Mobile-Manipulation

A repository for my final project in the course Mobile Manipulations (ME449) at Northwestern University.
Please visit my website for more information about this project.

Table of Contents

• Overview
• Package Description
• Usage and Configuration instructions
• Results
  • Motion planning with different initial and final cube location
  • Motion planning with different control gains

Overview

This project is the final project in the course Robotic Manipulation at Northwestern University. In this project, I wrote a software that plans a trajectory for the end-effector of the youBot mobile manipulator, performs an odometry as the chassis moves, and performs feedback control to drive the youBot to pick up a block at a specified location, carry it to a desired location, and put it down in the V-REP simulation software.
The project description can be found here.

The project covers the following topics:

1. Generate the kinematics simulator of the youBot - an omnidirectional mobile robot with a 5-DOF robotic arm.
   
2. Plan the end-effector's trajectory between waypoints.
   
3. Apply feedback control to drive the robot in the desired trajectory.
   
4. Simulate the planned trajectory in CoppeliaSim.
   

Package Description

This project contains 3 milestones, and was implemented in the code Full_Program.py. The main code calls the 3 milestone sub-code:

1. Next_State.py - Milestone 1 code. This code uses a function NextState(), that compute the configuration of the robot in the next time step.
   
2. Trajectory_Generator.py - Milestone 2 code. This code uses a function TrajectoryGenerator(), that generates the reference trajectory for the end-effector frame {e}.
   
3. Feedback_Control.py - Milestone 3 code. This code uses a function FeedbackControl(), that calculates the kinematic task-space feedforward plus feedback control law.
   

The code also uses functions from the Modern Robotics library. This library can be downloaded from this git repository - https://github.com/NxRLab/ModernRobotics (See "Usage and Configuration instructions" section for instructions).

Usage and Configuration Instructions

1. To run the program, download the modern robotics library (the python version) from https://github.com/NxRLab/ModernRobotics/tree/master/packages/Python, by running:

pip install modern_robotics

2. Run the Full_Program.py code.

Results

The results for this project can be split into 3 categories:

1. Best results - Planning and executing a motion without overshoot or steady-state error.
   
2. Overshoot results - Planning and executing a motion with overshoot but without steady-state error.
   
3. NewTast results - Planning and executing the trajectory with different start and finish configuration.
   

Motion planning with different initial and final cube location

In this part, I simulated the controlled motion with different initial and final cube location, and different initial robot's configuration.

1. For the default initial and final configurations, I used the following conditions:

   Initial robot's configuration:
   

   (0.1, -0.2, 0, 0, 0, 0.2, -1.6, 0, 0, 0, 0, 0, 0)
   

   Initial cube configuration:
   

   [1, 0, 0,     1],
   [0, 1, 0,     0],
   [0, 0, 1, 0.025],
   [0, 0, 0,     1]
   

   Final cube configuration:
   

   [ 0, 1, 0,     0],
   [-1, 0, 0,    -1],
   [ 0, 0, 1, 0.025],
   [ 0, 0, 0,     1]
   

   The simulated controlled motion with the following condition is:

   

2. For the different initial and final configurations, I used the following conditions:

   Initial robot's configuration:
   

   (pi/6, -0.5, 0, 0, 0, 0.2, -1.6, 0, 0, 0, 0, 0, 0)
   

   Initial cube location:
   

   [1, 0, 0,     1],
   [0, 1, 0,     1],
   [0, 0, 1, 0.025],
   [0, 0, 0,     1]
   

   Final cube location:
   

   [ 0, 1, 0,     1],
   [-1, 0, 0,    -1],
   [ 0, 0, 1, 0.025],
   [ 0, 0, 0,     1]
   

   The simulated controlled motion with the following condition is:

   

Motion planning with different control gains

In this part, I plotted the end-effector's twist error as a function of time, to explore the error's behavior when using different control gains.

1. For PI controller with feedback gains of Kp = 20 and Ki = 5, The error plot is:

   

   We can see that there is no overshoot, no steady-state error, and fast settling time.

2. For PI controller with feedback gains of Kp = 2 and Ki = 40, The error plot is:

   

   We can see that there is an overshoot at the beginning of the motion, no steady-state error, and fast settling time.