# Newb needs smooh 1 RPM for Barndoor Tracker Project

Thanks for the info on setting the current limit. As for the smoothness, yes, you are correct, it is not perfect, even at 1/16 microsteps, but it is well within acceptable limits since the gears
(or in my case belt) will easily absorb any irregularities that matter (I actually doubt there are any as most of this shooting is done with very short focal lengths).
As for the DC motor, it requires time consuming verification and adjustment to maintain a constant, precise (a major requirement)
speed, dependent on battery voltage. It is by all means workable, but I am seeking simplification as I usually am shooting time-lapse and stationary stills at the same time.

I set the current limit (.48 volts X 2.5 = 1.2A) and the heating problem is solved. (!)

My next question is regarding stepping mode. (please bare with me, this is all new to me…)

Having set up the a4988 for 1/16th microstep resolution, (MS1,2 and 3 all powered as per schematic below) I was expecting to feel a fine “vibration” (3200 per motor revolution) on the motor shaft when running.
What I am actually feeling (and seeing) is more like full step mode of 200 per rev.
Is this normal or am I, for some reason still in full step mode?

Thx

Update: using the sketch below I have the setup running at VERY close to 2 RPM and I am happy with that for sure.
I am however, curious about the values. I was under the impression that this was all mathematically calculable, but the values I ended up with make no sense to me, specifically, the line: stepper.setSpeed (426.45);
426.45 is … delay in microseconds between steps? Steps per second? What the heck? This is not making any sense to me, and I suspect there is a high likelihood that something is amiss in my sketch so I’m sure someone can explain.
I am a bit uneasy not knowing the explanation for this BUT, I gotta say this is fun in some kinda strange way- ha! (I’m a mechanical tech, not a sparky or coder person)

The following got me to as perfect a 2 RPM as my cell phone timer app, a printed degree wheel and 16 minuets could muster, but IDK exactly why…

[code]
#include <AccelStepper.h>
#include <MultiStepper.h>

// ConstantSpeed.pde
// -- mode: C++ --
//
// Shows how to run AccelStepper in the simplest,
// fixed speed mode with no accelerations
/// \author Mike McCauley (mikem@airspayce.com)
// Id: ConstantSpeed.pde,v 1.1 2011/01/05 01:51:01 mikem Exp mikem
#include <AccelStepper.h>
AccelStepper stepper; // Defaults to AccelStepper::DRIVER (2 pins) on 5, 4
void setup()
{
stepper.setMaxSpeed(1000);
stepper.setSpeed(426.45);
}
void loop()
{
stepper.runSpeed();
}[/code]

Hello.

Unfortunately for your battery life, that sort of temperature is normal for a stepper motor like that. Stepper motors generally draw full power when they are not moving in order to maintain their holding torque. Setting the current limit lower might help, but the motors will still probably be warm.

I am not familiar with the AccelStepper library. Different stepper motors can have different numbers of steps per revolution, and microstepping also changes the number of times the step pin is toggled per full revolution. I do not see anything that looks like it sets that up in the example code you posted that uses the AccelStepper library.

In both the programs you posted, it looks like you are using decimal numbers as arguments in some function calls that might not take decimal number arguments (stepper.setSpeed(426.45); and delay(18.75); for instance). It is possible that these numbers are being rounded or truncated.

It sounds like you had pretty good results with your original code. If you need more precision in your delay, you could use the delayMicroseconds(i); function. As you noted, you would want one step signal every 18.75ms (or 18,750 us) but you should keep in mind that the 1ms delay after you toggle pin 5 low in your code counts in the total for the loop.

Missed steps can occur if there is too much resistance in the mechanical load driven by the stepper motor or if the current limit is too low. In microstepping mode, these missed fractions of a full step can build up, which could make the motor feel like it’s taking larger steps.

-Nathan

With regard to the delayMicroseconds(i) function you referred to, I incorporated it into my original sketch and have it running, I have a question regarding the balance of delay between the first (HIGH to LOW) and second (LOW to HIGH). Should the total delay required (in my case somewhere near 9375 for 2RPM - 6400 steps) be split between the two delays or… ?

I have run the first delay at fifty and also at one with the second delay at 9375 and both run with slightly differing results, but I was wondering if there is a preference for some other reason I am not (yet) aware of.

The only means of checking is a stopwatch app and progressively longer test times to exaggerate error - The 9375 value will need some tweaking for whatever reason I think

Thanks again, I appreciate your help!

## Here’s the latest version (I like it because it’s simple as can be)

``````void setup() {

pinMode(4, OUTPUT);     // Dierction Pin

pinMode(5, OUTPUT);     // Step Pin

digitalWrite(4, LOW);

digitalWrite(5, LOW);

}

void loop()
{
digitalWrite(5, HIGH);   // sets the pin on

delayMicroseconds(1);        // pauses for _  microseconds

digitalWrite(5, LOW);    // sets the pin off

delayMicroseconds(9375);        // pauses for _ microseconds between steps,  close to 2.0 RPM
}``````

Hello.

There is a limit to the speed at which the stepper driver can respond to a signal and for the A4988, that limit is 1us. There is no real reason to be close to the limit, so you might want to change the timing of your delays to something like 5us/9370us. Other than that, I cannot think of a reason why the split between HIGH time and LOW time would affect the step rate.

I think it will be difficult to improve accuracy without making the code more complex. You should keep in mind that the operating frequency of the chip’s clock is about 1/16th of a microsecond and functions can hide code that can take many clock cycles to execute. For instance, the digitalWrite() functions might take several microseconds to execute. There are ways to further improve this, but these sorts of errors are similar in magnitude (one part in 10,000) to the sort of errors caused by variations in the frequencies produced by the clock crystals used for timing by the board itself. I would expect these sorts of timing variations to also be present in devices like stop watches or even camera timers.

If you are noticing errors smaller than 1 part in 1,000, you could look at the BlinkWithoutDelay example included with the Arduino IDE for a code structure that will have slightly better accuracy (your code is very similar to the basic Blink example). There is a micros() function that is similar to the millis() function. If you are noticing errors larger than that, you could be having problems with missed steps, so you could look at ways to decrease the mechanical load on the stepper or increase the current limit for your stepper motor if you are under the limit.

As a final note, I modified your post to use code tags around the code. If you use those in the future, it makes it easier for everyone to follow your posts. You can use them by writing the first part of the following tag before your code and the second part after it:

-Nathan

Thanks for your suggestions and help Nathan and everyone. It is appreciated very much.
I will adjust the delays per your suggestion, make some final tweaks ( to achieve accuracy far in excess of that which is required - ha) and call this part of the project complete!

Heyo! Haven’t checked in for ages, but wanted to give feedback about the “cogging” effect you sort of saw. I believe from what you described, the stepper current limit might be too high to effectively deliver the microstepping waveform you wanted.

What you could try is, if your power requirements allow it, reduce your current limit very slowly until you hear the discrete steps go away.

This is a common problem with extruder motors on 3D printing, that is why I think you might be having this experience (based on your descriptions.)

There may be other things going on and if it’s somethingy you wanted to explore more carefully please remind me again:
Your motor voltage rating, and current rating
Your expected current limit (I think you said it was 1.2A)

I am not sure I really know what it would be besides too high of a current limit, but maybe we can both notice something if we look at it. That said, it might also not be a big concern for you.

Thanks Tomek!
I will give that a shot. I was not sure the current limit could be safely adjusted with the motor running.
I have switched to a smaller (and lighter) motor so, I need to re-adjust the current limit anyway - but with the smaller motor I’m not sure what I will be able to get away with…

Ah! Ok, sounds like you’re still working on things. Great to hear that there’s incremental effort tweaking things.

May I ask what the reason is for changing to a smaller motor?

Weight. The whole mount, with a camera and lens (both pretty heavy) puts one heck of a moment on the tripod and head so, I attempt to minimize this as best I can dimensionally and physically.
I will post a pic of the setup when I finish the new motor installation.

Picture will help, cool. Yeah, sometimes you can also get away with moving the motor off-assembly, via clever use of lines and belt. Or you might just find a smaller motor plenty strong enough (especially if you gear it for your slow RPM) But I don’t have a good picture of your project.