Overhang · FRC Charged Up Robot CAD
A second Charged Up robot concept with a virtual 4-bar arm and faster ground intake.
Overview
Overhang was my second independent robot CAD project for the 2023 FIRST Robotics Competition game, Charged Up. It was designed after Backlash as another attempt at a competition-capable robot that could have realistically been manufactured by my old team, FRC Team 4079.
The goal was to create a robot that was easier to manufacture, easier to control, and still capable of handling the major scoring tasks in Charged Up. Like Backlash, Overhang relied heavily on COTS parts and was designed around FRC Team 4079's fabrication capabilities. It used the X001 Upgraded KOP Drivetrain as the base and focused on a simpler scoring architecture with fewer controlled degrees of freedom.
The final concept used a parallel virtual 4-bar arm for scoring cones and cubes across all three node levels, a non-parallel 4-bar ground intake for faster cube pickup and L1 cube scoring, and a polybelt manipulator shared in concept with Backlash for handling cubes, upright cones, and tipped cones.
Outcome
Overhang became a second complete Charged Up robot CAD concept. It provided a direct comparison against Backlash by exploring a virtual 4-bar architecture instead of a 2 DoF arm and wrist.
The final design could reach all three scoring levels, pick up from the ground and substations, score L1 cubes using the ground intake, and handle cubes and cones with the shared polybelt manipulator concept. It was not built, but it was designed as if it could have been manufactured and competed with by FRC Team 4079.
Problem & Goal
After finishing Backlash, I wanted to explore a simpler Charged Up robot architecture that could still be competitive. Backlash used a 2 DoF arm and wrist, which gave the robot flexibility but also added more motion to control.
The goal of Overhang was to create a second Charged Up concept that reduced the number of controlled degrees of freedom while still reaching all major scoring locations. I wanted the robot to be easier to manufacture, easier to control, and practical enough that my old team could have built it if they wanted to.
Game Context
Charged Up required robots to score cones and cubes onto low, mid, and high grid nodes. Robots also needed to collect game pieces from the ground, single substation, and double substation while staying compact enough for starting configuration and stable enough for Charge Station interaction.
For Overhang, the design goals were:
- Score cones and cubes on all three node levels
- Pick up from the ground, single substation, and double substation
- Handle cubes, upright cones, and tipped cones
- Score L1 cubes quickly using the ground intake
- Reduce mechanism complexity compared to Backlash
- Stay realistic for a COTS-heavy FRC build
Design Requirements
- Reach all 3 levels of the Cube and Cone nodes
- Use a parallel virtual 4-bar arm as the main scoring mechanism
- Use a non-parallel 4-bar ground intake for faster cube pickup
- Score L1 cubes by reversing the ground intake
- Use the same polybelt manipulator concept from Backlash
- Pick up cubes, upright cones, and tipped cones
- Pick up from the ground, single substation, and double substation
- Reuse the X001 Upgraded KOP Drivetrain as the base
- Keep the robot COTS-heavy and realistic to manufacture
- Design the full robot as a competition-ready concept, not just a mechanism study
Process
- 1Reviewed the Backlash design and identified complexity from the 2 DoF arm and wrist
- 2Chose a parallel virtual 4-bar arm as a simpler main scoring architecture
- 3Created a master sketch to validate arm reach, intake motion, and scoring positions
- 4Designed the robot around the X001 Upgraded KOP Drivetrain
- 5Modeled the virtual 4-bar arm and superstructure in SolidWorks
- 6Modeled the non-parallel 4-bar ground intake
- 7Reused the Backlash polybelt manipulator concept
- 8Checked pickup positions for ground, single substation, and double substation
- 9Packaged the full robot as a manufacturable Charged Up concept
Technical Decisions
- Used a parallel virtual 4-bar arm to reach all 3 scoring levels
- Reduced the number of controlled degrees of freedom compared to Backlash
- Used a non-parallel 4-bar ground intake for faster cube pickup
- Designed the ground intake to score L1 cubes by reversing the intake
- Reused the Backlash polybelt manipulator concept for cones and cubes
- Used a master sketch to lay out the robot before detailed modeling
- Built the robot on the X001 Upgraded KOP Drivetrain
- Kept the design COTS-heavy and realistic for Team 4079's manufacturing resources
- Designed for ground pickup, single substation pickup, and double substation pickup
Final Design
The final Overhang concept used a parallel virtual 4-bar arm for the primary scoring motion. This let the robot reach the low, mid, and high nodes while keeping the manipulator orientation more controlled than a simple rotating arm.
Compared to Backlash, this architecture had fewer degrees of freedom to control because the robot did not need a separately actuated wrist for the main scoring motion. That made the concept simpler from both a mechanical and driver-control perspective.
Overhang also used a non-parallel 4-bar ground intake. The intake was designed to pick up ground cubes quickly and score L1 cubes by reversing the intake to place the cube into the low node area. This helped separate fast low-node cube cycles from the main arm scoring task.
The manipulator reused the same general polybelt concept from Backlash. It was designed to pick up cubes, upright cones, and tipped cones, making the robot flexible enough to handle common Charged Up game piece orientations.
Master Sketch and Layout
A major part of the project was using a master sketch before detailed modeling. The master sketch helped lay out the arm geometry, intake motion, scoring positions, ground pickup, and frame perimeter constraints.
This was important because the virtual 4-bar needed to reach multiple node levels while still packaging inside a realistic robot frame. By checking the geometry first, I could make sure the arm and intake concept worked before committing time to detailed SolidWorks modeling.
Ground Intake
The ground intake was one of the main differences between Overhang and Backlash. Instead of relying only on the arm-mounted manipulator, Overhang included a dedicated ground intake for faster cube handling.
The intake used a non-parallel 4-bar linkage so it could deploy out of the robot, collect ground cubes, and then retract back into a protected position. For L1 cube scoring, the intake could reverse to place the cube into the low node area without needing to use the main arm.
This made low-node cube cycles faster and reduced the amount of arm motion needed for simpler scoring tasks.
Virtual 4-Bar Arm
The main scoring arm was a parallel virtual 4-bar. This allowed the manipulator to move through the scoring range while maintaining a more useful orientation than a single simple pivot.
The arm was designed to reach all 3 node levels for cones and cubes. It gave the robot the reach needed for high scoring while avoiding the added control complexity of the 2 DoF arm and wrist used on Backlash.
Manipulator
Overhang used the same manipulator concept as Backlash. The polybelt roller design was intended to handle cubes, upright cones, and tipped cones with one mechanism.
Reusing the same manipulator concept let me focus on the differences between the robot architectures. Backlash tested the 2 DoF arm and wrist approach, while Overhang tested whether a virtual 4-bar arm could achieve similar scoring goals with a simpler control scheme.
What I Learned
- How to design a 1 DoF virtual 4-bar robotic arm
- How a virtual 4-bar compares against a 2 DoF arm and wrist
- How to use a master sketch to validate robot geometry before detailed modeling
- How to design a cone and cube manipulator around polybelt rollers
- How to package a separate ground intake with a main scoring arm
- How reducing degrees of freedom can simplify driver control and mechanism design
- How to design a full FRC robot concept around manufacturability and competition use
