Close.

User-inserted image

Step 13

Now use the sliders to specify the Min and Max position that you wish this servo to move and press Close.

User-inserted image


You can now control the dynamixel servo with the horizontal servo control. To find out more about servos, consult the learn section of this website for activities on using your ez-robot product.

Source Code

Here is the sourecode for the plugin. If you wish to modify the code and create a fork, a new GUID and plugin name will need to be generated. Follow the plugin tutorial on how to do that. Here's the sourcecode:

January 27
So you removed all support for the servos introduced in the first plug in?
DJ Sures
January 27 — Updated January 27
i explicitly specified support of models in the plugin and on this description page that i verify and know work. Those servo models which are specified in the plugin are XL-320, AX-12, and XL430. Any servos outside of those 3 are not supported. If another servo model works for you, great. The only 3 that i will discuss and acknowledge supporting are XL-320, AX-12, and XL430.
January 27 — Updated January 27
The AX-12 servo controls are the same commands as the older servos. 

I had tried earlier today with the robot heads, with no movement. User error. Once I figured out what went wrong, I tried again with the most recent updated plug in and the heads came to life.

I now have both types of servos working in the same environment. Thanks again for all the hard work. I never stop praising the time and effort you guys put in. Hopefully you can accept apologizes.
DJ Sures
January 27
Thanks - there's no need for apologies. Eventually i have to draw a line on how far down the rabbit hole i go supporting a product that makes it impossible to support. In this case, i praise dynamixel servos for their robustness and quality but it's a full-time job maintaining the communication protocol differences between models. The only reason for not having a standard protocol across all models is poor planning. However, that's common with hardware companies because hardware people do not understand software and vice versa. Pick one thing to be good at and focus on that only.
January 28
Totally agree. Hopefully they don't change their products any further. Don't fix it if it ain't broke. I'll try and dump these $229 servos on ebay and stick with the $50 ones for now. Thanks again.