Background
Stiffness determines how a robotic system responds to contact, disturbances, and positioning errors. It directly affects interaction accuracy, impact forces, robustness, and safety. Changing stiffness according to the task is therefore a central principle in soft robotics.
Recent theoretical work shows that multirotors carrying a cable-suspended load can act as movable compliant anchors. Changing their positions and the cable tensions shapes the passive Cartesian stiffness perceived at the load. The method uses ordinary multirotors with position controllers and does not require the vehicles to detect physical interaction explicitly. [1]
The resulting mechanical response bypasses the sense-compute-act loop at the interaction level. This could provide rapid and robust reactions during transportation and physical interaction. The method has so far been investigated only theoretically and in simulation.
Objective
The objective of this thesis is to determine whether the passive stiffness of a cable-suspended load can be predicted and shaped using real multirotors.
The student will build a cooperative indoor setup, measure the load stiffness, validate the theoretical model, and demonstrate stiffness shaping in a physical task.
Main activities
- Assemble and control a group of small multirotors in an indoor motion-capture environment.
- Develop a cable-suspended load and the required communication, sensing, and safety infrastructure.
- Design experiments to measure the load’s passive Cartesian stiffness.
- Test whether different multirotor configurations produce the stiffness magnitudes and directions predicted by the model.
- Investigate relevant effects neglected by the current model, such as cable elasticity, damping, and sagging.
- Select multirotor positions that achieve desired stiffness characteristics.
- Demonstrate stiffness shaping in a task such as collision-tolerant transportation or peg-in-hole insertion.
Expected outcomes
- A cooperative multirotor platform carrying a cable-suspended load.
- An experimental method for measuring the load stiffness.
- Experimental validation and, if needed, extension of the existing model.
- A method for shaping stiffness through multirotor repositioning.
- A real-world demonstration of the benefits and limitations of passive stiffness shaping.
Required or preferred skills
- Background in dynamics, control, and mechanics.
- Experience with MATLAB/Simulink, Python, C++, or ROS.
- Interest in multirotors, cooperative robotics, and physical interaction.
- Experience with motion capture, force sensing, or experimental robotics is beneficial.
Supervisors
- Antonio Franchi
- Amr Afifi
- Chiara Gabellieri
Reference
- [1] Passive Stiffness Shaping in Cable-Suspended Aerial Manipulation via Movable Compliant Anchors, Antonio Franchi and Amr Afifi, arXiv:2609.40102. Preprint.