Launcher Systems Guide | Spartan Design

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Launchers vs Shooters

Flywheels and launchers both launch game pieces — but through completely different physics. Understanding the difference tells you which to choose for a given game and robot.

› Slip Gears › Elastic Loading › Release & Reset › Common Mistakes › Testing Checklist

Feature	Flywheel Shooter	Launcher (Catapult/Puncher)
Energy source	Rotational kinetic energy in spinning mass	Elastic potential energy in rubber bands or springs
Motor role	Motor keeps flywheel spinning — continuous power	Motor loads the elastic — power only during reset
Cycle time	Depends on spin-up and feed rate; can be very fast	Fixed by reset time; typically slower per shot
Power per motor	Moderate — limited by flywheel inertia	High — all elastic energy releases at once
Tuning complexity	RPM, compression, hood angle	Elastic count/type, hard stop position, release timing
Best for	High fire rate, consistent velocity-controlled shots	High-power single shots; large or heavy game pieces

🎯 Rule of Thumb

Launchers win on power-per-motor; flywheels win on rate and adjustability. If the game requires launching a heavy piece a long distance once per cycle, a catapult or puncher is usually more motor-efficient. If you need to shoot many small pieces quickly, a flywheel is almost always the right call.

The Three Launcher Types

Catapult: A rotating arm that flings a piece at the end. High arc trajectory. Classic for large game pieces. Accuracy depends heavily on hard stop position and arm weight distribution.
Slingshot / Puncher: A linear mechanism that snaps forward to push a piece horizontally. Lower arc than a catapult. Better for flat trajectories and compact robot packaging.
Linear Puncher: A piston-style mechanism (often pneumatic or spring-loaded) that fires a piece forward in a straight line. Extremely fast cycle time when pneumatic — near-instantaneous shot.

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// Section 02

Slip Gears

A slip gear is a modified gear with teeth removed from a section of its circumference. When the gear rotates to the gap, it disengages and the launch happens. This is the most common mechanism for triggering elastic-powered launchers in VRC.

How Slip Gears Work

The slip gear drives a rack, arm, or linkage connected to the launcher while its teeth are engaged. The drive motor compresses the elastic during this phase. When the gear reaches the toothless section, it slips past the driven gear — instantly releasing the elastic, which drives the launch arm forward faster than any motor could directly.

Designing a Slip Gear

Teeth removed = release angle. A larger toothless gap gives the launch arm more time to move freely after release. Too small a gap and the gear re-engages mid-launch. Too large and the reset takes longer.
Where the gap starts matters. The gap must begin exactly at the point where the elastic is fully loaded — not before (under-loaded shot) and not after (motor fights the elastic).
Keep the slip gear axle rigid. Any flex in the axle changes the mesh depth and causes inconsistent engagement. Use short shaft spans and bearing supports on both sides.
Mark the slip gear. Put a physical mark on the slip gear aligned with the gap. During setup and calibration, you need to see exactly where the mechanism is in its cycle.

⚠️

Slip gears wear faster than full gears. The entry and exit teeth of the gap experience much higher impact loads because the gear re-engages abruptly. Check these teeth for wear or chipping after every competition day. Replace the slip gear at the first sign of chipped teeth.

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// Section 03

Elastic Loading

The elastic is your power source. How much you use, where you attach it, and how consistently you load it determine your launch power and shot-to-shot consistency.

Choosing and Configuring Elastics

Rubber band count, not brand. More bands = more power = longer reset time and more motor load during reset. Start with fewer bands and add until you hit your required distance. Document the count.
Attachment point position. Moving the attachment point on the arm changes the moment arm — further from the pivot = more torque = more power. But it also increases reset motor load proportionally.
Preload vs stretch-load. Elastics that start pre-tensioned (loaded at rest) provide faster initial launch but also require the motor to fight them from the very beginning of reset. Find the balance.
Replace on a schedule. Rubber bands fatigue and stretch permanently over time. After every competition day or 100+ cycles, replace all elastics with fresh ones of the same type and count. A tired band loses 15–20% of its energy.

Consistent Loading = Consistent Shots

Every variation in how the elastic is loaded produces a variation in shot power. Use hard stops to define the fully-loaded position mechanically — do not rely on motor current or timing to determine when “fully loaded” means. The hard stop makes loading deterministic.

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// Section 04

Hard Stops, Release Timing & Reset Speed

The hard stop is where your launcher stops. The release timing is when the slip gear lets go. Reset speed determines your fire rate. All three must be designed together.

Hard Stop Design

Physical hard stop, not code stop. Your arm’s fully loaded position must be defined by a physical stop — a screw, a standoff, or a machined surface the arm physically contacts. Code limits drift over time; physical stops don’t.
Cushion the hard stop. The arm impacts the stop at high speed on every cycle. A rubber pad or Delrin cushion absorbs impact and prevents the stop from loosening. Check the stop for movement after 50 cycles.
The launch arc must be clear. From fully loaded to full extension, the arm must not contact any part of the robot. Model this in Onshape and verify the full range of motion.

Reset Speed and Friction Reduction

After launch, the motor must pull the arm back to the loaded position against gravity and the elastic. This is the limiting factor on fire rate. Reduce reset time by:

Minimizing friction. Every bearing, pivot, and sliding surface on the reset path adds resistance the motor must overcome. Use bearing flats at every pivot, smooth surfaces on sliders, and remove unnecessary contact points.
Reducing arm weight. Lighter arm = motor does less work on reset. Remove material wherever the arm is not structural. Every gram saved on a long arm reduces the reset motor load significantly.
Increasing motor reduction. More gear reduction on the reset motor increases torque and therefore reset speed under elastic load — at the cost of increased reset time per revolution. Find the balance between torque and angular speed.

⚠️ Stop Building If…

Hard stop loosens after 20 cycles
Apply Loctite and check the mount. A moving hard stop means inconsistent shots.

Motor stalls during reset
Too many bands, too much friction, or motor reduction too low. Reduce elastic or add reduction.

Slip gear re-engages mid-launch
Toothless gap too small. Remove more teeth or increase the gap angle.

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// Section 05

Common Mistakes

Launchers are simpler than flywheels in some ways — and trap teams in different ways. These are the failure modes that show up under match pressure.

Not replacing elastics on schedule. A stretched band from 200 cycles has noticeably less energy than a fresh one. Teams tune carefully at the start of a season and wonder why accuracy degrades by week 6. Replace on a fixed schedule and document it.
Slip gear teeth chipping unnoticed. The high-impact entry and exit teeth on a slip gear can chip after extended use. A chipped tooth causes the gear to skip or jam. Inspect visually after every competition day.
Hard stop drifting without Loctite. The hard stop screw or standoff takes thousands of impacts. Without thread locker, it backs out. Use Loctite Blue on the stop fasteners and check them weekly.
Firing before the piece is seated. A launcher that fires before the game piece is fully in position launches it off-center or not at all. Add a sensor or driver protocol — piece must be fully loaded before cycle begins.
Reset speed inconsistency. If reset time varies, shot timing from auton or from rapid driver input will be inconsistent. Measure reset time in cycles and verify it is constant.
Launch arc not cleared in design. The arm hits part of the robot at full extension because the range of motion was never modeled. Always animate the full arc in Onshape before building.

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// Section 06

Testing Checklist & Notebook Evidence

Launchers are sensitive to elastic fatigue and hard stop drift over time. Test before every competition day, not just when something seems wrong.

🔬 Launcher Testing Checklist

20 consecutive launch cycles — record landing positions

Mark each landing. Average distance from target and variance.

Reset time measured and consistent

Time 10 resets with stopwatch. Variance should be <5%.

Hard stop position verified with a measurement

Measure arm angle at hard stop with a protractor or encoder count.

Slip gear tooth inspection — no chips or cracks

Visual inspection of entry and exit teeth on every competition day

Elastic replaced if >100 cycles since last replacement

Document replacement date and cycle count in pit log

Motor current during reset is within expected range

Higher than normal = more friction or weaker battery. Find cause before competing.

Launch arc confirmed clear at all robot positions

Test while robot is turning, reversing, and at bumper contact

Notebook Evidence

Elastic configuration diagram: rubber band count, type, attachment points, preload distance — reproducible by anyone
Hard stop position documented with encoder count and physical measurement — so it can be restored if disturbed
Shot-to-shot consistency data table — 20 shots, landing position, average, variance
Slip gear design sketch showing tooth count, gap size, and engagement point
Elastic replacement log — date and cycle count at each replacement

🎯

Flywheel Shooter Guide

The other scoring projectile system

💨

Pneumatics Best Practices

Pneumatic punchers and actuators

🔁

PTOs & Motor Sharing

Free up motor budget for your launcher

🚫

Stall Detection

Protect the reset motor

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