Biologically inspired drone immobilisation
Finding the most effective way to stop a drone, through 109 experiments
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Rendered concept visual: an interceptor drone approaching a target drone entangled in cord under a parachute
- Client
- Master's thesis (MSc), 30 ECTS · Technical University of Denmark
- Context
- Supervisors: Torben Anker Lenau, David Bue Pedersen
- Year
- 2026
- Role
- Sole author
- Grade
- 12
- Tools
- Build-Measure-Learn loops · Biologically inspired design · Affinity mapping · Semi-structured interviews · High-speed video (240 fps) · Laser tachometer · FDM printing
- Contribution
- Sole author, designed, built and ran all 109 experiments
Master's thesis. Illegal drone incidents in Denmark rose from 62 in 2023 to 206 in 2024, however Danish police still have no local counter-drone tool other than a firearm, and this means that they usually decline to act, since the available response is either too slow or disproportionate to the threat. I ran 109 experiments against a spinning drone propeller in order to find out what physically stops a drone without destroying it, and then validated the best candidates on a free-flying FPV drone. The answer turned out to be a frayed rope, with five out of five instant stops on the rig, confirmed in flight.
Why this question
The project started after the Copenhagen airport incident in September 2025, and the reason for looking at a physical solution rather than an electronic one is that jammers are being outpaced by autonomous drones and are already defeated by fibre-optic control in armed conflict. This leaves a physical gap, since there is currently no non-destructive way to bring down a 250 g–2 kg quadcopter regardless of how it is being flown. In order to establish who is responsible for what, and what a usable tool would actually need to do, I interviewed 11 people across Danish police, military and emergency management, including a tour of a Danish police district's drone equipment, and used affinity mapping on the results.
How I tested
The rig was a brushless drone motor with a 7-inch propeller and an ESC on PWM control, with RPM verified by laser tachometer at roughly 10,000, which is equivalent to a hovering camera drone. Test objects were dropped into the spinning propeller and measured on RPM change, clean stops and entanglement, alongside slow-motion video at 240 fps. It is important to note that every test object began as a written, falsifiable hypothesis, and that the three Build-Measure-Learn loops covering 109 experiments were deliberately run for breadth rather than statistical significance, since only the promising results were repeated.
The error I had to fix mid-way
The acrylic safety enclosure turned out to be creating turbulence and causing test objects to ricochet off the walls back into the propeller, which was inflating the results. This is due to the enclosure restricting the airflow and giving ejected objects nowhere to go, and remounting the rig on a wooden pallet solved both problems at once. Furthermore every earlier result had to be re-read against that, since the ones recorded before the change could not be trusted in the same way.
What the experiments found
Phase 1, at 18 experiments, killed my starting assumption, since prior work suggested that looped strings were effective and that more loops would be better, however the loops correlated negatively with entanglement due to thrusting each other away on contact. The one exception was a spiderweb-inspired hexagon, which entangled and stopped the motor cleanly. Phase 2, at 38 experiments, then rejected its own hypothesis, as rigid hexagonal frames reached 75% entanglement at 6 of 8 but produced no full stops, only RPM reduction correlating with frame diameter, while magnets and fishing hooks did nothing at all. Here the real finding came by accident, since a magnet fell below the rig with twine attached above it, and the weight stopped the propeller flinging the string clear, which locked the motor. This became the drop-line principle. Furthermore the phase produced the contrast that mattered most, as 0.11 mm braided line entangled 60% of the time but was always cut, while 2 mm twine entangled only 9% of the time and stopped the motor nearly every time it did.
The resolution
Phase 3 reframed the problem after the Cape sundew, which catches insects with a fast adhesive and then closes slowly and mechanically, and instead of hunting for one optimal string I tested a two-part entangler-plus-stopper. This worked, however the standout result was simpler, since a 6 mm rope unravelled at the end stopped the motor in 5 of 5 trials, instantly, with no ricochet and even at full throttle, while a single strand from the same rope did nothing. This is due to the many fine frayed strands acting as the entangler and presenting too many contact points for the propeller to clear, which drags the solid rope into the motor where friction stops it.
Validating on a real drone
Static-rig results mean little if they do not transfer, so I removed the enclosure, tested from a 2.5 m staircase, and then tested against a custom FPV quadcopter in free flight, capable of 100 km/h at roughly 12,000 RPM. The frayed rope and the braided-line-plus-twine combination both stopped the propulsion instantly, and the frayed rope entangled two propellers at once. However the most useful finding was not about the material at all, since hitting the drone by hand was hard, and this means that area of effect matters more than elegance, which is what drove the concept toward an interceptor drone delivery system with a parachute release, so that the target descends under control instead of falling.
Design requirements derived
The entangler needs high shear strength, a small diameter below 0.3 mm and high flexibility, while the stopper needs high shear strength, high tensile strength, a larger diameter above 2 mm and a high-friction surface. Furthermore the delivery method needs a significant area of effect, since that turned out to be the limiting factor rather than the material itself.
Limits
It is important to note that the static rig was bolted down, and this means that the destabilisation principles could not be verified until the free-flight tests. Furthermore the sample sizes were small by design, since the loops were run for breadth, and the concept seems to have a real weakness against agile drones with collision avoidance and motor guards.
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Brushless motor and propeller test rig inside a clear acrylic enclosure
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Three-panel bench test: frayed line approaching, entangling and releasing from a mounted propeller
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Digital affinity map clustering interview findings into themes: counter-drone measures, detection, threats, regulation
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Top-down photo of the FPV quadcopter with a frayed blue line entangling two propellers
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Four-panel diagram of the interceptor aiming, releasing twine, entangling the target and detaching by parachute