Radio Technique

Radio Technique George M Myers THIS MONTH going discuss meas urement fundamental characteristic RC system fast servos move simple measure has prac tical significance because responds wear concealed damage system first thing need record player will turn piece paper constant speed provide chart known time base Place 12-in phonograph record unwrinkled piece newspaper tear out 12-in disk paper lifting against record Place four tiny pieces tape affix paper record Place record turntable paper side up Next fabricate pen-holder arm shown sketch mount firm support pen will trace approximate radius record moved servo used old trophy support worked fine pen expended Flair vent near tip sealed hot soldering iron end opposite tip cut off could fill red drawing ink needle heated flame melted through middle pen provide pivot side time wont leak mods provide pen faster flow rate stock Flair what need Everything must move freely pen should weighted just enough leave visible trail little work pocket calculator will convince 33 1/3 rpm paper uses 18 seconds per revolution 45 rpm uses 13333333 seconds Remember Get everything place checked out turn turntable let run get thing stabilized pen should making nice circle paper have landing gear switch transmitter plug servo channel receiver use other channel suits fancy Throttle good because doesnt center itself Just re member move stick much like switch possible much force excitment damage transmitter supposed nondestructive test isnt working did charge batteries turn transmitter receiver didnt Flip switch stick watch pen reaches end its travel starts making new different-sized circle flip switch stick opposite direction wait until pen gets back first circle Shut off equipment remove chart Record date equipment name serial number servo number right chart next speed wrote down previously servo doesnt have number Well can put its bottom using tape paint anything like Just remember will looking number long own servo neat Repeat exer cise rest servos Now have data Lets examine can determine transit time servo measuring angle defined endpoints sloped line chart fast servos move can determined trick record player Its based upon turning constant speed piece paper upon pen-holder arm traces different measurable patterns according departures g servo center chart calculate transit time applying formula Transit time seconds equals Transit Angle de grees measured chart divided 360 degrees multiplied 13333 seconds using 45 rpm 18 seconds using 33 1/3 rpm answer should between 1/2 3/4 seconds shorter 1/2 second either did make servo go end its travel other have made mistake time exceeds 3/4 second probably too much friction setup Repeat tests necessary Log answers can find again later Before file log look results probability servo will noticeably faster others Thats want ailerons Another servo may notice ably slower goes throttle shouldnt moved rapidly anyway Look sloped lines Are smooth continu ous jump Jumps indicate binding somewhere test setup dirty potenti ometer damaged gears unsteady hand stick Eliminate possibilities one decide potentiometer dirty have reached moment decision fix yourself send out Servo potentiometers lubricated special grease clean lose grease have either get some manufacturer send servo out service reas semble potentiometer dry bother Well new set will probably run batteries down least once fooling around test setup thats good should cycle bat teries least once before put set service just says instruction manual addition will become little familiar system before fateful day Most importantly though servo motors will deteriorate slowly throughout lives detectable evidence slowing down servo So long transit time remains within 10 percent what system new have good system transit time grows its time look trouble may have plug has used too much has lost its tension can sometimes remedied wedging point thin pin between female pin its shell increase contact pressure Sometimes needed good cleaning wood alcohol poisonkeep away eyes mouth etc get Out solidified castor oil another case trouble has nothing pins due shorted cell power pack wire someplace system has fractured its strands except Check fix whats needed Thats subject another column meantime start thinking up questions want answered send magazine offices wont promise answer per sonally may find answers suc ceeding columns Nominal payment made Model Aviation pictures drawings may use column address George Meyers 70 Froehlich Farm Rd Hicksville NY 11801 August1975 13