must b e considere d to begin devel oping  a complete  analysi s of th e perfo rman ce. Additionally, mech anical  characteristics such as coupling stiffness, b earing drag lo sses, motor an d load ine rtias, e tc. must al so  become a pa rt of the performance sim ulations. 

While  most of these p arameters are readily avai lable from t he system  descriptio n, m otor catalo g  specification s, and histori cal referen ces, it is essent ial that the performa nce anal yses in clude these ove r  the full rang e of op eratin g conditi ons. Whil e it is beyond t he scop e of thi s pape r to address how to  accompli sh a stepp er motor and me chanism  perform ance an alysis, the  prepa ration fo r doing such is wel l  known. So, it is wo rthwhil e to at least recogni ze the basi c performance an alysis p aramete rs as part of  establi shing adequ ate perf ormance margin for step pers: 

• Motor ste p angle  • Motor num ber of pha ses a nd win ding type  • Motor torque sensitivity, Kt, with toleran ces  • Motor wi nding resistance with tolera nces an d effect s of thermal rise  • Motor induc tance with tolerances   • Motor mou nting, heat dissi pation, and th ermal ri se m odel  • Motor rotor inertia  • Numb er of m otor pole s  • Minimum an d maximum motor detent to rque  • Supply voltage and toleran ces  • Supply cu rrent maximum and any pul se width re striction s  • Environme ntal temperature rang e  • Tempe rature range effects on bea ring d rag torqu es  • Load d rag to rque, load in ertia, and cou pling stiffness  • Operating p rofile and duty cycle  • Gear red uction characteristics. 

Failure to consider the worst -case  extremes of these parameters w ill result i n improper perform ance  asse ssment and o perating  anom alies. It  should be well understoo d but i s worth  mentioni ng that in stepp er  mech anisms the pe rform ance analy ses may dete ct areas of co ncern n ot related to m eetin g the m argin  goals but rela ted to dynami c stability at certain speeds, commo nly reso nances. Hen ce, it is i mpossibl e to  develop a th orough stepp er moto r me chanism performance ana lysis ba sed solely on stati c estim ates  asso ciated with margi n. In fact, a well-e stablished method fo r simulating the  steppe r mechanism m otion  over a broad range of o peration conditio ns is essential. Comm ercially avail able and cu stom software  are  used for acco mplishi ng the  motor and system level pe rforma nce si mulation s. 

Perform ance simulation i s best done using meth odolo gies th at have been succe ssful in the  past in  correlating wi th test results. Sometimes i t is dif ficult to repli cate the stepp er mechanism i n its p recise flig ht  config uratio n, becau se of model an d / or test set -up limitations. So, it is important  first of all to realize   what th e modeling  and test defi ciencies are and secondly to m ake sure that t he performance modeling  and la b testing a re inte nded to correlate well. Correlation m ust be present  betwe en performa nce  modelin g and lab te sts. Often it i s easer for the  performance simul ation to replicat e the flig ht config uratio n  than it is for the test set-u p. This ca n occur when th e flight configuratio n invol ves larg e ma sts or solar  panel s. If th e perfo rman ce modelin g accurately si mulate s the flight configu ration but no t the test lab   config uratio n, then anomal ies in test  can occur that reflect test set- up defi ciencies rathe r than potenti al  flight proble ms. 

Hardware testing sh ould consi st of te sts at eve ry level of the system, from th e stepp er moto r compo nents  to the me chanism asse mbly. Of prima ry importa nce i s identifying th e spe cific te sts and limit s that will  best  represent th e actu al flight conditions and then assu ring that th e design, sim ulations, a nd te sting foll ow  consistently. Testing at the motor comp onent level lo oks at the pa ramete rs that determin e torque, speed,  power, an gular movem ent, and po sition al stability. Test ing at the mech anism level looks at torque outpu t  and margin, rate and re solution, and step stability.  Testin g for both the m otor a nd m echanism  should  incorporate e nvironm ental factors, especially temp erature extrem es. It is  very desirable to use flight-li ke  126