The 3D simulator
hp-sim-3d is the current application. It combines the 3D machine model, physics, controls, diagnostics, and visualization in the browser.
Open hp-sim-3dHangprinter Project / Simulation
The hp-sim Project
hp-sim is a physics simulation used to develop Hangprinter machines and their control software.
It brings machine geometry, cable mechanics, spool behavior, firmware, and calibration into repeatable experiments.
In one sentence: hp-sim runs a Hangprinter machine model and its control software together so that the same experiment can be repeated and compared.
01 / START WITH HANGPRINTER
THE MACHINE
A robot suspended and moved by lines
Hangprinter is an open-source cable-driven parallel robot. It moves a tool through a workspace using synchronized lines instead of a conventional gantry.
This makes large workspaces possible with relatively little fixed structure. It also means that the parts of the machine are closely connected. A change to one line, spool, anchor, motor, or control setting can affect the rest of the system.
Cable-driven parallel robots have many strengths, but the coupled mechanics are challenging to control. Physical experiments are slow to reset and difficult to compare.
02 / WHY HP-SIM EXISTS
THE SIMULATION
Test the whole system before changing the machine
A useful Hangprinter simulation must include more than the path of the tool. It must also include the machine that creates that path.
hp-sim models the physical machine together with its motion commands. This makes it possible to study whether an observed behavior comes from geometry, cable forces, spool buildup, firmware, or calibration.
A proposed change can first be tested under controlled conditions. The inputs, measured outputs, and starting state can stay the same between runs. The change can then be judged against a baseline.
03 / HOW AN EXPERIMENT WORKS
From a machine description to comparable results
Each stage adds one part of the real system. Together they form a repeatable simulation run.
- 01
Describe the machine
Define the anchors, moving parts, masses, spools, lines, and other physical properties.
- 02
Send motion commands
Use the same G-code and firmware behavior that will control a physical machine.
- 03
Simulate the response
Calculate how the motors, spools, lines, and rigid bodies affect one another over time.
- 04
Compare the result
Record the tool path and diagnostics, then repeat the experiment after changing one part of the system.
04 / PLACE IN THE LARGER PROJECT
The shared simulation for the physical projects
RefWinch, RefRig, and full-size Hangprinters address different physical scales. hp-sim provides a common place to test machine models, control software, and calibration methods used across them.
010203
RefWinch
A reference actuator for controlling one line length accurately.
RefRig
A compact reference machine for testing several winches together.
Hangprinter
The larger cable-driven machine and the project that connects the work.
SHARED DEVELOPMENT TOOL
hp-sim
Tests machine behavior, firmware, and calibration before or alongside work on physical hardware.
05 / THE CURRENT SIMULATOR
HP-SIM-3D
The project now runs in three dimensions
hp-sim-3d is the actively developed application. It models rigid assemblies, driven spools, cable paths, and machine motion in a 3D workspace.
The move from 2D to 3D is complete. Full inertia tensors, three-dimensional rigid-body motion, rotational degrees of freedom, and generalized 3D joints are implemented. Basic spool buildup is also implemented by winding line in layers.
Spool rotors currently use a specialized one-axis model that fits the required motion. A generic hinge can be added later if bearing reactions or off-axis rotor behavior need to be studied, but it is not a prerequisite for the present simulator.
Read the 3D implementation notes
06 / THE REST OF THE PROJECT
Several tools support the same experiment
The repository contains the active 3D application and the supporting work needed to connect physics, firmware, calibration, and tests.
Firmware integration
Klipper and a host build of ReprapFirmware can generate the motor commands. This lets experiments include real control software instead of an approximation of it.
Read the firmware notesCalibration
The autocal tools run calibration procedures against simulated machines. They can test geometry fitting, force settings, and measurement strategies before physical trials.
Read the calibration notesEarlier and supporting solvers
The repository also contains the 2D simulator, related JavaScript and Python physics work, tests, and an optional Warp implementation for CPU or GPU experiments.
Open the 2D simulator07 / CURRENT STATUS
The core simulation is in place
Current work builds on the completed 3D physics foundation. The focus is shifting toward physical HP5 design, verification, and larger experiment workflows.
IMPLEMENTED7
- Three-dimensional rigid-body motion and full inertia tensors
- Position-controlled and torque-controlled spool motors
- Cable slack, stretch, wrap, friction, and damping
- Basic spool buildup by winding line in layers
- Several machines running in the same simulation world
- Klipper and ReprapFirmware integration
- Automated calibration and repeatable quality checks
CONTINUING WORK4
- Use simulation results while designing and documenting the physical HP5 machine
- Verify more design decisions against physical measurements
- Make larger batches of experiments easier to run and compare
- Continue testing the complete system on more machine configurations
The latest discussion of spool buildup is in the June 2026 post on winch precision and design findings. Read the post
08 / CONTINUE FROM HERE
See the simulator or read the project notes
The 3D application is the best place to see the current work. The repository contains implementation details, tests, and development history.