---
kind: concept
slug: origami-mechanism
title: Origami mechanisms
summary: >-
  A flat sheet folded along set creases gives one body several jobs: a folded cylinder can roll, flip, swim, pump liquid by folding and grip by spinning. Its geometry sets the locomotion modes and its cavity sets the storage. The trade-off: the folds set the function, so changing the job means a new fold pattern or a second part. Only one paper covers it so far.
tags: [robotics, origami, locomotion, drug-delivery]
papers: ["2203.10122"]
related: [magnetic-actuation]
status: draft
updated_at: 2026-10-18
---

## Overview

An origami mechanism is a body folded from a flat sheet along set creases, so
its shape and motion come from the pattern rather than from separate parts.
The one paper on this slug uses a Kresling cylinder, a hollow, triangulated
tube folded from a flat pattern [arxiv:2203.10122 p. 3]. The authors contrast
this with existing millimeter-scale origami devices, which usually need
separate geometric components for locomotion and for each function [arxiv:2203.10122
p. 2].

Three properties of the fold do the work. Its high geometric symmetry, with a
height-to-diameter ratio close to 1, lets it roll like a sphere [arxiv:2203.10122
p. 2]. Its tilted triangular panels act like propeller blades when it spins in
water [arxiv:2203.10122 p. 2-3]. Its hollow cavity shrinks when the body folds,
which pushes out liquid stored inside [arxiv:2203.10122 p. 4, p. 7-8]. The
body is monostable: once the field that folds it is removed, it recovers the
unfolded shape by itself [arxiv:2203.10122 p. 4-5].

The fold does not supply power. The shape only responds to an external
actuator; in this paper that actuator is a magnetic field, covered in
[Magnetic actuation](/concepts/magnetic-actuation) [arxiv:2203.10122 p. 4].

## Variants

### Single-plate Kresling for locomotion

One thin magnetic plate is attached to one hexagonal end. A rotating field
makes the body roll on the ground, flip over obstacles or spin to swim, and
the rotation axis of the field sets the mode [arxiv:2203.10122 p. 3-4, fig. 1E-G].
In this variant the fold supplies symmetry and panels rather than a shape
change. The paper reports that the robot
moves over a wall, spaced stairs, a 30 degree incline, a column array and a
cylinder of about its own size, switching between rolling and flipping
without a change to the field [arxiv:2203.10122 p. 6-7, fig. 2A-C]. Card:
[Spinning-enabled Wireless Amphibious Origami Millirobot](/papers/2203.10122).

A frontal hole and six radial cuts in the end caps are reported to raise
swimming speed from 66.0 to 81.2 mm/s at 10 mT and 30 Hz. The authors attribute
this to the hole drawing in water that is pushed out through the cuts, which
reduces the high-pressure region in front of the robot [arxiv:2203.10122 p. 10-11,
fig. 3C-E]. The same paper uses the spinning end as a suction grip: the low
pressure at the hole draws cargo in, and gravity releases it when the hole
faces down [arxiv:2203.10122 p. 14, fig. 4B].

### Two-plate Kresling for fold-and-release

Two plates sit on the two hexagonal ends, with magnetizations of equal size
set 90 degrees apart. Their vector sum gives a net magnetization. A field
applied along that net direction produces two opposite torques, which fold the
body. The cavity shrinks and pushes stored liquid out through the radial cuts,
and a needle at one end punctures a dye container at the other [arxiv:2203.10122
p. 7-8, fig. 2G-H]. Repeated fold and unfold cycles release liquid in what the
authors call controlled doses [arxiv:2203.10122 p. 8]. The paper gives no
volume per cycle, dose accuracy or residual volume, so the dose claim has no
number behind it [arxiv:2203.10122 p. 8].

## When to use which

| Situation | Use | Why |
|---|---|---|
| One body must roll or flip on the ground and swim in water, with no onboard power | Single-plate Kresling | Both modes come from one body, switched by the field's rotation axis [arxiv:2203.10122 p. 4, fig. 1E-G] |
| The robot must cross steps or obstacles without changing the field | Single-plate Kresling | Self-switching between rolling and flipping, reported for obstacles about robot size [arxiv:2203.10122 p. 6-7, fig. 2C] |
| Obstacles too large for rolling and flipping | Single-plate Kresling with an instant field | Jump of 23.5 mm high and 56.2 mm far at 40 mT and 120 degrees [arxiv:2203.10122 p. 7, fig. 2E-F]; height and distance change strongly with the angle [arxiv:2203.10122 fig. 2F] |
| Stored liquid must be released on command | Two-plate Kresling | Cyclic folding releases liquid under a field along the net magnetization [arxiv:2203.10122 p. 8, fig. 2H] |
| A known dose or cargo mass is required | Not established | The paper reports no dose or cargo numbers [arxiv:2203.10122 p. 8, p. 14] |
| Use inside a living body | Not established | All biomedical tests are ex vivo, in a pig stomach [arxiv:2203.10122 p. 8, p. 14] |
| The fluid is much more viscous than tested | Not established | Swimming was tested once, in one 12 mPa·s fluid [arxiv:2203.10122 p. 14] |

## Implementation sketch

The pumping variant is the only one in the paper that changes the body's
shape on purpose, so it is the clearest case of the fold as a mechanism. The
sketch below is the cycle as the paper describes it. Fluid volume per cycle is
not stated in the paper, so the code does not compute one.

```pseudocode
# Fold-and-release cycle of a two-plate Kresling body  [p. 7-8] [fig. 2G-H]
# Input:  reservoir (liquid in the inner cavity), n_cycles (int)
# Output: list of release events; volume per event is not stated

def pump_cycles(reservoir, n_cycles):
    events = []
    # Repeat the fold and unfold cycle  [p. 8]
    for _ in range(n_cycles):
        # Field along the net magnetization folds the body  [p. 7]
        apply_field(direction="M_net")
        # Cavity shrinks and pushes liquid out through the radial cuts  [p. 8]
        events.append(eject(reservoir))
        # Remove the field; the body recovers its unfolded shape  [p. 4-5]
        remove_field()
    return events
```

## Contradictions

None known. Only one card covers this slug so far.

## Papers

- [Spinning-enabled Wireless Amphibious Origami Millirobot](/papers/2203.10122):
  a magnetically driven Kresling cylinder that rolls, flips, swims, pumps
  liquid by folding and grips cargo by spinning. All results are author-reported.