Omnidirectional Ambulation Actuator
Biomimetic Underwater Robot Program
Marine Science Center
Northeastern University
East Point, Nahant, MA 01908

Forward

Backward

Leading

Trailing

These four movies represent the movements of the Northeastern Ambulatory Actuator during walking in the four directions. The ambulatory actuator segments move around three joints which are organized from the base of the leg out as:

  • Thoraco-coxal joint: Generates protraction and retraction of the limb
  • Coxo-basal joint: Generates elevation and depression of the limb
  • Merocarpopodite joint: Generates extension and flexion
  • During forward and backward walking translational propulsive forces are generated by the thoraco-coxal joint while during lateral walking they are generated by the mero-carpopodite joint. The four walking directions illustrated in the figure are:

    1. Forward Walking (upper left)
    2. Backward Walking (upper right)
    3. Lateral Walking on the Leading (Pulling) Side (lower left) and
    4. Lateral Walking on the Trailing (Pushing) Side (lower right)

    All that differs between these behavioral acts is the coordination pattern of current signals applied to the shape memory alloy (Nitinol) acturators which control the three different joints of the leg. The current is regulated by the INM (Integrated Nick Machine) which is in the upper left corner of the rear view of each frame.. The INM receives control signals from the ambulation controller through a serial line interface and generates current pulses to activate the SMA actuators which control the different limb joints. If you look closely, you will notice that the LEDS on the INM are active in three different patterns:

  • Early Swing Phase: when the limb is elevated to start a new step cycle
  • Late Swing Phase: when the limb tip is being brought down to the substrate and
  • Stance Phase: When the limb supports the vehicles weight against gravity and produces translational propulsive force.
  • The LEDªs are organised from right to left and indicate control of the following synergies
    1. Elevator of the Coxo-basal joint
    2. small Depressor of the Coxo-basal joint
    3. medium Depressor of the Coxo-basal joint
    4. large Depressor of the Coxo-basal joint
    5. small Protractor of the Thoraco-coxal joint
    6. medium Protractor of the Thoraco-coxal joint
    7. large Protractor of the Thoraco-coxal joint
    8. small Retractor of the Thoraco-coxal joint
    9. medium Retractor of the Thoraco-coxal joint
    10. large Retractor of the Thoraco-coxal joint
    11. small Extensor of the Mero-carpopodite joint
    12. medium Extensor of the Mero-carpopodite joint
    13. large Extensor of the Mero-carpopodite joint
    14. small Flexor of the Mero-carpopodite joint
    15. medium Flexor of the Mero-carpopodite joint
    16. large Flexor of the Mero-carpopodite joint
    Key personnel in the development of this actuator include:
  • Jan Witting (NU): Designed and built the leg
  • Nick diCaprio: (Massa Products): Designed and built the INM
  • Joseph Ayers: (NU): Designed the ambulation controller