Robot Model: Limit Documentation

Joint map

The joint ordering and naming on this page is the reference. Every consumer uses exactly this table.

Joint ordering rules

Twelve joints, IDs 1–12. The ID is a deterministic index derived from a fixed two-level rule:

Legs are numbered first: Left Front → Right Front → Left Rear → Right Rear (front row before rear row; within a row, left before right).
Within each leg, joints are numbered body-to-foot: hip → upper → lower.

Master joint map

joint_id	Joint name	Leg	Joint	Motion
1	`lf_hip`	Left Front	hip	upper swing, sagittal plane
2	`lf_upper`	Left Front	upper	upper → lower bend
3	`lf_lower`	Left Front	lower	lower → foot pitch
4	`rf_hip`	Right Front	hip	upper swing, sagittal plane
5	`rf_upper`	Right Front	upper	upper → lower bend
6	`rf_lower`	Right Front	lower	lower → foot pitch
7	`lr_hip`	Left Rear	hip	upper swing, sagittal plane
8	`lr_upper`	Left Rear	upper	upper → lower bend
9	`lr_lower`	Left Rear	lower	lower → foot pitch
10	`rr_hip`	Right Rear	hip	upper swing, sagittal plane
11	`rr_upper`	Right Rear	upper	upper → lower bend
12	`rr_lower`	Right Rear	lower	lower → foot pitch

Name grammar

Joint names are always {leg}_{joint}:

leg ∈ { lf, rf, lr, rr }
joint ∈ { hip, upper, lower }

Body frame

Axis	Direction
+x	forward (nose)
+y	right (left side is −y)
+z	up

base_link origin: robot center, at the hip joint height (z = 0 plane).
All 12 joints rotate about the body Y axis (0, 1, 0): lateral, planar legs; no roll or yaw at any joint.
Zero pose: all angles 0 → legs straight down, feet at rest positions.
Units: documentation and datasheets in mm; URDF/ROS in m.
Standard: the body frame follows the ROS REP 103 convention for transforms and xyz coordinates.

Hip origins & foot rest positions

Hip joint origin in base_link (m): directly above the foot rest position:

Leg	Hip x	Hip y	Foot z (rest)
Left Front	0.130	−0.105	−0.185 m (−185 mm)
Right Front	0.130	+0.105	−0.185 m
Left Rear	0.240	−0.105	−0.185 m
Right Rear	0.240	+0.105	−0.185 m

Foot rest positions, body frame (mm): Left Front (130, −105, −185) · Right Front (130, +105, −185) · Left Rear (240, −105, −185) · Right Rear (240, +105, −185).

Per-joint kinematics

Parameter	Value	Status
L1 (hip → upper, upper)	0.100 m	current estimate: split of the 185 mm rest reach
L2 (upper → lower, lower)	0.085 m	current estimate: L1 + L2 = 0.185 m matches documented foot drop
Lower → foot	fixed joint, not actuated	the chain is hip → upper → lower → foot
Joint axes	(0, 1, 0) all legs	per the body frame above

Limits / effort / velocity per joint type (same for all four legs):

Joint	Limit (rad)	Limit (°)	Max effort	Max velocity
hip	±1.20	±68.8°	10 N·m	10 rad/s
upper	±1.57	±89.9°	10 N·m	10 rad/s
lower	±0.60	±34.4°	5 N·m	10 rad/s

Telemetry wire mapping

Commands (JointTarget) and samples (JointSample) both address joints by the joint_id from the master map above. There is no second numbering.

Field	Type	Meaning
`id` / `joint_id`	uint	1–12, decoded per the master map (`lf_hip` … `rr_lower`)
`pos` / `pos_rad`	float	target/actual angle, rad, zero pose per body frame
`vel` / `vel_rads`	float	target/actual angular velocity, rad/s
`kp`, `kd`	float	PD gains
`max_tq`	float	per-joint torque clamp, N·m
`tq_nnm`, `cur_a`, `temp_c`, `flags`, `fault_code`	n/a	sample-side telemetry (50 Hz)

Gait pairing (trot)

Trot drives the two diagonal leg pairs in alternation:

Pair A: Left Front + Right Rear: joint IDs {1, 2, 3, 10, 11, 12}
Pair B: Right Front + Left Rear: joint IDs {4, 5, 6, 7, 8, 9}