Flywheel Shooter Guide | Spartan Design

// Section 01

How Flywheel Shooters Work

A flywheel shooter uses high-speed spinning wheels to accelerate a game piece and launch it. The flywheel stores rotational kinetic energy and transfers it to the piece in milliseconds.

› Single vs Double Flywheel › Compression & Hood › Velocity Control › Accuracy Tuning › Testing Checklist

When a game piece enters the flywheel gap, it contacts the spinning wheel surface and is accelerated by friction. The energy transferred determines exit velocity — which determines range and height. Consistency in exit velocity = consistency in shot placement.

🎯 Rule of Thumb

Consistency beats peak performance. A flywheel that puts 9 of 10 shots on target is worth more than one that sometimes makes incredible shots but misses 4 of 10. Design for repeatable energy transfer, not maximum power. Spin-up speed and shot consistency are the two numbers that determine your scoring rate.

The Three Variables That Determine Shot Outcome

Exit velocity: Set by flywheel RPM at the moment of contact. Varies if the wheel has not recovered from the previous shot (spin-down).
Exit angle: Set by your hood or backplate geometry. Fixed at build time — changes require physical adjustment.
Spin on the piece: Backspin from a single flywheel, topspin from a double flywheel. Affects trajectory arc and where the piece lands relative to where it hits.

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// Section 02

Single vs Double Flywheel

Two fundamentally different architectures. The choice affects spin-up time, motor budget, shot spin, and how easy the system is to tune.

Single Flywheel

+ Simpler build — one set of wheels, one motor
+ Lower motor budget (1–2 motors)
+ Easier to tune compression
− Puts backspin on the piece — affects trajectory
− Hood required to guide exit angle
− Spin-down between shots if flywheel is light

Double Flywheel

+ Two wheels cancel spin — piece exits without rotation
+ More energy transferred — faster exit velocity at same RPM
+ More consistent trajectory
− 2–4 motors (more motor budget required)
− Harder to tune — two wheels must be matched in speed
− Heavier, more complex mounting

💡

Which to choose? If your motor budget is tight or the game piece is forgiving (large target, close range), start with a single flywheel. If the game requires long-range accuracy or the piece needs to enter a narrow target without spin, a double flywheel is worth the complexity.

Flywheel Mass and Spin-Up

A heavier flywheel stores more rotational energy — which means less spin-down per shot, but longer spin-up time. A lighter flywheel spins up faster but loses more RPM per shot. Match your flywheel mass to your shooting rate: high fire rate needs a heavy flywheel; single-shot-per-cycle needs faster spin-up.

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// Section 03

Compression & Hood Design

Compression determines how much energy gets transferred to the piece. The hood controls the exit angle and backspin characteristics. Both must be tuned together.

Compression

Flywheel compression is the gap between the spinning wheel surface and the backplate or hood, measured at the point where the game piece passes through. Too little gap and the piece barely accelerates — the wheel slips over it. Too much compression and the motor stalls or the piece deforms.

Start wide, measure, then tighten. Begin with a gap slightly larger than the game piece diameter. Reduce 1–2mm at a time and measure shot consistency at each setting.
Adjustable gap is worth building. Use a slotted hole or a shim stack at the backplate mount. Being able to change compression without disassembly saves hours of tuning time.
Measure exit velocity, not just accuracy. At different compression settings, the piece exits at different speeds. Use a measuring tape to spot the range change — it tells you exactly where energy transfer improved.

Hood / Backplate

The hood is the curved or angled surface that constrains the game piece as it exits the flywheel. It controls exit angle (launch angle), backspin, and how consistently the piece leaves the wheel.

Material: A smooth, low-friction hood lets pieces exit cleanly. High-friction surface on the hood adds more backspin — useful if you want the piece to “grip” a goal lip.
Angle: A steeper hood means a higher launch angle. A shallower hood means a flatter trajectory. Build in adjustability — even a 5° angle change significantly changes where the piece lands.
Adjustable vs fixed: Start adjustable. Once you find the correct angle for your game and robot position, lock it and apply Loctite.

⚠️ Stop Building If…

Shot variance is high
Every shot landing in a different spot means inconsistent compression or the flywheel is not at target speed when you fire. Fix the mechanical issue first.

Piece deforms on exit
Compression too high. Reduce gap immediately — deformed pieces score unpredictably and can jam.

Flywheel speed drops after every shot
Flywheel mass too low for your firing rate. Add mass or reduce rate.

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// Section 04

Velocity Control & Programming

A flywheel running at inconsistent RPM produces inconsistent shots. Velocity control is the code that keeps the flywheel at its target speed across an entire match.

Why Raw Motor Power Is Not Enough

Running the flywheel motor at 100% power does not mean 100% speed. Battery voltage drops during a match. Motor temperature affects output. Each piece that passes through takes energy from the flywheel and momentarily drops its speed. Without feedback control, all of these cause shot-to-shot variance.

Velocity Controllers for Flywheels

Bang-Bang controller: Full power when below target RPM, zero power when above. Simple, works well for flywheels because the large rotational inertia smooths the on/off switching. See the Bang-Bang guide.
TBH (Take Back Half) controller: One gain, converges smoothly to target velocity, less oscillation than bang-bang for continuous-fire applications. See the TBH guide.
PID: More tuning parameters but most precise. Useful when you need the flywheel to hold exact velocity across different battery states. Start with bang-bang and move to PID only if consistency is not sufficient.

Ready-to-Fire Detection

Do not fire until the flywheel is at target speed. Add a “ready” indicator — an LED, a Brain screen indicator, or a controller rumble — that tells the driver the flywheel is on target. Fire-on-demand before spin-up is the most common cause of missed shots in competition.

✅

Log flywheel RPM data to SD card during practice sessions. You will see exactly how much the speed drops after each shot, how long recovery takes, and whether your battery state affects performance. See the Data Logging guide for implementation.

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// Section 05

Accuracy Tuning

Accuracy comes from isolating one variable at a time. If you change hood angle, compression, and flywheel speed in the same session, you cannot know what improved the shot.

Systematic Tuning Protocol

Fix a shooting position. Mark tape on the floor. All accuracy tests happen from the same spot. If you move, you are not comparing the same thing.
Fix flywheel speed first. Choose a target RPM and verify the velocity controller holds it consistently. Do not tune hood or compression until speed is stable.
Tune compression. At fixed speed and position, adjust compression until the average shot lands closest to target. Record: setting, average landing, variance.
Tune hood angle. At fixed speed and compression, adjust hood in 2° increments. Shoot 5 times per setting. Record landing position average.
Test at different distances. Once tuned at one distance, test at match-relevant distances. Only change flywheel speed to adjust range — do not retune hood and compression for each distance if avoidable.

Sources of Variance (Troubleshooting)

Shot-to-shot speed variance: Velocity controller not converged, or firing before spin-up is complete
Shots drifting left/right: Flywheel not perpendicular to shot direction; piece entering asymmetrically; sidespin from misaligned feed
Shots drifting long/short over a match: Battery voltage dropping — use velocity control, not open-loop power
High variance on first shot, consistent after: Flywheel taking too long to reach target speed — spin up faster or wait for ready signal

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// Section 06

Testing Checklist & Notebook Evidence

Flywheel accuracy is meaningless without documented testing. This data also goes directly in your notebook — it is engineering evidence, not just practice.

🔬 Flywheel Testing Checklist

Spin-up time measured from 0 to target RPM

Time with stopwatch from motor enable to ready signal. Record seconds.

RPM recovery time after each shot

How long from shot to back-at-target. Should be <1s for most games.

10 consecutive shots from fixed position — record landing

Mark each landing point. Measure average distance from target and variance.

Compression setting documented with measurement

Gap in mm, measured with calipers. Record the final tuned setting explicitly.

Hood angle documented

Angle in degrees from horizontal. Photograph the final setting.

Accuracy at multiple match distances tested

Test from every position your robot will shoot from in a real match

Low-battery performance tested

Discharge battery to 50%, retest accuracy. Velocity control should hold.

Notebook Evidence

Tuning table: compression setting vs. average shot landing — shows systematic iteration
RPM data log showing velocity held across a simulated match (from SD card log)
Accuracy scatter plot — 10 shot landing positions plotted on a field diagram
Spin-up time measurement before and after adding flywheel mass — shows tradeoff analysis

⚡

Bang-Bang Controller

Simplest flywheel velocity control

🎾

TBH Controller

Smooth velocity control for continuous fire

📊

Data Logging

Log RPM and accuracy to SD card

🚀

Launcher Systems

Catapults, punchers, slingshots

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