If Michelangelo had been born with a soldering iron in one hand and a robotics textbook in the other, he might have
come up with something very close to RoboCut – a dual-wielding robot that uses a warped, heated wire to carve smooth,
organic 3D shapes out of foam. First featured on Hackaday, this clever machine looks like a sci-fi sculptor, slowly
revealing bunnies, boat hulls, and complex surfaces from unassuming blocks of expanded polystyrene. It is part
robotics demo, part digital fabrication experiment, and part “wait, how is that even possible?” moment.

Under the hood, RoboCut combines a collaborative dual-arm robot, a flexible heated rod, and some serious kinematics
and path-planning software. Instead of the usual straight hot wire that can only do ruled surfaces and basic profiles,
this setup actively bends the cutting tool while it moves through the foam. The result? Concave curves, swooping
surfaces, and intricate 3D forms that traditional hot-wire foam cutters simply cannot manage in a single pass.

In this article, we will break down how hot-wire foam cutting works, what makes this dual-arm robot different, where
this technology could be used in the real world, and what lessons makers, engineers, and designers can borrow if
they want to experiment with robotic foam carving themselves.

From Simple Hot-Wire Cutters to RoboCut

How traditional hot-wire foam cutting works

Classic hot-wire foam cutting is one of the simplest digital-fabrication tricks around. You pass an electric current
through a resistive wire, the wire heats up, and as it’s pulled through foam it melts a narrow path. That path is
usually silky smooth, with almost no dust – a huge win compared with sawing or sanding foam, which tends to coat your
entire shop (and your lungs) in staticky white snow.

For decades, builders of model airplanes, architectural mock-ups, theater props, and packaging forms have relied on
this technique. Manual cutters use a tensioned wire stretched between two supports, while CNC systems move either the
wire or the foam block along a programmed path. Many 4-axis CNC hot-wire cutters move two ends of the wire
independently, enabling tapered shapes like aircraft wings or fuselages cut from polystyrene billets.

The catch is that the wire must stay straight. You can move the endpoints, but the segment between them is basically
a straight line. That gives you ruled surfaces and simple transitions, but not true freeform 3D geometry. If you want
concave shapes or complex curvature, you usually need multiple cuts, clever jigs, or a lot of hand finishing.

The limits of straight-wire CNC foam cutters

Industrial hot-wire CNC machines have become powerful tools for signage, insulation, and aerospace prototyping.
Commercial systems can handle multi-meter-long foam blocks and four or more axes, cutting letters, architectural
cornices, aircraft parts, and custom packaging inserts. Still, all of this is ultimately constrained by that straight
wire. You can tilt, twist, and translate it, but you’re always sweeping a line through the material.

That’s where RoboCut breaks the mold. Instead of accepting the straight-line limitation, the researchers asked a
deceptively simple question: what if the wire itself could curve on demand?

Meet RoboCut: A Dual-Arm Foam-Sculpting Robot

Dual arms, warped wire

RoboCut is built around an ABB YuMi collaborative robot – the same kind of dual-arm cobot often used for small
assembly tasks. Each arm offers seven degrees of freedom, roughly similar to a human arm with shoulder, elbow, and
wrist joints. Instead of holding screwdrivers or parts, though, the robot grips the ends of a flexible, 1-millimeter
rod that serves as the heated cutting tool.

When current flows through the rod, it heats up enough to melt a narrow channel through expanded polystyrene foam.
Because each arm can move independently, the system can not only position the rod in 3D space but also bend it into
controlled curves. Think of it like two hands shaping a thin metal ruler while simultaneously sweeping it through a
block of material.

The foam block is stationary; all the magic happens by coordinating these two arms and the flexible tool between
them. With the right motions, the robot can carve concave and convex surfaces and transition smoothly between shapes
without re-clamping or re-orienting the stock.

Why the warped wire changes everything

Traditional hot-wire CNC cutters approximate complex shapes via many straight-line passes or multi-step cutting
strategies. RoboCut effectively upgrades the cutting tool from a simple line to a dynamically controllable curve. As
the robot sweeps the heated rod through the foam, it behaves more like a continuously deformable spline than a rigid
line segment.

In practice, this means you can carve 3D test models like the Stanford bunny or intricate organic parts in just a
handful of carefully planned passes. Instead of thinking in terms of “slices” or “profiles,” the path-planning
software focuses on which regions of foam need to be removed and how the curved rod can be guided to remove them
efficiently while staying within safe bending limits.

Inside the Kinematics: Bending Without Breaking

Fourteen degrees of freedom and one squishy tool

Coordinating two 7-DOF arms with a flexible rod between them is not trivial. Each pose of the tool depends on both
endpoints and the forces they apply. Bend it too far and the rod yields permanently or snaps. Bend it too little and
you can’t achieve the target geometry.

The RoboCut system models the rod as a deformable curve and uses optimization algorithms to find joint trajectories
that produce the desired bend while keeping stresses within allowable limits. On top of that, the planners must
account for collisions with the foam block and ensure that the heated rod passes through the right regions in the
right order to gradually reveal the final shape.

Because each pass removes a finite thickness of foam, the surface is approached progressively. The software selects
sequences of “sweeps” that remove as much material as possible in each step without compromising accuracy or tool
safety. The final surface error can be on the order of a couple of millimeters over most of the part – impressive for
such a nontraditional tool.

Balancing speed, accuracy, and surface quality

Like all digital fabrication processes, there is a trade-off between cutting speed and precision. Move the robot too
fast and the rod may flex unpredictably or leave rough trails where the foam didn’t fully melt. Move it too slowly
and you waste time and risk excessive heating.

In practice, a system like RoboCut is tuned for specific foam densities and rod temperatures. The researchers focused
on expanded polystyrene, which melts cleanly and is reasonably forgiving. With the right parameters, you get smooth
surfaces that require little post-processing, especially compared with routing or sanding.

What Can You Make With a Warped-Wire Robot?

Prototypes, props, and architecture

Foam is the “sketchbook material” of many industries. Architects slice it into building massing models, film and
theater crews turn it into rocks and set pieces, and product designers use it for quick mock-ups. A dual-wielding
foam robot could accelerate all of that.

Imagine quickly carving a family of architectural façade panels with subtle curvature, or generating custom sculptural
forms for an art installation. Instead of sculpting by hand or building complex molds, designers can go straight from
a 3D model to a carved block of foam that can be coated, cast, or simply displayed as-is.

Aerospace and aerodynamic shapes

Hot-wire cutting has a long history in aviation, particularly for wing cores and fuselage forms. By bending the wire,
RoboCut can create more complex airfoil transitions, winglets, and fairings in one go. Concave curves and blended
surfaces that would usually require multiple cuts or machining steps become feasible in a single, continuous motion.

Beyond hobby aircraft, similar techniques could be useful for wind-tunnel models, turbine blade prototypes, and
aerodynamic housings for drones or small robots. Foam models are fast to iterate and relatively cheap, making this a
compelling workflow for early-stage design work.

DIY Inspiration: Bringing Robotic Foam Carving to the Home Shop

Start simple with a manual hot-wire cutter

Let’s be honest: most of us do not have a dual-arm ABB cobot sitting in the garage. But the ideas behind RoboCut can
still influence more modest builds.

A good first step is to build a simple hot-wire foam cutter using nichrome wire, a low-voltage power supply, and a
sturdy frame. Even a basic bow-style cutter lets you understand how temperature, feed rate, and wire tension affect
the cut. You quickly learn to let the wire do the work and avoid forcing it through the foam, which can lead to
ragged edges or broken wires.

Scaling up to CNC and small robots

Once you are comfortable with manual cutting, it’s natural to look at CNC options. Many hobbyists build 4-axis
hot-wire foam cutters using stepper motors, threaded rods or belts, and open-source control software. These machines
can cut wing cores, letters, and simple 3D forms with impressive accuracy.

Taking the next leap toward something RoboCut-like would mean using a small robotic arm or even two arms, plus a
flexible cutting element. Off-the-shelf hobby robots do not usually have the stiffness, precision, or control
bandwidth of an industrial cobot, but they are great platforms for experimentation. Even partial control over the
wire’s curvature – for example, by adding an intermediate guide or a spring-loaded point – can expand the range of
surfaces you can carve.

Safety, Materials, and Practical Considerations

As fun as hot-wire cutting is, it does come with safety and environmental considerations. Heating expanded
polystyrene and similar foams releases fumes that you definitely do not want to inhale in a closed room. Any robot or
CNC setup should be paired with good ventilation or fume extraction and, ideally, a filtered enclosure.

Temperature control is another concern. The cutting rod or wire should be just hot enough to melt a clean kerf through
the foam, not glowing red-hot. Overheating can char the material, widen the cut, and shorten the life of the tool.
For robotic systems, this becomes part of the control loop: current, temperature, and feed rate all interact.

Finally, there is the question of what happens after the foam is carved. In many applications, the foam is just a
“lost” pattern for casting, laminating, or vacuum forming. In others, it becomes part of the final product and must
be protected with coatings to improve durability and reduce environmental impact. Designing with end-of-life in mind
is especially important when working with plastic-based foams.

Hands-On Experiences With Robotic Foam Carving

To really appreciate a system like RoboCut, it helps to think about what it feels like to work with hot-wire foam
cutting in general. If you have ever built a foam wing or carved a prop by hand, you know the strangely satisfying
feeling of the wire sliding through the material, leaving behind a clean, glossy surface. Now imagine handing that
task to a robot – and then asking it to do curves you would struggle to capture even with careful hand sculpting.

In a makerspace context, a robotic foam-carving setup quickly becomes a magnet for collaborative projects. One person
wants to prototype a freeform chair shell, another wants a giant mascot head, and someone else inevitably shows up
with a 3D model of a dragon. The workflow tends to follow the same pattern: rough 3D design in CAD, export to the
robot’s planning software, simulate the toolpaths to make sure the wire does not exceed its bending limits, and then
watch, slightly mesmerized, while the robot sweeps its “hot ribbon” through the foam block.

The first few cuts rarely go perfectly. Maybe the rod flexes a bit more than expected on tight curves and leaves a
shallow groove, or the foam density is inconsistent and you end up with minor surface ripples. These imperfections
become feedback. You tweak the cutting speed, adjust temperatures, or break a complex surface into a couple of
overlapping passes. After a few iterations, the machine starts to feel less like a mysterious black box and more like
a very patient, very precise apprentice.

One of the most interesting discoveries people report is how much the robot changes the design process itself.
Because you can carve relatively large shapes quickly, you are more willing to experiment. A design that would have
felt too risky or time-consuming to sculpt by hand suddenly becomes a one-evening test. You might try more radical
curvature on a winglet, or a more sculptural facade panel, simply because the barrier to trying is so much lower.

There is also a subtle creative tension between digital perfection and material reality. On screen, the model is
flawless. In foam, tiny deviations – a degree or two of extra bend here, a slightly uneven melt there – give the
object a physical personality that is hard to capture in pure simulation. Instead of fighting that, many designers
lean into it, treating the robot not just as a duplicating machine but as a collaborator with its own “handwriting.”

For teams working on more serious applications, like aerospace or prosthetics, the experience is different but just
as transformative. Having a robot carve repeatable foam forms means you can iterate fit, ergonomics, or aerodynamics
rapidly while keeping the manual finishing and human craftsmanship where it matters most. The robot handles the heavy
lifting – the big cuts, the consistent geometries – and humans focus on fine-tuning and final detailing.

Whether you are a hobbyist cutting your first shaped wing or an engineer testing complex geometries, the lesson from
systems like RoboCut is clear: give robots smarter tools, and they do not just automate old workflows – they open the
door to entirely new ones.

Conclusion: Why This Dual-Wielding Robot Matters

The dual-wielding robot from Hackaday’s spotlight is more than a neat lab demo. It is a glimpse of how combining
flexible tools, clever physics models, and multi-robot coordination can unlock fabrication capabilities that do not
fit neatly into existing categories like “3D printing” or “CNC machining.” By turning a straight hot wire into a
dynamically warped cutting spline, RoboCut bridges the gap between sculpting and automation.

For makers and engineers, the takeaway is both inspiring and practical. You do not need an industrial cobot to start
exploring these ideas, but paying attention to projects like this can reshape how you think about tools, materials,
and motion. Foam may be cheap and humble, but in the hands of a dual-arm robot with a warped wire, it becomes the
canvas for a whole new kind of digital craft.

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