53 A single actuator (in purple and blue) drives three cam mechanisms with detents in series inside the  prototype blade section; the cam mechanisms, which pos sess respectively different profiles to produce an  overall gradient deflection in the blade, are located on 15-cm (6-inch) centers to distribute the load. This  preliminary design layout drawing also resulted in a fi rst-order approximation of t he size and weight of the  actuator/mechanism assembly. The electrolysis/combustion team initially estimated the actuator would weigh approximately 0.2 kg (0.5 lb). Including the other masses shown in Figure 14 for which The  Aerospace Corporation was responsible (actuator and power transfer mechanism), the weight goal levied  for the entire subsystem was 0.45 kg (1.0 lb) plus miscellaneous attachment hardware. The weight goal was a large challenge, as one can see from the packing factor in the end view in Figure 14. The weight of  the actuator development hardware shown in Figure 13 was approximately 0.59 kg (1.3 lb), which was  significantly over its allocated weight. However, the mechanism portion of the assembly weighed just  under its 0.2 kg (0.5 lb) allocation, so the final over all assembly weighed approximately 0.82 kg (1.8 lb).    The next step in the process was the creation of a multi-body dynamic model of the system, using  Dynamic Analysis and Design System (DADS), a comme rcially available multi-body dynamics software.  DADS aided in the evaluation of necessary actuator  pressure and load to twist the rotor blade. Cam  profile shapes, friction, and local blade stiffnesses were all incorporated into the model. Figure 15 shows images from the DADS model. The view is looking from the top of the blade downward, similar to Figure 14. The forward spar structure is in green (fixed refe rence frame), and the aft spar structure, which gets  separated (and thus twists the blade via the previous disc ussion) is in orange. The pin (in red) is fixed to a  lug mounted to the aft spar, which protrudes throug h an access hole in the forward spar. The actuator  moves the guide blocks (shown in blue, and constrained to a fixed distance from the forward spar by pillow blocks) to the left and right. As it does so, it forces the red pin (and aft spar) fore and aft relative to the forward spar through the cam profile. In the model,  the pin slides in the cam groove with an assumed  friction coefficient of 0.1 (sliding but lubricated condit ion). Initial designs considered the inclusion of a  rolling element bearing at this joint, but that option was quickly ruled out due to the very tight volume constraints and relatively large loads; Hertzian cont act stresses were prohibitive. The purple model  springs between the forward and aft spars represent the torsional st iffness of the blade at each cam  location. Using the blade’s finite element model resu lts of applied deflections at each cam location and  their respectively required forces, values were calcul ated for use as spring constants. Note that the three  cams are slightly different in the amount of forward/aft spar separation that they produce (3.81, 2.54, and 1.27 mm (0.150, 0.100, and 0.050 in)). This separation grad ient is what actually produces the twist in the  blade. 

Figure 15.  Screen Images of DADS Model  0.150” Cam K=353#/.122”=2900lb/in0.100” Cam K=470#/.081”=5800lb/in0.050” Cam K=278#/.041”=6800lb/inPiston  I/F 0.150” Cam K=353#/.122”=2900lb/in0.100” Cam K=470#/.081”=5800lb/in0.050” Cam K=278#/.041”=6800lb/inPiston  I/F Fore 

 Aft  3.81 mm Cam  Kout 2.54 mm Cam Kmid 1.27 mm Cam  Kin  NASA/CP-2010-216272