AirDrums

A whole drum kit in one small case — six drones hold the drums in the air, anywhere

Late afternoon in the middle of a desert. A woman walks in with one small case, opens it by a flat rock and sets six drones into the air one at a time — snare, hi-hat, crash, toms and ride — each holding a ring of watched air. She clips a tag to each shoe, sets a speaker on the sand and sits on the rock to play. Halfway through, the film goes inside a stick: its tip sees the ring and a spring kicks it back up. She plucks a drone from the air, packs up and walks off.

What this is

A full drum kit you can carry in one small case and play anywhere. Six micro-drones hover where the drums and cymbals would be. Each is a short cylinder with two counter-rotating rotors stacked inside its top, and each watches a ring of air with LiDAR — a band 4 to 22 inches across, exactly where a drumhead or a cymbal would sit. When a stick's tip crosses a ring, the hit is heard, and a mechanism inside the stick kicks it back up so the stroke rebounds as if off a head. There are no stands and no pedals: a small tag on each shoe reads the kick and the hi-hat foot. A speaker the size of a Beats Pill, or earbuds, makes it heard.

The technical shape

Kit: six micro-drones — snare, hi-hat, crash, tom, floor tom, ride · no stands, no pedals
Drone: a 6–8 cm cylinder · two counter-rotating rotors stacked inside its top · hovers 1–4 ft up and holds its place
Surface: a LiDAR ring of watched air, 4" inside to 22" outside · level for a drum, tilted up to 45° for a cymbal
Sticks: tip retroreflector and photodiode · SMA latch · pre-loaded spring · voice-coil motor · battery and board in the grip
Feet: a 1" × ½" low-latency tag clipped to each shoe — right foot plays the kick, left foot the hi-hat
Sound: a Pill-sized speaker on the ground, or earbuds · a 20–25 ms motion-to-sound budget
Carry: drones, sticks, tags and speaker all fit one small case
Stage: concept specification · system design, ring logic, latency budget and stick control loop

The deep end · full technical outline

Outline v2 · expanding

The kit is air

A drum kit is mostly furniture: stands, pedals and shells that exist to hold a few surfaces at the right height. AirDrums keeps the surfaces and drops the rest. Six drones hover where the snare, hi-hat, crash, toms and ride would be, and each one watches a ring of air where its drumhead or cymbal would sit — level for a drum, tilted up to 45° for a cymbal, 1 to 4 feet off the ground. Setting up is setting each drone in the air; packing up is plucking it back out.

The drone

Each drone is a short matte cylinder 6–8 cm across. The propellers live inside it: two rotors stacked in the top, turning opposite ways, so their torque cancels and the column holds its place without a tail or a gimbal. The coaxial cylinder is proven ground — Proxflyer showed a passively stable coaxial rotor in 2002, and Ascent AeroSystems' Helius is a 249 g cylindrical coaxial drone. Low on the body sits the LiDAR band that draws the ring; UWB radios let the drones know where each other are.

Rings that overlap

Close together, the rings overlap, and one drone's laser can pollute another's returns. The design does not try to decide which drone owns a return. UWB puts every drone in one shared frame to within 5–15 cm; from that the system predicts which sectors of each scan another drone will contaminate and gates them out; every point of the merged surface is still seen by a neighbour from a different angle, which fills the gap. Overlap is the error correction. If UWB degrades, each drone falls back to its own ring.

The stick that bounces

A drummer plays off the head's rebound, and air has none — so the stick supplies it. The tip carries a retroreflector and a photodiode that sees the drone's LiDAR the moment it enters a ring. That fires a shape-memory latch, which lets go of a plunger held against a pre-loaded spring; the spring throws it into the tip and the stick kicks back up. A voice-coil motor then shapes the stroke and pulls the plunger home for the next one. Firing on the tip's own detection, before the hit is confirmed, saves 10–15 ms.

Tightness

The voice coil sets how tight the head feels. Driven with I = I_max × (T − 0.5), it adds to the spring above the midpoint for a lively bounce, sits idle at 0.5 for the spring alone, and resists below it for a dead, low-bounce feel. The coil is also its own sensor: in each 500 µs cycle it drives for 400 µs and floats for 100 µs while its back-EMF reads the plunger's speed, so a 20–50 ms rebound stroke gets 40–100 corrections and needs no position sensor.

No pedals

The kick and the hi-hat foot are a tag, 1 by ½ inch, clipped to each shoe: an inertial sensor that reads the foot's stroke and sends it on a low-latency radio link. Nordic's ESB protocol carries it in about half a millisecond; tuned Bluetooth LE in 7.5–15 ms. Ordinary Bluetooth audio would add more than all of that together, so the sound path is kept off it. With those choices, motion to sound comes in around 20–25 ms — inside what a player feels as instant.

What is still open

This is a specification, not a built kit. The shape-memory latch is the weak point: it takes 50–100 ms to let go and 2–3 s to cool, far slower than drumming; a piezo latch, releasing in under a millisecond, is the named alternative. The drones' flight time rests on a semi-solid-state battery that is not yet sold in small cells, and a single prototype is costed at about $1,700, most of it the LiDAR and that battery.

Related in the lab

Spatial surface

Built at this bench

The machine, the instrument, the film that explains it — all designed and built in-house. The same bench works for hire.

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