SO101 Follower

SO101FollowerCfg configures The Robot Studio’s SO101 follower: a five-axis arm and one actuated gripper jaw. The canonical catalog ID is SO101Follower.

embodichain data download --name SO101FollowerAssets
embodichain preview-robot --robot SO101Follower --renderer fast-rt

For browser joint controls, add --viser. Native DexSim rendering displays the yellow printed parts and dark STS3215 housings; Viser uses simplified colors.

Usage and control parts

from embodichain.lab.sim import SimulationManager, SimulationManagerCfg
from embodichain_robots import SO101FollowerCfg

sim = SimulationManager(SimulationManagerCfg(headless=True))
cfg = SO101FollowerCfg.from_dict({})
robot = sim.add_robot(cfg)
sim.prepare()

arm_ids = robot.get_joint_ids("arm")
gripper_ids = robot.get_joint_ids("eef")

Control part	Independent joints
arm	shoulder_pan, shoulder_lift, elbow_flex, wrist_flex, wrist_roll
eef	gripper

There are six independent control DOFs and no mimic followers. The base is fixed; self-collision is disabled by default. Initial joint positions are zero in the source’s new calibration convention. The gripper is a revolute joint in radians; LeRobot’s normalized 0..100 gripper command is not a simulation joint position and requires an explicit mapping.

Kinematics and frames

The simulation and build_pk_serial_chain() use the same official so101_new_calib.urdf component, retaining all asset-defined names.

Chain	Root	End	DOFs
arm	base_link	gripper_frame_link	5
eef	gripper_link	moving_jaw_so101_v1_link	1

The arm ends at the source’s fixed gripper frame, including its authored TCP translation and rotation. The jaw chain is local to the gripper body. PytorchSolverCfg supplies arm FK and DLS position-only IK: five arm joints cannot satisfy every arbitrary 6D target pose. The jaw has no IK solver.

Dynamics and provenance

The preset pins The Robot Studio’s SO-ARM100 repository at commit a758567c3978dfeefe282ede0500085a48fe8f78. Its unmodified URDF, thirteen mesh files, motor-reference XML, README and Apache-2.0 license are cached by SO101FollowerAssets. Every file has a pinned SHA256. The first construction requires network access; later constructions verify and reuse the revision-specific cache. EMBODICHAIN_DATA_ROOT selects its root.

The seven physical links retain their source CAD mass, COM and full inertia tensor; the preset does not scale or replace them. Their total mass is approximately 0.732006 kg, excluding the negligible dummy TCP link. The source’s fixed dummy TCP link has zero inertia; DexSim applies its normal small-inertia fallback to that frame while retaining the seven physical links.

Motor parameters follow the official joints_properties.xml, which adapts STS3215 simulation properties from Open Duck Mini. They are simulation references, not hardware-identified parameters or guaranteed servo specifications. Actual torque depends on the servo voltage/model.

Joint property	Default	Source / interpretation
Drive type	force	Torque-based position/velocity drive
Position gain	17.8 N·m/rad	XML position actuator kp
Velocity damping	0.60 N·m·s/rad	XML joint damping, represented as drive damping for zero-velocity position holds
Friction	0.052	XML frictionloss; interpretation/enforcement depends on backend
Armature	0.028 kg·m²	XML joint-space artificial inertia
Maximum effort	3.35 N·m	XML actuator forcerange, replacing the URDF’s generic 10 N·m limit
Maximum velocity	10 rad/s	Published URDF limit
Position limits	Source URDF	Retains the pinned model’s calibration offsets

Standard overrides remain available:

cfg = SO101FollowerCfg.from_dict(
    {"joint_drive_props": {"max_effort": 1.6, "stiffness": 20.0}}
)

Choose hardware-specific limits separately when connecting a real arm. The upstream reference’s passive damping and this drive’s damping are equivalent for zero-velocity position holds; nonzero velocity-target control has different semantics. The preset does not simulate the optional upstream backlash joints.