The Shop > Electronics & IC Programing

Simple way(s) to run a bipolar stepper motor?

<< < (4/5) > >>

sorveltaja:
Well, after testing quite a few things that don't work, I think it's time for a sub-project. It has to do with voltage vs current, and how to visualize it, using a scope.

For me, just that - visual preference - has been really helpful in making sense of what happens in certain circuits. But so far, that has only been about voltage.

What comes to alternating or pulsing current, it apparently isn't as simple to 'show nice current waveforms' on a scope, although it seems to be possible by using 'current probe' or 'current clamp'.

Commercial ones tend to be rather expensive (like Owon's model that is available from my local supplier, is over 200 euros).

Obviously I started to look for a cheaper diy version. One possible candidate is at https://electronoobs.io/project/48#

He uses Hall effect sensor and a simple circuit to amplify its output. I should have most, if not all required components (plus some ferrite cores to butcher), except SS49E, which is 'linear' one.

I'm not sure if unipolar TLE4905L's or bipolar TLE4935L's (Hall effect sensors), that I have, are suitable, as there is no mention about linear(linearity?) in their datasheet. 

I'll test them anyway with that circuit, to see how it goes. And if it doesn't, I'll order some SS49E's.

sorveltaja:
Previously mentioned Hall sensors that I have, doesn't seem to be suitable for this purpose, as they behave like on-off devices. In other words, when waving a strong magnet near the sensor, its output is either 9V(or whatever the supply voltage is) or near zero volts.

With that in mind, the term 'linear' makes more sense (at least for me). If a Hall sensor is mentioned to be linear(like SS49E), it somehow implies, that its output could be anything between, lets say, its supply voltage and zero/ground. And linearity is perhaps a way to explain, how faithfully it follows(or reacts to)  'path', that has variable values (relation between input and output).

But enough of that babbling for now.
     

sorveltaja:
Bit more testing - this time something that uses split power supply. First one was a simple 'class B' or push-pull amplifier using dual op-amp and two pairs of transistors to feed the stepper coils.

It sort of worked, but the output was far from being smooth, causing the stepper to rumble quite badly.

From what I understand after some searching, transistors are current devices, while mosfets are voltage devices. I have no idea what that might mean in practice.

Anyways, I remembered having some old mosfets, J50's and K135's, and that they were meant to be used as complemetary pairs.

So I started to look info about 'mosfet push-pull amplifier'. One of the simplest circuit I could find is just that - simple.



That circuit might work without an op-amp, but it would have cross-distortion, unless there is something else to alleviate that issue.

I breadboarded a "stereo" version of that circuit, and so far have tested it using two 9V batteries in series to form a split supply.


Quite a mess at this point, but for some reason it seems to drive the stepper coils  smoother, and when the outputs are viewed on a scope, they retain sine waveform a lot better than any other circuits I've tested.

Also there appears to be plenty of torque (again, using finger meter), so perhaps the driving voltage and current follow each other more closely?

Working frequency range of that circuit appears to be from 1(and perhaps below that) to about 100Hz, when nema 17 was driven.

I'll take scope shots once I get more permanent split power supply hooked up.

Noitoen:
Old post but to run a simple stepper motor as a regular small speed motor, an AC supply of 24V and 2 none polarized 4,7 uF capacitors in parallel will drive the motor like a single phase motor at mains frequency. Capacitors may vary depending on the motor

JHovel:
Would you like to elaborate? Principles of function, likely speed of motor wave form to the motor etc?
Because I don't think that works at all. My expectation would be that the stepper motor will just sit there humming or growling, certainly not running. It needs 2 offset phases at 90 deg and reversing at 180 and 270 to make 400 steps per revolution. 50hz - with a phase shifted close to 90 deg would make it try to run at 3000rpm, when a stepper driver would make it run at 400steps : 50hz x 60 sec= 480rpm.... just my take on the idea.

Navigation

[0] Message Index

[#] Next page

[*] Previous page