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Vision-Guided Morphing Quadcopter for Multi-Geometry Payload Transport through Narrow Passages

Aashish Sahu, Shriram Hari, R. Prasanth Kumar

arXiv:2608.21879v1cs.RO

TL;DR

Aerial payload transport is challenging when payload geometry, grasp stability, flight control, and passage width vary together. The paper presents a vision-guided morphing quadcopter using a single-actuator caging mechanism, and simulation completes transport for three payload geometries while substantially reducing footprint.

  • Problem

    Aerial transport requires grasping payloads with different geometries while maintaining flight stability and traversing narrow passages.

    Source: §I · p. 1

  • Method

    A quadcopter uses four hybrid arm–leg structures, onboard vision, endpoint force feedback, phase-wise planning, and a single tendon-driven actuator for adaptive grasping and footprint morphing.

    Source: §II · p. 2, §III · p. 3

  • Results

    0.31 m maximum RMS position error and 75.0–89.7% footprint reduction were achieved across box, cylindrical, and spherical payload simulations.

    Source: §IV · p. 5, §V · p. 5

  • Takeaways & Limitations

    The single-actuator morphology-adaptive design provided shape-tolerant payload confinement while reducing the effective vehicle footprint for constrained-space transport.

    Source: §IV · p. 5, §V · p. 5

Abstract

from arXiv · show

Aerial payload transport using multirotor unmanned aerial vehicles is challenging because payload geometry, contact interaction, grasp stability, flight control, and narrow-passage traversal are strongly coupled during pickup and transport. Object-specific grippers often cannot adapt their footprint or grasp geometry when the payload shape or passage width changes. This paper presents a vision-guided morphing quadcopter for multi-geometry payload transport through narrow passages. The proposed platform uses four hybrid arm-leg structures that function as both landing supports and grasping members. A centrally placed actuator drives a tendon-based morphing mechanism, enabling all four arms to synchronously retract or expand for object grasping, footprint reduction, and post-transport release. Onboard vision estimates the payload geometry and passage width, while endpoint force feedback is used to confirm grasp contact during payload engagement. A phase-wise mission planner, PID-based flight stabilization, and morphology-adaptive grasp controller are implemented in a MuJoCo simulation environment. The framework is evaluated using box, cylindrical, and spherical payloads, representing flat-faced, rolling-curved, and fully curved contact conditions. Across the three cases, the simulated system completes the pickup-transport-release sequence with a maximum RMS position error of 0.31 m, a final drop-zone error below 0.18 m, a compact grasp footprint of 0.09-0.21 m2, and a footprint reduction of 75.0-89.7 percent. The results demonstrate that a single-actuator morphing quadcopter can adapt its grasp footprint for the transport of payloads with different geometries while reducing its overall footprint for narrow-passage traversal.

I. INTRODUCTION

Aerial payload transport is difficult because flight stability, contact, grasping, payload geometry, and narrow-passage traversal are coupled. The paper addresses these constraints with a vision-guided quadcopter whose single morphing mechanism supports multi-geometry grasping and footprint reduction.

  • Aerial grasping couples stable flight with payload contact, grasp force, center-of-mass variation, rotor disturbances, and navigation constraints during transport.Source: §I · p. 1
  • Conventional aerial graspers often depend on known grasp points, specific payload geometries, or dedicated mechanisms, limiting reuse across object shapes.Source: §I · p. 1
  • Fixed quadcopter footprints can restrict safe traversal through windows, corridors, door frames, collapsed structures, and industrial openings.Source: §I · p. 1
  • Geometric caging constrains objects within a controlled contact envelope, offering a grasping principle suited to contact uncertainty and rotor disturbance.Source: §I · p. 1
  • A centrally actuated tendon mechanism synchronously retracts or expands four hybrid arm–leg structures for grasping, footprint reduction, and release.Source: §I · p. 2
  • The integrated framework combines onboard vision, endpoint force feedback, phase-wise trajectory generation, morphology-adaptive grasping, and PID-based flight stabilization in MuJoCo.Source: §I · p. 2

II. SYSTEM ARCHITECTURE

The system architecture combines hybrid arm–leg structures, onboard perception, mission sequencing, morphology adaptation, and flight control. A single central actuator changes the quadcopter between open and compact configurations for grasping and narrow-passage transport.

SYSTEM ARCHITECTURE

  • Four hybrid arm–leg structures serve as landing supports during touchdown and grasping members during payload engagement.Source: §II · p. 2
  • A centrally located motor synchronously retracts or expands all four members, changing the vehicle’s effective footprint with one actuator.Source: §II · p. 2
  • The MuJoCo framework models the quadcopter, morphing actuator, arm–leg members, contact interaction, corridor geometry, and box, cylinder, and sphere payloads.Source: §II · p. 2
  • A downward-facing camera estimates payload size and shape, while a front-facing camera estimates passage width for configuration selection.Source: §II · p. 2
  • Endpoint force sensors confirm contact and sufficient payload confinement during the compact caging-style grasp.Source: §II · p. 3
  • θm(t) = θmaxs(t) maps the mission-phase transition variable to the commanded morphing angle; decreasing s(t) during release expands the structure.Source: §II · p. 3
  • Reduced effective arm radius and grasp-footprint area indicate compact morphology supporting payload confinement and narrow-passage footprint reduction.Source: §II · p. 3

III. METHODOLOGY AND CONTROL DESIGN

The methodology combines vision-based localization, phase-wise trajectory generation, force-verified caging, morphology adaptation, and PID flight stabilization for payload transport through narrow passages.

Mission planning

  • The mission planner generates sequential commands for takeoff, approach, alignment, descent, grasping, transport, release, and exit.Source: §III · p. 3
  • A scouting circle followed by centering and descent reduces abrupt motion near the payload and improves alignment before contact.The reference trajectory uses the estimated payload location, scouting radius, and angular rate.Source: §III · p. 3

Perception and morphology

  • Camera measurements of payload dimensions and passage width determine whether the quadcopter remains open or reduces its effective footprint.The downward-facing camera estimates payload size and shape, while the front-facing camera estimates the gap between obstacle boundaries.Source: §III · p. 3
  • A single central motor synchronously retracts or expands four hybrid arm–leg members, forming a compact caging grasp during transport and reopening during release.The mechanism supports open flight, compact grasping, narrow-passage traversal, and post-transport release.Source: §III · p. 3, Figure 2 · p. 4

Grasp verification

  • Endpoint force feedback validates confinement within a safe force range, with positive grasp-force margin indicating sufficient contact for transport.The force condition is used with vision-based alignment as logical grasp confirmation rather than as a separate optimization objective.Source: §III · p. 4

Evaluation

  • The evaluation measures tracking, drop-zone error, morphology reduction, passage clearance, and successful completion of pickup, transport, release, and exit.Success requires localization, compact grasp formation, narrow-passage transport, goal-region release, and stable exit.Source: §III · p. 4

IV. SIMULATION RESULTS AND DISCUSSION

MuJoCo simulations show that the morphing quadcopter completes payload transport across box, cylindrical, and spherical cases while adapting its morphology and grasp footprint for narrow-passage traversal.

Simulation setup

  • The same mission sequence was executed for box, cylindrical, and spherical payloads, covering takeoff, alignment, grasping, constrained transport, release, and exit.The payloads represent flat-faced, rolling-curved, and fully curved contact conditions.Source: §IV · p. 5

Morphology adaptation

  • A compact caging-style grasp forms when the central motor synchronously retracts the four hybrid arm–leg members during grasping.The open configuration is retained during approach for rotor clearance and flight stability.Source: §IV · p. 5

Flight performance

  • The vehicle remains stable and completes the pickup–transport–release sequence for all payload geometries despite a small transient overshoot during grasp transport.The overshoot occurs while payload contact, morphology change, and inertial coupling happen simultaneously.Source: §IV · p. 5

Quantitative performance

  • 0.31 m maximum RMS position error and below 0.18 m final drop-zone error were achieved across the evaluated payloads.These values summarize the quantitative task-performance metrics.Source: §IV · p. 5

Footprint modulation

  • 75.0–89.7% footprint reduction was obtained as grasp-footprint area decreased from 0.84–0.87 m2 open to 0.09–0.21 m2 compact.The reduction reflects active changes in grasp geometry and effective vehicle footprint.Source: §IV · p. 5

Grasp confirmation

  • Endpoint force feedback verifies contact establishment before transport, preventing premature motion before payload engagement.The force condition serves as the grasp-confirmation criterion.Source: §IV · p. 5

Payload geometry

  • The box, cylinder, and sphere require different contact adaptations, yet the same hybrid arm–leg and single-actuator strategy transports all three.The box offers face and edge contact, the cylinder requires radial closure, and the sphere requires a wider compact grasp envelope.Source: §IV · p. 5

V. CONCLUSION AND FUTURE WORK

The paper presents a single-actuator morphing quadcopter for multi-geometry payload transport through narrow passages. Simulations across three payload geometries show successful transport with reduced vehicle footprint, while future work targets physical validation and improved perception and control.

Conclusion

  • Four hybrid arm–leg structures serve as both landing supports and grasping members, while one central actuator synchronously retracts or expands them.The tendon/thread mechanism supports grasping, footprint reduction, narrow-passage transport, and release.Source: §V · p. 5
  • 0.31 m maximum RMS position error, below 0.18 m final drop-zone error, and 75.0–89.7% footprint reduction were achieved in MuJoCo simulations.The framework was evaluated with box, cylindrical, and spherical payloads.Source: §V · p. 5

Future work

  • Future work includes depth-based perception, contact-aware control, improved force regulation, disturbance modeling, and physical prototype validation with varied payload properties.The stated validation scope includes different shapes, masses, and surface properties.Source: §V · p. 5
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