Technician Curriculum

CAN is a two-wire differential serial bus. All nodes share the bus; each listens to every message and decides based on ID whether to act.

Arbitration is lossless: lower IDs win. This is why safety-critical messages are assigned low IDs.

The bus requires 120 Ω termination at each physical end. A missing or extra terminator is one of the most common sources of intermittent errors.

Connect a CAN sniffer to a T-junction — never break the bus during diagnosis.

Filter by node ID first, then by message type. Joint state messages are typically 0x100–0x1FF; commanded torques 0x200–0x2FF.

A node that stops transmitting but still ACKs is alive but faulted. A node that stops ACKing is powered down or disconnected.

Error-active: normal. Transient errors are logged but the bus recovers.

Error-passive: the node is generating errors but is being quiet about it. Check wiring and termination.

Bus-off: the node has disconnected itself. Power-cycle to recover, and investigate whatever drove it off the bus.

The rotor is the permanent magnet; the stator is the coil. There are no brushes, so commutation is done electronically by the ESC.

The ESC needs to know rotor position to energize the right coil pair — this is why Hall sensors or encoders matter. A failed encoder makes a BLDC motor misbehave in ways that look like mechanical bind.

Field-Oriented Control (FOC) is the modern commutation scheme. It delivers smooth torque at low speed and is what most humanoid actuators use.

Cogging: the motor rotates in discrete steps instead of smoothly. Usually a bearing issue or partial demagnetization of the rotor.

Current oscillation: the motor draws bursts of current at steady speed. Usually a mechanical bind — the winding is compensating for something.

Thermal rise: the motor runs hotter than its baseline for the same duty cycle. Usually a winding insulation breakdown — retire immediately.

LOTO first. Always.

Remove the actuator as a unit if possible — the motor, gearbox, and encoder are calibrated together.

Match torque specs exactly on reinstallation. Humanoid joints are torque-sensitive and an over-torqued flange can pre-load the bearing.

Re-home the joint against its hard stop and re-register the encoder offset in TechMedix.

Static calibration: place the robot on a level surface, run the calibration routine, capture accelerometer bias across six orientations.

Dynamic calibration: rotate the sensor through all axes at varying rates to capture gyro scale factor and drift.

A post-calibration gyro drift over 0.02 deg/s is out of spec for humanoid balance control — recheck or replace the sensor.

Unload the end-effector completely and run the zero routine. Any residual mass biases the reading permanently until the next zero.

After zero, apply a known weight and verify the reading is within 1% of truth on each axis.

Intrinsic: focal length, principal point, distortion coefficients. Use the platform's calibration target at the published distances.

Extrinsic: the transform from camera frame to robot base frame. Extrinsics drift any time the camera mount is touched — always re-validate.

LiDAR to IMU: rotate the robot at a known rate and confirm the LiDAR point cloud derotation matches the IMU's gyro integration. A mismatch means one of the two is miscalibrated.

A healthy FOC motor shows a sinusoid at low speed and a more trapezoidal shape at high speed. The envelope should be stable.

An oscillating draw inside the envelope points to mechanical bind — the motor is fighting something on every rotation.

A clipped or flattened peak on one phase usually indicates a winding short on that phase. Retire the actuator.

Mechanical: full ROM on every joint, no unexpected current spikes.

Sensor: all sensors in healthy noise-floor range, no disagreements between redundant sensors.

Balance: the robot can stand, shift weight, and step without correction.

Thermal: no joint over baseline by more than 8 °C after a 15-minute warm-up.