Why a spinner hits so hard

A spinner weapon is a flywheel: a wheel you pour energy into by spinning it up, then dump all at once on impact. Two numbers decide how big that hit is.

1. The energy bank

All the punch is stored as rotational kinetic energy:

The ω² is the part students always miss: double the spin speed and you don't get twice the energy, you get four times the energy. Speed counts double.

2. Where you put the weight (the big one)

Same mass, same size, but it matters where the metal sits. Push it all out to the rim and you bank twice the energy at the same speed:

That factor of 2 is a real engineering choice, and it is exactly why real combat spinners pack their weight out at the rim. The catch: a ring takes longer to get up to speed.

3. Tip speed is what actually bites

The rim is the business end. Both a higher RPM and a bigger radius push the tip speed up, which is why arena spinners are wide and fast. Crank the Spin Lab up and watch the readout blow past 150 mph at the edge, faster than a big-league fastball.

4. The catch: spin-up

Banking more energy isn't free. The same thing that makes a ring store more (mass far from the center) also makes it harder to get spinning. With a fixed motor, more spread-out weight means a longer wind-up before you're dangerous. That is the trade every spinner makes: bank more, wait longer, and take longer to recover after each big hit.

This is your BotForge weapon

This isn't a metaphor. The RumbleBots arena scores spinner damage on the same core physics. Here's the line-by-line map — including the one spot where the game keeps things simple:

Real physics	In BotForge / RumbleBots
KE ∝ ω² — speed counts double	damage uses (RPM / maxRPM)² — that squared term is the ω²
vtip = ωr — a faster, bigger tip hits harder	damage scales with tip radius (ref 0.6 m) and spin (ref 1200 RPM)
More metal = more mass = bigger hit	damage ∝ weapon mass, and the shape sets how much metal it holds: drum 1.25 (heaviest) > blades 0.95 > disc 0.9 > bar 0.8 > ring 0.75 (lightest)
Heavier flywheel → slower to spin up (τ = Iα), but a bigger bank	the spin-up time slider; a longer wind-up earns a flywheel bonus √(t / 3s) (capped 0.8–1.8×) but recovers slower after a hit
Energy leaves the wheel on impact	a clean hit sheds ~35% of its rate on a normal hit (up to 70% on a hard one) — then it must spool back up

Where else flywheels show up

This isn't just a battlebot trick. Anything that needs to bank energy and then release it fast leans on a flywheel:

• Hybrid race cars. Some catch the energy of braking by spinning up a flywheel (Le Mans winners have done exactly this), then dump it back as a boost down the straight.
• Power grids. Rooms full of heavy spinning rotors bank energy and release it within seconds to steady the grid when demand suddenly spikes.
• Engines and potter's wheels. A heavy spinning wheel smooths out jerky power and keeps things turning between pushes.

Spin to store, slow down to release. Your spinner is the same machine, just aimed at another robot.