Hardware Setup#

BAM’s identification pipeline requires a single-axis pendulum test bench. The actuator drives a pendulum arm; gravity provides a natural, controllable load that depends on the arm’s angle and mass distribution. Recording the resulting trajectories is enough to identify both the motor model and the friction model.

Pendulum geometry#

pivot (actuator)
     |
     | length l
     |
  [mass m]

  • The arm is attached directly to the actuator output shaft, with no intermediate gearbox or coupling.

  • The zero angle is defined as the arm pointing downward (stable equilibrium). Positive angles are measured counter-clockwise.

  • The pendulum can swing freely on both sides up to roughly ±π/2.

The gravity torque at angle \(\theta\) is:

\[\tau_e(\theta) = (m + m_\text{arm}/2)\, g\, l\, \sin(\theta)\]

where \(m\) is the load mass, \(m_\text{arm}\) is the arm mass, and \(l\) is the arm length. These three values must be measured and passed to the recording scripts.

Bill of materials#

  • The actuator to identify, mounted rigidly on a fixed frame.

  • A pendulum arm (rod or profile) attached to the output shaft.

  • A calibrated load mass fixed at the end of the arm.

  • A scale to measure \(m\) and \(m_\text{arm}\) precisely.

  • A ruler or caliper to measure \(l\) (pivot to center of mass).

  • A power supply set to the target voltage.

  • A USB-to-serial adapter (Dynamixel / Feetech) or an EtherBan interface (eRob).

Supported actuators#

The following actuators have bundled recording scripts and pre-identified parameter files:

Motor

Bus

Default Vin

Notes

mx64

Dynamixel TTL

15 V

mx106

Dynamixel TTL

15 V

xl320

Dynamixel TTL

7.5 V

xl330

Dynamixel TTL

7.5 V

erob80_50

EtherBan

48 V

Reduction 1:50

erob80_100

EtherBan

48 V

Reduction 1:100

sts3215

Feetech TTL

7.4 V

Mechanical recommendations#

  • Keep the arm as light and stiff as possible to reduce parasitic modes.

  • The load mass should be large enough to excite a range of load torques, but small enough that the actuator can move it across the full ±π/2 range.

  • Make sure the arm is level at the zero position before recording, to avoid a systematic angle offset that would corrupt the gravity term. The fitting pipeline includes a q_offset parameter to absorb small calibration errors, but a large offset degrades identifiability.