Hardware

What	How many	Interface
Leg motors	12	CAN (buses 0-1)
IMU	1	I2C bus 8

The arms, torso, hands, and head are defined but not enabled yet.

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Motors

30 DOF total, but only the legs (12 motors) are enabled right now.

Part	Motors	CAN Bus
Left Leg	6	0
Right Leg	6	1
Left Arm	6	2 (disabled)
Right Arm	6	3 (disabled)
Torso	2	4 (disabled)
Hands + Head	4	5 (disabled)

Left Leg (CAN Bus 0)

ID	Name	CAN ID	Joint	Min	Max	Max Torque
0	L_Hip_Pitch	0x01	Hip flexion/extension	-120°	+57°	120 Nm
1	L_Hip_Roll	0x02	Hip abduction/adduction	-45°	+45°	90 Nm
2	L_Hip_Yaw	0x03	Hip rotation	-45°	+45°	60 Nm
3	L_Knee_Pitch	0x04	Knee flexion/extension	0°	+86°	70 Nm
4	L_Ankle_Pitch	0x05	Ankle dorsi/plantarflexion	-70°	+70°	30 Nm
5	L_Ankle_Roll	0x06	Ankle inversion/eversion	-70°	+70°	30 Nm

Right Leg (CAN Bus 1)

ID	Name	CAN ID	Joint	Min	Max	Max Torque
6	R_Hip_Pitch	0x07	Hip flexion/extension	-57°	+120°	120 Nm
7	R_Hip_Roll	0x08	Hip abduction/adduction	-45°	+45°	90 Nm
8	R_Hip_Yaw	0x09	Hip rotation	-45°	+45°	60 Nm
9	R_Knee_Pitch	0x0A	Knee flexion/extension	-86°	0°	70 Nm
10	R_Ankle_Pitch	0x0B	Ankle dorsi/plantarflexion	-70°	+70°	30 Nm
11	R_Ankle_Roll	0x0C	Ankle inversion/eversion	-70°	+70°	30 Nm

Note: Left and right leg angles are mirrored. Left knee extends positive, right knee extends negative.

Control Gains

The RL policy uses these PD gains:

Joint Type	Kp (N·m/rad)	Kd (N·m·s/rad)
Hip Pitch	257.4	5.0
Hip Roll	394.8	5.0
Hip Yaw	135.4	5.0
Knee	130.3	5.0
Ankle Pitch	93.2	5.0
Ankle Roll	93.2	5.0

Action Scaling

Policy outputs get scaled before becoming motor commands:

Joint	Offset (rad)	Scale
Hip Pitch	0.0	0.140
Hip Roll	0.0	0.068
Hip Yaw	0.0	0.133
Knee	0.0	0.173
Ankle Pitch	0.0	0.116
Ankle Roll	0.0	0.116

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CAN Buses

6 CAN buses, but only 0 and 1 are enabled (legs).

Bus	Thread	CPU	Motors	Status
CAN0	can0	6	Left leg (0-5)	Enabled
CAN1	can1	5	Right leg (6-11)	Enabled
CAN2	can2	5	Left arm (12-17)	Disabled
CAN3	can3	5	Right arm (18-23)	Disabled
CAN4	can4	6	Torso (24-25)	Disabled
CAN5	can5	6	Hands + Head (26-29)	Disabled

Protocol

500 kbps, standard SocketCAN.

Command Frame (Host → Motor)

Byte	Field	Type	Description
0-3	target_pos	float	Target position (rad)
4-7	target_vel	float	Target velocity (rad/s)
8-11	target_torque	float	Feedforward torque (Nm)
12-13	kp	uint16	Position gain (scaled)
14-15	kd	uint16	Velocity gain (scaled)

Feedback Frame (Motor → Host)

Byte	Field	Type	Description
0-3	position	float	Measured position (rad)
4-7	velocity	float	Measured velocity (rad/s)
8-11	current	float	Phase current (A)
12-13	temperature	int16	Motor temp (0.1°C units)
14-15	error_code	uint16	Motor error flags

Update Rates

Bus	Rate
CAN0-1	200 Hz
CAN2-5	250 Hz (disabled)

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IMU

BNO085 on I2C bus 8. Runs at 500 Hz with built-in 9-DOF sensor fusion.

Thing	Value
Sensor	BNO085
Bus	/dev/i2c-8
Address	0x4A
Rate	500 Hz
Protocol	SHTP via official CEVA SH2 library

What It Outputs

Field	Type	Unit	Description
quat[4]	float	-	Orientation quaternion [w,x,y,z]
ang_vel[3]	float	rad/s	Angular velocity in body frame
accel[3]	float	m/s²	Linear acceleration (gravity removed)
gravity[3]	float	-	Normalized gravity vector pointing DOWN (0,0,-1 when upright)

Calibration

BNO085 handles calibration internally using Dynamic Calibration Data (DCD). No manual calibration required.

Error Recovery

The driver automatically recovers from I2C errors and sensor resets:

• I2C failure → HAL sends soft reset, sensor reinitializes

• SH2_RESET event → Driver re-enables all configured sensors

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Coordinate Frames

All frames follow ROS REP-103: X forward, Y left, Z up (right-handed).

Body Frame

              Z (up)
              │
              │    X (forward)
              │   /
              │  /
              │ /
              └──────── Y (left)

        Top-down view:
              X (forward)
              ▲
              │
        ┌─────┼─────┐
        │     │     │
  Y ◄───┼─────●─────┼  (robot facing up)
        │           │
        │   L   R   │
        └───┼───┼───┘
            │   │
           legs

IMU → Body Frame

The IMU is mounted so its axes align with the body frame.

IMU Output	Body Frame	Description
ang_vel[0]	ωx	Roll rate (rotation about X)
ang_vel[1]	ωy	Pitch rate (rotation about Y)
ang_vel[2]	ωz	Yaw rate (rotation about Z)
gravity[0]	gx	Gravity X component
gravity[1]	gy	Gravity Y component
gravity[2]	gz	Gravity Z component

Joint Sign Conventions

    Hip Pitch:   + = leg forward     - = leg backward
    Hip Roll:    + = leg outward     + = leg outward
    Hip Yaw:     + = toe outward     + = toe outward
    Knee:        + = extend          - = extend       ← MIRRORED!
    Ankle Pitch: + = toe up          + = toe up
    Ankle Roll:  + = sole outward    + = sole outward

Left/Right Mirroring

The legs are mirrored about the sagittal plane:

Joint	Left Leg (+)	Right Leg (+)
Hip Pitch	Leg forward	Leg forward
Hip Roll	Leg outward (left)	Leg outward (right)
Hip Yaw	Toe points left	Toe points right
Knee	Extend (straighten)	Flex (bend)
Ankle Pitch	Toe up	Toe up
Ankle Roll	Sole faces left	Sole faces right

Key point: Knee signs are opposite! Left knee extends positive, right knee extends negative.

For symmetric standing: L_Knee = -R_Knee

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Source Files

File	What it does
source/hal/hardware/motor/motor_map.h	Motor IDs, limits, gains
source/hal/can/can_interface.c	CAN bus interface
source/hal/hardware/imu/bno085_driver.c	BNO085 driver
source/app/imu/imu_thread.c	500 Hz IMU thread