Electronic circuit design discusions :: How much do different stepper motors have in common?


	How much do different stepper motors have in common? Ive been looking at a little control project and using stepper motors. However, I would like to design a control board that will work with a number of different steppers without modification (apart from perhaps some jumpers to change from uni to bi polar). Whilst I am fairly confident I could take a particular stepper spec and design a driver, are there common characteristics that would allow a wide range of steppers to work with one driver board? I should make it clear that I understand how a stepper motor works, unipolar, bipolar etc and bridge configurations. However I am unclear on whether I can get away without current limiting (perhaps only on small motors with higher restistance windings?). It seems if I use a resistor that would affect startup torque and need to be changed depending on motor used. And if I use current limiting that would have to be programmable? Also does microstepping always require strict current control? Or can you just instead of connecting say 12V to one winding, connect 12V to one and a PWM'd 12V to another (to control microstep position). Any advice on how to make driver circuits as generic as possible gratefullly received! Thanks Andy On May 14, 2:36 pm, bigorangebus <bigorange@yahoo.com> wrote: > Ive been looking at a little control project and using stepper > motors. > However, I would like to design a control board that will work with a > number of different steppers without modification (apart from perhaps > some jumpers to change from uni to bi polar). > Whilst I am fairly confident I could take a particular stepper spec > and design a driver, are there common characteristics that would allow > a wide range of steppers to work with one driver board? > I should make it clear that I understand how a stepper motor works, > unipolar, bipolar etc and bridge configurations. However I am > unclear on whether I can get away without current limiting (perhaps > only on small motors with higher restistance windings?). Unless you are going in for really slow stepping applications, you need to drive stepping motors from much higher voltages than the manufacturer's rated voltage - which is merely the maximum DC voltage you can put across a static coil without over-heating the motor. Some kind of current limiting is pretty much essential. Stepper motors present such a wide range of coil resistances, coil inductances and torque/back emf ranges that a universal controller is going to be vastly sub-optimal and over-priced in 99% of applications. The moment of inertia of the rotor and the stifness of the magnetic coupling - which determines the first resonance frequency of the stepper motor - is another variable that your controller is going to have to deal with, but at least it is easy enough to make the electronics fast enough to cover the commerically available range, and slower electronics aren't siginificantly cheaper or more compact. Note that the torque rating, in newton.metres per amp, of a stepper motor is numerically equal to the back emf rating in volts per radians per second. -- Bill Sloman, Nijmegen -----------------------------------------------Reply----------------------------------------------- Thanks Bill, this is useful. What do you mean by "fast enough"? Ive heard that stepper resonances can be overcome by using higher frequency pulsing... On 14 May, 14:41, bill.slo@ieee.org wrote: - Hide quoted text - > On May 14, 2:36 pm, bigorangebus <bigorange@yahoo.com> wrote: > > Ive been looking at a little control project and using stepper > > motors. > > However, I would like to design a control board that will work with a > > number of different steppers without modification (apart from perhaps > > some jumpers to change from uni to bi polar). > > Whilst I am fairly confident I could take a particular stepper spec > > and design a driver, are there common characteristics that would allow > > a wide range of steppers to work with one driver board? > > I should make it clear that I understand how a stepper motor works, > > unipolar, bipolar etc and bridge configurations. However I am > > unclear on whether I can get away without current limiting (perhaps > > only on small motors with higher restistance windings?). > Unless you are going in for really slow stepping applications, you > need to drive stepping motors from much higher voltages than the > manufacturer's rated voltage - which is merely the maximum DC voltage > you can put across a static coil without over-heating the motor. Some > kind of current limiting is pretty much essential. > Stepper motors present such a wide range of coil resistances, coil > inductances and torque/back emf ranges that a universal controller is > going to be vastly sub-optimal and over-priced in 99% of applications. > The moment of inertia of the rotor and the stifness of the magnetic > coupling - which determines the first resonance frequency of the > stepper motor - is another variable that your controller is going to > have to deal with, but at least it is easy enough to make the > electronics fast enough to cover the commerically available range, and > slower electronics aren't siginificantly cheaper or more compact. > Note that the torque rating, in newton.metres per amp, of a stepper > motor is numerically equal to the back emf rating in volts per radians > per second. > -- > Bill Sloman, Nijmegen On May 15, 12:53 am, bigorangebus <bigorange@yahoo.com> wrote: - Hide quoted text - > Thanks Bill, this is useful. > What do you mean by "fast enough"? Ive heard that stepper resonances > can be overcome by using higher frequency pulsing... > On 14 May, 14:41, bill.slo@ieee.org wrote: > > On May 14, 2:36 pm, bigorangebus <bigorange@yahoo.com> wrote: > > > Ive been looking at a little control project and using stepper > > > motors. > > > However, I would like to design a control board that will work with a > > > number of different steppers without modification (apart from perhaps > > > some jumpers to change from uni to bi polar). > > > Whilst I am fairly confident I could take a particular stepper spec > > > and design a driver, are there common characteristics that would allow > > > a wide range of steppers to work with one driver board? > > > I should make it clear that I understand how a stepper motor works, > > > unipolar, bipolar etc and bridge configurations. However I am > > > unclear on whether I can get away without current limiting (perhaps > > > only on small motors with higher restistance windings?). > > Unless you are going in for really slow stepping applications, you > > need to drive stepping motors from much higher voltages than the > > manufacturer's rated voltage - which is merely the maximum DC voltage > > you can put across a static coil without over-heating the motor. Some > > kind of current limiting is pretty much essential. > > Stepper motors present such a wide range of coil resistances, coil > > inductances and torque/back emf ranges that a universal controller is > > going to be vastly sub-optimal and over-priced in 99% of applications. > > The moment of inertia of the rotor and the stifness of the magnetic > > coupling - which determines the first resonance frequency of the > > stepper motor - is another variable that your controller is going to > > have to deal with, but at least it is easy enough to make the > > electronics fast enough to cover the commerically available range, and > > slower electronics aren't siginificantly cheaper or more compact. > > Note that the torque rating, in newton.metres per amp, of a stepper > > motor is numerically equal to the back emf rating in volts per radians > > per second. Don't top post. "Fast enough" depends both on the back-emf of the coils and the inductance of the motor coils, so it varies a lot from motor to motor. I've seen people rotate a motor at the target rotation speed with an electric drill and monitor the voltage induced across the drive coils with an oscilliscope, which can tell you something about the back-emf in terms that even a boss can understand, even though it doesn't tell you anything about the effects of coil inductance. Microstepping doesn't make any dramatic difference to the voltage you need to put across the motor to make it step reliably at a specific rate of rotation. Microstepping a stepper motor usually does raise the frequency of pulses going to the motor above the first resonance, which does reduce the problem quite a lot. There will be a - relatively slow - rotation rate for which even the microstepped drive currents will have significant harmonic content at the resonant frequency, but it will be a much lower amplitude component than it is with half-step and full step operation so the amplitude of the wobble on the motor's rotation won't build up to anything approaching a full step, so the resonance is - even then - most unlikely to cause the motor to lose or gain steps. -- Bill Sloman, Nijmegen

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Electronic circuit design discusions

How much do different stepper motors have in common?