146  The stator and rotor cores were re-designed with the design objective of a solid rotor core in order  to eliminate any possibility of de-lamination. This was obtained by increasing the slot area of the  stator cores to increase the coil turns in order to compensate for the eddy current losses in the solid rotor and to achieve the required transformation ratio.    The stator cores were masked at the edges and were electrostatic powder coated using the  Scotchcast Electrical resin 5133 allowing for a thinner and more consistent insulation thickness with no chipping observed.    All machining of the rotor core was minimized by machining the solid rotor core to final  dimensions less the O.D. which once bonded to the hub would undergo a minimal O.D. grind to  improve concentricity.  The second generation single speed VRR showed significant enhancement in performance once the  design improvements had been implemented. Testing of the second generation VRR produced an accuracy reading of approximately 15 arc-minutes as listed in Table I. Comparing to the initial reading of 85 arc-minutes it was a great achievement.      Development of Multi Speed Variable Reluctance Resolver 

Description of first generation multi speed VRR  The multi-speed VRR was designed and built with a single laminated stator core with specifically designed tooth profile for optimized sensitivity of variable air gap and a slot-less laminated rotor core. The resolver was developed with an axial length of 6.35 mm (0.250 in) offering a compact design, which resulted in a 30% reduction in mass compared to that of a conventional resolver of similar O.D. The excitation windings and the sense windings were placed on the stator core alone. Its air gap was varied such to produce a sinusoidal change in the magnitude of the output voltages of the two sense windings.   Observations and test results of the multi speed VRR  The performance of the multi-speed VRR was exceptional and produced accuracy test results much higher than required of the design. The short coming of the initial design was limited to the insulation material Scotchcast resin #260 which was chipping as it had in the single-speed VRR.  Accuracy testing was performed and the resolver accuracy was measured in every 1 degree increments from 0 – 360 degrees and its results are summarized in Table II. The highest reading was found at 350 degrees at a value of approximately 35 arc-seconds which is listed and highlighted in the Table. Comparing to the design requirement of 360 arc-seconds (6 arc-minutes) the multi-speed VRR performed much greater than anticipated.   Table II –Accuracy Test Results of Multi-speed VRR  Angle (degree) 0 20 60 100 140 180 220 260 300 340 350 360 Accuracy Test (arc-sec)  0.0 36.7 0.1 -21.5 27.9 6.5 -20.5 25.5 3.9 -24.9 35.2 0.0

Conclusion / Summary  The Ducommun team has developed Variable Reluctance Resolvers with sufficient accuracies to be in used in the Aerospace and Defense Industries in angular position feedback applications. The single-speed and multi-speed designs have been fully qualified and were shown to meet internal as well as external customer requirements. The latest development of the variable reluctance resolvers has made them competitive to conventional resolvers and offers an alternative solution in the application of brushless DC motor commutation.