This repository is an implementation of a novel robotic manipulation capability for transporting an object on the ground in a dynamic and nonprehensile manner. The object is manipulated to rock from side to side repeatedly; in the meantime, the force of gravity enables the object to roll along a zigzag path that is eventually heading forward. We call it rock-and-walk object manipulation. Our work is motivated by an interesting question in archaeology, how the giant rock statues of Easter Island (known as “moai”) were transported several hundred years ago, and a recent demonstration done by archaeologists that it is possible to “walk” the statue by repeated rocking.
Our rock-and-walk object transport technique is implemented in multiple robotic settings: 1) one robot arm with an end-effector that can cage the object, 2) two robot arms to interact with the object via cables, and 3) an aerial robot with the caging end-effector.
- Matlab for object's passive dynamics simulation
- ROS and python-urx for robot control
- rosserial to acquire data from Arduino 9 Axis Motion Shield
- teleop_twist_keyboard to perform teleoperated rock-and-walk on a treadmill
The following provides a brief description of each folder contained in this repository
1. /aerial_manipulation: contains ROS packages for rock-and-walk implementation with a quadrotor using mocap
2. /cad_models: contains .stl files for the object models used in the experiments
3. /media: contains visual images/gifs of rock-and-walk
4. /rockwalk_kinematics: ROS package to acquire data from motion shield and process to obtain object state as it rolls without slipping
5. /rockwalk_ur10_control: ROS package to implement rock-and-walk in a single- or dual-arm setting
6. /simulation: Matlab codes for passive dynamic simulation of object rolling on ground with its control point fixed
7. /simulation_rviz: ROS package to visualize passive dynamic simulation in RViz
For ROS packages, first downloaded them into your catkin workspace. Then use catkin build command from catkin_tools to install them. Matlab scripts can be executed directly from Matlab.
Our Matlab implementation computes passive dynamics of the object, modeled as an oblique-cone that has a circular base and a vertical rod attached to it, as it rolls without slipping on a flat surface. Our dynamic formulation only considers the center of mass of the object, while ignoring its moment of inertia. The motion of the object is visualized in RViz.
To first obtain and then solve the dynamic model in Matlab
>> cd simulation/
>> rolling_disk_eom.m
>> fixed_apex_sim.m
Parmeters for the oblique-cone model can be altered in the simulation/cone_parameters.m file. To visualize the simulation in RViz
roslaunch simulation_rviz fixed_apex.launch
First, publish motion shield data in ROS using rosserial. Then calibrate the motion shield and use the output to compute object state:
rosrun rosserial_python serial_node.py _port:=/dev/ttyACM0 _baud:=115200
*calibrate motion sheild*
rosrun rockwalk_kinematics rockwalk_kinematics_node
Then run the following nodes to implement rock-and-walk in a single-arm setting with a caging end-effector, or, in a dual-arm setting with cables:
rosrun rockwalk_ur10_control single_arm_caging_labfloor_rockwalk
rosrun rockwalk_ur10_control dual_arm_cable_labfloor_rockwalk
Detailed instructions on executing rock-and-walk using a quadrotor equipped with a caging end-effector can be found in aerial_manipulation/README.md
- A. Nazir and J. Seo, "Passive Dynamic Object Locomotion by Rocking and Walking Manipulation," 2019 International Conference on Robotics and Automation (ICRA), Montreal, QC, Canada, 2019, pp. 7926-7932, doi: 10.1109/ICRA.2019.8794163.
For technical enquiry, please contact Abdullah Nazir (a.nazir[at]connect.ust.hk) and Pu Xu (pxuaf[at]connect.ust.hk)