Actuator Trade-Off Analysis for DARPA/BOSS Prototype II

The servomotor actuation method used in the first flight prototype zoom lens was chosen because it is simple, small, lightweight, easily available, and can be rapidly integrated into existing UAV systems. Unfortunately, it has proven to be unsatisfactory in several ways. Commanding the servo to positions outside of its displacement-force envelope results in the PID controller hunting for the commanded position and burning out the motor. The gearing system linking the servo and plunger is rudimentary and does not allow for much precision in positioning, despite the digital control used in recent versions of the prototype. The form factor of the servo requires it to be placed outside of the optical assembly and complicates the mechanical interface of actuation components. Finally, because model aircraft hobbyists are the main market for these servos, rather than the research or manufacturing communities, very little technical information on the construction or operation of them can be obtained from the manufacturer. An actuator trade-off analysis was undertaken to identify actuation technologies that may better suit our objectives in the next prototype Prototype II.