TECHNICAL FEATURE JAMESHORNE,VE50B + E-MAIL:[email protected] MAY2010 + RADCOM Homebrew rotator Made from junkbox parts and powerful enough for small HF beams INTRODUCTION. This articledescribes the constructionofa homebrewrotatorthathas beenin usefor over18 monthsand has survivedawinterwith temperaturesbelow -30°C. It can bemadeusinga drill pressand handtools, butaccessto a metalworking lathewas usefulin oneor two situations.The rotatoris basedona wormgearsandwiched betweentwo aluminium discs.Useof a worm gear providesthebenefitof notrequiringa brakingsystem,which wasthe majorsource of problemsin mypreviouseffortsto builda rotator.It is not likelythat it can be copied exactly,becausemanypartswereobtained from localscrapmetalandsurplusdealers, but it is hopedthat thereareenoughideasin this projectto leadotherstotryandmaketheir' own rotator.Thepicturesshouldshowmost ofthenecessaryconstructionalinformation. CHASSIS.Themainchassisframeconsists of two thick 8 inchdiameteraluminiumdiscs separatedbysixmetalspacersarrangedaround theperimeter.Photo1 showsthegeneral form oftheconstruction. Themaindriveshaftrisesup throughthecentre,passingthroughbothdiscs. PHOTO1: Generalview of the completedrotator, lesscovers. ' ToachieveaccuratealigP.~tofthe shaft holesandthespacer '1o/eS, thetwodiscswere clampedtogetherdur'lg medrilling process. Thediscswere "larked ir orderto maintain alignmentofaI..ne 'Jolesduringassembly. Otherholeswere dr!~~ed;r> thebottomdisc, as needed, foro;r..erparisofthe rotator. DRIVESYSTEM..',""'li' the exceptionofthe worm gearOf'me G'...~ shaft, all partsof the drivesystemare~ou~ted on the bottomdisc, asshown il"Photo 2..")e drivetraincomprises a surplus24'. ~"".Olor and gearhead that drivestheW{XTT' .ia a sa'.es ofspurgears.The spurgears erese!ectedto givea convenient linkageIJetwe€pthe motor and the worm and to provide a rrG 'OIaOOn speed of about1 RPM. A singlestart,sl'1glej->roated wormgear was used.SingiestaItis Tlportant in order to gain maximumsef ~ and singlethroated givesaddedstrerrgtl'".',';'i:h 32 teeth, the worm geargaveGspeed reduction of 32 to 1. Theworm ..'as "lO'J'Ti:edbetween two L-shaped bracI'.Ets ..,h:& FJeededcareful placementto :'I.9Ep.w-Jash low. It is also veryimporta~tmc:~~ brackets aremade asstrongaspossr1tetoavoidmovementand distortion frW' ~ h7gt> stressesimposedby movement of ~ rea"", The shaft "0:"j'>e .;.o.r"" -Has made from 5fsinch steel rod. ~ er:ds weretu rneddown to 1/4 inch,usi'lgG~, to fitthe spurgear andto providesho'u.:delS on the shaft. A small ball race was;~ iJelween eachshoulder andthe L-brad:asw,~ to reducethe frictionfrom tt'e lai:aG:tPrust. Aslotfora keyalsohad to be at;: ~ fuis shaft. The waIT!" gear is "'"'OU'1ted on the main PHOTO2: Thebaseplate "oIds the motor,gear train and feedbackpot.. driveshaft,which in this casewasthe front fork of an old bicycle.Theworm gearis held in placewith a one inch lengthof 1/4 inch keystockanda setscrew.Theslotfor the keystockwascut in the driveshaft usinga cut-offwheelon a Dremel tool. POSITIONINDICATOR. A 10 turn 5kQ potentiometerwascoupledtothe maindrive shaftvia two spurgears,which provided approximately5 turnsofthe potentiometer for onefull turn of the beam.The largergear wasscrewed,with 1/4 inchspacers,to the uppersurfaceofthe worm gear.Thesmaller gearwas mountedon to the potentiometer shaft.This arrangement is shownin Photo3, which alsoclearlyshowsthe substantial wormgear.Thepotentiometermounting bracketwas madeofthin steelto provide someflexibility.Thisspringactionensured constantmeshingof thetwo gears.It also facilitatessettingthe potentiometer. LIMITSWITCH ASSEMBLY. Thelimit switchesandassociatedcamareusedto preventover-rotationofthebeam.Thecam alsoservesasaspacerbetweenthe worm gearandthe top disc. It isfastenedto the main shaftwith a setscrew.In my prototype, the notchin the camis positionedto stopthe beameithersideof duesouth.The limit switchesweremountedon a platescrewed to the topsof the worm L-brackets. Photo 4 showsthe switchesandcam in position, alongwith an upperbearingrace.Thecontrol cablewith connector can alsobeseen. FINAL ASSEMBLY. Thecompleted (but un-cased)assemblyisshownin Photo1. The U shapedshaft is a forkfrom an old bicycle.Theflangeat the bottomof the fork concealsa ballrace,throughwhich mostof the verticalloadistransferredtothe upper aluminium disc. Sixlong 1/4 inchboltsholdthecomplete assemblytogether.Theheadsarecovered with siliconesealanto helpkeepoutmoisture. A coverforthe rotatorwascut from paper- PHOTO3: Addingthe worm gearand feedback gear.