work to slow the falling body. This mechanical energy was transferred to a small DC motor via a highly efficient ball-screw and burned off across a resistor to determine output power. A uniquely tuned spring was placed in series with the ball screw to reset the starting position during the swing phase. This method allowed the production of 3.5 watts of continuous power output from one ankle device while walking at 6.4 km/hr (4 mph.)

The work by Hitt et al. was intended as proof of principle; typical performance parameters for each ankle are given in Table I-4. The authors conclude that the results provide confidence that biomechanical energy harvesting may be a viable “augmentative and emergency power supply for the future network-centric dismounted Soldier.”4

TABLE I-4. Energy and Weight of Biomechanical Prototype.

  Speed 4.8 (km/hr) 6.4 Knee Bends
Average power (W) 2.5 3.5 9.2
Average energy/step (J) 2.7 3.2 7.7
Total device weight (kg) 1.4 1.4 1.4
    Average W/kg 1.8 2.5 6.6
Generator-only weight (kg) 0.3 0.3 0.3
    Average W/kg 8.3 11.7 30.7

SOURCE: LTC Joseph Hitt, et al., Program Manager, DARPA, “Dismounted Soldier Biomechanical Power Regeneration,” presented at the Proceedings of the 27th Army Science Conference, Orlando, Fla., November 29 – December 2, 2010.

Biomechanical harvesting of energy from a Soldier’s locomotion will continue to mature in the near to mid term, with systems increasing in efficiency and decreasing in mass. This technology will become even more important as parallel efforts to reduce the demand for energy for a Soldier’s electronics suite are successful.

Other harvesting mechanisms that have been investigated and may have far-term potential:

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4LTC Joseph Hitt, et al., Program Manager, DARPA, “Dismounted Soldier Biomechanical Power Regeneration,” presented at the Proceedings of the 27th Army Science Conference, Orlando, Fla., November 29 – December 2, 2010.



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