Stepper Motor Basics

What is of interest in motor voltage is that it leads to a maximum value of the power supply

32 * VL = VMAX

The reason for this is iron losses (eddy currents) heating up the motor. But, this is almost academical since most stepper motors i encountered have motor voltages over 1,5V and supplies over 45V are seldom used. Also most drivers set the upper voltage limit at 35V which is safe for almost all motors.

Ecellent text, and really needed. What could be added is that power supplies should be unregulated with a filter/reservoir capacitor with a value of:

(80,000 * I) / V = C(uF)

nilton61:
Ecellent text, and really needed. What could be added is that power supplies should be unregulated with a filter/reservoir capacitor with a value of:

Thank you (and everyone else) for the kind words.

I have noted your very useful views about power supplies elsewhere but I don't feel competent to write a text about it myself. Perhaps you could find the time to write a few sentences which can either stand here as a separate post or I might incorporate it into my text.

My own experience is that a computer power supply (18v or so) and a large 12v lead-acid battery work fine. I haven't tried an unregulated supply myself to see if it would be better.

And I don't want to discourage or prevent newcomers from using a satisfactory power supply that they happen to have, even if it is sub-optimal.

...R

The reason for advocating unregulated supplies is that regulated ones more often than not have quite small reservoir/filter caps. This has two negative effects

  • The small caps cannot absorb the returning energy when deaccelarating
  • The very transient currents can interfere with the voltage regulator

So the main issue is having large enough caps which should be stated.

nilton61:
So the main issue is having large enough caps which should be stated.

I've been thinking some more about the possibility of a text about power supplies and the problem is that I keep running into more questions which leads me to think that it needs an entire Thread of its own.

For example does the piece I have quoted mean that it is a good idea to attach a very large capacitor to a regulated power supply as well as to an unregulated supply?

And, to confirm my understanding, I have 3 motors that each have a coil current of 0.33 A. That would mean 0.99A for all 3 - say 1.5A to give a margin. And, supposing they are powered at 20v your formula would be
80,000 * 1.5 / 20 which gives a capacitor value of 6,000 microFarads.

And without intending the least disrespect to your knowledge I have not yet got any sense of how much difference it would make to have an unregulated rather than a regulated power supply with the same voltage assuming both can deliver enough amps.

...R

just a note on my router I have 1400w 16 amp 80vdc power supply's the motors don't get hot at all I can push them to 150vdc then they will get hot.

having a decent stepper driver takes care of its motors.

robin it would be a good idea to add in the steeps need to work out what size stepper a person would need to get

daniellyall:
robin it would be a good idea to add in the steeps need to work out what size stepper a person would need to get

I thought about that. But it can get very complex - especially if you try to keep it simple. So much depends on the reader's level of knowledge. That's why I just left it at "To figure out what motor you need you will have to measure or estimate the torque required ..... It is not too difficult to make a rough measurement of the torque required but it is beyond the scope of this note.".

If you have time to submit a suggested text I would really appreciate it.

...R

daniellyall:
just a note on my router I have 1400w 16 amp 80vdc power supply's the motors don't get hot at all I can push them to 150vdc then they will get hot.

having a decent stepper driver takes care of its motors.

robin it would be a good idea to add in the steeps need to work out what size stepper a person would need to get

I believe that the purpose of this thread is to hand-hold a newbie and get them past the common problems. As Robin2 stated, this thread addresses the repeated problems newbies encounter.
It is a superficial introduction, touching only on the needed parts, but considering the limited space and the capacity of the newbie to grasp the concepts, it is at exactly the right level. a good idea and pretty well executed.

Robin2:
And without intending the least disrespect to your knowledge I have not yet got any sense of how much difference it would make to have an unregulated rather than a regulated power supply with the same voltage assuming both can deliver enough amps.

...R

I believe the whole concept of this thread is to get the NEWBIE to connect a stepper and make it move.
that said, almost any power supply will work for this purpose. and old brick that has the current, an old PC power supply. whatever. I am content on building my own, but IMHO building a power supply is about 5 steps down the road, and does not belong at this level.
suffice it to say that to get started, a power supply that has enough current should be good enough to use to get the motors moving and it is is an old PC power supply with 12 volts or one from an old laptop, it does not matter in order to get that motor spinning. once you have gotten the motor to spin and step forward and back and things look good, it would be desirable to try to improve the performance by either building or buying a power supply that is selected for the application.
as a note, the back EMF being delivered to the power supply from coil-A will be immediately send to coil-B and not stored. for that reason, the regulated power supply will often work fine. in addition, many regulated power supplies are designed to handle the higher voltage. lastly, I sincerely believe that AT THIS LEVEL, no newbie will be running high power, high current motors under a load with sufficient deceleration as to create enough back EMF to be of any concern.

I think that generally speaking, this is a good start. It is apparent that the writer does not like the L298 boards that so many newbies have and ask about. I would offer that more technical discussion would be called for. It appears to me that the section about them is dismissive.

the L298 does have sense resistors to limit current, check the data sheet.

IMHO, it would be appropriate to remove the writers (negative) evaluation of the board and be more technical.

the L298 is a full or half step driver that can power a stepper. it takes 4 pins from the Arduino and is used on a bi-polar motor. running a full step at slow speed will have the motor appear to jump and shake. a half step will remove much of the apparent motor movement. The cost of the L298 is comparable to the A4988. in the opinion of the writer the A4988 is a much better choice.

a micro-stepper breaks each step by sending each of the two coils some energy. if you think of it as taking the power and one coil gets 90% and the other gets 10%, then 80/20, 70/30... and so on, you can see that the movement will be much more fluid. this is most apparent at reduced speeds.

at higher speeds the micro-stepping actually takes more time and can become a problem. at this introductory level, we do not need to address these things, but only bring them to your attention. This is mentioned because you will find both the jumpy movement at low speeds with a full step driver and a limit to high speed when using a high number of micro-steps,.

motor speed :

a DC motor delivers full power and full torque at high speeds. as the speed is reduced, the power drops off.
a stepper delivers maximum power at it's lowest speeds and as speed increases, power drops off.
each type of motor has applications that they are best suited for.

dave-in-nj:
motor speed :

a DC motor delivers full power and full torque at high speeds. as the speed is reduced, the power drops off.
a stepper delivers maximum power at it's lowest speeds and as speed increases, power drops off.
each type of motor has applications that they are best suited for.

Not quite correct.

  • A brushed Dc motor delivers a torque that is almost proportional to its current and hence at maximum for a stalled motor and zero for a free running motor (assuming constant voltage). The output power (N(rpm)*M(Nm)/9,55) is zero at these two points and at its maximum at about half the free running speed. The efficiency is at its maximum at about 70%-80% of the free running speed.
  • A stepper motor (as all ac motors driven with variable frequency) delivers aproximately a constant torque up to its corner speed which depends on the supply voltage and after that aproximately constant power, that is above the corner speed torque decreases inversely with speed

It seems that a similar text on rotating machinery is also needed

dave-in-nj:
but considering the limited space and the capacity of the newbie to grasp the concepts, it is at exactly the right level. a good idea and pretty well executed.

dave-in-nj:
It is apparent that the writer does not like the L298 boards that so many newbies have and ask about. I would offer that more technical discussion would be called for. It appears to me that the section about them is dismissive.
....SNIP....
IMHO, it would be appropriate to remove the writers (negative) evaluation of the board and be more technical.

I find it very difficult to reconcile these quotes from 2 different posts?

I agree I am dismissive about L298 drivers. Compared to using a proper stepper motor driver board they are the equivalent of painting the outside of a house with a 25mm paint brush.

...R

L298 are only good for new bees who don't know any better they are a pain

to drive a stepper so it does not over heat it and do stupid things it needs a proper stepper driver like a A4988 or equivalent, steppers are holding torque to its curve drop off nothing else

  1. working out what size stepper to get is what's the amount of torque will it need for the load it needs to move.

  2. what is the amount of current needed to drive said stepper for load being moved.

  3. what is the max current that the said stepper be needing to be driven at the speed required up to the top of its curve

  4. then you get a stepper driver that can handle said amount of current plus a bit extra for back emf.

  5. A power supply that can produce the amount of current needed under its max load.

also some one say what a stepper they are using gets, it`s is a good thing to have in any discussion as if someone work out they need a power supply and driver of simmaler size they can ask that person what is there set up, I use big and small steppers.

in a discussion I have had I asked people who have the same size stepper as the machine I have (was meant to have) what there set up was people with same size machine and smaller said they had no problems with there steppers what where the same as mine so what was wrong with my set up. simple answer miss labled steppers.

if I did not ask what peoples set ups where I probley would not have worked out the stepper where miss labled.
so anything in a discussion about correct set ups of stepper, power supply's and drives can`t be bad if a person does not under stand they can just ask.

@daniellall, I'm not sure if your Reply #19 is partly a response to my Reply #12.

I think I have covered your points 1-4 in my original text.

I haven't covered power supplies (point 5) - apart from the question of voltage. I assume the user is sensible enough to use a power supply with sufficient amps. That aspect is not specific to stepper motors.

@nilton61 and others have added useful posts about power supplies.

...R

yes it is, its as simple as I can put it.

its the way I work it out

its in 5 lines with all the correct words that anyone can find with Google or I could have just said read this
http://www.geckodrive.com/app-notes.html

that has all what is need to know

Robin2,

A really well written, concise tutorial for the benefit of all us novices.

Ken

Robin2,

Very nice, I am not a newbie to stepper motors, and you pulled me in. I read the whole thing!

A person certainly would not get the performance they need in many cases if they stuck to the rated voltages. The availability and price of stepper drives have drastically improved in the recent years. These new cheaper drives control the amps by your setting and then chops the voltages as needed. This generally gives you more speed and torque. The newbie has a lot less to worry about these days.

Well written tutorial Robin!

I'm just missing a more detailed description, how to connect a unknown stepper to a driver board.

Describe how a ohm-meter can be used to find out which are the ends/centers of a coil and if it makes a difference which way you connect a coil to the driver. A newbee might be confused which coil is A or B and which end of the coil is A1 or A2.

o_lampe:
I'm just missing a more detailed description, how to connect a unknown stepper to a driver board.

I guess that's why I didn't write it :slight_smile:

Describe how a ohm-meter can be used to find out which are the ends/centers of a coil and if it makes a difference which way you connect a coil to the driver. A newbee might be confused which coil is A or B and which end of the coil is A1 or A2,

Can you post a few sentences that may be suitable to incorporate in the text?

I don't actually know if it matters which end is A1 - I don't think it does.

...R

as far as what I have done it does not matter what end is A+ or A- as long As B+ and B- are the same order as A+ and A- flipping A+ A- B+ B- just changes direction.