Big Blue · Alpha Competition Robot
KUdos VEX-U's 24" Over Under alpha robot with an over-the-frame intake, slip-gear catapult, and pushing wings.
Overview
Big Blue was my second KUdos VEX-U competition robot and my introduction to designing a complete robot in Onshape. I researched, prototyped, designed, modeled, fabricated, and built the robot as project lead, lead designer and fabricator, and build lead.
The robot served as the 24" Robot for the VEX-U Over Under competition. Its primary job was to intake Triballs from the Match Load Zone, transfer them into the catapult, launch them across the field, and use its wings to push groups of Triballs offensively or defensively.
I also used the project to establish a more collaborative CAD workflow for the team. Onshape allowed members from Kettering's alternating A-Section and B-Section groups to review and contribute to the same robot model remotely.
Outcome
I delivered a fully modeled, documented, fabricated, assembled, and competition-tested 24" robot. Big Blue gave KUdos VEX-U a working Match Load robot and helped the team qualify for VEX Worlds 2024.
The project also established my Onshape workflow for collaborative robot design. I applied FeatureScripts, master sketching, version control, full-robot CAD, BOM management, CAM, CNC routing, and additive manufacturing within one project.
Competition Results
Key Specs
| System | Specification |
|---|---|
| Robot class | 24" VEX-U robot |
| Target drivetrain footprint | Approximately 17.5" x 17.5" |
| Drivetrain | 6 motors at 360 rpm |
| Drive wheels | Omni wheels with center traction wheels |
| Intake | Over-the-frame non-parallel 4-bar with 3 sprocket rollers |
| Catapult | 2 motors with a 4:1 torque ratio |
| Catapult indexing | 24-tooth slip gears |
| Catapult power | Rubber bands |
| Wing actuation | Pneumatic cylinders |
| Estimated BOM cost | Approximately $1,100, including the brain but excluding hardware |
Problem & Goal
Over Under required KUdos VEX-U to operate two robots with different roles. Big Blue needed to handle rapid Match Loading while still being able to cross the field barriers and contribute to Goal scoring.
The goal was to build a reliable 24" alpha robot that could collect Triballs over the Match Load Bar, position each Triball consistently, launch it using a catapult, and deploy wings for offensive and defensive pushing.
Design Requirements
- Fit within the 24" x 24" x 24" VEX-U robot size limit
- Target a compact drivetrain footprint of approximately 17.5" x 17.5"
- Pick up Triballs over the Match Load Bar
- Transfer each Triball into a repeatable catapult position
- Launch Match Load Triballs across the field
- Cross the horizontal field barriers without damaging drivetrain components
- Deploy wings for offensive and defensive Triball pushing
- Protect the battery, pneumatic reservoir, brain, and radio
- Use sensor feedback for Match Load cycling
- Support fabrication with the team's 3D printers, CAM workflow, and CNC router
- Maintain a complete CAD model and BOM for purchasing and assembly
Process
- 1Analyzed the Over Under field, scoring rules, Match Load Zone, and role of the 24" robot
- 2Researched existing drivetrain, intake, catapult, and barrier-crossing concepts
- 3Prototyped the drivetrain, sleds, Triball holder, intake, and slip-gear catapult
- 4Increased the catapult reduction after testing showed that the first version needed more torque
- 5Modeled the full robot in Onshape using FeatureScripts, master sketches, configurations, and version control
- 6Used a parametric intake sketch to adjust linkage geometry around the Match Load Bar and Goal
- 7Completed the 24" robot CAD and custom-part designs in September 2023
- 8Created a full BOM and compared required parts against the team's existing inventory
- 9Generated CAM and CNC-routed the custom polycarbonate intake plates
- 10Manufactured aluminum components and 3D printed PETG and Onyx parts
- 11Assembled the drivetrain, intake, catapult, wings, electronics, and pneumatic system
- 12Tuned the intake, rubber-band tension, catapult position, optical sensor, and barrier-crossing sleds
- 13Tested the robot through skills practice and competition
Technical Decisions
- Used an over-the-frame non-parallel 4-bar intake to reach across the Match Load Bar and pull Triballs into the robot
- Used sprockets and rubber bands as the intake's rollers after the prototype demonstrated reliable Triball contact
- Designed the robot to sit approximately 17 degrees from the Match Load Bar toward the Goal
- Used a parametric master sketch so the critical intake spacing could be changed without remodeling the subsystem
- CNC-routed the final intake side plates from 1/4" polycarbonate after printed prototypes were determined to be too fragile
- Used three sprocket-driven rubber band rollers mounted between the polycarbonate side plates
- Used tapped 1/4" diameter 6061 aluminum rods as intake crossbars with rubber tubing around the outside
- Replaced individual shaft collars with long 3D printed spacers because repeated intake motion loosened the collars and allowed the rollers to shift
- Added adjustable printed hardstops to control intake extension
- Powered the catapult with two motors through a 4:1 torque ratio
- Used 24-tooth slip gears to reset the catapult after each launch
- Added a ratchet to prevent the rubber bands from back-driving the catapult
- Used an adjustable hardstop to control the resting position and launch angle
- Designed a custom Triball cup to keep the game piece in a repeatable launch position
- Added an optical sensor to detect when a Triball entered the catapult
- Used pneumatically actuated wings to push Triballs and protect the battery, reservoir, brain, and radio
- Used a six-motor 360 rpm drivetrain with omni wheels and center traction wheels
- Added sleds and gear guards under the drivetrain to cross the horizontal barriers and protect exposed components
- Tested 55-degree and 60-degree sled profiles at approximately 1.75" tall during prototyping
Challenges
- Learned Onshape while managing the CAD of a complete competition robot
- Coordinated design work between team members in alternating academic sections
- Increased the catapult reduction after the first prototype did not provide enough torque
- Tuned rubber-band combinations to balance launch distance with a repeatable reset position
- Iterated the Triball cup because early versions did not hold the game piece consistently
- Adjusted the intake after it jumped when contacting the floor
- Replaced printed intake plates with CNC-routed polycarbonate for greater strength
- Replaced loosening shaft collars with continuous printed spacers
- Lengthened and revised the sleds after early versions did not cross the barrier consistently
- Modified the front C-channel and catapult structure to remove mechanical interference
- Worked through optical-sensor detections that did not always register when a Triball entered the catapult
Onshape Workflow
Big Blue was the first complete robot I modeled in Onshape. I used the project to learn and apply several tools that improved the team's design process.
- Used cloud CAD so multiple team members could view and edit the robot remotely
- Used version control to preserve design milestones and review changes
- Used master sketches to control subsystem geometry and robot packaging
- Used FeatureScripts to speed up repeated modeling tasks
- Used parametric dimensions to update mechanism geometry without rebuilding the CAD
- Modeled the full robot before fabrication to identify packaging and interference problems
- Connected the robot CAD to a structured BOM for inventory and purchasing
Programming Skills Plan
- Matchload 23 Triballs for 46 points
- Cross through the red alley for 2 points
- Deploy the wings and push at least 4 Triballs into the Goal for 12 points
- Park for 5 points if time remained
Driver Skills Plan
- Matchload 23 Triballs for 46 points
- Cross through the red alley for 2 points
- Deploy the wings and push at least 7 Triballs into the Goal for 21 points
- Park for 5 points if time remained
What I Learned
- How to model and manage a complete robot in Onshape
- How cloud CAD improves collaboration between remote team members
- How to use FeatureScripts to reduce repetitive modeling work
- How to use master sketches for faster subsystem integration
- How to use version control during an active robot-development cycle
- How to design and tune a non-parallel 4-bar linkage
- How to design a slip-gear catapult around torque, geometry, and elastic power
- How to manage a robot project from research and prototyping through fabrication and competition
- How to use 3D printing for rapid prototypes and CNC-routed polycarbonate for final competition parts
- How a complete BOM supports budgeting, purchasing, inventory, and assembly
