Dependency Installation and Parameter setup

Package Dependencies

As this package is created for the ground vehicles which uses pixhawk(APM/PX4), the package mavros is required for obtaining the sensor data from pixhawk. Also to command the motors from using ROS framework, Arduino-rosserial is required.

dependency installation links

MavROS Installation

• mavros-pkg-installation

If Arm device is used(Odroid, Raspberry Pi, etc) then follow instructions given below

• mavros-pkg-installation-ARM-devices

Arduino-ROSSERIAL Installation

• arduino-rosserial-installation

Configuration

MAVROS configuration

In order to use mavros-pkg, the necessary port number(/dev/ttyUSB* or /dev/ttyACM*) and a baudrate of 921600 need to be set inside the mavros launch files apm2.launch (if APM stack autopilot is used) or px4.launch(if px4 stack autopilot is used). This is already mentioned on mavros-pkg-config website.

asl_gremlin_pkg configuration

1. Encoder configuration
   • As quadrature encoders are used for the rover, the number of encoder ticks per meter needs to be set.
     • edit params wheel/motor/left_encoder_ticks_per_meter and wheel/motor/right_encoder_ticks_per_meter in file asl_gremlin_pkg/asl_gremlin_pkg/config/rover_parameters.yaml
2. Motor configuration
   • The control commands generated are wheel angular velocities. These need to be transformed to motor PWM voltage signal. So an appropriate relationship needs to be set for accurate interpolation.
     • edit params wheel/motor/omega_to_pwm/omega and wheel/motor/omega_to_pwm/pwm in file asl_gremlin_pkg/asl_gremlin_pkg/config/rover_parameters.yaml
   • Also the maximum angular velocity of the wheel need to given,
     • edit param wheel/max_angular_vel in file asl_gremlin_pkg/asl_gremlin_pkg/config/rover_parameters.yaml
3. Simulation rate
   • The rate at which the trajectory and control signals needs to be updated(default 10Hz)
     • edit param sim/rate in file asl_gremlin_pkg/asl_gremlin_pkg/config/rover_parameters.yaml
4. Waypoint Proximity radius
   • This is the value that will be used by the rover for creating trajectory for the next waypoint when rover it at a distance of sim/waypoint_proximity(default 0.8m)
   • edit param sim/waypoint_proximity in file asl_gremlin_pkg/asl_gremlin_pkg/config/rover_parameters.yaml
5. Maximum Rover Acceleration
   • This is the value that will be used by the trajectory_generator to create acceleration constrained trajectory
   • edit param sim/max_accel in file asl_gremlin_pkg/asl_gremlin_pkg/config/rover_parameters.yaml. The units are in (m/s^2)
6. Rover Turning
   • As the trajectory generator stitches the successive minimum jerk trajectory with a constant velocity circular trajectory, the following parameters can be changed(default values are set)
   • sim/min_turn_radius in file asl_gremlin_pkg/asl_gremlin_pkg/config/rover_parameters.yaml (default 2 m).
   • sim/const_turn_vel in file asl_gremlin_pkg/asl_gremlin_pkg/config/rover_parameters.yaml (default 0.5 m/sec).

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