Secord et al:
The authors present a dynamical analysis of a prototype PZT based actuator, describing the novel cellular architecture and its application toward flapping flight. 

There exist some minor spelling errors in the paper. Cutkosky's name in the second paragraph in the introduction should have an apostrophe.  There exists an unknown word, “reasonablent” after eq 18. The second and third sentence in the second paragraph of “C. Model Competence” should read , “The unmodeled dynamics of the wiring tend to act as increased stiffness, serving to raise the natural frequencies in the real system over the theoretical case (word “would” ommitted). Also, recall that the axial stiffness and mass of the flexures have been neglected and the torsional spring approximation introduces some error for the large value of Lf (the word “was” changed to “have”).  Three cases were not considered by eq 4. However, the reviewer considers these cases to be covered by the aforementioned equation.  If these “special” cases are to be listed, then the case where i = 0, and j = 0 should be listed as Vc_00 instead of  Vc_ij

The authors describe the strain amplification design and the exponential increase in strain due to the cellular architecture.  A similar analysis performed on the amount of force gained or lost would have been very interesting.  Some clarity is needed on whether or not the resultant strain is  contractile or extensile in nature for a given cell hierarchy. 

The modeling assumption assumes 5 degrees of freedom. While not complex, at the very least, Greubler’s equation should be listed for the reader.  Performance of the analysis would be appreciated. The authors have opted to use i_hat and j_hat as their local coordinate system when analyzing the actuator.  This may cause confusion to the reader as component identification also use i and j.

The data lines in Fig 11 for the double wing mass case are too similar to the graph lines, especially in the phase diagram.  Some color would be greatly appreciated and promote readability. 

The Vector –Adaptive analysis performed and mentioned prior to eq 17 should be further expanded upon. The resulting Bode and/or Nyquist should be included in the paper. 

Especially in the flapping wing application, a power to weight ratio analysis would have enabled comparison of this actuator to others.