RBE 2001: Unified Robotics I: Actuation
Worcester Polytechnic Institute
2013
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01 Background
RBE 2001: Unified Robotics I[1] focused on mechanical concepts in the design, construction, and actuation of a robot — the effective conversion of electrical power to mechanical power, power transmission and control for locomotion and payload manipulation, and the application of kinematic principles. Recommended background for the course included:
Labs applied classroom knowledge including Arduino programming in C/C++, laser cutting, soldering, voltage dividers, stepper motors, worm gears, conductivity sensing, back-drivable mechanisms, H-bridge motor drivers, autonomous operation, and advanced sensing.
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02 Component Development
Early lab work focused on testing individual components before integrating them into the final robot. We worked with an Arduino Uno, an LCD display, potentiometers for analog input, and H-bridge motor driver circuits on breadboards to control DC motors and stepper motors. Understanding how to properly drive motors with PWM signals and H-bridge direction control was foundational for the final project.
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03 Chassis & Drive System
The chassis was designed in AutoCAD, dimensioned for precision laser cutting, and fabricated from 1/4" acrylic panels. The drive system used a unique approach — four standard wheels for forward and reverse movement, plus a single omni-directional center wheel for lateral (left/right) movement. This eliminated the need to turn the robot entirely, giving us a significant competitive edge during both teleoperation and autonomous mode.
We implemented a suspension system on the center wheel to fine-tune its contact depth with the playing surface. The acrylic top plate served a dual purpose — structural rigidity and precise centering of the gripper arm directly above the robot's center axis, which simplified positioning during fuel rod operations.
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04 Arm & Actuation System
The robotic arm was driven by a stepper motor using microstepping for precise positional control — the stepper's known step count allowed us to calculate exactly how far the arm had traveled without additional feedback sensors. The stepper motor was offset from center to avoid interfering with the left/right drive motor and wheel assembly, connected to the arm sprocket via a VEX chain and sprocket system. We tensioned the chain by removing individual links to minimize jitter and noise in the arm's movement.
A separate motor controlled the lift and descent of the arm. The arm rotated on top of the chassis rather than the chassis itself rotating — a key design decision enabled by centering the arm on the acrylic top plate. We also 3D printed custom adapters, including a VEX-to-stepper adapter visible at the lowest reach of the robotic arm. Reusable battery zip ties were mounted to the chassis for quick battery swaps during extensive testing sessions.
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05 Electronics & Sensing
The electronics were packed onto a breadboard that was nearly full by the end of the project. The system included the Arduino, H-bridge motor drivers, a transmitter/receiver for the VEX controller, Bluetooth communication, and an LCD display for live debugging and status feedback in the field.
For sensing, we exposed wire leads on forks at each orthogonal end of the robot. Because the nuclear fuel rod holders on the field were conductive, we simply monitored the GPIO pins for an electrical short to determine when the robot had successfully docked with a fuel rod receptacle — essentially a continuity sensor. The gripper arm used a servo for grasping the acrylic dowel fuel rods.
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06 Robotic Arm Range of Motion
The arm assembly demonstrated a full range of motion — from its lowest reach for ground-level fuel rod pickup, through mid-height positioning, to horizontal alignment for inserting fuel rods into elevated receptacles. The LCD display, capacitive/continuity sensor, and gripper servo were all visible in the arm assembly. A 3D printed VEX-to-stepper adapter connected the drive system at the end of the arm.
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07 Autonomous Mode & Competition
The competition required both teleoperated and autonomous modes. For autonomous line following, we mounted multiple optical sensors on the bottom of the robot that detected black electrical tape lines on the playing field. The control logic would navigate the omni-directional drive system — using the left/right center wheel — until the robot docked with a fuel rod receptacle, confirmed by the continuity sensors.
The objective was to retrieve spent nuclear fuel rods (acrylic dowels) from receptacles around the field, transport them to a containment area, and deploy fresh rods back into the empty receptacles. Teams competed to handle the most fuel rods within the time limit.
Robot in action during testing on the competition field.