To connect your Dynamixel XL430-250T to the Arduino Uno using a Dynamixel Shield, you will need to follow these steps:

1. Connect the Dynamixel Shield to your Arduino Uno. Make sure the pins align correctly.

2. Connect the Dynamixel XL430-250T to the Dynamixel Shield using the provided 3-pin cable. The cable should be connected to the port labeled "DYNAMIXEL".

3. Connect the Arduino Uno to your computer using a USB cable.

4. Open ARC and create a new project.

5. Add the Dynamixel robot skill to your project. You can do this by clicking on the "Project" tab, then "Add", and then selecting "Dynamixel" under the "Servo" category.

6. In the Dynamixel robot skill configuration, set the baud rate to match your servo's configuration. The default baud rate for the XL430-250T is 57600.

7. Specify the port that the servo is connected to on the controller. For the Arduino Uno, this will be the hardware serial port, which is labeled as "Serial" in ARC.

8. Enable the servo ID that matches your servo. The default ID for new Dynamixel servos is 1. Also, specify the protocol version of the servo. The XL430-250T uses protocol 2.0.

9. Save your configuration.

10. Connect ARC to your Arduino Uno. You can do this by clicking on the "Connection" tab and then selecting your Arduino Uno from the list of available connections.

11. Once connected, you should be able to control your Dynamixel XL430-250T using the Dynamixel robot skill in ARC.

Remember, the Dynamixel servos require a sufficient power source. 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.

For more detailed instructions, you can refer to the Dynamixel robot skill manual on the Synthiam website: https://synthiam.com/Support/Skills/Servo/Dynamixel?id=16142.