Page 144 - Toucpad robotics C11

21 st #Coding & Computational Thinking
project 2 Century #Experiential Learning
Skills
The Pick-and-Place Robotic Arm
Objective: Design and build a small, desktop robotic arm that can pick up a lightweight object from one location
and place it at another pre-defined location.
Steps of the Solution:
1. Project Planning & Design (Project Management):
∑ Define the Scope: Specify the arm's reach, payload capacity, and the objects it will handle (e.g., a small
plastic block).
∑ Component Selection:
Brain: Use a microcontroller (like an Arduino Uno) to control the arm.
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§ Muscles: Choose three or four servo motors to actuate the joints (manipulators). A simple gripper
will also be controlled by a servo motor.
Senses: A basic touch sensor on the gripper can be used to detect when it has successfully grasped
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the object.
§ Power: A dedicated power supply unit or a suitable battery will be needed to power the servo motors.
∑ Structure: Design the arm's links and a stable base using acrylic for its lightweight properties and ease of
fabrication with a laser cutter. The design should follow the principles of a planar open-chain mechanism.
2. Hardware Assembly & Wiring:
∑ Fabricate the Links: Cut the acrylic links and other structural parts from the design.
∑ Assembly: Assemble the robotic arm, attaching a servo motor at each joint.
∑ Wiring: Connect all the servo motors and the touch sensor to the microcontroller.
3. Programming & Control (Fundamentals, Logic, Kinematics):
∑ Manual Control: Write a simple program to manually control each servo motor using a variable or a
potentiometer to understand how each joint moves.
∑ Forward Kinematics (RP or 2R configuration): Manually calculate the forward kinematics for
the arm's configuration. This will help you understand the relationship between the joint angles and the
gripper's position.
∑ Basic Control Program:
§ Step 1: Write a series of commands to set the joint angles to move the gripper to the pickup location.
For a simple robot, you can find these angles by manual trial and error.
§ Step 2: Activate the gripper's servo motor to close and grab the object.
§ Step 3: Set the joint angles to move the arm to the drop-off location.
§ Step 4: Activate the gripper's servo motor to open and release the object.
§ Step 5: Return the arm to its original starting position.
∑ Object Delivery: Program the servo motor to activate at the destination point to either lift or drop the item.
4. Debugging & Testing (Ensuring Performance):
∑ Calibration: Fine-tune the joint angles to ensure the arm reaches the correct pickup and drop-off locations
accurately. This is a form of dynamic error compensation.
∑ Repeatability Test: Run the program multiple times to see if the robot can consistently pick up and place
the object in the same location. This is a key measure of a manipulator's performance.

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Touchpad Robotics - XI