Import your own robot

Import URDF File… is how every robot gets into Blender — a client's machine, an in-house design, something a manufacturer published, or one of the 186 the catalog pointed you at and you cloned. Kinema does not download robot descriptions; it reads the files you already have.

What you can import

Kinema reads three formats. See URDF, xacro and MJCF for what each one is.

Extension	Format
.urdf	URDF, the common robot description format
.xacro	A URDF template, expanded on import
.xml	Usually MJCF (MuJoCo); occasionally URDF

.xml is ambiguous, so Kinema looks inside

MJCF and URDF both commonly use .xml, so the extension decides nothing. Kinema reads the opening bytes of the file and picks the right reader. You do not have to tell it which you have.

Import it

Kinema panel → Import URDF File…, then pick your file. The file browser filters to the three extensions above.

The options sit in the sidebar of the file browser, and the same set is in the sidebar's Import Options panel:

Option	Default	What it does
Bone Size	0.0 (auto)	Display size of the joint bones. Auto scales to the robot.
Enforce Joint Limits	on	Apply the real range-of-motion limits from the file
Import Meshes	on	Load the visual geometry and parent it to the rig
Import Collision Meshes	off	Also load the planner's coarse hulls, into a hidden collection
Create TCP	on	Add a tool centre point at the end of the chain
Xacro Arguments	empty	Substitutions for a .xacro, as name:=value — see xacro files

When to change them

Bone Size — leave on auto unless the bones are visually swamping a very small robot (a gripper, a finger) or vanishing inside a very large one. It is display only; it changes nothing about the kinematics.

Enforce Joint Limits — turn off only when you know the file's limits are wrong or missing, and you would rather have free rotation than a wrong constraint. With it off, IK can produce poses the real machine cannot reach.

Import Meshes — turn off for a fast look at the kinematic structure alone, or when the meshes are enormous and you only need the skeleton. You can always re-import.

Import Collision Meshes — leave off unless you need them. These are the coarse hulls a motion planner sweeps, not what the robot looks like: boxes and cylinders where the visual mesh has fillets and bolt heads. They arrive in a ⟨robot⟩ Collision collection that starts hidden, so they cost you nothing on screen, but on a large cell they double the object count. Useful when checking why a robot fails a reach.

Create TCP — leave on. Without a TCP there is nothing for an IK target to attach to, and you would have to create one by hand.

Where meshes come from

URDF files refer to their meshes by path, very often using a package:// URL that assumes a ROS workspace you do not have. Kinema resolves these by searching the file's own directory tree, which handles the overwhelming majority of real-world robot packages without configuration.

If meshes do not appear, the usual causes are:

• You have the .urdf but not the meshes/ folder next to it — download the whole package, not just the description file
• The meshes are in a format Blender cannot read
• The paths point outside the tree entirely, to an absolute location on someone else's machine

The rig itself is still correct in all three cases. Joints, limits and IK work fine on a robot with no visible geometry — you just cannot see it.

COLLADA meshes

Blender 5.0 removed its own .dae importer, and a great many robot packages ship COLLADA meshes. Kinema brings that support back: it handles .dae files during robot import automatically, and also adds File → Import → COLLADA (.dae) for importing them on their own.

xacro files

A .xacro is a URDF with macros, variables and conditionals in it — the format manufacturers use to describe a family of robots in one file. Kinema expands it on import, so you can point straight at the .xacro without generating a URDF first.

Arguments

One file describing a family of robots has to be told which one. Those are xacro arguments, and some descriptions will not render without them — Universal Robots' ur.urdf.xacro is the common example: it uses $(arg name) on the line above the one that declares it, so the default never applies and the file simply does not load until you supply a name.

Select a .xacro in the file browser and Kinema lists the arguments it declares, with their defaults, so you can see what it wants before importing rather than after failing. Fill in the Xacro Arguments field using the same syntax the xacro command line takes:

name:=ur5e ur_type:=ur5e

Get one wrong and the error names the argument xacro asked for and lists the rest, instead of the bare Undefined substitution argument name the underlying tool produces.

The arguments are stored on the rig, because the solver reloads the description later to build its own model — a rig that imported cleanly and then quietly lost the good solver would be a poor trade.

Packages a xacro reaches for

A xacro refers to other packages by name: a KUKA arm pulls its materials from a sibling kuka_resources. Kinema indexes the repository containing the file you picked, which covers the usual case of one checkout holding everything.

When the pieces live in separate clones side by side, add the directory above them to Package Search Paths.

MJCF files

MuJoCo's format. Kinema reads the kinematic subset it needs: bodies, joints, limits and visual geometry.

Two things to know:

• MJCF robots often ship OBJ meshes without their companion .mtl files. Blender's OBJ importer prints errors about this. They are harmless — MJCF carries its own colours.
• The solver reads URDF internally, so an MJCF rig is bridged by writing the parsed structure back out as a minimal URDF. This works, and is one more moving part; if an MJCF rig behaves oddly where a URDF one does not, that bridge is the first place to look.

Unsupported joints

Ball joints are rejected. A 3-DoF spherical joint has no honest single-axis bone equivalent, and pretending otherwise would give you a control that lies about what the machine does. A robot containing one will not import.

This is rare — exactly one catalog robot (Cassie) is affected. Everything else parses.