Nerf Guns: Flywheels vs. Springs

In the Nerf Hobby world (yes, there is a professional Nerf scene), there are two warring factions: Springers and Flywheelers.

• Springers (e.g., The Retaliator, Longshot, Jolt): You pull a lever back, compressing a metal spring. When you pull the trigger, a piston slams forward, using air pressure to launch the dart.
• Flywheelers (e.g., The Stryfe, Rapidstrike): You hold a “Rev Trigger.” Electronics scream to life. Two spinning wheels grab the dart and fling it out the barrel using friction.

In FTC Robotics, we play games that involve shooting foam balls, plastic rings, or frisbees. And every single year, engineers have the exact same debate. Do we build a Catapult (Spring)? Or do we build a Flywheel (Motor)?

The Physics of the Launch

1. Spring/Air Power (The “Puncher”)

These systems store Potential Energy in elastic material (Steel spring or Surgical Tubing).

• Pros: Consistency. An elastic band releases the exact same amount of energy every single time. If you aim correctly, you hit the target.
• Cons: Cycle Time. You have to “reload.” A motor has to slowly wind the spring back (Draw Phase) before you can fire again. Fire rate is limited to maybe 1 shot per second.

2. Flywheel Power (The “Shooter”)

These systems use Kinetic Energy. We spin a heavy wheel at 4,000–6,000 RPM.

• Pros: Rapid Fire. As long as the wheels are spinning, you can shove ammo into them as fast as you want (10 rounds per second).
• Cons: Spin-up time.
  • Shot 1: Fast (100% speed).
  • Shot 2: The wheel slows down because it transferred energy to the first ball.
  • Recovery: You have to wait for the motor to speed back up, or the second shot will fall short.

Engineering the Perfect Flywheel

In robotics, Flywheels usually win because “More Shots = More Points.” But making them accurate is hard. We use Moment of Inertia.

• If the flywheel is too light (plastic), it loses all its speed after one shot.
• The Fix: We add weight to the rim (Heavy Brass Rings). This acts like a heavy battery of momentum. When the ball hits the wheel, the wheel barely slows down because it has so much stored energy.

”Modding” is Engineering

If you’ve ever modded a Nerf blaster—removing the air restrictor, upgrading to a K26 spring, or soldering in new 180-size motors—you have done System Optimization. You identified the bottleneck (air flow, spring constant, or voltage) and fixed it to increase muzzle velocity. That is literally 90% of what we do in robotics. We just shoot at goals instead of our younger siblings.