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Topic: a4988 clone won't work after current limiting. (Read 604 times) previous topic - next topic

Yogue

The outputs of a stepper motor driver like this must either be completely open (in which case
nothing happens), or connected to an inductive load like a motor winding.  Using a resistive load
Thank you MarkT. This was extremely helpful in understanding how I was risking my a4988.

 Method of shunting is an excellent idea. I tried it over the weekend using a 0.1 Ohm 2W resistor. But I didn't get any reading in my multimeter(in Ammeter mode).

Upon testing my a4988 and stepper motor in the grbl shield, both seem to work fine.

And troubleshooting continues for me! more ideas welcome!





Railroader

Following this topic I just got an idea and tested it on my stepper, a NEMA 17.

Connect Your multimeter in volt-AC-mode to one of the coils and try to run the stepper. Either I read 0 volts or some 8 - 9 volts. It depends of the position of the stepper. Then I know that the stepper driver delivers power.
Another way to check is connecting the stepper and power up the stepper power supply. Then try to rotate the stepper manually. If the stepper rotates easily You have no power to the stepper. If it rotates stepwise but with some effort from You, the stepper, and driver, is alive.

Robin2

#17
Sep 17, 2018, 07:51 pm Last Edit: Sep 17, 2018, 07:53 pm by Robin2
Method of shunting is an excellent idea. I tried it over the weekend using a 0.1 Ohm 2W resistor. But I didn't get any reading in my multimeter(in Ammeter mode).
If you measure the voltage across the 0.1 ohm resistor you can use the formula V / R  = I (Ohms law) to convert the voltage to amps. For example if the reading is 100mV then the calculation would be  0.1 amps / 0.1 ohms = 1 amp

Be sure to do it when the motor is stationary. If there is no reading move the motor by a single step (with the Arduino) and check again.

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

Yogue

Following this topic I just got an idea and tested it on my stepper, a NEMA 17.
I like the idea!

I've a desktop cnc milling machine that I am building, and two motors don't quite rotate, but they are stiff, and as you said, that means they have current in them!

Railroader

Good. If You mechanicaly disconnect Your motors and turn the shafts by hand, how does it feel to rotate them? They should rotate quite easily. Otherwise the problem might be that the motors are overloaded. That should be audioble visible. A stalled, overloaded, stepper, makes a rather characteristc sound very different from normal.
Does Your motors run when being mechanicaly disconnected?

Yogue

Update:

1. My Stepper motor and a4988 worked with grbl shield when I tried the first time.

2. My Stepper motor and a4988 did not work when wired as shown in the picture in original post. I tried setting Enable to low. that made no difference.

3. My Stepper motor and a4988 did not work with grbl shield when I tried the second time with the same grbl shield. Actually, the problem was that there was no grbl prompt on my serial monitor. I had the right port set.
This was really weird, because I had tried the exact same setup successfully a few days ago. Upon researching further, I found that my grbl shield has Arduino nano, and grbl doesn't officially support nano!

My next course of action is to try another shield. but i'm out of ideas on what to do with the simple circuit with a4988 without shield

@Railroder: My steppers don't make any sound. the shaft is free when disconnected ( in grbl shield). the shaft is free when connected with the simple a4988 circuit without grbl shield regardless of power.

Railroader

Oops, Nano... I use UNOs and Protooner boards.
Your reply in #18 tells the motors are powered.
Have You tried to use low level software? I mean creating code that controls the neccesary outputs like enable, set direction, set pulse output high, delay the needed time, set pulse low that ends the step….. This would verify the hardware one step forward.
The issue migh be on a higher level, mismatch between Grbl version, shield version, processor board.

Yogue

Oops, Nano... I use UNOs and Protooner boards.
So, I have not tried the low level code. As of yet, I don't have a good grasp over low level coding for this situation.

Also, sorry for not clarifying it, but I have got two different projects going on:

1. A nano based grbl shield for my cnc router, that has been behaving weirdly-

I could only get one motor to get working. To be fair, I unintentionally ripped the socket on the original nano that was part of the shield, and manually replaced it with another nano. My guess is that the original nano may have been overridden by manufacturer to have uno firmware and was wired internally in the shield as an uno.

2. A bare-bone one a4988 circuit for one stepper motor.

it feels like the theory that I understand superficially isn't working great, and I trying to get a grasp over how to get these a4988s work with stepper motor in a predictable manner and then take my understanding of a4988 to ultimately getting the shield work in a predictable manner.


Robin2

Try this Simple Stepper Code. You may need to adjust the I/O pins to suit your situation.

...R
Stepper Motor Basics

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

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