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Topic: Stepper Motor Basics (Read 229282 times) previous topic - next topic

dave-in-nj

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,.

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.

nilton61

#17
Dec 12, 2014, 02:43 pm Last Edit: Dec 12, 2014, 02:47 pm by nilton61
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

Robin2

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.
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
Two or three hours spent thinking and reading documentation solves most programming problems.

daniellyall

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.

Robin2

@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
Two or three hours spent thinking and reading documentation solves most programming problems.

daniellyall

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

neksmerj

Robin2,

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

Ken

weldsmith

#23
Dec 13, 2014, 09:36 pm Last Edit: Dec 13, 2014, 09:38 pm by weldsmith
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.
David Smith

o_lampe

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.


Robin2

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   :)

Quote
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
Two or three hours spent thinking and reading documentation solves most programming problems.

daniellyall

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.

dave-in-nj


Quote
These can be made to control a stepper motor but they are a very poor choice - mainly because they have no method for limiting the current and therefore cannot use high voltages.
reading the data sheet is in order.
the L298 certainly does have limiting resistors and many of the available boards on the market have them out to pins.   the vast majority of the super-cheap e-bay ones are set for full power,




.

daniellyall

reading the data sheet is in order.
the L298 certainly does have limiting resistors and many of the available boards on the market have them out to pins.   the vast majority of the super-cheap e-bay ones are set for full power,




.
you have all ready said most of that

the l298 are a poor choice for controlling stepper 4 wires, proper stepper driver 2 wires which one is better 4 wires or 2

Robin2

#29
Feb 17, 2015, 04:57 pm Last Edit: Feb 17, 2015, 05:00 pm by Robin2
A simple method to get a rough measurement of the required torque.

Attach some sort of wheel or drum to the shaft that the stepper motor will be required to turn. Wrap some strong thread or fine string around the drum and suspend a small plastic beaker from it. This will obviously only work if the shaft is horizontal.

Add coins to the beaker until the weight is just sufficient to make the drum rotate. Weigh the beaker with the coins in it.

Measure the diameter of the drum where the thread is wrapped and calculate the radius. Suppose the radius in 2cm and the weight is 100grams. Then the torque is 200gm-cm.

Repeat the measurement several times and take an average. Choose a motor with perhaps twice that amount of torque to provide a good safety margin.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

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