Big Easy "but it aint"

Ok, I need a bit of help. Fustrated with this simple example here... http://bildr.org/2012/11/big-easy-driver-arduino/#mototPairs

I'm trying this example verbatim. I do get a bit confused with libraries though(importing them and making them work. But my code compiles and uploads fine(the same code in the link). My environment is...

I've tripled checked my connections and verified each phase of the stepper with a meter.

If someone could lend a helping hand with this or point me to another tutorial to get me up and running I'll send you a pound of boiled peanuts whose aroma is reaching me from the kitchen:-)

Regards- Paul

Code compiles, and uploads, great. What seems to be the problem? What do you expect to happen, and what is different than that?

The motor has 2 ohm windings, with 1.7 amps current per winding maximum. With a 12 volt supply, the motor will draw about 6 amperes per winding.

The A4988 chip on the Big Easy driver can supply a bit over 1 ampere/winding before it starts to overheat and shut down, so it is absolutely essential for you to follow the instructions in the BED manual to set the current limit appropriately.

TY! I'll take a look at the manual. Would this happen to involve the pot on the board? I haven't made any adjustments on that.

starmatter:
Would this happen to involve the pot on the board?

I thought the natural sequence of events would be

  • Read the manual
  • Order the device
  • Receive the device
  • “Oh look, there is a pot on the board”
  • “I wonder what it does?”
  • Read the manual again
  • “I wonder how I should use that with the motor I have?”
  • Ask questions

It is perfectly reasonable to ask a question like “I have read the manual and it says XXX and I don’t understand what they mean”. It is not reasonable to try to use a complex device without reading the manual first.

…R

Manual ?? You mean that little book in the empty box in the landfill? Never done that myself. :roll_eyes:

Ok, got a question. The section on current limiting has me baffled. Can you interpret for me please...


Internal PWM Current Control. Each full-bridge is controlled by a fixed off-time PWM current control circuit that limits the load current to a desired value, ITRIP . Initially, a diagonal pair of source and sink FET outputs are enabled and current flows through the motor winding and the current sense resistor, RSx. When the voltage across RSx equals the DAC output voltage, the current sense comparator resets the PWM latch. The latch then turns off either the source FETs (when in Slow Decay Mode) or the sink and source FETs (when in Mixed Decay Mode). The maximum value of current limiting is set by the selection of RSx and the voltage at the VREF pin. The transconductance function is approximated by the maximum value of current limiting, ITripMAX (A), which is set by ITripMAX = VREF / ( 8  RS) where RS is the resistance of the sense resistor (Ω) and VREF is the input voltage on the REF pin (V). The DAC output reduces the VREF output to the current sense comparator in precise steps, such that Itrip = (%ITripMAX / 100) × ITripMAX (See table 2 for %ITripMAX at each step.)

Got it running. Had some wiring issues. But it's rather jumpy and noisy. I'm trying to understand this manual. I have attempted to adjust the pot little by little but the stepper either turns REAL slow or not at all. But in either case it is attempting to move. I just don't want to break the pot by turning it too far. Am I on the right track here? Thanks!

I don’t have a BigEasy driver but it uses the same A4988 as the Pololu A4988 stepper driver and Pololu has very clear advice for adjusting the current limit. I don’t know if the BigEasy driver uses the same value for the current sense resistor.

Make a pencil drawing showing all the wiring connections and post a photo of the drawing. Note that a photo of your hardware is not suitable.

Also post your code.

And please use the code button </> so your code looks like this and is easy to copy to a text editor

…R

Thanks. Sure, I can make a drawing and code sample. Working on it but in the meantime you can follow the link to the example I posted above and there you will see the wiring and code just as mine is.
BTW, I do have the Pololu driver you mentioned.

Here is basically what I have, please pardon my schematic(or lack of) knowledge…

!(http://C:\Users\Paul\Documents\Brake Alert)

and the code…

//This is an example of how you would control 1 stepper

#include <AccelStepper.h>

int motorSpeed = 9600; //maximum steps per second (about 3rps / at 16 microsteps)
int motorAccel = 80000; //steps/second/second to accelerate

int motorDirPin = 2; //digital pin 2
int motorStepPin = 3; //digital pin 3

//set up the accelStepper intance
//the "1" tells it we are using a driver
AccelStepper stepper(1, motorStepPin, motorDirPin); 



void setup(){
 stepper.setMaxSpeed(motorSpeed);
 stepper.setSpeed(motorSpeed);
 stepper.setAcceleration(motorAccel);
 
 stepper.moveTo(2000); //move 32000 steps (should be 10 rev)
}

void loop(){
 
 //if stepper is at desired location
 if (stepper.distanceToGo() == 0){
  //go the other way the same amount of steps
  //so if current position is 400 steps out, go position -400
  stepper.moveTo(-stepper.currentPosition()); 
 }
 

 
 //these must be called as often as possible to ensure smooth operation
 //any delay will cause jerky motion
 stepper.run();
}

One thing I noticed while reading about the pololu is that they recommend a capacitor across power source especially for longer cables. And my power is about 3 feet long. And also my wiring to the stepper is about 3 feet. Both are probably 22guage or larger. Don’t know if this could be an issue.

Appreciate your support.

BTW, I do have the Pololu driver you mentioned.

Then why did you tell us you have the "Big Easy Driver"? They aren't the same. Follow the Pololu instructions for adjusting the current limit on the Pololu driver.

Don't know if this could be an issue.

Yes, it is an issue. Use the recommended capacitor on the power leads, as close to the board as possible.

I meant that I own a Pololu, I'm NOT using it but rather the Big Easy.

Does the BigEasydriver documentation recommend external capacitors?

...R

Does the BigEasydriver documentation recommend external capacitors?

It is a good idea to add one and certainly can’t hurt.

As an aside, the Pololu folks are far more conscientious than most hobby board manufacturers, like Sparkfun and Adafruit. I would not expect Sparkfun engineers, or the designer of the Big Easy Driver to follow up on complaints of occasional device failures due to something like long leads.

The document is not easy for an amateur to read. In fact the words “Big Easy” are not even mentioned. I believe the document is more about the main chip and not much at all to do with the Big Easy itself. That’s what has made this whole experience difficult for me. Actually I did go over it and many other documents before my first post. There may be another document out there but I failed to locate it.

I will try a capacitor across the motor supply. Beyond that I think I will simply switch to the Pololu. I’m getting tired of fighting this battle.

Thanks to all!
SM

starmatter: The document is not easy for an amateur to read.

I don't know what document you are referring to. I was referring to the Sparkfun web page and all of its links

...R

Oh my! You should see what I’ve been reading! This is much better!! I purchased mine from robotshop. And when I downloaded their documentation on the Big Easy well, that’s what I had to work with(yuk).

TY!