SML Nexus

Repositotry for code and documentation on the customized Nexus 4WD holonomic robots of the SML (Smart Mobility Lab) of KTH.

Using the Nexus Robot

Bringing up the Nexus robot

Every Nexus robot includes a companion computer (usually a NVidia TX2) connected to the internal Arduino low-level controller. To use the Nexus, one needs first to connect by SSH to the companion computer (credentials available by asking a lab member, replace COMPANION_COMPUTER_IP by the companion computer IP):

ssh sml@COMPANION_COMPUTER_IP

Then the ROS_MASTER_URI and ROS_IP environnement variables need to be set accordingly. Check ROS network setup for more information.

To bring up the robot, run the following launch file from the companion computer:

roslaunch sml_nexus_robot sml_nexus_bringup.launch

After a successful launch, command and feedback topics should be available under the namespace /nexus_ROBOT_ID

Sending commands

The robot can be commanded in velocity by publishing ROS Twist message on the topic /nexus_ROBOT_ID/cmd_vel

Receiving feedback

TODO

Robot description

The robot is a modified 4 mecanum wheel holonomic robot from Nexus Robotics (https://www.nexusrobot.com/product/4wd-mecanum-wheel-mobile-arduino-robotics-car-10011.html).

Characteristics

• max speed: 0.6m/s forward
• wheel base: 300mm

Actuators

• Motors: (4x) Faulhaber 12V DC Coreless Motor 16002, with 45° 50mm radius mecanum wheel.
• Optional manipulator: Either a Robotis ViperX 250 or a Robotis WidowX depending on the platform.

Controllers

• Onboard computer: Either NVidia TX2, NVidia Jetson Nano or Intel NUC depending on the platform.
• Low-level controller: Arduino Mega for interfacing with motor drivers, ultrasonic range sensor and encoders.
• Motor drivers: Two Cytron MDD3A motor drivers.

Sensors

• (4x) Encoders: Encoder on each wheel with a resolution of 12CPR before motor gearbox and 768CPR after gearbox.
• (4x) Ultrasonic range sensor: URM04 v1.0 ultrasonic range sensors with RS-485 interface.

ROS package description

Packages:

• sml_nexus_description
• sml_nexus_robot

sml_nexus_description

Contains the robot URDF description and meshes.

Launch files

• sml_nexus_description.launch: Load the SML nexus 4WD mecanum robot description parameter and the robot state publisher.

• sml_nexus_rviz.launch: Load the SML nexus 4WD mecanum robot description parameter and a RViz session.

sml_nexus_robot

Package to be run from the robot onboard computer.

Launch files

• sml_nexus_bringup.launch: Load config files and connect to the low-level controller using rosserial.

Config files

• nexus_pid_params.yaml Parameters of the motor controllers