Post by thread:[OT] Stepper motors

Next week I've got to know everything there is to know about stepper motors, (and drive them with a PIC! don't kick me Mark! <G> ) So far I've found a couple of links and articles... but I'm still curious: When runningfrom a PIC, is it more common to use a dedicated IC or four transistors to drive steppers? Which IC's? Do steppers ALWAYS have two coils? Obviously they have speed limits - what are they for common steppers? How efficient are they versus regular DC motors? At low speeds it seems they would run jerkily (step-step-step) Is that true at higher speeds or do they smooth out? Here's some information I've gathered so far, but have not completely digested: http://www.eio.com/stepindx.htm Surplus supplier kindergarden intro to stepper motors. Has a neat link to an artist/genius who made a stepper motor controlled easter egg painter... http://servolink.com/gearspec.htm Servolink corp - CHEAPEST good quality delrin gears and good engr. information. Online gear calculators! ftp://ftp.armory.com/pub/user/rstevew/ FTP site with several interesting articles about steppers, H bridges, electronics, etc.

> Obviously they have speed limits - what are they for common steppers? The speed limit is based on the load. You have to be sure that you do not miss a step because if the load is to high and you try to step to fast, you would lose position. Stepper motors don't offer any position feedback as servos require. > How efficient are they versus regular DC motors? Personally, I like the power of a servo over a stepper motor. The stepper motor is most efficient for holding a steady position... > At low speeds it seems they would run jerkily (step-step-step) Is that > true at higher speeds or do they smooth out? This is not completely true. Most steppers allow partial steps, instead of sending square waves to the stepper, you can send sine waves into the coils. Each coil would have a 90 degree offset, assuming we are using 2 coil steppers. I wish you luck. Here is a good link - http://www.cs.uiowa.edu/~jones/step/ Bill

1) Rip off some steppers from old diskette or hard disk drives. 2) Rotational movement in steps, so it is not smooth. Magnetic forces moves from one step to another, when then it is locked, what causes the stepping movement. 3) The maximum speed is a characteristic of every motor, associated to how you control it. Some cheap motors can not achieve more than 100 or 200 steps / second. 4) The biggest advantages when compared to linear DC motors is the precision of movement and positioning. It is supplied in different degrees/step, from 1.x to more than 7¡. More steps per revolution also means more expensive motor. 5) 2, 3, 4 or more coils, center tap or not. 6) Smoothness in high speed is just a result of mechanical inertia. 7) Driving circuits are dependent on coil characteristics. Center tap coils can be controlled by draining transistors to ground (center tap to +VCC). Certain coils need a bridge driver configuration, what requires isolated transistors or driving circuits. The use of a bridge eliminates the possibility of certain coil simultaneous operation, so the center tap coil motors are better to play with the phases. For example, a center tap coil to +VCC and both coils grounded cause a strong lock brake, this is impossible to do using a bridge in a non center tap coil. 8) The use of specialized chips or discrete transistors is just a design decision. It is not so rare to have a driving circuit blown up, so it is easy to exchange a transistor. Some specialized microchips use current protection and so on, so more reliability. Playing with the coils (phase control) is something nice to learn about stepper motors. Low speed, fast break, high speed, coarse control, how you superimpose phases, or use them isolated in time, can result in power saving or even motor heating... it worth the experience. Quality ones allows you to drive it in audible frequencies, so you can play a song. The first thing about to use stepper motors, you need to have a nice power supply, that can generate a lot of steady current. So forget about 12V,500mA wall warts, because the only thing you would get is just headache and problems.. Some motors use high current but low voltage, what is not really recommended since it would require high current transistors. Easy to use are those about 12V, 500mA to 2 Amps per phase. Wagner Lipnharski - UST Research Inc. http:/http://www.ustr.net - Orlando, Florida

Wagner Lipnharski wrote: > 1) Rip off some steppers from old diskette or hard disk drives. Great idea for experimentation! http://www.doc.ic.ac.uk/~ih/doc/stepper/ > 7) Driving circuits are dependent on coil characteristics. Center tap > coils can be controlled by draining transistors to ground (center tap > to +VCC). Certain coils need a bridge driver configuration, what > requires isolated transistors or driving circuits. Single coils you mean? Isolated transistors? You use an "H-bridge" configuration to drive single coils, but that's no great problem, in fact there are plenty of integrated drivers for this. > The use of a bridge eliminates the possibility of certain coil > simultaneous operation, so the center tap coil motors are better to > play with the phases. For example, a center tap coil to +VCC and both > coils grounded cause a strong lock brake, this is impossible to do > using a bridge in a non center tap coil. This is confused thinking. Energising both counter-wound coils will result in *no* net magnetic field, and *no* static braking. Maximum static braking occurs with one or two phases energised as normal. A *dynamic* braking effect can be obtained by short-circuiting the coil, which can be done by an H-bridge with a single coil. > 8) The use of specialized chips or discrete transistors is just a > design decision. It is not so rare to have a driving circuit blown > up, so it is easy to exchange a transistor. Or an IC. Finding the correct replacement transistor can be as difficult as difficult and costly overall as the proper IC. > Some specialized microchips use current protection and so on, so more > reliability. So they are what you'd design for, instead of transistors! > Playing with the coils (phase control) is something nice to learn > about stepper motors. Low speed, fast break, high speed, coarse > control, how you superimpose phases, or use them isolated in time, can > result in power saving or even motor heating... it worth the > experience. Sounds good. > The first thing about to use stepper motors, you need to have a nice > power supply, that can generate a lot of steady current. So forget > about 12V,500mA wall warts, because the only thing you would get is > just headache and problems.. I'm presently, amongst other things, servicing my el-cheapo flatbed scanner, which decided to overheat. It runs from a wall-wart, which was entirely adequate to smoke the ballast resistor for the stepper. Haven't reached a conclusion yet about the problem... -- Cheers, Paul B.

On Thu, 22 Apr 1999 22:13:55 -0400 Your Name <.....wyckoffKILLspam.....worldnet.att.net> writes: >.... and the motor runs fine, except >that it gets really HOT in about 3 minutes. What am I missing? It's the nature of a stepper motor. The constant DC current needed to hold the rotor in position while the motor is not stepping causes a lot of resistive loss. Small motors are designed to just waste this power to heat (in this case, about 2.5 Watts, 12 V x 240 mA). Larger motors are driven with constant current instead, using a switch-mode driver to keep the driver from dissipating a lot of power. Even so, the motor gets hot. Maybe in your case it would be possible to just reduce the motor voltage some when it is not stepping. If the mechanism drivem by the motor will allow it, you could even turn the motor fully off when it's not in use. But it will very likely miss a step or two when restarting. ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]

>.... and the motor runs fine, except >that it gets really HOT in about 3 minutes. What am I missing? Plot in a paper a timing chart for the power applied to the motor. Some motors can be controlled a little bit different and it makes them run really cool. For example, a motor with 4 coils, A, B, C and D. Driving it in different ways, you get different torque and heat: A B C D - - - - 0 0 1 1 Step 1 0 1 1 0 Step 2 1 1 0 0 Step 3 1 0 0 1 Step 4 or A B C D - - - - 0 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 makes a great difference. Also, the pulse timing relationship can influence it. At the first example above, from Step 1 to Step 2, the "D" drive turns off and the "B" drive turns on, while the "C" drive still on, if "D" turns on while "B" still active yet (even overlapping in a fraction of time) it will be possible to heat the motor. Sometimes when turning off D driver some current still flowing into the coil. To test it, first turn off D, then wait some time (lets say 1/10 of the driving time), then turn on the B drive. It means to insert a "blank" period between offs and ons. Sometime ago I was playing with lasers reflected in mirrors attached to fast stepper motors, and I went through all this situations, noise, heat, speed, torque, then after a week I started to use "galvos" and forgot about stepper motors. Changes in pulse timings, "blank" periods, controlling current, controlling voltage, create a vast different situations. Wagner.

-----Mensaje original----- De: Wagner Lipnharski <wagnerlspam_OUTEARTHLINK.NET> Para: @spam@PICLISTKILLspamMITVMA.MIT.EDU <KILLspamPICLISTKILLspamMITVMA.MIT.EDU> Fecha: Viernes, 23 de Abril de 1999 11:33 a.m. Asunto: Re: [OT] Stepper Motors |Sometime ago I was playing with lasers reflected in mirrors attached to |fast stepper motors, and I went through all this situations, noise, |heat, speed, torque, then after a week I started to use "galvos" and |forgot about stepper motors. Changes in pulse timings, "blank" periods, |controlling current, controlling voltage, create a vast different |situations. | |Wagner. Wagner: I've playing too with laser reflected in mirror attached to stepper motors, trying to make simple figures in a wall. But my major problem was that the motors (small steppers from an EPSON matrix printer)didn«t run the fast enough I needed. What steppers have You used for it? What is galgo? A type of servomotor? Thank You, and please excuse my bad English. Sebastian.-

> I've playing too with laser reflected in mirror attached to stepper motors, > trying to make simple figures in a wall. > But my major problem was that the motors (small steppers from an EPSON matrix > printer)didn4t run the fast enough I needed. > > What steppers have You used for it? > What is galgo? A type of servomotor? The stepper has a high mass on it's core, (The magnet) so it can't be accelerated rapidly. The inductance dosen't help much either. A galvo is designed to rotate fast, but it can't spin all the way around like a motor, it's restricted to a small range of rotation. It is more like a servo motor than a stepper is, in that it is relatively easy to put it at exactly any point in it's rotation. You can do that with a stepper, but it's harder, slower, and less precise.

part 0 480 bytes I just used two motors and that was fine with me. I just got two of those things that move the pen on an EKG machine. They are quite precise. Only turn about +-15 degrees. Only one of them has feedback, Try to find some old hospital equipment, you should be able to get something like that from there... Med venlig hilsen Benjamin Petersen Mark Product A/S Maglebjergvej 11 DK-2800 Lyngby Phone (+45) 45 93 98 80 ext. 21 Fax (+45) 45 93 18 11 E-mail RemoveMEbenjaminTakeThisOuTmark-info.com

part 0 2129 bytes content-type:text/x-vcard; charset=us-ascii; name="vcard.vcf" (decoded 7bit) Wagner Lipnharski wrote: {Quote hidden}> >.... and the motor runs fine, except > >that it gets really HOT in about 3 minutes. What am I missing? > > Plot in a paper a timing chart for the power applied to the motor. Some > motors can be controlled a little bit different and it makes them run > really cool. > > For example, a motor with 4 coils, A, B, C and D. > > Driving it in different ways, you get different torque and heat: > > A B C D > - - - - > 0 0 1 1 Step 1 > 0 1 1 0 Step 2 > 1 1 0 0 Step 3 > 1 0 0 1 Step 4 > > or > > A B C D > - - - - > 0 0 0 1 > 0 0 1 0 > 0 1 0 0 > 1 0 0 0 > > makes a great difference. > > Also, the pulse timing relationship can influence it. At the first > example above, from Step 1 to Step 2, the "D" drive turns off and the > "B" drive turns on, while the "C" drive still on, if "D" turns on while > "B" still active yet (even overlapping in a fraction of time) it will be > possible to heat the motor. Sometimes when turning off D driver some > current still flowing into the coil. > > To test it, first turn off D, then wait some time (lets say 1/10 of the > driving time), then turn on the B drive. It means to insert a "blank" > period between offs and ons. > > Sometime ago I was playing with lasers reflected in mirrors attached to > fast stepper motors, and I went through all this situations, noise, > heat, speed, torque, then after a week I started to use "galvos" and > forgot about stepper motors. Changes in pulse timings, "blank" periods, > controlling current, controlling voltage, create a vast different > situations. > > Wagner. Content-Type: text/x-vcard; charset=us-ascii; name="vcard.vcf" Content-Transfer-Encoding: 7bit Content-Description: Card for David Christie Content-Disposition: attachment; filename="vcard.vcf" Attachment converted: wonderland:vcard.vcf (TEXT/CSOm) (0002EA57)