diff --git a/README.md b/README.md
index becf74d..956d8e6 100644
--- a/README.md
+++ b/README.md
@@ -32,3 +32,20 @@ To encode the microphones signals onto Spherical Harmonics signals (i.e. Ambison
 See http://www.sekisushai.net/ambitools/docs/mic_encoder.html for more infos.
 
 # SMA calibration with a robotic arm
+The following instructions are made for a [Trossen-Robotics WindowX 250](https://www.trossenrobotics.com/widowx-250-robot-arm-6dof.aspx) robotic arm driven with Python-ROS API under Linux Ubuntu.
+
+## ROS 2 installation
+The robotic arm is driven with ROS (Robot Operating System) 2. To install the latter, follow the [Trossen Robotics instructions](https://www.trossenrobotics.com/docs/interbotix_xsarms/ros_interface/ros2_software_setup.html).
+Currently, the Humble distribution is used.
+
+## Robotic Arm Modification
+For the task of SMA calibration, the robotic arm is modified in the following way:
+1. The gripper is removed and replaced with a 3D printed part holding a threaded rod,
+2. The robot description files for ROS are modified accordingly.
+
+### Hardware modifications
+The arm gripper is removed with its servo. A 3D printed part, available at [/cad/robotic_arm_attach.stl](http://sekisushai.net/git/sekisushai/small/src/branch/master/cad/robotic_arm_attach.stl), is mounted in place of the gripper servo.
+By default, it allows to hold a M6 threaded rod aligned with the forearm axis. You can modify this part from the openSCAD file [/cad/robotic_arm_attach.scad](http://sekisushai.net/git/sekisushai/small/src/branch/master/cad/robotic_arm_attach.scad)
+according to your needs.
+
+### Software modifications