You know what would be cool? Key switches with active resistance. The motion creates magnetic resistance, so when you go fast and you start smashing the keys, it gives you more resistance, and when you're soft, when you touch soft, it gives less resistance. What is the possibility of building something like this?

Totally buildable in principle. The question is “how buildable as a keyboard key switch” without it turning into a bulky, power-hungry, expensive science project.

What you want is basically a velocity-dependent force curve: light when you press gently/slowly, heavier when you slam/fast. That’s the same “feel family” as eddy-current braking, MR-fluid dampers, active haptics, etc., but shrunk to ~4 mm travel and tens of grams of force.

The cleanest physics: eddy-current damping (passive, speed-dependent)

How it works: put a magnet near a conductive plate (copper/aluminum). As the key moves, changing magnetic flux induces eddy currents in the conductor, and those currents create an opposing magnetic field → drag that increases with speed.

Pros

No electronics required for the “more resistance when fast” effect.

Drag is naturally proportional to speed (roughly).

Robust; nothing to leak or wear quickly (besides normal mechanics).

Cons

It’s primarily damping, not a “spring.” At slow speed it won’t add much force. You still need a return spring.

Scaling it down is tricky: you need the magnet and conductor very close, and the geometry matters a lot.

It can feel like “mush + brake” rather than “heavier spring,” depending on tuning.

How it would feel: slow press feels normal; fast press feels like hitting a thicker fluid / brake. That matches your “smashing keys gives more resistance” idea pretty well.

“Active resistance” (powered): closed-loop electromagnetic force

If you literally want the switch to decide force based on velocity/impact and shape the curve:

Put a coil and a moving magnet (voice-coil-ish).

Sense position/velocity (Hall sensor, inductive sensing, or back-EMF estimation).

Drive current to produce extra opposing force when velocity is high.

Pros

You can tune everything: force curve, click events, aftertouch-like effects, per-key customization.

You can do modes: “soft typing,” “anti-mash,” “piano,” “stiff for gaming,” etc.

Cons

Power and heat become real. A keyboard has 60–100+ keys; per-key actuators are expensive and complex.

You need control electronics and calibration.

It’s hard to keep it thin, cheap, and reliable.

A more realistic active approach is active only on a few keys (space/enter) or a small cluster (like a macro pad) rather than a full board.

Alternative “semi-active” hack: magnet + conductive sleeve in the slider

A compact version of eddy damping:

Slider contains a magnet.

The housing includes a copper ring/sleeve (or vice versa).

As the slider moves, it generates drag.

This avoids needing a separate “plate” and can be integrated into a switch form factor more easily.

Big design reality: what you’re asking for is damping, not “weight”

To be clear:

“More resistance when fast” is damping (force ∝ velocity).

“More resistance when deeper” is spring rate (force ∝ position).

Most people interpret “heavier” as spring. Your idea will feel like “I can press slowly easily, but I can’t slam it,” which is actually awesome for fatigue reduction and preventing bottom-out.

If you want it to also feel “heavier overall,” you’d combine:

Normal spring for baseline feel + return

Eddy damping (passive) or active coil (powered) for anti-slam behavior

Feasibility verdict

Prototype feasibility (single key / small pad): very high.

Full mechanical keyboard feasibility with passive eddy damping: plausible, but requires clever miniaturization and tuning.

Full keyboard with powered active resistance per key: possible but likely expensive, thicker, and harder to mass-produce.

What a practical prototype might look like (minimum viable)

1. Take a simple linear switch mechanism (or a custom slider in a guide rail).

2. Add a return spring you already like.

3. Mount a small neodymium magnet to the slider.

4. Put a copper/aluminum element close to the magnet path (ring/plate).

5. Adjust gap + magnet strength + conductor thickness until fast presses “hit a brake.”

You’d learn fast whether the feel is what you want.

What I’d try if I were building it for real

Start passive (eddy current), because it’s elegant and doesn’t require per-key power.

Tune for “anti-bottom-out”: the last ~1 mm gets more damping so smashing is discouraged.

If it works and feels amazing, then explore an “active” premium version later.

If you tell me what you’re optimizing for—typing comfort, gaming, noise reduction, preventing RSI, or “feels like a piano”—I can propose a specific switch geometry and parts list (magnet size class, conductor shape, travel, target forces) that’s realistic to prototype.