Encore · Publicity T-Shirt Cannon Robot
FRC Team 4079's off-season t-shirt cannon publicity robot
Overview
Encore was a 130 lb publicity robot designed to bring FRC Team 4079 to school events, district-wide events, rallies, and outreach demonstrations. Unlike a competition robot, Encore was built for crowd engagement, safe long-range t-shirt launching, mobility, sound, lights, and repeatable event operation
The robot used a 10-barrel pneumatic revolver, a Geneva drive barrel indexer, an articulating barrel assembly, a 6-wheel pneumatic drivetrain, built-in airhorns, and RGB lighting. It was the first full robot build I led, the first robot I designed from the ground up, and the first full robot I CADed in SolidWorks. This project gave me the chance to take a robot from research and concept development through CAD, fabrication, wiring, pneumatics, testing, and event use
My Role
FRC Captain. As Project Lead and FRC Captain, I researched previous FRC t-shirt cannon robots, owned the overall design direction, modeled the robot in SolidWorks, coordinated the parts list, helped fabricate and assemble the robot, and worked through the pneumatic and electrical systems needed to make it safe and usable
Outcome
Encore became a 130 lb publicity robot for FRC Team 4079 with a 10-barrel pneumatic launcher, 6-wheel pneumatic drivetrain, articulating barrel, 100 ft+ shooting distance, airhorns, lights, and music. The robot gave the team a more exciting way to promote robotics at school and community events while also serving as a major learning project in SolidWorks, pneumatics, electrical wiring, project planning, and full-robot integration
The final tracked parts cost stayed under the $1,000 project budget while using a mix of purchased components, donated components, and parts the team already had on hand
Key Specs
| Feature | Spec |
|---|---|
| Weight | 130 lb |
| Size | 27 in x 32 in x 40 in |
| Launcher | 10-barrel pneumatic revolver |
| Barrel indexing | Geneva drive mechanism |
| Barrel articulation | AndyMark DART 12 in stroke electric linear actuator |
| Firing outlet to barrel interface | About 1/4 in air gap with no physical seal |
| Drivetrain | 6-wheel pneumatic drivetrain |
| Top speed | 30.47 ft/s or 20.78 mph |
| Shooting distance | 100 ft+ |
| Main event features | Airhorns, lights, and music |
| Budget | $1,000 target |
| Estimated tracked project cost | $882.60 |
Problem & Goal
FRC Team 4079 wanted a reusable publicity robot that could safely launch t-shirts at school and community events while representing the team in a more exciting way than a static display. The goal was to create a robot that was reliable, crowd-friendly, visually recognizable, and budget-conscious while using as many on-hand team parts as possible
Design Requirements
- Launch t-shirts 100 ft or farther
- Hold and fire 10 shirts before reloading
- Use a safe pneumatic system with regulated pressure stages
- Size the barrel inner diameter so baseballs, softballs, and tennis balls could not be loaded or launched
- Index between barrels quickly and repeatably
- Control barrel pitch independently from barrel indexing
- Drive reliably at events using an FRC-style control system
- Include airhorns, RGB lighting, and music for crowd engagement
- Fit within a compact publicity robot package
- Stay under a $1,000 budget by using parts the team already had on hand when possible
- Track parts, costs, and available inventory through a project parts list
- Be serviceable enough for students to maintain and operate at events
Process
- 1Researched existing FRC t-shirt cannon robots, Chief Delphi posts, CAD references, and pneumatic safety practices
- 2Created a brainstorm document covering robot concepts, pneumatic layout, drivetrain options, electronics, audio, lighting, and outreach features
- 3Defined the main architecture around a 10-barrel revolver, Geneva drive barrel indexer, independent pitch control, and KOP-style drivetrain
- 4Built a parts list to track what the team already had, what needed to be purchased, and estimated costs
- 5Modeled the robot in SolidWorks, including the frame, barrel assembly, Geneva indexer, drivetrain, actuator mounting, and pneumatic layout
- 6Fabricated frame and launcher components using available team tools and CNC-routed parts
- 7Wired the FRC control system, motor controllers, lighting, speaker power, sensors, and pneumatic controls
- 8Built and tested the pneumatic system, including the donated SCUBA reservoir, regulator stages, operating tank, solenoids, release valves, and launcher plumbing
- 9Tested firing, indexing, driving, and event features before using the robot for team publicity
Technical Decisions
- Used a 10-barrel revolver to allow multiple shirts to be loaded and fired before reloading
- Used 3 in OD, 2.5" ID barrel tubing with a 24 in barrel length target for the launcher
- Selected the barrel inner diameter to fit rolled t-shirts while preventing baseballs, softballs, and tennis balls from being inserted, reducing the risk of the robot being used to launch unsafe projectiles
- Designed and modeled a Geneva drive mechanism to index the revolver and mechanically align each barrel with the firing outlet
- Left about a 1/4 in air gap between the firing outlet and the rotating barrel instead of designing a physical seal
- Used an AndyMark DART 12 in stroke electric linear actuator for barrel articulation
- Used a motor-driven indexer for the revolver to keep the mechanical system simpler and easier to control
- Built the drivetrain around FRC-style components, including a RoboRIO, PDP, PCM, VRM, RSL, radio, motor controllers, and CIM drivetrain motors
- Used 8 in pneumatic wheels and ToughBox Mini gearboxes for event mobility and to be safer around gym floors
- Designed a two-stage pneumatic system using a SCUBA reservoir, regulator, 120 PSI operating tank, and fast solenoid valve for firing
- Used smaller tubing from the SCUBA reservoir to the operating tank because that line only needed to refill the operating tank
- Used larger tubing from the operating tank to the barrel so the firing path would not be heavily flow-limited
- Placed the firing solenoid close to the barrel outlet to reduce wasted air volume and improve launch consistency
- Added release valves for stored air and a 120 PSI release valve on the operating tank
- Avoided unsafe pressure-vessel materials like PVC and designed around metal pneumatic components rated for air pressure
- Added airhorns, RGB lights, and a Bluetooth speaker to make the robot more engaging at events
- Powered non-robot media features separately with an Anker battery bank
- Kept the robot under the $1,000 project budget by reusing parts the team already had and purchasing only the parts needed to complete the launcher, drivetrain, and pneumatic system
Challenges
- Learning pneumatic system design and pneumatic safety from scratch
- Designing my first full robot from the ground up in SolidWorks
- Designing a launcher that could safely and consistently fire shirts 100 ft+
- Packaging the SCUBA tank, operating tank, solenoids, barrel assembly, actuator, and drivetrain into a compact robot
- Designing and fabricating a Geneva drive mechanism that could index the barrel assembly repeatably
- Keeping the revolver aligned with the firing outlet during indexing
- Managing airflow so the operating tank to barrel path was not limited by small tubing or fittings
- Managing separate systems for driving, aiming, indexing, firing, lights, sound, and airhorns
- Tracking which parts the team already owned and which parts needed to be purchased
- Building my first complete robot outside the structure of a normal FRC competition season
- Seeing how parts that looked reasonable in CAD became harder to fabricate and assemble in the real robot
Mechanical System
Encore's mechanical system centered on a 10-barrel revolver and a Geneva drive indexing mechanism. The Geneva drive indexed the barrel assembly one position at a time, helping align the active barrel with the pneumatic firing outlet before each shot
The barrel inner diameter was also a deliberate safety decision. It was sized to accept rolled t-shirts while preventing baseballs, softballs, and tennis balls from fitting inside the launcher. This mechanically limited the types of projectiles that could be loaded instead of relying only on operator procedures.
The barrel did not use a physical sealing mechanism against the firing outlet. Instead, the final design left about a 1/4 in air gap between the firing outlet and the active barrel. I originally expected this to be a major efficiency issue, but testing showed it worked well enough for the robot's intended range and event use
The barrel assembly articulated using an AndyMark DART 12 in stroke electric linear actuator, giving the robot independent pitch control for aiming without needing to rotate the full robot. The drivetrain used a 6-wheel pneumatic setup with 8 in pneumatic wheels for event mobility over typical school and outreach environments
Pneumatic System
Encore used a staged pneumatic system so high-pressure stored air could be reduced to safer working pressures before firing. The system started with a donated SCUBA tank used as the main reservoir, regulated down into a 120 PSI operating tank, then controlled through a larger fast-acting solenoid between the operating tank and the active barrel
The reservoir-to-operating-tank side used smaller tubing because it only needed to refill the operating tank. The operating-tank-to-barrel side used larger tubing because that was the actual firing path, where airflow needed to leave the operating tank as quickly as possible. A small fitting or tubing bottleneck in this path would have limited flow and reduced shooting distance
The system also used release valves so stored pressure could be safely vented after operation. The operating tank included a 120 PSI release valve, and the design avoided PVC because pressurized PVC can fail dangerously under air pressure. The pneumatic layout was also used as a teaching tool so newer students could understand the path of air through the robot
Electrical System
Encore used an FRC-style electrical system built around a RoboRIO, PDP, PCM, VRM, RSL, radio, motor controllers, and pneumatic controls. The drivetrain, indexer, barrel articulation, sensors, pneumatics, and lighting were planned as separate subsystems so the robot could drive, aim, index, fire, and run event features reliably
The larger firing solenoid drew too much current to run directly from the PCM, so it was controlled through a motor controller instead. The robot also included a Blinkin LED driver for RGB lights and a separate speaker system for music, helping the robot function as both a mechanical project and a publicity tool
Budget & Parts Planning
The project was planned around a $1,000 budget and a mix of newly purchased parts and parts already available to the team. The parts list tracked major robot systems, including controls, drivetrain components, barrel and indexer hardware, articulation hardware, pneumatic components, lighting, sound, and miscellaneous event features
The tracked total came in under budget at $882.60, while reusing available FRC control system parts, drivetrain components, motors, and other hardware where possible. The SCUBA tank was also donated by a local SCUBA shop after the team explained what the project was for, which helped keep the project within budget
What I Learned
- How to lead and design a full robot project from concept through fabrication and testing
- How to CAD a complete robot in SolidWorks with drivetrain, launcher, electrical, and pneumatic systems
- How to design and package a pneumatic launcher system
- How regulators, operating tanks, solenoids, valves, and air plumbing work together
- Why the operating tank to barrel path needs large fittings and tubing to avoid limiting airflow
- How to think about pneumatic safety, stored pressure, release valves, and safe material selection
- How to create and use a parts list for budgeting, purchasing, and inventory planning
- How to integrate mechanical, electrical, pneumatic, and outreach-focused features into one complete robot
- How fabrication difficulty can reveal design-for-manufacturing issues that were not obvious in CAD
- How to improve future designs by thinking more carefully about machining, part access, assembly order, tolerances, and manufacturability before sending parts to be fabricated
- How physical dimensions can prevent unsafe use by making unintended projectiles incompatible with a launcher
