The Shop > Electronics & IC Programing
Simple way(s) to run a bipolar stepper motor?
philf:
--- Quote from: sorveltaja on July 12, 2023, 07:27:57 PM ---What I'm also trying to find out, if I can make something, that produces a half-step sequence using only discrete, analog components. If I manage to do that, it's fine. If I don't, that's also fine. Be it either way, next step is to see what plan B has to offer.
--- End quote ---
In 1984 I made some 1/2 step drivers for a plotter I was building. They just used cmos chips to generate the 1/2 step sequence.
The basic circuit:
The power circuit (to use constant current):
(Transistors used BC107 and BD645 Darlingtons)
And the finished board:
Phil.
sorveltaja:
Thanks for all for the replies.
I had to test, how to 'emulate' a correct sequence, to get a 'hands on' -feeling, using four spdt switches.
Finally, I think I got it right, as the stepper rotates in the same direction - step by step, when turning the switches on and off in certain order.
First image(stepper_and_switches_1) is just to show how I connected switches and stepper motor's wires, while the second one is the actual breadboarded circuit(rest of the breadboard wires and stuff isn't involved):
Anyways, I simulated Phil's circuit to see what kind of waveforms it makes:
As I don't have 4028's and 4075's, it was time to test how to make similar-ish waveforms, using 4017 and some diodes:
Then comparison, first is Phil's circuit and second one is 4017-based:
It seems to be kind of there, but after all, it's just a simulation.
I'll do breadboarding and see how it goes.
philf:
If you were in the UK I could have sent you plenty of chips and a driver board. I'm unlikely ever to use them. I also have several L297/L298 stepper ics.
sorveltaja:
Phil, I'm from Finland, but thanks anyway for the offer :beer:
I've been testing how to keep stepped waveform - to preserve its form - when there is a load.
I guess, when there is enough current, that's what gives the voltage(be it in stepped form, or whatever) "power" to maintain its shape under load (Nema 17 stepper coils are about 4 ohms).
Circuit that I used for testing, is based on LM317's datasheet, which has several examples of how it can be used. One of them is "Digitally Selected Outputs":
That led to using 4017 to make a sequence:
It keeps its waveform under load, after adjusting the pots. I had to put a heatsink to 317, as I was using max 1300mA. So far so good, but then I realized, that the waveform appears only as a positive voltage. I was like: "how to get the dark negative side involved?"
I think it may well require a split power supply to get both sides. I remember using diy one on one of past projects, but haven't yet found where the heck it is.
In the meantime, I was looking another ways to test how to make the stepper turn smoother than choppy full-wave. I was getting frustrated, but then I remembered Bill's reply about using sine waves 90 degrees apart. At first, I have to admit, I thought that nah, it just can't be that simple.
But in practice, it works. I tested it with function generator, and it made that Nema 17 turn rather smoothly. There isn't awful lot of torque, but I think still enough(using finger-meter) to take the idea further.
Also, it was surprising to see, that this kind of stepper doesn't require hefty current to run(at least for the purpose I have in mind).
Next thing that came to mind was, "how about little more grunt, if some future project requires it".
Besides, I'd like to use something else to run the stepper, than function generator.
So I'm trying to figure out, how to amplify a sine wave against 4 ohms load.
What comes to that 90 degrees phase shift, I already have an idea, of what to try - one or two stages of an op-amp based phase shifter, which was originally controlled with ldr-led based optoisolators, and was intended for musical use.
Earlier I breadboarded that phase shifter(four stages, everything else stripped, most basic version of it), and yeah, it was rather easy to use just pots to adjust difference between phases.
sorveltaja:
After some testings with Nema 17, there is still a problem with vibrations it makes, when driven with amplified sine wave. I guess it has to do with something like 'flywheel effect' - in other words, mass of the rotating part(rotor?), which would need a specific driver to compensate that(slow decay, mixed decay and that kind of stuff), in order for it to run smoothly.
Since I'm looking for a lot simpler way to accomplish what I have in mind, I thought that why not try the smaller stepper from HP flatbed scanner:
When using same setup(with pesky LM386's), as it has far less mass, it might be more suitable for the purpose. And when used with gears on the picture, it obviously has more torque.
This stepper's coils are about 3,5 ohms.
For testing it I used 4-5V and max 400mA.
Usable driving frequency is about 50-200Hz
So far I've tested it through 386's with function generator, and it seems that with this smaller motor, there isn't much of a difference, whether it's driven with sine- or square wave(unless higher voltages and therefore more amperage is used).
Well, the circuit I'm using is far from perfect, but if one has small bipolar steppers and likes to see if they could be used for something, or maybe just take first steps to learn how to make these buggers run at all(like I did), it doesn't have to be overly complicated.
And, if sine wave (generator) isn't required, it alone makes things simpler. Two square wave generators(based on cmos ic's), that have 'quadrant' or 90 degrees phase difference(at least for bipolar steppers) - I think I'm going to revisit that one at some point(to replace function generator), if(when) possible next project proceeds.
In the end, here is the most 'dirtiest and simplest' circuit, that I've found when (ab)using it:
Besides the + and ground connections and two caps, as it can be seen, there is no connection to 386's second pin. Usually it's tied to ground, but leaving it unconnected seems to lessen or remove the excess noise.
2,2uF caps help to keep the noise/stuttering of stepper down, when there is no input. And the 1000uF(I guess more might be better) ones add a 'punch' to drive the stepper's coils.
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