retrofitting the x3 milling machine (3) · february/march 2005 31 d. 500va toroidal transformer 2 x...

30 Model Engineers’ Workshop

Wiring up theStepper MotorsIn part 1 of this series of articles, Table 1(MEW Issue 102 page 33) gave thecharacteristics of the MAE 23 Frame HSXstepper motors. The Table indicates thatthe motors can be connected in either auni-polar or a bi-polar configuration. Themotors produce the greatest torque when

connected in a bi-polar configuration. Fig 6shows the lead colours of the 8 leads forthe beginning and end of each of the 4 coilwindings in the motor. To connect themotor in bi-polar parallel configurationeach pair of coils is connected in parallelwith the beginning of each coil and theend of each connected together. Thus forthis arrangement, the following leads areconnected : -1. Red and Yellow-White.2. Yellow and Red-White.3. Brown and Orange-White.4. Orange and Brown-White.

This gives four leads 1 and 2 ; 3 and 4.The four conductors in the screened cableI used to connect the motors werecoloured Red, Yellow, Blue and Green, thescreen is used as the earth lead. Thesewere paired Red & Yellow; Blue & Green. Iconnected Red to 1, Yellow to 2, Blue to 3and Green to 4. Connect all three motorsup in exactly the same way so that whenyou come to connecting up to the motordrivers there is little chance of an error. Ifsubsequently when the motors are beingrun one of the motors rotates in the wrongdirection all that is required to correct therotation is for the connection one pair ofthe leads at the driver to be interchanged.

When connecting the leads in theterminal block, professional panel builderswould probably use the purpose made

crimp on connectors. For my purposes, Ibelieve in tinning the bare ends withsolder to make the connection secure.Photo 16 illustrates the completed wiringof one of the motors. The cable screen,used as the earth lead, is connected to themounting back plate. Use a solder tagattached to the back with a 2.5 mm screw.It is very important to ensure that themotors are securely earthed. The cable issecured to the back plate using a cablegrip, and is further restrained by a rubbergrommet fitted into the aluminium motorcover.

Assembling theStepper Motor DriveUnit In earlier articles in MEW (issues 88 & 89) Idescribed a stepper motor drive unitincorporating Gecko drives and softwareand control card from DeskCNC. A numberof readers found the article useful,however they did not feel there wasadequate information for the electronicsbeginner to construct the unit. I amtherefore offering a step by stepdescription of the construction of the unit.Potential constructors are advised tofollow the construction carefully as theunit operates with high voltages andsubstantial current. If any reader is at allconcerned by any aspect of theconstruction and does not have access toqualified assistance, he should contact meand I will endeavour to help. My telephonenumber is given at the end of the article.

Materials requiredfor electronics1. Four Gecko 201 micro stepping drives.

Three would be fine for normal X, Y, Zworking. Adding a fourth makesprovision for driving a rotary table. Ihave used these drivers for some timeand have found them excellent. Contactwww.geckodrive.com.

2. All the following items are supplied byRS Components RSwww.com or Tel01536 201201a. Enclosure 222-086b. 4off, 4-way “X” plugs 460-755c. 4off, 4-way Chassis “X” sockets

460-783

Dick Stephen concludes the CNC conversion with a description ofthe wiring details and an “Electronic handwheel”

RETROFITTING THEX3 MILLINGMACHINE (3)

16. Stepper motor wiring (Bipolar parallel)

17. Showing enclosure with transformer, capacitor, rectifier, and 5v module.

MEWED200504013.qxd 11{01{2005 13:00 Page 30 G4_115 Quark:QuarkDocs:ed:MEW:200504:

February/March 2005 31

d. 500VA Toroidal Transformer 2 x 30V223-8263

e. Bridge Rectifier 12A/200V 262-056f. Electrolytic Capacitor 63V 15,000 ìf

381-9122g. Mains switch dpst Rocker on/off

illuminated red 440-6890h. 2off spst mini vis switches 664-525i. DC-DC converter to generate a 5V

regulated supply 459-8270j. Pack of terminal blocks 464-9738

and 464-9722k. Pack of 10 0.25w 36 k Resistors 148-

865l. Tube of heat sink compound 217-

3835

3. The following are required if the readerintends to build the manual control unit.a. 2off Rotary switches “break before

make” 4-pole 3-way 320-708b. Momentary open switch 103-6296c. 1off, 6-way panel socket 115-2089d. 1off, 6-way cable plug 413-7522e. 1⁄10 inch pitch strip board 70 mm x

100 mm (tracks running lengthwise).

f. 2off, 14 pin dil sockets, 1 8pin dilsocket.

g. 4off, 1k resistors 148-506 (contains10)

h. 1off, 1.8 M resistor 133-245(contains 10).

i. 4off, 2N2907A PNP transistors 349-9043 (contains 5).

j. 22 swg tinned copper wire.k. 24 swg tinned copper wire.

4. The following are available from USDigital www.usdigital.coma. 1, 500 line optical encoder S1-500b. 1⁄4 inch coupler for the encoder c. Cable CA-434-1FTd. LS7184 Quadrature Clock converter

5. In addition to the above you will need a3 m length of 5 amp 3-core mains cable,3m of 6-core screened 5.9 mm diametercable (hard to find in short lengths youwill need to shop around), 3 mm 4 ampstranded cable red, an assortment ofcolours of stranded electronic wire, heatshrink in various sizes, cable ties, rubbergrommets.

6. 1 piece of aluminium 300 mm x 150 mmx 3 mm

7. 1 piece of aluminium 300 mm x 100 mmx 3 mm

8. 1 piece of pvc sheet 300 mm x 100 mmx6 mm

9. 1 piece of Vero strip board 80 mm x 80mm 1⁄10 inch pitch.

10. 3off, double pole double throwswitches 283-8914

The assemblyThe most difficult part of the assembly ofthe driver unit is mounting thecomponents in the enclosure and cuttingthe holes in the front and rear panels forthe switches and sockets. Photos 17, 18, &19 illustrate the mounting of thecomponents in the enclosure. Photo 17shows the toroidal transformer, the bridgerectifier and the electrolytic smoothing

18. DeskCNC and one Gecko drive added.

19. Front panel viewed from rear showing component layout.

20. Wiring the SLR sockets.



capacitor mounted on the 100 mm x 300mm aluminium plate. To improve thermalconduction between the rectifier and theplate (which acts as a heat sink) coat the

underside of the rectifier with heat sinkcompound before screwing it to the plate.Also attached to the plate are 3-terminal32Amp terminal block (block 1) and a 6-

terminal block (block 2) and two soldertags for earth connections. Mounted onthe PVC shelf are a 5-terminal block (block3) and the DC-DC converter soldered onthe piece of Vero strip board. The stripboard is attached by 4, 3 mm screwssupported on PVC spacers (note the wiresolder tags attached to the strip board).Photo 18 illustrates the unit with the 300mm x 150 mm aluminium shelf on whichare mounted the 4 Gecko drive units andthe DeskCNC control board. The Geckodrive units are attached to the aluminiumplate with 3 mm screws. Heat sinkcompound is applied to the undersides ofthe Gecko units to improve the thermalcontact between them and the plate, whichalso acts as a heat sink (not strictlynecessary given the current drawn by themotors). The positions of the holes for thescrews are given in Fig 7. The aluminiumplate I used wasn’t quite 150 mm wide soto install the control board I added a pieceof PVC as shown. The shelf is supportedon two pillars 40 mm long to givesufficient clearance between the Geckodrive units and the top of the enclosure.Also illustrated in Photo 18 is the rearpanel with the 4 SLR sockets forconnecting the stepper motors to thedrivers. Photo 19 illustrates the layout ofthe front panel switches. The positions arenot critical.

Begin by fitting all the components asillustrated in Photos 17, 18, 19. The 6-waychange over switch to select CNC or“manual” should be assembled and fitted.The switch consists of 3 dpdt (double poledouble throw) switches mounted side byside. I tried to find a suitable rotary switchbut was unsuccessful, so I had to resort tomaking something suitable. The plate formounting the switches is shown in Fig 8.Attach a bar to the three levers to operateall three switches simultaneously. Do notfit the Gecko drives or the DeskCNCcontroller board at this stage. I have madeextensive use of terminal blocks tominimise the number of solder jointshaving to be made in the confined spaceof the enclosure. All the connections to theGecko units as well as the control boardare with screw terminal blocks as well.

With all the hardware for the unit fittedin the enclosure and on the front and rearpanels work can begin on connecting upthe drive unit. You will need two sizes ofsoldering iron, a small electronics one witha tip diameter about 1.5 mm and a largerone with a tip diameter of about 3 mm.You will also need some rosin coredelectronics solder.

Begin by soldering the leads to connectthe SLR sockets to the Gecko drive units.Connect the four earth points togetherusing 22 swg tinned copper wire coveredwith heat shrink (the yellow wire in Photo20). Connect a length of green cable to theearth point of one socket and solder a tagon the other end. This will be connected toa convenient earth point in the enclosure.Now solder the connections to the Geckodrives to the socket pins. Choose the samefour colours as in the motor cable. Cut offfour equal lengths of each colour andremove the insulation for 6 mm from eachend. Now tin both ends of all the wireswith solder. Poke the end of the solder intohole in a socket pin and heat the pin until asmall amount of solder melts into the hole.Poke the tinned end of a cable into the

21. Working on the front panel.

Fig. 6 23HSX stepper motor lead colours:

Fig. 7 Gecko drive mounting plate

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MEWED200504013.qxd 12~1~05 15:04 2


hole and re-heat the pin. When the soldermelts push the wire in as far as it will goand hold until the solder sets. Solder in therest of the cables. Pair the cablesconnected to each of the motor coils andjoin them together with heat shrinksleeving (see photo 20).

The front panel should be wired upnext. In Photo 21 the mains switch is onthe extreme left, the next two switches arethe switch to disable the Gecko drive unitsand the switch for the Estop (emergencystop) on the control board. One side ofthese switches is connected to ground.The two terminals are connected and asingle lead then connects the two to aconvenient earth point. Make the two leadsthat connect to the Gecko drives and thecontrol board over long as they will be cutto length later. The manual-CNC switchand the 6-pin socket are wired up next.Begin with the socket. Solder in the centralearth lead first (green) this is made longenough to reach a convenient earth pointand terminated with a tag. Next connectthe manual X,Y and Z step leads to pins1,2 and 3 the single direction lead isconnected to pin 4 and a lead for +5 Voltsto pin 5 (this lead needs to be long). Nowconnect the X,Y and Z step leads to thebottom left contact of each of the switches(see Photo 22). Connect the singledirection lead (black) to the bottom rightcontact of the left switch and then connectthis contact to the remaining two contacts(see photo 22). Now connect a pair of stepand direction (orange and black) leads tothe two centre terminals of each switch.These paired leads need to be longenough to reach the X,Y and Z Geckounits. Finally connect pairs of step anddirection (orange and black) to the twoupper contacts of each switch long enoughto reach the step and direction terminalson the control board.

The power supply is wired up next.There are two power supplies one highvoltage at approximately 45 volts whichpowers the stepper motors and a second+5 volt regulated supply derived from the45 volt supply which operates the opto-isolators on the Gecko drives, the CNCcontrol board and the “Manual” controlunit. Together these three draw less than 1⁄2an amp. To derive the regulated 5 voltsupply a DC to DC converter is used as thisis the simplest method of generating the

required 5 volts. Constructors with someknowledge of electronics may choose tosave a few pounds by building analternative arrangement based on a 7805or similar chip. To make connections to the

DC-DC converter, the device is solderedonto a piece of 1⁄10 inch pitch Vero stripboard. Photo 18 shows the convertermounted on the piece of Vero board. Fourpins connecting the leads to the device can

22. Detail of wiring for the six way switch.

Fig. 8 Switch plate

Fig. 9 Manual control circuit Fig. 10 Rotary encoder

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also be seen .The device is fitted into thecentre of the piece of board and the tracksbetween the pins cut using a sharp 3mmdrill bit turned with the fingers. Making theconnections to the converter is straightforward as the converter is clearly labelled.The mounted converter is attached to thePVC shelf with 3mm screws in the cornersand insulated spacers between the boardand the shelf (see photo 18).

The transformer is connected up next.The transformer suggested has twosecondary windings each producing 30volts at 8.3 amps. To get the requiredcurrent for the driver these two windingsare connected in parallel. This wouldappear to give a total available current of16.6 amps. As a full wave rectifier withcapacitor smoothing is being used thisreduces the available current to 62% orjust over 10 amps. The transformerwindings must be connected togethercorrectly. Connect the start of each(VSecondary) together and the end of each (0V) together. For the transformer suggestedthis means (Red + Yellow) and (Black +Orange). The two ends are solderedtogether and secured in the terminal block1. Red cable with a current rating of over10 amps is used to connect the secondarywindings from the terminal block to the acterminals of the bridge rectifier. Thesecond ac terminal of the rectifier isconnected to ground via the terminal blockagain using suitably heavy earth cable.The positive terminal of the rectifier isconnected to the 6-way terminal block andthe negative terminal to ground. Photo 23shows how this terminal block is wired up.The four terminals from the left are usedfor the power to the drive units. A lead istaken from terminal 4 to the +ve terminalof the smoothing capacitor. Connect the -ve terminal of the capacitor to ground. Thebacks of these 4 terminals are linked. Alength of 2 amp red cable is connected toterminal 4 and soldered to the + inputterminal of the DC-DC converter. The –input and the – output terminals connectedto ground. The + output (+5 volts) isconnected to terminal 5 of the terminalblock and then link to terminal 6. From therear of terminal 6 two cables carry 5 voltsto the control board and to pin 5 on the“Manual” socket in the front panel.Connect two lengths of 2 amp cable to thefront of terminal 5 and a second two toterminal 6 of the terminal block. Thesecables carry 5 volts to the Gecko units tooperate the opto-isolators on the units.This completes all the wiring, which canbe seen in photo 23. It does look a bit of a“jungle”; however readers will notice thatwherever possible cables have been colourcoded and paired together with heat shrinkto minimise the possibility of makingsubsequent incorrect connections.

The CNC control board and the fourGecko units can now be fitted. Smear asmall amount of heat sink compound onthe underside of each Gecko unit beforescrewing them in place. To fit the two frontscrews it is necessary to remove the blueterminal blocks. These terminal blocks liftoff; they fit on pins attached to the circuitboard and are quite a tight fit. The terminalblocks on both the Gecko units and thecontrol board are clearly labelled. Neverthe less readers should consult theinstallation notes provided with both.When connecting up the units check at the

23. Completion of wiring.

Fig. 11 Frame

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same time all the wiring very carefully. Ifyou are unfamiliar with electronics have afriend who is check it over for you. When itis all connected connect the steppermotors to the unit. Do not turn on thepower. If you have a universal test metermeasure the resistance between eachmotor terminal on the Gecko units (phasesA – D) and ground. The resistance shouldbe about 20k. If by chance there is a shortto ground at any of the connections theGecko unit will be damaged if the power isturned on.

Manual control unitI have been using a CNC mill for about 5 years. I possibly have used the mill as amanually operated machine almost asmuch as in the CNC mode. The problemusing stepper motor drives manually is theback e.m.f generated by the motors whenthe armatures are rotated. This back e.m.f.generates a resistance, which I foundunacceptable. It also seemed a bit daft tohave a motor drive, which wasn’t beingusefully employed! This prompted thedesign of the manual operating unit. Inessence the device is a box having ahandwheel and switch arrangement.Turning the handwheel rotates an encodergenerating signals which then cause thespecified axis to move in sympathy.Having now made the unit and tried it Icannot understand why I didn’t make oneyears ago! Similar devices have becomeavailable over the last few years forprofessional machines, and will frequentlybe described as “Electronic handwheels”.

Photo 24 illustrates the unit. Sortingout the design, and sourcing some of theparts was the most difficult aspect of theproject. US Digital is by far the cheapestsource of encoders that I could find, aswell as the only source I could find ofQuadrature clock converters. Encodersare available from RS-Componentscosting considerably more. Theconstruction of the electronic controlboard is very straight forward. Thecircuit diagram for the control board isshown in Fig 9. The layout of the boardillustrated in Photo 25 follows thediagram given in Fig 9. Readers shouldhave little difficulty constructing theboard if they follow the circuit diagram.Connect the Reset line to one terminal ofthe momentary open switch and theother terminal to ground. Pressing theReset switch will set both dividers tozero. A problem with strip board ismaking neat secure cable connections.RS-Components supply strip board pinsfor this purpose. I have never foundthese pins satisfactory. Photo 26illustrates the method I employ, using 24swg tinned copper wire. The hole in theboard needs to be slightly enlargedusing a tapered broach. A length of wireis bent to form a loop and the endspushed through the enlarged hole. A 1.5mm panel pin is passed through the loopand the ends of the wire are pulled tight,bent parallel to the copper track, cut off1mm long and then soldered in. Theloop is twisted through 90 degrees, thecable passed through and soldered in.The result is a neat secure connection.

A test meter is required for wiring upthe rotary switches as it isn’t obvious howthe tags on the switches are connected.

24. Exterior view of manual control unit.

25. Components of manual control unit.

26. Technique for making stripboard connections.


The range switch selects the basicencoder clock rate (500 x 4) of 2000 perrevolution of the encoder giving amovement of 2 mm on X and Y and 1mm on Z. The second switch positionselects the 1⁄10 clock rate giving a 0.20 mmmovement on X and Y and 0.1mm on Z.On my original version, a final positionselects the 1⁄100 rate. These clock rates aresent to the second rotary switch, whichselects the axis. With benefit ofhindsight, the divide by 100 feature hasbeen found to be an unnecessary luxury.Thus the circuit diagram does not includethis feature.

The encoder connections areillustrated in Fig 10 as well as beingclearly shown on the unit. The framefor mounting the encoder isillustrated in Photo 27 and Fig 11.Fig 12 shows the other small partsassociated with the encoder. Theindex disc is made out of 2 mmengraving brass and has 20positions. I have not shown a designfor the detent I made as I am surereaders will be able to make a betterone than mine! The length of the 1⁄4 inch shaft for connecting theencoder to the knob is also notshown as this is determined whenfitting the encoder in the frame. It isimportant the line up the encodershaft and the connecting shaftaccurately. I was unable to source asuitable knob for the unit so Iresorted to making one out of apiece of Paxolin I had. The knobs forthe axis and range selection I madeas well, as RS-Components didn’thave what I wanted.

Final comments Photo 28 illustrates the completedmachine. I transferred the Newalldigital readout from my Wabeco tothe new mill. A digital readout is, Ithink, essential in order to get thebest out of your mill. I had to resort tothe Newall as I cannot read theVernier type easily. A digital readoutalso makes calibration of the axesextremely easy. I was amazed when Icalibrated the three axes to find thatthe backlash on all three was zero.

The entire conversion has taken

me about 2 months to complete. Asignificant amount of this time involvedhead scratching, trying to work out howbest to carry out some of the jobs. Now itis done I am very pleased with the endresult and consider that I now have a mill

that would have cost me many times theamount it finally cost, which was less than£2000 (including the cost of the X3).

As noted above, should prospectiveconstructors require further guidance, I canbe contacted on 01572 770 416.


27. Encoder and detent assembly.

28. Project completed.

Fig. 12 MCU components

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retrofitting the x3 milling machine (3) · february/march 2005 31 d. 500va toroidal transformer 2 x...

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