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Shooter Designs

Projectiles in FRC: A Practical How-To Guide

1) Pick a launcher style (pros/cons & when to use)

  • Hooded flywheel (single/dual wheel): Most common, accurate over a range; add an adjustable hood for multiple shot locations.

  • Good for balls/notes.

  • To achieve backspin on the game piece, use one flywheel. 

  • For flat spin and front spin, use two flywheels.    Chief Delphi+1                        

1678-2022-shooter.webp

 Hooded shooter built by 1678

  • Catapult/puncher (spring/elastic/motor-latched): Great for heavier/softer objects or when you want consistent set-shot”shot” distances; needs careful energy storage & release sizing.

  • A common mechanism for tension-based launchers is the choo-choo.

  • This works similarly to a train wheel, where a wheel rotates and at a certain point, it will engage a linkage, priming it.

  • It will then rotate and let go of the linkage, releasing energy.  Chief Delphi+1   

    Bh6rpmtCMAArr3a.jpgEeZi2PZ.png

           Puncher built by 1114                                               Choo-Choo mechanism diagram

  • Turret vs. fixed: Turret simplifies driver alignment and allows shooting while driving; a fixed shooter is lighter and simpler.

  • A fixed shooter will use its drivetrain (usually swerve) to aim. 

  •  Fixed shooters will commonly use a two-plate design.

  • Turret shooters also may have to be zeroed before each match. (See 254’254’s turreted designs & feeder integration.) Chief Delphi+2media.team254.com+2

download.jpgS916RRu.jpeg

 Turret shooter built by 254                                    Fixed shooter built by 2910


2) Shooter geometry & compression (for hooded flywheels)

Goal: Control contact time and spin so the game piece leaves at a repeatable speed/angle.

How to:

  1. Start with compression: Distance from wheel to hood smaller than the game-piece diameter. Typical starting point many teams reported in 2020: ~1.5–5–2.5 in; tune per game piece. Chief Delphi+1

  2. Choose hood material: Polycarbonate is common; grippier liners increase spin if the piece slips on the hood. Chief Delphi

  3. Wheel diameter & inertia: Bigger wheels give higher surface speed at the same RPM and generally more energy storage (flywheel effect); trade against weight & packaging. Chief Delphi

  4. Adjustable hood: Enables one mechanism to hit multiple distances/angles; CAD your arc so the normal force and compression stay reasonable across angles. Chief Delphi

  5. Rear “kicker”“kicker”/pre-spin roller (optional): Can improve feeding and reduce shot-to-shot variation; prototype to validate. Chief Delphi


3) Motors, gearing, and energy

How to:

  1. Pick motor(s) to match your RPM/torque needs (NEOs/Falcons/775pros). Prototype one motor, log RPM recovery, then scale; example community configs exist (e.g., multi-775pro setups). Chief Delphi

  2. Gearing: Target a no-load free-speed that’that’s 10–10–30% above your on-shot speed to allow headroom for control.

  3. Flywheel inertia: Add mass (steel plates or heavy hub) for better velocity hold-up during a shot—shot—balance vs. spin-up time. (See CD compression threads discussing plate “disks”“disks”.) Chief Delphi


4) Feeding, centering, and serialization

Why it matters: Consistent entry orientation & speed reduces shot variance.

How to:

  1. Center & single-file: Use “serializer”“serializer” rollers/geometry to turn wide intakes into a single, well-registered stream. (Great example write-ups in 254 tech binders.) media.team254.com+1

  2. Metering sensors: Beam breaks/hall sensors before the shooter to time the feed when RPM is on-target.

  3. Isolation: Use compliant wheels and passive rollers to control the ball and avoid jams before the throat. media.team254.com


5) Control: getting repeatable velocity (and fast recovery)

Core strategies you can implement in WPILib:

Practical steps:

  1. Characterize the shooter (SysId or logged step tests) and compute feedforward. FIRST Robotics Competition Documentation

  2. Tune: hit open-loop near the target, then close the loop; verify recovery time between rapid shots. FIRST Robotics Competition Documentation

  3. Disable motor-safety for flywheels (keeps them spinning during control loops). FIRST Robotics Competition Documentation


6) Trajectory, spin, and aim

How to:

  1. Backspin/topspin: More backspin often stabilizes flight and can help drop-in”in” style goals; tune with hood friction and wheel-hood speed ratio. Chief Delphi

  2. Distance tables: Build RPM/hood-angle lookup tables per range—range—collect data at marked distances, interpolate in code.

  3. Turret/hood strategy: Decide fixed hood + turret + velocity”velocity” vs. adjustable hood + fixed shooter”shooter” based on game tasks and protected zones. (Notes from Spectrum & 2024 meta.) Chief Delphi


7) Catapults & punchers (elastic or motor-latched)

How to:

  1. Pick energy storage: Surgical tubing, gas springs, torsion springs; estimate spring rate and energy (½½ k ). Old but useful CD references give ballpark tubing rates—rates—always validate on a test rig. Chief Delphi

  2. Size the actuator/gearbox: Use a simple simulation or spreadsheet to match wind-up torque, angular speed, and release angle (see Electric Catapult Design & Optimization”Optimization”). Chief Delphi

  3. Latch & release: Robust hard latches or dog clutches; ensure pre-load can’can’t self-release and add physical hard-stops.

  4. Cycle time: Design for safe reset under defense (ratchets or worm-gear holds).


8) Prototyping plan (fast & reliable)

How to:

  1. Bench rigs first: 4 frame, adjustable hood arc, sliding wheel-to-hood distance. Swap wheels/materials quickly.

  2. Log everything: RPM before/after shot, time-to-recover, ball exit speed (phone high-fps), hit rate vs. distance.

  3. Parameter sweeps: Try compression steps (e.g., +0.25 in), wheel durometer, hood liners, release angles—angles—record a matrix.

  4. Durability checks: Shoot 100+ cycles and re-measure your “dialed”“dialed” values to see drift (wheel wear, liner glazing).

Resources with examples & prototyping ideas: Spectrum resources hub and build blogs. spectrum3847.org+1


9) Software integration: from sensor to shot

How to:

  1. Sensor suite: Encoder on flywheel; beam break at exit; gyro/odometry for range estimate; (optionally) vision for pose/aim assist.

  2. Shot gating: Only feed when abs(vel - setpoint) < tolerance for N ms.

  3. Auto-aim options: Turret PID to vision target or odometry-based dead-reckon”reckon” with distance→distance→RPM/angle tables. (WPILib control tutorials cover tradeoffs.) FIRST Robotics Competition Documentation


10) Mechanical details that matter

  • Stiff mounting: Shooter & hood need rigidity (avoid deflection changing aim). Elite teams detail robust interfaces between turret and shooter. Chief Delphi

  • Ball path sealing: Close gaps so you don’don’t lose pressure/energy.

  • Serviceability: Quick-change wheels/liners; access panels for cleaning debris.

  • Safety: Shields around flywheels; never stand in plane of the wheel; interlocks for test mode.


11) Strategy fit & on-field use

How to:

  1. Decide shot families you’you’ll own (e.g., protected zone, subwoofer, mid-field). 2024 takeaways: multi-location shooting boosts cycle flexibility but increases complexity—complexity—picking one or two money shots can still be very effective. Chief Delphi

  2. Warm-up & calibration: Spin up on enable; auto-zero hood; shoot a short drill to confirm RPM table after field reset.

  3. Maintenance: Re-index compression (liners wear), check set screws, re-true wheels weekly.


12) Build-season checklist

  • Define target ranges/angles and cycle goals (with strategy).

  • Select launcher type; CAD the geometry (arc, compression, packaging).

  • Prototype quickly; collect a data table and pick initial control strategy.

  • Integrate a reliable feed path with sensors.

  • Lock in materials, fasteners, guards.

  • Code gating & recovery; validate with drill cards (e.g., 10 rapid shots at 2 ranges).

  • Create pit procedures for inspection, alignment, and upkeep.


Suggested Further Reading”Reading” blocks for your wiki