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Please read all of the instructions in this HTML documentation (Web site), and also read the circuit's parts manufacture's specifications sheets, data sheets, and technical literature before trying to build the BIPOLAR2 circuit board. You will have to get the part's manufactures information directly from the manufacture or from the manufacture's published works. The BIPOLAR2 board was only designed for use in the testing of DANCAM.EXE (tm) and DANPLOT.EXE (tm) and is not intended, and is not recommend, to be used with other programs, or to be sold as a product, or to be sold or given away as part of some product.
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Although stepper and servo motor driver modules are probably available from motor distributors all over the world, you may want to build your own in order to save some money. Also you may find that no commercially available product meets your needs as well as a circuit you can easily modify and repair yourself.
If you are not experienced in the construction and trouble shooting of electronic logic and power circuits you might save money purchasing ready built circuits, since you will not save anything if you burn out a lot of parts and have a problem wiring up the circuits or making printed circuit boards. When calculating the cost of your circuits you should probably allow for 50% to 100%, or more, cost overrun to take care of the inevitable mishaps that come with any do-it-yourself project.
Steps to build BIPOLAR2 circuit:
Determine the speed and power requirements of your machine. Try to establish a maximum feed rate for your machine that is as low as you can use in order to be able to use smaller motors with timing belt reduction to the lead screws. Using smaller motors will reduce noise and vibration, as well as require less expensive electronic drive circuits and power supplies. If your machine will require more power than the BIPOLAR2 circuit can be safely operated at you should re-design your machine or use another stepper motor driver circuit.
Purchase new, surplus, or used motors with enough torque that have power requirements compatible with the BIPOLAR2 circuit. When you pick out motors be aware of how many leads the motor has, since some motors are wired to be run on Uni-polar drivers which can reduce the torque when operated from the BIPOLAR2 circuit. Since low voltage motors with high current requirements can require using some other type of stepper motor drivers, using motors rated at medium voltage, e.g. 24 volts, and less current might give the same torque and allow the use of the BIPOLAR2 driver circuit.
Calculate the value of the current limiting resistors by using the stepper motors rated current requirements and the supply voltage that you can use at the current required. With the BIPOLAR2 circuit the supply voltage used will be reduced for motors with higher current ratings. You need to keep the total voltage, amperage, and wattage required by the stepper motor within the manufactures ratings for the components on the circuit board.
Buy the necessary parts to build the circuit. If you are building circuits for the first time it is probably a bad idea to try to "improve" the circuit by making component substitutions before you have completed your first specimen of the circuit that works as it was designed. If you cannot find the parts listed, look for another source elsewhere.
Assemble the circuit. Do not build circuits that you do not understand, since you will not be able to proofread the plans to see if they contain mistakes.
Check the wiring to make sure you made no mistakes. Test for cold solder joints, and short circuits. If you are making printed circuit boards and using the dry toner transfer films, you will probably need to "touch up" the traces with at resist pen, and scrape off smudged toner that will make the traces too close together and cause arcing.
Test the circuit. You can use a normally closed, N.C., push button and a 2.2K ohm pull up resistor on the step input, and a switch and a 2.2K ohm pull up resistor on the direction input. To de-bounce the step pulse and direction inputs you may need to put a capacitor from the input to common, perhaps 0.1 mf to 10 mf or more. The N.C. push button and switch would go from the inputs to common. Each time you push the button the motor would make one step, and the switch would reverse the direction of the motor. If the capacitor on the step input does not fix the push button bounce problem you might try using two 7414 inverters in series before the step input, and a larger capacitor of about 100mf to 1000mf on the input of the 7414.
Hook up the BIPOLAR2 circuit to your parallel port. Be careful in hooking up your circuits to your parallel port, you do not want power from the circuits flowing into your parallel port and destroying your parallel port or computer's mother board. If you are nervous about making direct connections you might try using optical isolators, but with junk computers being so cheep, the cost of the isolators might be more than the shop computer is worth.
Use DANCAM.EXE (tm)/DANPLOT.EXE (tm)'s motor test utilities to configure your set up. Be sure that you test your motors after they are mounted in your machine since they may react differently when under full load. It is better to have your machine run slower and not lose position, than have it run fast and stall or make messed up reject parts. Check the values of the p.w.f, overdrive p.w.f., p.w.f. increaser, and pulse rate multiplier. Be sure to use the automatic self calibration command in v2.7 before you execute any tool path files so that the feed rates and timing will be calibrated to the speed of your computer.
The ability to build, repair and modify a motor driver translator module circuit yourself, rather than just buy a ready made module, can save you money, but only if you can avoid wasting and burning out a lot of parts. Stepper translator module manufactures have taken to "potting" their modules in black plastic so that if anything goes wrong and a part burns out you are probably out the price of the whole unit.
If you ran the macro file BIPOLAR2.MAC, which was supplied as part of the original v2.6 distribution, under DANCAD3D (tm) v2.6, schematics and printed circuit board foil pattern files would have been produced that correspond to the version of the BIPOLAR2 circuit as it was in the v2.6 era. The circuit of the BIPOLAR2 circuit board was intended only for testing and use with my CAM programs by the individual hobbyist that built and set up his automated machine.
Remember to double check any connections before you turn the power on that will energize the BIPOLAR2 circuit. I assume that you have plenty of experience building circuits and know all of the hazards and problems that can arise, if you have no such experience you would most likely do better to buy ready built modules. Making changes to the design of circuits probably would reduce their performance, or produce other problems including fire and damage to your computer.
The BIPOLAR2 stepper motor translator module circuit has three parts, the up and down counter, the power amplifiers, and the Current booster.
The BIPOLAR2 stepper motor translator module circuit takes the step pulse and direction signals from the parallel port and switches the coils in the stepper motor to positive and negative power to make the stepper motor turn. The translator portion of the circuit is really a counter that counts the pulses from the parallel port. When the direction pin is low (D < 0.3 volts) the counter counts up, i.e. 1-2-3-4-1-2-3-4 and so on, and when the direction pin is high (D > 2.8 volts) the counter counts down, i.e. 1-4-3-2-1-4-3- 2. Counting up turns the motor clockwise, counting down makes the motor turn counter clockwise.
To reduce the step angle of the stepper motor shaft from 90 degrees to 1.8 degrees most stepper motors have 50 grooves cut in the surface of the rotor. By also grooving the poles of the four coils the motor will give 200 steps per revolution, i.e. every fourth step moves one groove width because the grooves on the successive poles are 1/4 of 50 parts per revolution advanced. So step 1's pole is 0/200 advanced, step 2's pole is 1/200 advanced, step 3's pole is 2/200 advanced, and step 4's pole is 3/200 advanced (step 5 lines up at pole 1 again but with the rotor one groove ahead.)
The counter portion of the BIPOLAR2 stepper translator module connects to two Bi-polar power amplifier to supply the current to the motor windings. The Bi-polar power amplifiers put out positive then negative power, with one or the other kind of power being on all the time from both power amplifiers, which holds the motor shaft in position when the motor is not turning. Each of the Bi-polar power amplifiers is made of a PNP and NPN Darlington power transistor. Just using two transistors for each motor coil reduces the number of transistors required to four from the eight required if H bridge power amplifiers had be used in the circuit design. A split power supply is required by the BIPOLAR2 circuit, so the motor power supply requires two capacitors rather than just one. Do not substitute regular power transistors into the BIPOLAR2 circuit, it will not work with them, high gain Darlington power transistors are required.
Bipolar amplifiers may generate more torque from some stepper motors by applying both positive pulling power and negative pushing power to all of the motor windings. When some motors are connected to the BIPOLAR2 circuit, such as a 5 lead motor, two of the coils are not normally used so there probably would be little or no improvement over Uni-polar drive circuits. The BIPOLAR2 circuit was designed with a common connection of the motor coils, so that three wire 72 RPM sync motors could be used as stepper motors, this "center tapped" connection also allows motors designed for Uni-polar connection to be operated, so almost any two or four phase stepper motor can be operated if its current and voltage requirements are with in what the circuit can handle.
Since I had limited room on the v2.6 program disks I had designed a single Bi-Polar full step board that was a "universal" circuit that would work with many 72 RPM sync, Uni-polar, or Bi-polar stepper motors. My circuit is a bit odd and is not like many commercial Bi-polar circuits in that it can operate 3 and some 5 lead "stepper" motors, as well as 4, 6, and 8 lead two phase stepper motors. I also use just 4 output transistors rather than the usual 8, since I do not use "H bridge" output stages. To get my circuit to work, a split power supply is required for the motor coils, and so you have to be careful how you connect your common connections, since I use what would typically be the "negative" terminal of the split power supply as the common, if you do not understand how I am getting this to work you should not try to build this circuit.
The metal case of the split power supply, and the cable shields should not be connected to the "center tap" of the power supply, since the motor power supply negative terminal is connected to the signal common and therefore the computer's common ground. The stepper motor coil's "center tap" is "floated" at the power supply "center tap" voltage which is one half the total voltage from the motor power supply measured from the positive terminal to the negative terminal, such that measured from the negative terminal the motor supply "center tap" terminal is at positive "v/2" from the signal common, and the motor supply positive terminal is at "v" from the signal common.
Because the motor windings are a coil, i.e. an inductor, the current moving through the coil decreases as the frequency (speed) of the motor steps increases (when a constant voltage source is used.) Because the torque is roughly proportional to the current going through the motor coils you will want to have the voltage supplied to the motor increase as the motor step frequency increases in order to hold the motor coil current constant (Ohm's law, E/(I*R).) If you used a raised the voltage all the time the motor would burn up when it slowed down or stopped. One solution to getting fairly constant coil current is to put a resistor in series with the motor coil such that the resistor limits the current when the motor is stopped to the motor's rated current, but lets you use a higher supply voltage (up to about 6 times the motors rated voltage) so that the motor will get more voltage when the motor steps quickly.
The reason the resistor gimmick works is that the resistor and the motor coil form a voltage divider. When the translator amplifier switches the power on to a coil the inductance of the coil is very high, so no mater how big the series resistor is, (nearly) all the voltage is dropped across the motor's coil. As time goes on (about a hundredth of a second) the impedance (resistance) of the coil drops and more, and more, of the voltage is dropped across the resistor. After about a tenth of a second the impedance of the coil stabilizes and the coil acts like a resistor in series with the series resistor dividing the voltage to the value required for the motor's holding torque current rating.
To improve the high speed torque further the BIPOLAR2 circuit board has some transistors arranged in parallel to the current limiting resistors that "short circuit" the motor current limiting resistors for about a thousandth of a second each time the polarity of the power through the resistors reverses. The value of the capacitors between the collector and base of those transistors controls how long the "short circuit" lasts.
Because of the amount of voltage and current going through the motor windings the series current limiting resistors need to be of a special high power kind made of ceramic and metal parts to withstand the high temperatures that they will reach while dissipating the power. Since the power resistors get very hot after they are on for a time, you need to mount them so that there is a good air flow around them, and be careful that they are not mounted on or near anything flammable or that will melt.
To calculate the value of the power resistors to use in series with the stepper motor winding, to limit the current, you can use this equation:
Ro = ((Vs - Vd) - Vm) / Im
WHERE: Ro = Series resistor value in ohms.
Vs = Motor coil supply voltage, larger than Vd + Vm.
Vd = Voltage drop from transistor & diode, about 1 to 2 volt.
Vm = Rated voltage for motor when stopped.
Im = Rated current (amperes) for motor when stopped.
To calculate the wattage rating for the series resistor use the following equation:
Rw = ((Vs - Vd) - Vm) * Im
WHERE: Rw = Series resistor value in watts.
Vs = Motor coil supply voltage larger than Vd + Vm.
Vd = Voltage drop from transistor & diode, about 1 to 2 volt.
Vm = Rated voltage for motor when stopped.
Im = Rated current (amperes) for motor when stopped.
In practice Vs will be about six times the motors rated voltage. Vd would only be significant when Vs is less than about 20 volts. The motor and series resistors get hottest when the motor is stopped. Since raising the supply voltage increases the wattage dissipated in the transistors of the motor driver amplifiers you may be limited as to how much voltage you can use. Also the maximum voltage that the transistors of the motor driver amplifiers can handle independent of the current and wattage limits will also limit how much voltage you can use for the motor coil power supply.
An example may help you work out the values for the resistors that go with your motors. Assume we have a motor rated at 9.6 volts and 2.1 amperes. You are going to use a supply voltage of +/- 22 volts, and the translator power amplifier circuit drops 1.4 volts in its semiconductors.
EXAMPLE: Ro = ((22 - 1.4) - 9.6) / 2.1
Ro = (20.6 - 9.6) / 2.1
Ro = 11 / 2.1
Ro = 5.25 ohms
Rw = ((22 -1.4) -9.6) * 2.1
Rw = (20.6 - 9.6) * 2.1
Rw = 11 * 2.1
Rw = 25 watts
To assemble the BIPOLAR2 circuit board use a low wattage, 27 to 30 Watt, pencil type soldering iron, and rosin core tin and lead alloy solder to make the connections.
To transfer the foil pattern, created by BIPOLAR2.MAC, to a blank copper clad circuit board, you can use a laser printer, or copy machine, to print the pattern onto the special dry transfer materials now available. Then iron the toner from the transfer material to the board, and etch and drill in the usual way. The toner transfer material may not do a good job of transferring the toner, so you may have to go over the traces with a etch resist marking pen, and scrape toner away from between the traces and pads so that when the board is etched you do not get open traces, or traces and pads that are too close together and will short out or arc over.
Be sure to watch the streaming video segment in this Web site about making your own printed circuit boards, before you try to make any of your own circuit boards.
The macro file BIPOLAR2.MAC made five DANCAD3D (tm) ASCII files:
BP2FOILS.ASC Foil patterns for both sides of circuit board. BP2PARTS.ASC Parts placement and identification drawing. BP2SHOLE.ASC Small (0.047", 1.2mm) hole placement. BP2MHOLE.ASC Medium (0.0625", 1.6mm) hole placement. BP2LHOLE.ASC Large (0.128", 3.25mm) hole placement. BP2SUPLY.ASC Schematic for two types of power supply.
The PCB foil patterns for the BIPOLAR2 circuit board are created into the ASCII drawing file BP2FOILS.ASC when you run the macro file BIPOLAR2.MAC. Since this is a two sided board the PCB drawings for the component side and back of the board are included as mirror images so you can iron them onto the toner transfer film without having to flip any of the PCB drawings. Special attention was made in preparing the PCB foil pattern drawings to have the points where the traces connect from the component to the back have a sizable tolerance for misregistration of the etched foil patterns on the two sides. Just solder a piece of wire from the component trace to the back trace through the hole. If you want to make the board "single sided" you can replace the component side traces with jumper wires. Several registration marks are located at the corners so you can use different size blank PCB boards: 4" by 6", 4.5" by 6", 4.5" by 6.25", and the recommended board size of 4.5" by 6.334".
The meaning of the abbreviations at the BIPOLAR2 board's terminals is:
STEP.....Step signal from parallel port. DIR......Direction signal from parallel port. S-COM....Signal common to parallel port, and the +5 volt supply. +5V......Positive five volt supply for logic. COM......Common for motor coil power supply, 0 (actually supply negative, -v). +V1......+v1 volts from motor coil supply, +v * 1 (actually supply center, 0). +V2......+v2 volts from motor coil supply, +v * 2 (actually supply positive, +v). RED......"Red" coil lead from the stepper motor. R/W......"Red & White" lead from the red coil of the stepper motor. GRE......"Green" coil lead from the stepper motor. G/W......"Green & White" lead from the green coil of the stepper motor. R2B......One end of the current limiting power resistor R2. R2A......The other end of power resistor R2. R1B......One end of the current limiting power resistor R1. R1A......The other end of power resistor R1.
Note that the wire colors on your motor may be different than the wire colors indicated from the terminal names. You should check the motors you have with a resistance meter and mark the leads with my lead color codes, so that you can make the proper connections. In stepper or 72 RPM sync motors that have two coils, one coil is RED to R/W, and the other coil is GRE to G/W. You can sometimes reverse the rotation of the motor by reversing the GRE and G/W ends of that coil. In motors such as 3 and 5 lead stepper motors where the ends of the two coils are connected inside the motor, you may not be able to reverse one of the motor coils, and so would use software, on a TTL XOR gate on the direction signal, to make the reversal of the motor rotation.
Various stepper motor companies use different lead colors or different connections for the same lead colors, so you will need to use a VOM to figure out which leads connect to a common coil, which leads are a center tap, which leads are the free ends of the stepper motor's coils, and which leads make up just one single coil. Even if the colors match what is given here you should check the resistance of each coil to make sure that the coils all have the same resistance, and that you have not gotten one of the coil center taps mixed up with the free ends of the coils, which might result in burning out the (half) coil by putting too much current through the (half) coil.
If your motor has center tapped coils, make sure that you know if your stepper motor's rated voltage is for the whole coil, or half of the coil. If you apply the whole coil voltage to the half coil you will probably burn out your stepper motor. This can get confusing in 8 lead stepper motors because the coils might be connected in series or parallel to get different ratings.
Three, four, five, six, and eight lead or terminal two or four coil stepper motors might have been connected to the BIPOLAR2 circuit as follows below. Sometimes you will make the connections to the stepper motor by leaving some of the stepper motor's terminals or leads unconnected.
To make hooking up the stepper motors easier I use the same color codes for wiring up all of my stepper motors, this requires six colors of wire: red, pink or white with a red stripe, green, light green or white with a green stripe, white, and black. Unfortunately some stepper motor manufactures use other colors of wire on their stepper motors, or have just terminals marked with numbers, so to avoid confusion you can solder wires onto your motors by using the "standard" six colors and be less confused when you need to change things and reconnect the motors years from now.
Four lead stepper motors have two coils, one coil goes to the "RED" and "R/W" terminals, and the other coil goes to the "GRE" and "G/W" terminals.
Since four lead stepper motors have just two coils all of the stepper motors leads are connected to the BIPOLAR2 circuit.
"RED" = RED lead (start of coil 1.) "R/W" = RED and WHITE lead (end of coil 1.) "GRE" = GREEN lead (start of coil 2.) "G/W" = GREEN and WHITE lead (end of coil 2.)
Most commercially available stepper drivers will not operate three lead stepper motors. I specially developed my BIPOLAR2 circuit to drive the three lead 72 RPM "sync" motors as stepper motors, since at that time you could get a 750 in/oz motor for less that $30. Over the last few years these surplus motors have gotten harder to find, but if you find some they are often the cheapest high torque "stepper" motor you can find. Be sure to figure the voltage and current limiting resistors carefully since 72 RPM sync motors are rated for AC voltage and not DC voltage!
With the 72 RPM motors being rated at 120 VAC, you will probably find that about 15 to 20 VDC will give the rated current when the motor is not turning, but be sure and carefully measure coil current since these motors may overheat and burn out if you meet or exceed their rated current.
Three lead 72 RPM motors have the two coils connected together at one end, so they are like a four lead motor with one end of each of the two coils connected internally to a single lead, therefore when you check the motor's three leads with a VOM it looks like the motor that has one center tapped coil.
To find the center tap of the motor connect the black lead of your VOM to one of the three terminals of the motor. Put the VOM on Rx1 scale, and measure the resistance to the other two motor terminals. If you get the same resistance, say about 20 ohms, to both of the other terminals then the black lead should be on the center tap, but if your read 20 ohms on one terminal and 40 ohms on the other terminal, then the black VOM lead is not on the center tap (common) terminal of the motor. Your motor will give different resistance values, but the idea is that two coils in series will read twice the resistance that one coil will read. When you find the lead that is the center tap lead or terminal, mark the other two leads "RED" and "GRE" or use red and green wire to connect to the motor's terminals, the center tap can be wired with white wire. In the BIPOLAR2 circuit the R/W and G/W terminals are connected together, so the center tap or common coil connection on three or five lead stepper motors can be wired with white or black wire since there is only one center tap on 3 and 5 lead stepper motors, and that one wire can go to the R/W or G/W terminal on the BIPOLAR2 circuit board.
Do not put your fingers on the motor terminals since the power from the VOM can make a high voltage in the motor coil when you make and break contact that might give you a shock, which might make you drop the heavy motor on your foot, hurt yourself, or do something else undesirable.
"RED" = RED 72 RPM motor lead. "R/W" = WHITE lead (center tap of coils.) "GRE" = BLACK 72 RPM motor lead.
If the 72 RPM sync motor has a fourth green lead, that may just be a ground wire, you can use your VOM to measure from the green lead wire to the motor case and see if there is a connection. You may need to scrape some of the paint off to get a good contact with the motor's case.
The color code for five lead stepper motors is sometimes red, red and white, green, green and white, and white. Where the white lead is the common for all four of the stepper motor's coils.
When connected to the BIPOLAR2 circuit only two of the four coils are used normally so the GREEN & WHITE, and RED & WHITE stepper motor leads are not connected, i.e. they do not normally connect to the G/W and R/W terminals on the BIPOLAR2 circuit board when five lead stepper motors are used.
Five lead motors are normally operated from a Uni-polar driver circuit, but can also be used on my BIPOLAR2 circuit if only two of the four coils are used. It might take some experimenting to figure out which two of the four coils to use. When you pick the wrong combination the motor may wiggle back and forth rather than rotating. Always make sure the power is off before you change the connections, or you may blow out the driver circuit and give yourself a shock or burn.
The procedure to figure out which motor terminal is the common for all the coils is the same as was mentioned above for the three lead motor, pick one terminal or lead for the VOM's black lead, then measure the resistance to the other four motor terminals or leads with the VOM's red lead, the black VOM lead is on the coil common terminal or lead when the resistance measured to the other four terminals or leads is the same, i.e. if you measure 8 ohms to all four of the other terminals you have found the common, but if you measure 8 ohms to one terminal and 16 ohms to the other three then you have not found the common. Your motor will give different resistance values, but the idea is that two coils in series will read twice the resistance that you measure for one coil.
After you find the common lead you need to try the other at the RED and GRE terminals on the BIPOLAR2 board to see which two make the motor step properly when you use the Jog command in the CAM programs to generate the step pulses.
"RED" = RED lead. "R/W" = WHITE lead (common of all four coils.) "GRE" = GREEN lead.
Six lead stepper motors have two center tapped coils. One of the two coils has the free ends with red and red and white colored wire leads, and a center tap colored black. The other of the two coils has the free ends with green and green and white colored wire leads, and the center tap colored just white.
Six lead motors can be operated by Uni-polar or Bi- polar stepper motor driver circuits
Six lead motors would usually be operated in Half Coil mode when used with my BIPOLAR2 circuit.
"RED" = RED lead. "R/W" = BLACK lead (center tap for red coil.) "GRE" = GREEN lead. "G/W" = WHITE lead (center tap for green coil.)
The GREEN & WHITE, and RED & WHITE leads are left unconnected when six lead motors are used with just one half of each of the coils connected. It might be possible to get more torque on some six lead motors by using the full coil, but you might find that your motor turns faster for a given supply voltage if the half coil connections are used.
Six lead motors have two separate center tapped coils, referred to here as the "red" and "green" coils. The red coil has three lead wires, the red for one end, black for the red coil center tap, and "R/W" or red and white stripped wire lead for the other end of the red coil. Likewise the green coil has a green wire lead for the end of the green coil, a white terminal for the center tap of the green coil, and a "G/W" or green and white stripped wire lead for the other end of the green coil.
To figure out which terminal or lead is which on a six lead stepper motor using a VOM, put the black VOM lead on one of the six motor terminals, measure to the other five motor terminals, three of the terminals will read more than 1M ohm or more, they are the other coil's terminals. Of the remaining two terminals you will read either the same resistance, perhaps 12 ohms, or you will read 12 ohms and 24 ohms, if you read 12 ohms to the two terminals the black lead of your VOM is on one of the center tap terminals, if not move the black VOM lead to the terminal that you measured 12 ohms (not the 24 ohm one) to and check that terminal is now the center tap terminal. Then do the same thing for the three terminals for the other coil to find the center tap, the other coil was the one you measured 1M ohm or more to its three terminals before, i.e. move the black VOM lead to one of those three terminals and measure as before. Your motor will give different resistance values, but the idea is that two coils in series will read twice the resistance of one coil, and no connection will read high resistance.
Note that the voltage and current requirements are different for operating a six lead stepper motor in full coil or half coil modes. Check the manufactures specifications to see how the voltage and current ratings change for various connections to the motors you will be using. The values of the current limiting resistors and the supply voltage used will also need to be adjusted depending on the coil mode selected.
Eight lead motors can be hooked up with the coils hooked up in parallel or series, you will need to look at the manufactures drawings and figure out the voltage and current to be used for different connections. Parallel connection of the coils draws two times the current of series connection, e.g. if each coil draws 2 amperes then two coils in parallel will pass double the current, 4 amperes, where as series connection of the coils will add the resistance of the coils, so the voltage will need to be doubled and the current will stay 2 amperes.
The motors rated voltage for one coil is the same for two coils in parallel, e.g. if one coil is rated for 3 volts then two coils in parallel will also be supplied with 3 volts, but if you wire the coils in series then you would need to increase the voltage across the total of both coils to 6 volts. If you do not double the voltage for series connection the current across each coil would not be enough for the motor to operate properly.
In this example parallel wiring would use 12 watts, single coil would use 6 watts, or series wiring would use 12 watts. The current for the whole motor would be twice this current because two coils or two pairs of coils are used. If your driver cannot work with the amount of current needed for parallel connection, you can try one coil or series connection. For a given supply voltage you may get more speed using one coil rather than series connection because the "over voltage" will be greater. Series connection may give more torque than one coil, but with a lower maximum speed. Parallel should give good speed and torque, but might require more current than the driver circuit can supply.
If you use one coil connection four of the motor terminals or leads would be left unconnected. If you use series or parallel connection all the motor terminals or leads would be used, but in different arrangements.
The drawing in file BP2PARTS.ASC, generated by BIPOLAR2.MAC, the part drawing outlines show the placement of the of the components on the board. Where you buy the parts might make a difference in the final cost of building your circuit boards. If you shop carefully this board might be able to build for less than about $60 (1996 prices). Mail order surplus electronic suppliers are generally good for surplus parts, but even among them there is a large price spread, the TIP122's for instance have been listed at prices ranging from about $0.35 to $0.75, which can add up since you will need 24 of them to build three boards (.75*24)-(.35*24) = $9.60 (1996 prices).
Do not substitute Mylar, or other types of plastic film, capacitor where ceramic type has been specified. The components listed are for the normal configuration, it is possible to omit the booster section of the board and get reduced performance at a cost savings. If you reduce the supply voltage to the right amount R1 and R2 can be replaced with pieces of #12 gauge wire, but the motors may not run as fast. Other substitutions might be possible, such as higher current diodes, but do not make any changes unless you know what you are doing and understand all the problems your changes might cause in the other components.
Be sure to check the semiconductor manufactures specification literature to make sure you do not exceed the parts ratings for the power supply voltages and load currents you will be using. Increasing the supply voltage while keeping the motor current constant will increase the wattage dissipation in the components in the board, so use a supply voltage that does not overheat the parts with the amount of current your motor needs. With higher current motors you may need to reduce the supply voltage, perhaps all the way down to the motors rated voltage. Some low resistance motors may draw more current than this BIPOLAR2 circuit board can be used with even if you reduce the supply voltage.
PARTS LIST FOR CIRCUIT BIPOLAR2: PART QUANTITY DESCRIPTION R1,R2 2 Power resistors to limit motor current, see text. R3,R4 2 100 ohm 0.25 watt. R5,R6, R7 3 2.2K ohm 0.25 watt. R8,R9, R10,R11, R12,R13, R14 7 1K ohm 0.25 watt. R15,R16 2 2.2K ohm 5 watt. R17,R18, R19,R20 4 300 ohm 0.25 watt, see text. C1,C2 2 1000 pf 10 volt ceramic capacitor. C3,C4 2 100 mf 6 volt electrolytic capacitor. C5 1 0.1mf 10 volt ceramic capacitor. C6,C7, C8,C9 4 1 mf 63 volt electrolytic capacitor, see text. D1,D2, D3,D4 4 LED type XC556R D5,D6, D7,D8 4 1N4004 rectifier D9,D10, D11,D12 4 1N5404 rectifier Q1,Q2 2 TIP127 100 volt PNP Darlington transistor. Q3,Q4, Q5,Q6, Q7,Q8, Q9,Q10 8 TIP122 100 volt NPN Darlington transistor. U1 1 7414 TTL IC. U2 1 7486 TTL IC. U3 1 7476 TTL IC. J1 1 4 screw terminal block 0.2" spaced PCB mount. J2 1 12 screw terminal block 0.2" spaced PCB mount.
In addition you can use two 14 pin and one 16 pin IC sockets. All the transistors need large heat sinks, except for Q3 and Q4. The LED D1 blinks for the step pulse signal, D2 is the direction signal indicator, and D3 & D4 show the polarity of the power going out to the two motor coils.
With the parts indicated motors rated in the range of about 45 volts at 0.5 ampere to something like 1 volt at 3 amperes might be able to be driven, depending on how hot the parts get, the supply voltage, and if R1 and R2 are greater than zero ohms. The supply voltage would need to be reduced for motors that have higher current ratings. The actual maximum current and voltage depend on the SOA of the transistors and rectifiers used, and how well your heat sinks and air flow keep the parts cool. A cooling fan must be used on the heat sinks if the current is over 1 ampere. Higher power parts might be able to be substituted to improve the power capacity, but since the space on the board is very cramped there is not much room to jam anything more in there. High gain Darlington transistors must be used for the circuit to work. Remember that the 1N5404 parts must pass the full motor current as well, if you make a substitution. I do not recommend your trying to "beef up" this circuit board, you would probably do better to use timing belt reductions on smaller motors and live with a slower maximum feed rate.
The value of R17-R20 effects the amount of high speed torque boost. Values from 1K ohm to 100 ohm are useful. The higher the value the more current the motor gets at high speed. Start with small values and increase until the motor has sufficient torque. Setting the high speed torque too high will make the motor over heat, and may also cause lost steps due to over shooting. C6-C9 can also be changed to effect the amount of boost, values from 2 mf to 0.5 mf are useful, the larger value giving more boost. A simple way to tell if the boost transistors are working is to run the motor at high speed (e.g. use the RPM test in the CAM programs) and then see if the heat sinks on Q7-Q10 get warm, be sure to turn the power off before checking the heat sinks. If you have an oscilloscope you can put a 0.1 ohm 10 watt resistor in series with the motor winding and put the oscilloscope across the 0.1 ohm resistor to measure the current through the motor coil at different speeds. Without the boost, the current will fall off as the speed increases, and, with too much boost, the current may more than double at full speed.
The holding torque current is set by the power resistors R1 and R2 and the amount of the supply voltage. Use the equations given above to find the correct resistance and wattage. The power resistor values will generally be between 10 and 100 ohms at 15 to 25 watts depending on the motor you are using. R1 and R2 can be replaced with pieces of #12 gauge wire if the motor coil power supply voltage is adjusted for the motor holding current value, but the torque booster section of the circuit will not operate.
Be sure you have a good signal ground wire going back to the parallel port, otherwise you will get spurious motor steps. If you get spurious steps try turning off the motor coil power and look at the signal display LED's on the BIPOLAR2 circuit board to see if the signals are getting to the board properly. Electrical noise can "feedback" from the motor coil wires into the step pulse and direction signal inputs through the ground wire if you have not been careful about using separate ground wires for the signal and stepper motor coil power.
Full Step Bipolar drive of a stepper motor applies either positive or negative current to the two coils used in the stepper motor all the time.
The sequence for Full Step Bipolar drive of a stepper motor is:
-------------------------------------- | BIPOLAR COIL "A" | COIL "B" | -------------------------------------- | STEP 1 | POSITIVE | POSITIVE | | STEP 2 | NEGATIVE | POSITIVE | | STEP 3 | NEGATIVE | NEGATIVE | | STEP 4 | POSITIVE | NEGATIVE | --------------------------------------
Using Bi-polar drive has an advantage in that it might give more torque when a three or four lead stepper motor is used in part because all the motor windings are constantly in use, as apposed to six lead motor on a Uni-polar drive where half to three quarters of the windings are always off. Five, six, and eight lead stepper motors can also be driven from the Bi-polar drive with half the coils disconnected and still be serviceable.
To get negative power from two positive supplies the BIPOLAR2 circuit "floats" the common end of the motor coils at a voltage half way between the maximum voltage and signal common. When the switched end of the motor coil goes high the voltage flow through the coil is positive, and when the switched end of the motor coil goes low the voltage flow through the coil is negative. Two amplifiers are used in the BIPOLAR2 circuit to operate just two stepper motor coils.
The files BP2SHOLE.ASC, BP2MHOLE.ASC, and BP2LHOLE.ASC, generated by running the macro file BIPOLAR2.MAC, can be taped on the board to help you see where to drill the holes. These files might also be used as tool path files with DANPLOT.EXE (tm) to automatically drill the PCB circuit boards.
The BIPOLAR2 circuit requires two isolated power supplies, a low current +5 volt power supply for the TTL logic portion of the circuit, and a dual or split higher voltage and current power supply for operating the stepper motor's coils. So there are three voltage input terminals on the BIPOLAR2 circuit board, and two common ground terminals, although the motor coil supply common ground terminal is connected in an unusual way. The common connection for the two stepper motor coils is NOT at signal common ground, and should never be connected to the other common or ground points on anything.
The BIPOLAR2 circuit requires a "split" power supply for the motor coil supply. You might be able to wire two commercially built power supplies in series to get the +V1 and +V2 volts required. Really the +V1 terminal is what would normally be called the common of a split supply, but I have connected the -V terminal of the split supply to common, and "floated" the supply common to +V1 to allow the circuit to drive three and five lead stepper motors. Be very careful that you do not connect the supply incorrectly. As an example, if you use two positive 5 volt supplies, you would connect the common of supply 1 to COM on the BIPOLAR2 circuit board, connect together the +5 of supply 1 and the common of supply 2 and use that for +V1, and use the +5 volts of supply 2 for +V2. Make sure that the common on the supplies does not connect to their case or the AC line ground, or you will probably start a fire, blow a fuse, ruin your computer, shock yourself, and destroy the power supplies, i.e. the supply outputs must be isolated from everything! If you use a positive +5 volt supply, and a -5 volt supply for the motor coil supplies the two supply commons would be connected together and used for +V1, the -5 supply volts would be used for the COM, and the +5 volts would be used for +V2.
If you are confused about the power connections do not turn the power on, as you will probably blow out your board and much of what is connected to it.
To avoid some of the potential problems with commercially built supplies, you can build the supply circuits shown in the drawings SUPPLY2A and SUPPLY3A that are in the ASCII drawing file BP2SUPLY.ASC. The terminals on the SUPPLY2A and SUPPLY3A drawings are marked for: COM, +V1, and +V2 to correspond to the markings on the BIPOLAR2 board.
AC power is transmitted in the form of a sine wave form at a frequency of 50 Hz or 60 Hz. To make DC power you need to use a rectifier and capacitor. AC voltage is measured in RMS value usually which means that the peek of the wave crest is higher in voltage than the RMS value. Because, the rectified DC will have a higher voltage than the stated RMS secondary voltage of the step down transformer, you need to select a transformer that has a RMS output less than the required DC voltage. Generally you will want an amperage rating twice the required current for your stepper motors to prevent excessive voltage drop under full load.
You can build one motor coil power supply to operate more than one of the BIPOLAR2 circuit boards at the same time if you increase the current ratings proportionately. The capacitor values also need to be increased proportionally.
How to figure DC voltage from AC transformer:
Vo = Vs * 1.414
WHERE: Vo = Approximate output DC voltage.
Vs = Transformer secondary rated RMS AC voltage.
Power supply SUPPLY2A can use up to a 62 volt center tapped transformer to supply up to about +45 & +90 volts DC as measured from terminal COM. Since this supply uses the transformer center tap, at the center tap of a 62 volt transformer you get 31 volts * 1.414 which comes out to about 44 volts DC. If you use a 12 volt center tapped transformer you would get 6 volts on the center tap which would produce about +8.4 and +16.8 volts DC. The rating of the transformer, diodes and capacitors needs to be adjusted to your amperage requirements. The actual voltage of the transformer used would need to be adjusted depending on the current requirements of the stepper motors that will be used, i.e. reducing the voltage for higher current stepper motors.
PARTS LIST FOR CIRCUIT SUPPLY2A:
PART QUANTITY DESCRIPTION
1 AC line cord.
T1 1 4 to 62 volt RMS, center tap secondary, transformer.
D1-D4 4 Rectifier, e.g. 25 ampere at 400 piv.
C1,C2 2 4000 mf per ampere, 75 volt.
R1,R2 2 47K ohm at 1 watt resistor.
Power supply SUPPLY3A can use up to a 31 volt transformer to supply up to about +45 & +90 volts DC as measured from terminal COM. A 6 volt transformer would give about +8.4 and +16.8 volts DC. Only two rectifier diodes are used. The value of the capacitors needs to be increased since SUPPLY3A uses "half wave" rectification. The rating of the transformer, diodes and capacitors needs to be adjusted to your amperage requirements. The actual voltage of the transformer used would need to be adjusted depending on the current requirements of the stepper motors that will be used, i.e. reducing the voltage for higher current stepper motors.
PARTS LIST FOR CIRCUIT SUPPLY3A
PART QUANTITY DESCRIPTION
1 AC line cord.
T1 1 2.5 to 31 volt RMS transformer.
D1-D2 2 Rectifier, e.g. 25 ampere at 400 piv.
C1,C2 2 10000 mf per ampere, 75 volt.
R1,R2 2 47K ohm at 1 watt resistor.
See the information on testing used, unmarked, and surplus stepper motors in SECTION: 3.2.8.0 since you need to know the power requirements of any stepper motor before you connect it to the BIPOLAR2 circuit, or even if the stepper motor is within the range of voltage and current that would allow the BIPOLAR2 circuit to be used with that stepper motor.
If, after testing the stepper motor to determine the stepper motor's approximate ratings, you connect an unmarked stepper motor to the BIPOLAR2 circuit you should start with the stepper motor coil supply voltage at no more than 1 volt and very slowly increase the voltage, otherwise you will probably blow out the power transistors in the stepper motor coil amplifiers. You should have an ampere meter in series with each of the stepper motor coils, and do not raise the supply voltage past the point where the stepper motor current times the supply voltage for each coil exceeds about 25 Watts. You need to raise the supply voltage very slowly in order to find out how hot the stepper motor will get, only raise the voltage about 0.1 volt per hour. If the stepper motor gets hotter than you can comfortably hold in your hands you probably have the supply voltage set too high, the stepper motor should though normally get somewhat warm after being on for several hours. Do not raise the supply voltage above the safe BIPOLAR2 board maximum for the parts installed. You would normally do stepper motor testing with the current limiting resistors R1 and R2 replaced with shunts since you would not be sure of what the stepper motor's ratings are until you get the stepper motor operating properly as slow speeds, e.g. 0 to 1 RPM. After you have figured out the stepper motor's ratings you can make adjustments to the supply voltage and introduce the current limiting resistors as may be needed.