ROS Gremsy Gimbal Interface

A ROS interface to control Gremsy gimbals. Based on the gSDK_V3_alpha interface and the MavLink protocol.

Disclaimer: This software package is not officially developed by or related to Gremsy.

Description

This package includes a ROS Node which warps the gSDK for the Gremsy Gimbals which are mainly used for physical image stabilization.

The gimbal is connected via UART with a Linux host device running this node. Devices such as the Raspberry Pi feature a built-in UART interface others like most PCs or Laptops need a cheap USB Adapter. The config.yaml file allows you to configure the serial device used and many other gimbal-specific parameters. The node publishes the gimbal's encoder positions, imu measurements, and the camera mount orientation.

Setup

Run the following commands to clone this repository and update all submodules (needed for the external gSDK repository).

We use gitman to handle the submodules of this repository. The list of submodules is given in the .gitman.yaml file.

git clone https://github.com/fly4future/ros1_gremsy.git
cd ros1_gremsy
git pull && gitman update

to update all the submodules (default: will update all repositories to their predefined branches).

Now you need to install all dependencies using rosdep. To execute this command make sure that the correct catkin workspace is sourced and the repository you just cloned is (linked) inside the src directory.

rosdep install --from-paths . --ignore-src -r -y

After installing the dependencies you should be able to build the package using:

catkin build

Launching

Type the following command to run the node. Make sure that the gimbal is connected properly, the Linux permissions regarding the serial interface are correct (this depends on your distro) and the config features the correct device and baudrate.

Nodelet:

roslaunch ros1_gremsy gremsy_nodelet.launch

ROS API

Coordinate System

Earth Frame

The earth frame convention used is in ENU coordinates. (X: East, Y: North Z: Up).

Body Frame

The body frame has the X-axis pointing forward the UAV heading, the Y-axis pointing to the left, and the Z-axis pointing up.

Work Modes

When using Angle Mode, the gimbal moves to the target attitude in earth frame if operating in Lock mode. Otherwise, the gimbal moves to the target attitude in the Body frame if operating in Follow mode.

Messages:

The node publishes:

• /diagnostics:

  • setpoint: with a geometry_msgs/Vector3 message with current gimbal goal.
  • encoder_values: with a geometry_msgs/Vector3 message containing the encode values around the x (roll), y (pitch) and z (yaw) axis.
  • attitude_quaternion: with a geometry_msgs/Quaternion message representing the camera mount orientation in Quaternion representation, in the global frame except for the yaw axis which is provided relative to the gimbals mount on the vehicle or robot.
  • attitude_euler: with a geometry_msgs/Vector3 message representing the camera mount orientation using Euler Angles, in the global frame except for the yaw axis which is provided relative to the gimbals mount on the vehicle or robot.

• Transformations:

  • gimbal_link: Gimbal link relative to fcu_frame. Static TF configured within the gremsy_nodelet.launch file. All the following transformations need to be configured in the config.yaml under the section "frames".

  Dynamic TF's based on gimbal attitude:

  • gimbal/yaw: Dynamic TF relative to the gimbal_link frame.
  • gimbal/roll: Dynamic TF relative to the gimbal/yaw frame.
  • gimbal/pitch: Dynamic TF relative to the gimbal/roll frame.

Services:

• /set_gimbal_attitude expects a message containing the desired angles for each axis: roll, pitch, yaw (float64).
• /goals expects a geometry_msgs/Vector3Stamped message containing the desired angles for each axis. The frame for each axis (local or global), as well as the stabilization mode, can be configured in the config.yaml file.
• /set_gimbal_mode expects a string message for the desired operation mode (follow/lock).