Flywheels

Overview#

A flywheel is a spinning wheel or disk that stores rotational energy and then quickly transfers that energy to a game object — launching it through the air!

Flywheels are used in robot launchers and shooters. Instead of a single explosive push, the flywheel spins up to a steady speed and then gives every game piece the same consistent burst of energy. This means each shot travels the same distance and speed, making the robot much more accurate.

Why does this matter?

If your game involves launching balls, discs, or other objects, a flywheel lets you automate the shooting process. Once the wheel reaches the right speed, the robot can fire many shots rapidly and consistently — without recalculating every time.

The four key ideas for flywheels are:

• Rotational Inertia — how much energy the wheel stores
• Compression — how tightly the wheel squeezes the game piece
• Speed Recovery — how quickly the wheel gets back up to speed after a shot
• Hood Angle — the angle at which the game piece exits the launcher

How It Works#

A flywheel launcher works on three physics principles:

1. Rotational Inertia and Energy Storage

Think of a flywheel like a spinning top. A heavy, wide spinning top is much harder to stop than a tiny light one — it has more rotational inertia.

The more inertia a flywheel has, the more energy it can store and deliver. The kinetic energy (stored spinning energy) of a flywheel is:

Where:

• I is the moment of inertia (how heavy the wheel is and how far that weight is from the center)
• ω (omega) is the angular velocity (how fast the wheel is spinning)

In simple terms: a heavier wheel spinning faster stores more energy.

2. Compression and Traction

When a game piece is pushed into the spinning flywheel, it gets squeezed between the wheel and a fixed backing called the hood. This compression creates friction, which grabs the game piece and flings it forward.

More compression = more friction = faster launch. But too much compression can slow the wheel down or jam pieces.

3. Speed Recovery

Every time the flywheel launches a piece, it gives away some of its stored energy, causing the wheel to slow down slightly. Speed recovery is how quickly the motor can spin the wheel back up to full speed for the next shot.

A heavier flywheel with more inertia actually helps here — it does not slow down as much per shot, so recovery is faster.

Key Vocabulary#

• Rotational Inertia: How hard it is to change the spinning speed of a rotating object. Heavier and wider = more inertia.
• Compression: How tightly the game piece is squeezed between the flywheel and the hood.
• Speed Recovery: How quickly the flywheel returns to its target speed after launching a piece.
• Hood Angle: The angle of the backing surface behind the game piece. Changing the hood angle changes the launch trajectory (higher angle = higher arc).
• Traction: How well the wheel surface grips the game piece. High traction means the wheel transfers more energy to the piece.

How It Shows Up in VEX Robotics#

VEX teams build flywheel launchers in games involving balls or discs. The exact design depends on the current game. Before finalizing your design:

• Check the official VEX game manual for legal parts and launcher rules.
• Test with actual game pieces, not substitutes — the weight and feel of the real pieces matter.
• Check the VEX documentation for motor speed limits and cartridge options that affect flywheel RPM.

Testing and Iteration Tips#

• Test one thing at a time. If you change the hood angle AND the wheel speed at the same time and the shot improves, you will not know which change helped.
• Measure your results. Record where the game piece lands each shot. “It went further” is less useful than “it landed 6 inches further to the left.”
• Watch the wheel slow-down. After each shot, observe whether the wheel recovers speed before the next piece enters. If shots get shorter over rapid-fire attempts, speed recovery is your problem.
• Check for jams. Pieces jamming means too much compression or misalignment. Loosen the hood slightly and retry.

Common Mistakes#

• Setting the wheel speed too low — the piece dribbles out instead of launching.
• Setting compression too high — pieces jam or the wheel stalls.
• Ignoring speed recovery — the first shot works but later shots go shorter.
• Not testing with the real game piece — different weights need different settings.
• Changing multiple things at once and not knowing what fixed the problem.

When something does not work, start with the simplest possible test — just roll a game piece through by hand and see if it exits cleanly. If that works, add motor power and test again.