TECHNICAL FEATURE JAMESHORNE,VE50B + E-MAIL:HORNEJ@SASKTEL.NET MAY2010 + RADCOM

Homebrew rotatorMade from junkbox parts and powerfulenough for small HF beams

INTRODUCTION.Thisarticledescribestheconstructionofa homebrewrotatorthat hasbeenin usefor over18 monthsand hassurviveda winterwith temperaturesbelow-30°C. It can bemadeusinga drill pressandhandtools,butaccessto a metalworkinglathewas usefulin oneor two situations.Therotatorisbasedona wormgearsandwichedbetweentwo aluminiumdiscs.Useof awormgear providesthe benefitof not requiringabrakingsystem,which wasthe majorsourceof problemsin my previouseffortsto buildarotator.It isnot likelythat it can becopiedexactly,becausemanypartswereobtainedfrom localscrapmetalandsurplusdealers,but it is hopedthat thereareenoughideasinthis projectto leadothersto try andmaketheir'own rotator.Thepicturesshouldshowmostof the necessaryconstructionalinformation.

CHASSIS.The mainchassisframeconsistsof two thick 8 inchdiameteraluminiumdiscsseparatedbysixmetalspacersarrangedaroundthe perimeter.Photo1 showsthegeneralformoftheconstruction.Themaindriveshaftrisesupthroughthecentre,passingthroughbothdiscs.

PHOTO1: Generalview of the completedrotator,lesscovers. '

ToachieveaccuratealigP.~tofthe shaftholesandthespacer'1o/eS,thetwodiscswereclampedtogetherdur'lg medrilling process.Thediscswere"larked ir orderto maintainalignmentofaI..ne 'Jolesduringassembly.Otherholesweredr!~~ed;r>thebottomdisc,asneeded,foro;r..erparisof the rotator.

DRIVESYSTEM..',""'li'the exceptionof thewormgearOf'me G'...~ shaft,all partsof thedrivesystemare~ou~ted onthe bottomdisc,asshownil"Photo 2..")e drivetraincomprisesa surplus24'. ~"".Olor and gearhead thatdrivestheW{XTT'.ia a sa'.es ofspurgears.Thespurgears erese!ectedtogiveaconvenientlinkageIJetwe€pthe motor andthe wormandto providea rrG 'OIaOOnspeed ofabout1 RPM.Asinglestart,sl'1glej->roatedwormgear wasused.SingiestaItis Tlportant in orderto gainmaximumsef ~ and singlethroatedgivesaddedstrerrgtl'".',';'i:h32 teeth, thewormgeargaveGspeed reduction of 32 to 1.

The worm ..'as "lO'J'Ti:edbetween twoL-shapedbracI'.Ets ..,h:& FJeededcarefulplacementto :'I.9Ep.w-Jash low. It isalsovery importa~tmc:~~ bracketsaremadeasstrongas possr1tetoavoidmovementanddistortion frW' ~ h7gt>stressesimposedbymovement of ~ rea"",

The shaft "0:"j'>e .;.o.r"" -Has made from

5fsinch steel rod. ~ er:ds wereturneddownto1/4 inch,usi'lgG~, to fitthe spurgearandto providesho'u.:delSonthe shaft.Asmallball racewas;~ iJelweeneachshoulderandthe L-brad:asw,~ to reducethefrictionfrom tt'e lai:aG:tPrust. Aslotforakeyalsohad to be at;: ~ fuis shaft.

The waIT!" gear is "'"'OU'1ted on the main

PHOTO2: Thebaseplate "oIds the motor,geartrain and feedbackpot..

driveshaft,which in this casewasthefrontfork ofan old bicycle.Thewormgearis heldin placewith aone inch lengthof 1/4 inchkeystockanda setscrew.Theslotfor thekeystockwascut in the driveshaft usingacut-offwheelon a Dremeltool.

POSITIONINDICATOR.A 10 turn 5kQpotentiometerwascoupledto the maindriveshaftvia two spurgears,which providedapproximately5 turnsof the potentiometerfor onefull turn of the beam.The largergearwasscrewed,with 1/4inch spacers,to theuppersurfaceofthe worm gear.Thesmallergearwas mountedonto the potentiometershaft.Thisarrangementisshownin Photo3,which alsoclearlyshowsthe substantialwormgear.Thepotentiometermountingbracketwas madeof thin steelto providesomeflexibility.Thisspringactionensuredconstantmeshingof thetwo gears.It alsofacilitatessettingthe potentiometer.

LIMITSWITCHASSEMBLY.Thelimitswitchesandassociatedcamareusedtopreventover-rotationof the beam.Thecamalsoservesasaspacerbetweenthe wormgearandthe top disc. It isfastenedto themainshaftwith asetscrew.In my prototype,the notchin the cam is positionedto stopthebeameithersideof duesouth.The limitswitchesweremountedon a platescrewedto thetopsof the worm L-brackets.Photo4showsthe switchesandcam in position,alongwith an upperbearingrace.Thecontrolcablewith connectorcan alsobeseen.

FINALASSEMBLY.Thecompleted(butun-cased)assemblyisshownin Photo1.The U shapedshaft isa forkfroman oldbicycle.Theflangeat the bottomof theforkconcealsa ball race,throughwhich mostofthe vertical loadis transferredto the upperaluminiumdisc.

Sixlong1/4 inchboltsholdthecompleteassemblytogether.The headsarecoveredwith siliconesealantto helpkeepout moisture.

Acoverfor the rotatorwascut from paper-

PHOTO3: Addingthe worm gearand feedbackgear.

I RADCOM. MAY2010

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CI470~40V18V

18VECG168

200V PIV

2Amp

C2

470~ 1+40V

FIGURE1: Circuitdiagramof the rotatorcontrol and positionindicator unit.

OV

thin aluminiumand wrappedaroundtheassembly.Siliconesealantwasusedforwaterproofingandthe coveris heldin placebytwo hoseclamps.Thisarrangementcanbeseenin Photo5.

ATTACHINGTHEROTATORTOTHEMAST.A four inch pipeflangewas boltedto theundersideof the bottomdisc.Thiswas usedto screwthe rotatoronto a threaded111z inch

aluminium pipe.Theoriginalarrangementusedasetscrewto discouragethe pipefromunscrewingitself,but this wasfoundto beinadequatesothreestruts,madefromelectricalconduit,wereadded.Photo5showsthedetails.

ROTATORCONTROLBOX.A simplecontrolcircuit (Figure1)wasdevelopedto operatethemotor.Thecircuitproducesan unregulated:1:24 volt supply,which is usedto drivetherotatormotorvia centreoff, momentary,twopositionswitchSl. Motorcurrentis indicatedbyacentre-zerometerwired in serieswith themotor.Themeterisshuntedwith a suitablelengthof nichromeresistancewire sothatthe normalmotoroperatingcurrentindicatesabouthalfscale.

Powerto the motorisfedviasteeringdiodes06 and 07 andthroughthe limit switchesS2and S3to the motor.Whena limit is reachedin eitherdirection,the voltageis fed backtothe controlboxto light a 24 volt incandescentlamp.Bothlimit switchesarein thedepressedstateexceptwhenthe rotatorreachesoneofthe limit pointsnearduesouth.

Tomeasurethe positiona 12Vspanwasrequired,arrangedas +9 and -3V.The +9Vsupplyisderivedfromthe + 24V supplybyR2and Zenerdiode05, while the -3Vsupplycomesfromthe-24V railvia R1andfourforward-biased1N4005 diodes.The 12Vsupplyisfedto thepositionindicatorpot,VR2,locatedin the rotator.Asmentionedearlier,VR2isa 10 turnpotentiometer,gearedsothattherearefiveturnsofVR2for one revolutionof therotatorshaft. It isbestto havethesefiveturnsin the centreof theVR2to avoidany riskof

+24V Moto,

R2 ! S1 cucrenl1k2 .~O.5W ~----

-24V

R12k2O.5W

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;nd;calo,24V

R3

12k O.5W059V

3V I O.5W01-041N4005

Control box

overrunningthe endsof travel.Themeterzeropoint isonthe left handside,sothe -3voltselevatesthe OVpointabovethe bottomendofVR2byabout2112turns.SeriesresistorsR3andVRI arechosento suit the currentratingof the meterusedfor positionindicator.VR1setsthe span.Thezerovoltspointof thepotentiometer,relativeto the maindrives~aft,issetby pullingthetwo gearsapartandturningthe gearonVR2.Thesearebenchadjustmentsmadebeforetherotatoris installed.

Photo6 showsthe prototypecontroller.Thiscasealsocontainsacontrolcircuittoelevatethe mast;the rotatorcontrolsandindicatorsareonthe left.Therearetwo metersassociatedwith the rotator;the upperoneshowsdirectionandthe loweroneindicatesmotorcurrent.A lamp indicateswhentherotatorhasreacheda limit.

FINALREMARKS.Theweightofthe rotatorworkedoutto about7kg.Thebronzewormgearisthe heaviestcomponent.Itwassurprisinghow thesmallelementsaddedup in thefinal assembly.

A shaftcollarwasfitted belowthe bottomdisc(locatedinsidethe11/2inchaluminiumpipe)to help restrictverticalmovementof themaindriveshaft.

Setscrewsweretreatedwith threadlockingcompound,and self-lockingnutswereusedwheneverpossible.

Ballbearingswerenotusedinthealuminiumdiscs, in orderto simplifythe machining.Aspreviouslyrnentioned,mostoftheverticalloadistakenbythebicycleforkbearing.Consideringthe slowrotationspeedand infrequentuse,it wasthoughtthat thesteeldriveshaftagainstthe well-greasedbarealuminiumplatewould beOK.Keepaneyeonthe motorcurrent;a risein currentindicatesthat allis notwell andthe internalsof the rotatorshouldbe investigated.

I hopethat this reportshowswhat can bedonewith a littleskillandsomedetermination,and inspiresyouto havea goat makingsomethingmechanicalyourself.

TECHNICALFEATURE]

1N4005

07 11N4005

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24V OC I M

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PHOTO 4: Detail of drive train and limit switches,including cam.

PHOTO 5: Looking up the mast, showing the footplate and anti-rotation arms.

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PHOTO 6: The control box. Rotator controls areon the left side.