of its low pro file, high stiffness, low ba cklash, high efficien cy an d drive train robustness. The cycl oidal   drive ha s a large num ber of “lobe” teeth in conta ct, which minimi zes the operating stre sses and makes i t  ideal for hi gh reliability ap plicatio ns. A cro wned sp line dog b one shaft bri dged  the output of the cycloid al  transmissio n and pinio n gear. This wa s req uired because the pinion gea r was sp ring loaded into the  sector ge ar and all owed t o float ve rtically in order to elimi nate backlash and absorb  thermal vari ation s  within the gear mes h.   

       MOTORS  ARC CYCLOIDAL  Figure 10.  Cuta way View of the Flap EMA As sembly   Figure 11.  EMA installed. 

The offset att achment of the foot to the flap create d signifi cant mom ent loa ding on the a rc that rai sed  concern over gea r mesh alignme nt. To counte ract this effect t he sector ge ar was moun ted in side an  Incon el arc that wa s supported by  three v-sh aped coni cal roll ers in a trip od arrang ement inside the  support b ox. An eccent ric beari ng cam pin in the bottom rolle r was then adjusted to minimi ze the ra dial  play of the sector arc in relation to the  three ro llers. The pini on gear was also crowned to a ccommo date  any addition al misalign ment problem s.  

The d rive uni t was m ounted on trunion s alon g the a xis of the pin ion gea r. Thi s mou nting configuration   allowed the a ctuator to rotate due to the  thermal varia tions in the a ctuator and flap mount s. 

The flap  position was mo nitored  by a  geared, d ual-tandem, brushless resolve r (1 m odel chann el / 3   positio n) that was connected to th e pini on gear via a quill shaft a rrangement. A triply redun dant fail safe  brake held th e actu ator i n positio n during shuttle tra nsport a nd provided  the l ast def ense of cont rol by  snubbing the energy and l ocking the fla p in a fixed p osition in th e event of an all out po wer failure. The   brake enga ged the same bull ge ar as the drive moto rs. The brake inco rporated friction plate s coated with  plasm a sprayed ch romiu m oxide for stable ope ration in a vacuu m environm ent. Dual mechani cal limit  switches attached to the output of the cycloidal d rive prote cted th e actuato r when a si ngle channel was  active as well as providi ng an over travel  limit. 

Vehicle Inte gration an d Testing     Integration  of the a ctuatio n system with the flap s and compl eting the associated vehicle attachme nt  proved  to be a very challenging  process. Th e process requi red integrating  the flaps which are very large  delicate, and expen sive, to the vehicl e. The axis of rotation of the flaps had to be positio ned to extremely  tight tolera nces, a nd the  rotation ne eded to b e on an ax is that was precisely parallel to th e axis of the  EMA rotating  mount. Th e com binatio n of tight tole rances, close cl earan ces, extremely heavy EMAs  (approximatel y 136 kg (300 pounds) ea ch), and precision alignment provided  unique challen ges to th e  integratio n team. 

The total weight of e ach flap was approximately 61  kg (135 pounds). Fo r the ir size they a re relativel y  lightwei ght, but due to the special processes involve d in fabrication  of them, spe cial ha ndlin g pro cedures  386