[scales11]

DoorKnob,

Thank you for clearing that up. I will try and find some 4-wire motors and read up on the difference between the two.

The TB6560 board has some problems - some people are successful using it but others are not - see How I fixed my Chinese TB6560 controller (updated)

is there another driver board that has better success?

[doorknob]

There are a number of relatively inexpensive driver boards that people use with NEMA 23 stepper motors with torque ratings of 100 to 200 oz-in or more, however I do not have direct experience using most of them, so I'm hesitant to make a recommendation. Perhaps others will chime in. But for example there is the HobbyCNC driver (it supports 3 axes, unipolar motor drive, but you need to solder the parts because it is a kit), or the Chinese import KL-4030 drivers (one driver per axis, bipolar motor drive, so you would also need a breakout board to hook them up to your parallel port), the Linistepper board (for unipolar drive, it comes as a kit for each axis, you will need a breakout board, I have a couple of them but have not yet wired them up), the Geckodrive G540 (up to 4 axes, bipolar motor drive, no need for a breakout board, gets high marks for performance and support, but it's more expensive than the other solutions, I have one of those), and so on.

[scales11]

OK. After more consideration, I decided to go with this arduino shield.
Reactive - Storefront
which works with the Pololu 4988 drivers.

I prefer the simplicity of the hardware (since I already have a small netbook and an arduino). I realize that GUIs are limited and software may be lacking, but I am going to bet/hope that that will improve some. I have already found a couple of useful programs for the arduino/usb option.

So, to go with this board and drivers, I was looking at 4 of these stepper motors:
https://www.sparkfun.com/products/10847
It is rated at 3V and 2A and has sufficient torque.

What kind of power will I be running it at? I read that stepper motors typically are run at higher voltages (and lower currents I assume).

Using that info, I could then figure out whether a 24v, 4.5A switching power supply that I have would suffice...

[rinthesun]

Those are Nema 23 motor needing 2 amp per coil. The Pololu 4988 was designed for Nema 17 and is used mainly in 3D printers You would need heat sinks and a big fan and even with that they would probably overheat. I have a friend who uses the HobbyCNC driver and unipolar NEMA 23 motors and the system works well with LinuxCNC.

If you want to use GRBL look at the ShapeOko site. This is a small kit CNC router using NEMA 17 motors and many people are using GRBL with shields like the Reactive.

[scales11]

If the motors are 2A per coil, and I were to run them as bipolar, then each motor needs 4A? If they were run as unipolar, then each motor draws 8A?

What happens if I limit the current draw to 2A total per motor? Would they just run slower or with less torque?

[doorknob]

Interesting - I decided to order that board today for some Arduino experiments that I plan to do.

It is on sale for $25 here (if you have not already ordered it): Reactive/Substance | CNC Stepper Shield v3.0 - Kit with Components | Online Store Powered by Storenvy

You probably already realize that the drivers must be ordered separately, either from Pololu or Reactive Substance - I'm getting the Pololu "black edition" stepper drivers to go with it. Those drivers are rated for max of 2A per winding as long as you have "sufficient additional cooling". Be sure to read the power dissipation warnings at the Pololu site and in the A4988 datasheet - you will need to add a heat sink to each chip and maybe also a fan in order to handle 2A winding current. The motor has a good, low inductance rating, and you should be able to use 24 volts with it (and your power supply should be OK) - but it would be a good idea to double check that the shield does not apply the motor voltage directly to the Arduino board - in any case, separating the motor power supply from the Arduino supply is probably a good idea when using any motor shield. BTW, reducing the current below 2A will reduce the available torque proportionally.

[doorknob]

If the motors are 2A per coil, and I were to run them as bipolar, then each motor needs 4A? If they were run as unipolar, then each motor draws 8A?

What happens if I limit the current draw to 2A total per motor? Would they just run slower or with less torque?

You would set the driver to supply 2A.

[scales11]

Doorknob,

I too ordered that board 2 days ago. I also ordered those Polou drivers from the site (though I did not opt for the super cool black edition ).

I had contacted the vendor and he recommended that stepper motor. If you ordered the Polou drivers from the same site, it says that they come with heatsinks.

I had planned on having a dual-y setup (4 axis, 4 motors) This way I wouldn't have to worry about having too little torque with the moving gantry, especially if I were to limit the current. I haven't purchased the motors yet. I was slightly hesitant to do so because I wanted to be sure that they can drive my (yet to be seen/made) cnc to cut wood and aluminum. I planned on mounting everything in a box and having a fan running. If they got too hot, then I guess worst case scenario, I turn down the current to less than 2A and run things with less power?

[doorknob]

Yes, you can start with a lower current setting and then increase it while monitoring the temperature of the driver chips (do not monitor the temperature by putting your finger on the chip, because it is possible that they could get hot enough to burn you).

I did not order my Pololu drivers from Reactive Substance - I see from your link that they do ship them with heat sinks, which is great.

[rinthesun]

It looks like you have decided on these plug in drivers. You should look here before you order

SureStepr SD8825 Stepper driver

The TI 8825 can carry more current and these boards are made the best way. Heat is dissipated thru the bottom of the chip and you will see these boards plug in upside down and the heat sink and current pot are located on the top once plugged in. With a nice big fan these may handle the 2 amps.

To use a unipolar motor you can either connect across the whole coil or half the coil. Using half, it will have about the same torque as running it unipolar.
Look here UniPolar vs BiPolar wiring schemes for 2-phase Stepper Motors

[scales11]

Thanks for the reply Rinthesun.

I cannot say that I "approve" or suggest the Polou drivers or the arduino shield I ordered. I simply preferred the usb approach for a first try and my options were limited. I would be happy to give some feedback once I receive and test these components. So far I have yet to hear back from the vendor...ofcourse he did accept the paypal transaction.

Those drivers that you pointed out seem like an excellent find. I will be sure to try them next.

I also am familiar with Unipolar vs Bipolar, I just was not sure how much power/torque I would loose when I ran at a lower current. That page has some good info on it. I would next like to investigate how much torque/speed I will loose if I run my motors (which I have not ordered yet) at a lower current/voltage. Since the Polou drivers I ordered have a max current of 2A, I anticipate running them a little under to be safe.

[scales11]

Sorry to resurrect this thread.

I am finally ready to test out my electronics, my question is regarding the stepper motors and the power supply I have. The motors are rated at 3V 2A per phase, I have 4 of them, how can I be sure that my 24V 4.5A supply will NOT be too much?

Thanks.

[doorknob]

As mentioned above, I would not be particularly concerned about the power supply being "too much" for the stepper motors. It is normal to use a higher voltage than the nameplate voltage on stepper motors which are used with current-limiting drivers such as the Pololu ones.

However it would be a good idea for you to monitor the temperature of the heat sinks on the driver chips to make sure that they do not get too hot. You could start with a lower current setting (such as 1 amp) and then gradually increase it as you become confident that the drivers are not overheating.

I finally received my board from Reactive Substance, although I have not yet soldered it up (nor have I yet soldered the headers onto the Pololu driver boards).

[scales11]

I finally got everything wired up. For reference, I am using the following:

Nema 23 motors from Sparkfun:
https://www.sparkfun.com/products/10847

GRBL Arduino shield from Reactive substance:
Reactive - CNC Stepper Shield

Polou Stepper drivers:
Pololu - A4988 Stepper Motor Driver Carrier

I also am using a 24V 4.5A power supply to power everything.


Once everything is plugged in (since the motors have 6 leads, I simply left the center-taps unplugged) I fire up G-Code sender and start talking to the stepper shield and motors. I also adjusted the potentiometers on the stepper drivers so that the Vref = 0.6 (thinking that this would limit the current to 1.5-1.6A, as described on the reactive substance site).

Here is where I run into trouble. The motors make noise, even a whirring noise as if they are spinning; however, they just appear to "twitch" and they never actually spin. I suspect that my GRBL settings are incorrect, since I am likely using different motors. After trying to get the motors to move for a few minutes, they actually stop making any noise and I am forced to reboot my arduino in order to get some kind of feedback from them. The stepper drivers do not appear to be getting very hot, they maybe feel slightly warm when I touch the heatsink.

Can anyone point me in the right direction for configuring these settings? Or is there something else I am missing?

[doorknob]

The 'whirring noise' is probably the typical chopper driver noise that you would hear from any current-limited stepper driver.

Even though SparkFun recommends just leaving the center tap wires unconnected (giving a "full-coil" hookup), I believe that it would be better for you to use a "half-coil" hookup (for example, use black and yellow for one phase and tape off green, and use red and white for the other phase and tape off blue). Make sure that the motor power is off before disconnecting and reconnecting the stepper wires.

Check to make sure that you have "holding torque" on each motor when power is applied but GRBL is not running (maybe load the 'blink' sample code into your arduino instead). Double check the Vref value.

Then I would try driving each motor one at a time from a simple arduino sketch, not using GRBL.

Here is some example code that you could try (but make sure that the step and direction I/O pins of the arduino correspond to the ones used by each driver in turn). It would probably be good to define a variable for the step pin and another one for the direction pin, rather than using hard-coded pin numbers 5 and 3 respectively as shown in the code below. I haven't used this code yet with the Pololu drivers, but I did use it when testing a Linistepper driver. It assumes that the step pin is normally LOW, but it goes HIGH for 100 microseconds and then back LOW to make a step pulse. Maybe it would be reasonable to check the A4988 datasheet just to make sure that it is looking for a positive-going step pulse, and that a 100 microsecond pulse is within its specs.

int Distance = 0; // count the number of steps

void setup() {
pinMode(3, OUTPUT); //X-axis direction
pinMode(5, OUTPUT); //X-axis step
digitalWrite(3, LOW);
digitalWrite(5, LOW);
}

void loop() {
digitalWrite(5, HIGH); //step
delayMicroseconds(100);
digitalWrite(5, LOW);

Distance = Distance + 1; // increase step count

delay(50); //wait 50 ms

// Check to see if at the end

if (Distance == 100)
{
// Reverse direction
if (digitalRead(3) == LOW)
{
digitalWrite(3, HIGH);
}
else
{
digitalWrite(3, LOW);
}

// Reset distance to 0
Distance = 0;

// pause for half a second
delay(500);
}
}

That should get your motors turning. If not, perhaps there is a wiring problem of some sort.

[scales11]

Thanks for the advice, here are my results:

I unplugged all motors and stepper drivers except for 1 (leaving the yaxis motor and stepper driver).

Switched wiring to half coils.

I loaded the blink code on my arduino.

With everything powered up, I notice that there is not a significant holding torque. That is to say that it is not much harder to turn the motor when voltage is applied as compared to when the power is off.

I have not tried your custom code yet, but just as an FYI, here are my GRBL settings:
$0=200.000 (x, step/mm)
$1=200.000 (y, step/mm)
$2=200.000 (z, step/mm)
$3=30 (step pulse, usec)
$4=750.000 (default feed, mm/min)
$5=1100.000 (default seek, mm/min)
$6=0 (step port invert mask, int:00000000)
$7=0 (step idle delay, msec)
$8=9.800 (acceleration, mm/sec^2)
$9=0.050 (junction deviation, mm)
$10=0.100 (arc, mm/segment)
$11=25 (n-arc correction, int)
$12=3 (n-decimals, int)
$13=0 (report inches, bool)
$14=1 (auto start, bool)
$15=0 (invert step enable, bool)
$16=0 (hard limits, bool)
$17=0 (homing cycle, bool)
$18=0 (homing dir invert mask, int:00000000)
$19=25.000 (homing feed, mm/min)
$20=250.000 (homing seek, mm/min)
$21=100 (homing debounce, msec)
$22=1.000 (homing pull-off, mm)


I am sure that they are wrong, I initially set them based off of this calculator:
http://homepage.ntlworld.com/r.j.nob...eOko/grblcalc/

But started playing with them once I realized that my motors were not responding.


Does this shine any light on my situation? I am going to look up the wiring right now, but I have already checked it a few times...

[doorknob]

My first thought is that without adequate holding torque, you are not supplying sufficient current to the motor.

If it is a small motor, maybe it's hard to say what "adequate" holding torque is. But if you are using those NEMA 23 motors from SparkFun, the holding torque should make it noticeably harder to turn by hand.

I suppose that I should get my act together and solder up my Pololu drivers and the carrier board, and then I can see for myself how it works with my NEMA 17 motors.

[doorknob]

One other note - if you are going to try the sample code that I listed above, that code does not set the driver's /EN enable signal to enable the driver, nor does it set the /RST high, nor does it set the microstepping mode input pins.

So at the least, you would want to handle the enable LOW and reset HIGH signals in your code (I'm not sure offhand which arduino pins they are connected to). The default setting of the microstepping mode pins is LOW, LOW, LOW (which should give you single-stepping).

[scales11]

I think I will try another power supply. I have a 5V 6A supply that I will try out tonight. It should be enough if I wire up just one driver and motor...right? The motors are rated at 3V 2A.

[doorknob]

5V is going to be too low.

The Pololu A4988 drivers are rated for operation from 8 to 35 volts.

The symptoms that you have described do not sound like your power supply is the cause of the problem. Have you measured the power supply voltage while everything is hooked up? If it shows something close to 24 volts, then you would probably be better off devoting your attention to other things mentioned previously.