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The Machine

The Machine · Elements

Pellet drum

Design stage

Updated 2026-10-18

A motorized pellet drum, after the damaru. The drum rocks back and forth about a vertical axis and beads on cords strike its head, two hits per rock.

Pellet drum frame, three drums at two heights. Current layout. Front view, one drum rocking from above, one drum from the side.
Fig. 1Pellet drum frame, three drums at two heights. Current layout. Front view, one drum rocking from above, one drum from the side.
First concept. A small damaru-style drum on a shaft.
Fig. 2First concept. A small damaru-style drum on a shaft.

How it works

  • One head per drum, facing the audience. The axle runs vertically just behind the head, so the head pivots in place and its left and right edges swing toward and away from the audience.
  • Both cords tie to the same hoop, one near the left edge and one near the right, through small standoffs so each bead hangs just in front of the head without resting on it. Rocking one way swings one edge forward into its bead; rocking back swings the other edge into the other bead. Two hits per rock on the same head.
  • Different beads on the two cords (for example wood and metal) give the two hits contrasting sounds. Moving the standoffs inward along the hoop moves the hits toward the center for a fuller sound.
  • Snare wires sit behind the head, pressed against it.
  • When a motor stops, its beads swing on and trail off. No reset needed.

Mount and drive

  • The axle runs in bearings on the top and bottom bars of a rectangular extrusion frame and attaches to the drum through flanged collars (drilling is fine), with rubber washers to stop buzzing. Counterweight any off-center hardware so the drum doesn’t lurch at each reversal.
  • Each drum has its own motor and crank-rocker, so each can run its own tempo, drift, and lock. First version is fixed loudness (fixed linkage). Motor speed sets tempo.
  • Rocking reverses the drum’s weight several times a second. Keep drums light, use a sturdy geared motor, and add a small flywheel on the crank.

Layout

Three drums in one rectangle at two heights (high, low, high). Leave enough side clearance and height offset that each drum’s beads stay clear of its neighbors.

Choosing a drum

Used Remo Rototoms are a good candidate: cheap used, single-headed, and their open back gives direct access to the head for the snare wires (8” snare wires in a printed holder, or a Remo Rhythm Lid snare clip, whose fit on a small Rototom is untested). Off-the-shelf 8” snares run $100 or more each, which is over budget.

References