Alternative Launchers
Flywheel shooters are the default for most ball-launching games, but they're not the only option. Catapults, punchers, and other stored-energy launchers offer different tradeoffs and are sometimes a better fit depending on the game piece, the goal geometry, and the team's priorities.
When to consider an alternative to a flywheel
Flywheels are great at high fire rate, adjustable range through RPM control, and consistency over many shots. But they struggle with:
Very heavy or rigid game pieces that don't compress well against a spinning wheel
Games where you only need one shot distance and absolute repeatability matters more than adjustability
Packaging constraints where a flywheel and hood don't fit
Situations where the game piece shape doesn't interact well with a spinning wheel (odd shapes, large objects)
If any of those apply, the mechanisms below are worth evaluating.
Launcher types
An arm on a pivot, loaded by springs or elastic, that swings forward and launches the game piece from a cradle at the end of the arm. A motor winds the arm back against the spring tension, a latch holds it, and the latch releases to fire.
How it works: The motor (through a high-reduction gearbox) pulls the arm back, stretching the springs or elastic. This stores energy. When the latch releases, the spring snaps the arm forward and the game piece flies out of the cradle. The release angle, spring force, and arm length determine the shot distance.
Energy storage options:
Surgical tubing
Cheap, easy to adjust by adding or removing loops. Force varies as tubing stretches, so shot distance can shift as tubing fatigues. Replace regularly.
Torsion springs
More consistent force curve than tubing. Harder to adjust.
Gas springs
Very consistent, high force in a compact package. Not adjustable without swapping the spring.
Motor direct drive
No springs at all. A powerful motor with a high gear ratio accelerates the arm directly. Simpler mechanically but requires a lot of torque and precise motor control.
Advantages:
Very repeatable if the spring force and release angle are consistent
Handles heavy or odd-shaped game pieces well (the cradle just holds whatever you put in it)
Mechanically straightforward concept
Disadvantages:
Slow fire rate (arm has to wind back after every shot)
Less adjustable than a flywheel (changing distance means changing spring tension, arm angle, or release point)
Spring fatigue changes shot distance over time if not monitored
Requires a robust latch mechanism that won't release accidentally under preload
FRC examples: 118's 2014 catapult, various 2016 Stronghold launchers, 2468's pneumatic catapult
A linear mechanism that strikes the game piece with a plate or paddle, launching it forward. The energy is stored in springs or elastic that pull a carriage back, and the carriage is released to punch the game piece.
How it works: A motor (through a gearbox and usually a winch or cam) pulls the punch carriage back against spring tension. A latch holds the carriage. When released, the springs snap the carriage forward, and a flat surface on the carriage hits the game piece and sends it flying.
Advantages:
Very consistent because the energy transfer is a simple linear impact
Can launch game pieces that don't interact well with spinning wheels (flat objects, rigid shapes)
Fast reset possible if the spring force is moderate
Disadvantages:
Limited range adjustment (you control distance by changing spring tension or punch travel, which is less flexible than changing RPM)
The impact can deform soft game pieces unpredictably
Requires careful alignment so the punch hits the game piece squarely
FRC examples: 1114's puncher designs
A cam-driven mechanism where a continuously spinning wheel engages a linkage at one point in its rotation, pulls the launcher arm back, and then releases it. Named because the motion looks like a steam train's wheel-and-rod mechanism.
How it works: A motor spins a wheel with a pin or cam on it. As the wheel rotates, the pin engages a slot or linkage connected to the launcher arm. During part of the rotation, the pin pulls the arm back (storing energy in the arm's elastic or spring). When the pin reaches the release point, the arm snaps forward and launches. The motor keeps spinning and the cycle repeats automatically.
Advantages:
Self-cycling. The motor spins continuously and the mechanism automatically winds and fires. No latch needed.
Potentially fast fire rate since the motor never stops
Relatively simple control (just spin the motor, the mechanism handles timing)
Disadvantages:
Fire rate is locked to motor RPM (can't fire on demand, fires every rotation)
Harder to tune distance without changing the mechanism geometry
The linkage geometry needs to be right or the mechanism jams
More complex mechanically than a simple latched catapult
FRC examples: Various VEX and FRC catapults using the choo-choo cam pattern
Comparison to flywheel
Fire rate
Fast (limited by RPM recovery)
Slow (wind, latch, fire, repeat)
Medium (fires every rotation)
Range adjustability
Excellent (change RPM in software)
Limited (change spring tension or release angle)
Limited (change motor speed or geometry)
Consistency
Good with PID control
Very good if springs are fresh
Good if linkage is well-tuned
Game piece flexibility
Best for balls and soft objects
Handles anything that fits in a cradle
Same as catapult
Complexity
Moderate (motor, flywheel, hood, PID)
Moderate (motor, gearbox, springs, latch)
Moderate (motor, cam, linkage)
Software effort
Higher (PID tuning, RPM tables)
Lower (just latch release timing)
Lowest (motor on, mechanism cycles)
Latch design (for catapults and punchers)
The latch is the part that holds the arm or carriage in the loaded position and releases it to fire. It's also the part most likely to fail, because it's holding the full spring preload and needs to release cleanly every time.
What makes a good latch:
Holds securely under full spring preload with no possibility of accidental release
Releases quickly and cleanly (a slow release absorbs energy and weakens the shot)
Can be actuated by a small motor or servo (the latch itself shouldn't need a lot of force to open if designed correctly)
Includes a physical hard stop so the arm can't over-travel past its loaded position
Common latch approaches:
A servo-actuated pin or dog that engages a notch in the arm. Servo retracts the pin to release.
A cam or eccentric that holds the arm by geometry. A small rotation of the cam releases the arm.
A motor-driven ratchet where the motor winds the arm and the ratchet holds it. Release the ratchet to fire.
Always add a mechanical safety so the launcher can't fire when the robot is being handled. A spring-loaded arm at full tension is storing enough energy to injure someone. Use a physical pin or block that prevents the arm from releasing when the robot is disabled or being carried.
Energy storage and fatigue
Springs and elastic lose force over time and with repeated use. This means your shot distance will change throughout a competition day as the elastic fatigues.
Surgical tubing: Replace between events, or even between matches if you notice shot distance decreasing. Keep spare tubing pre-cut in the pit.
Torsion springs and gas springs: More consistent over time than tubing, but still check them periodically.
Motor direct drive catapults avoid this problem entirely because there's no elastic to fatigue. The tradeoff is needing a powerful motor and gearbox to accelerate the arm.
Past game examples
2014 Aerial Assist (large exercise ball)
The game piece was a large, heavy exercise ball that didn't interact well with flywheels because of its size and weight. Catapults were extremely common and effective. 118 Robonauts ran one of the most well-known catapult designs from this game.
2016 Stronghold (boulders)
Boulders were heavy foam balls. Both flywheel shooters and catapults were viable. Some teams used puncher-style mechanisms. The weight of the game piece made catapults competitive with flywheels because the energy storage in springs matched the launch energy needed.
2021/2022 (lighter inflated balls)
These games used lighter inflated balls where flywheels dominated. Catapults were rare in the competitive meta because flywheels offered better fire rate and range adjustability. However, some teams successfully used catapults for consistent short-range shots when simplicity was the priority.
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