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Stepper Motor Failing--Electrical Interference?

12/20/2016 4:06 AM

Background: I've built a 6' x 6' 'H' style plotter as a drawing machine. It has 2 stepper motors controlling the Y axis and 1 stepper for the X axis (the "bar" in the "H"), layout below. The Y axis motors branch from the Y axis stepper driver and the wiring on the "far" motor is reversed so that the motors move the carriage in the same direction. There is also a smaller stepper for the Z axis, which is powered but not used yet.

I am using matched stepper motors for the X and Y axes (specs below). They are rated at 5v 1A. I am controlling this whole thing using an Arduino and a grbl shield. The grbl shield usesTI DRV8818 stepper drivers which are rated at 2.5A. I was powering the motors first with a 24v 3A max bench power supply and today tried a 12v 20A power supply. I have a small fan to cool the board.

Problem: The "far" (from the power source) Y axis stepper is intermittently failing. When the problem occurs it stutters (as though it were wired incorrectly) or doesn't turn at all.

I realize that it is hard to diagnose a problem like this from what I have provided, but maybe there is something I can test? Here is what I have done so far:

Switched the Y axis motors to check if there is actual motor failure. Again, only the "far" motor failed, so the motors seem okay.

Removed the load (removed the belts) so the motors could run free. Similar failure symptoms on the "far" motor.

The stepper drivers are "chopper" type (variable current) and the grbl shield has current adjustment pots for each axis so I've tried dialing the current up and down.

I've tried various feed rates (affecting the speed at which the motors turn) as well as testing other settings (acceleration, etc).

What I don't get and am really stumped by is why only one of the Y axis motors is failing. The "near" motor works fine. If my power supply was inadequate or the stepper drivers were in thermal shutdown, both motors should fail.

Long-winded question, I realize, but I have tried to provide as much detail as possible. I don't know what else I can try to diagnose the problem.

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#1

Re: Stepper motor failing. Electrical interference?

12/20/2016 4:16 AM

The motors remained wired together as shown even when swapped and the 'far' motor still failed? When you swapped motors did you change the connections also? If so is it possible the phases on the far motor are not connected properly?

I'd also put each motor on its own dedicated driver. Wiring them together as you have can introduce electrical weirdness.

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#2
In reply to #1

Re: Stepper motor failing. Electrical interference?

12/20/2016 4:42 AM

the 57BYGH001 stepper motor has six leads. You show four.

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#25
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Re: Stepper motor failing. Electrical interference?

12/21/2016 4:19 AM

How many leads you use, depends on the type of driver used. A 6 lead motor can use either type of driver, that is 4 or six leads, but he may have a wiring error because one motor's leads, colour coded, but wrong....

4 leads = Bipolar. 6 Leads = Bipolar (center connections not required) or Unipolar all connections needed (I hope I got them the right way round!!)

The Bipolar changes the polarity of both connections to any pole coil, and the Unipolar, keeps the center connection usually on ground and applies a positive voltage to one or the other end for a change in direction.

Because only half a coil is used at any one time, the unipolar connection does not get as much torque from the motor as Bipolar does....at extreme speeds, the Bipolar can run faster and more accurately and is usually preferred by professionals....

Its easy to use an ohmmeter to identify all the leads 100%.

See here:-

https://en.wikipedia.org/wiki/Stepper_motor

Here is a Unipolar diagram, illustrating as to why it can be driven with either driver type:-

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#28
In reply to #25

Re: Stepper motor failing. Electrical interference?

12/21/2016 4:17 PM

Sorry, correction, Unipolar needs 6 leads. Finger trouble!!

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#33
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Re: Stepper motor failing. Electrical interference?

12/21/2016 7:25 PM

Yes. Some also connect the two centre leads together internally and bring it out as a 5th lead.

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#24
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Re: Stepper motor failing. Electrical interference?

12/21/2016 4:03 AM

Good start, I would ask him to actually show us the connections he made for each motor, exactly as he did it..

For example, if he reversed both coils, he has simply kicked himself in the butt!!

Also, he should unplug the "good" motor and see if the "bad" motor reacts correctly.

My guess is wiring. But he may have a bad motor, swapping them would show this better I feel....

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#27
In reply to #24

Re: Stepper motor failing. Electrical interference?

12/21/2016 10:35 AM

Good thought, reversing both coils sounds like the kind of mistake that someone might make without thinking.

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#42
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Re: Stepper motor failing. Electrical interference?

12/27/2016 9:48 AM

You and I both know that more often than not, one picture has the weight of an entire lengthy tome.

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#43
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Re: Stepper motor failing. Electrical interference?

12/27/2016 11:17 AM

How true!

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#3

Re: Stepper motor failing. Electrical interference?

12/20/2016 4:59 AM

What happens if you disconnect Y1? Does Y2 run OK then?

The problem is intermittent: is one of the connectors at Y2 a little bit loose? Try re-crimping and some contact cleaner.

Have you got an oscilloscope so that you can see what signals are actually getting to the stepper motor?

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#4

Re: Stepper motor failing. Electrical interference?

12/20/2016 7:12 AM

What you are doing is very interesting. I would love to dig into the data sheets and try to give great suggestions but I just don't have time now.

After several decades of electronics I still find myself and others repeating some of the same beginner mistakes. With respectful intent I ask the following beginner questions:

  1. Are you confident that the wall wart supplying power to your Arduino is rated IN EXCESS of your power requirements?
  2. Are all connectors properly soldered/crimped and in good condition?
  3. Are you confident that it is wired the way you think it is?
  4. Is the motor inrush that the stepper driver might be passing causing problems?
  5. Any chance you have a "not wire" in a place where you think you have a good wire?
  6. Are you sure your motors are wired up correctly?
  7. Are there any polyfuses in the circuit that act properly when you are debugging but cause problems when you are operating?
  8. Are you making any assumptions that are possibly not valid? Remember what "they" say about assumptions, they make an ASS out of U and Me (PTIONS).
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#5

Re: Stepper motor failing. Electrical interference?

12/20/2016 8:03 AM

The most likely diagnosis given the symptoms you've described is a bad connection to one of the windings on the "failing" motor.

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#6
In reply to #5

Re: Stepper motor failing. Electrical interference?

12/20/2016 8:26 AM

..which cannot be seen from here.

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#7

Re: Stepper motor failing. Electrical interference?

12/20/2016 9:33 AM

Check the resistance between the far motor and the driver, or check for voltage drop (AC) in the wiring between the driver and motor while the driver is turning the motor. Having swapped the motors, wiring and connections are the only difference between the two motors.

Another thought: Possibly your driver is only marginally capable of driving two motors. A slight added resistance in the far circuit could make the difference.

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#8

Re: Stepper motor failing. Electrical interference?

12/20/2016 10:03 AM

On general principles I don't like two motors driving the same axis of motion, unless there is some designed in slip mechanism (e.g. friction clutch, fluid bypass, flexible shaft). If there isn't a planned slip then there will often be times where the two motors will be fighting each other due to some random misalignment. I also do not like the idea of driving these two motors in parallel with the same driver electronics. The available torque from each motor will be different and uncontrolled. Thus a misalignment of the axis of motion will more likely happen. However, this is just my preference. I would not be surprised to find this configuration does work in some application. Most likely the designer got lucky instead of carefully engineering around my concerns but I don't dispute that a clever engineer might succeed.

I wish you good luck.

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#14
In reply to #8

Re: Stepper motor failing. Electrical interference?

12/20/2016 2:11 PM

My feeling also.

But in paragraph 6 of initial post it says taking drive belts off motors does not stop fault symptom.

I have asked for a connection list.

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#9

Re: Stepper motor failing. Electrical interference?

12/20/2016 10:19 AM

Is this just a plan stepper motor or is it a hybrid stepper motor (Closed loop with an encoder)

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#11
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Re: Stepper motor failing. Electrical interference?

12/20/2016 12:17 PM
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#10

Re: Stepper motor failing. Electrical interference?

12/20/2016 11:44 AM

As you probably know, wiring to/from Arduino boards can be a bit tricky, and often times there

will be intermittent connections, or "no wires" where you think there is a solid wire.

Go through the wiring with resistance or continuity checks. Make sure never to apply negative

voltage on any part of Arduino.

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#12

Re: Stepper motor failing. Electrical interference?

12/20/2016 1:26 PM

It would help if you explained what you mean by "reversing the connections".

Give us a list e.g.

Driver , Y1 , Y2

AOUT1, RED, YELLOW

AOUT2, GREEN, BLUE

BOUT1, YELLOW, RED

BOUT2, BLUE, GREEN

As pointed out, that the motor has 6 leads and the Driver 4 needs

addressing.

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#13
In reply to #12

Re: Stepper motor failing. Electrical interference?

12/20/2016 1:48 PM

The symptoms sound to me like the phases are out-of-order on the far motor. I don't know why the OP doesn't just use an idler where the far motor is. If he needs more torque, use a bigger motor. As mentioned earlier, two motors driving the same load sets the scene for all kinds of problems, even when the phases are done right.

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#22
In reply to #12

Re: Stepper motor failing. Electrical interference?

12/20/2016 7:03 PM

If two connections to a step motor winding are exchanged (such as A+ and A-, or B+ and B-), the motor will behave exactly the same but with the direction of rotation reversed.

As these are steppers, they should exactly track each other (within the minimum step angle, typically 1.8º (or 0.9º in half-step mode), unlike e.g. servo motors which can lead or lag by a few degrees, leading to "crabbing", which could jam the drive system.

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#15

Re: Stepper Motor Failing--Electrical Interference?

12/20/2016 3:09 PM

Here's someone who is trying to the same thing as you are (unless it is you ), i.e., driving two stepper motors at the same time.

http://forum.arduino.cc/index.php?topic=1

You just may have to bite the bullet and use another DRV8818 driver for the second y-axis motor.

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#16
In reply to #15

Re: Stepper Motor Failing--Electrical Interference?

12/20/2016 3:16 PM

I'm just wondering if the signal pulse is just too weak.

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#17
In reply to #15

Re: Stepper Motor Failing--Electrical Interference?

12/20/2016 3:39 PM

Why not put a relay into the mix? As long as it is not a solid state relay, it might work. (SSR's are notorious for not turning off when the relayed power is DC.)

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#21
In reply to #15

Re: Stepper Motor Failing--Electrical Interference?

12/20/2016 4:41 PM
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#18

Re: Stepper Motor Failing--Electrical Interference?

12/20/2016 3:40 PM

I could be mistaken, but the 57BJGH001 is described as unipolar [4 windings, the third wire of each winding is power common centre-tap, 6 leads],

while the Driver circuit is bipolar [two windings, 4 leads].

Maybe a three-legged race by donkey and monkey, falling over sometimes.........

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#19
In reply to #18

Re: Stepper Motor Failing--Electrical Interference?

12/20/2016 4:12 PM

A unipolar motor can use a unipolar power supply, using the center tap as ground and energizing one end or the other of each winding to step. It makes for a simpler driver. Of course, you can ignore the center taps on the motor if you have a bipolar, 4-wire, driver (as in this case).

Unipolar stepper motor coils

https://en.wikipedia.org/wiki/Stepper_motor

A bipolar driver has an output circuit resembling the letter H for each of the motor coils. The top of the vertical bars of the H are connected to the positive side of the power supply and the bottom to the negative supply. The motor coil is the crossbar of the H. The switching circuitry turns on either the right-top and bottom-left switches to allow current to flow right-to-left through the coil, or left-top and bottom-right to allow current to flow left-to-right through the coil.

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#20
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Re: Stepper Motor Failing--Electrical Interference?

12/20/2016 4:17 PM

And H drives make really powerful pulsed power in some applications such as electrolysis, as I understand.

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#23
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Re: Stepper Motor Failing--Electrical Interference?

12/21/2016 12:17 AM

H-drives aren't really necessary for pulsed power per se. If you really need a shitload of pulsed power, Marx generators can produce titanic pulses. It's what Sandia's Z Pulsed Power Facility uses (formerly known as the 'zeta-pinch-' or 'z-machine'). The pulse-compression subsystem in this machine uses ultra-pure, deionised water for the dielectric (water is a fantastic dielectric actually, or would be were it not prone to electrolysis, but these pulses happen so fast - under 100 ns - that it isn't an issue).

An even more powerful pulse generator, called a Linear Transformer Driver, will be used in subsequent z-machine designs; in one of them, called the Z-IFE, the LTD is anticipated to produce current pulses on the order of 70 million amperes, for a peak power of 1 petawatt (1015 watts).

Not related to stepper motors, to be sure (hence the OT), but I thought you'd be interested as you brought up the subject of pulsed power.

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#30
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Re: Stepper Motor Failing--Electrical Interference?

12/21/2016 4:33 PM

That is highly interesting to me. At University of Illinois Champaign-Urbana, back in 1983, one of the guys in our research group

was working on Theta-pinch, only about 100,000 amps through a spectrographic spark. The thing was able to ionize aluminum atoms all the way up to the fifth ionization, according to the spectra.

Heck, I am just electrolyzing some water, but it is for LENR research. I know of one company that is using about 100,000 amps to perturb the crystal structure of nickel wire loaded with hydrogen, and they are getting heat COP of about 2-3. I think they went public. Brillouin Energy is the name...as I recall. Seems to be a very adept exploitation of the Heisenberg principle.

If one has a Petawatt, will not one burn one's hand?

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#26
In reply to #19

Re: Stepper Motor Failing--Electrical Interference?

12/21/2016 10:16 AM

So the motor will work with bi-polar. I have tried several times to trace proper data sheet for motor on internet - without success.

No one has yet referenced more than connection and resistance data for the motor type - in the vague way of some data, it is not clear whether 5 volts and 5 ohms and 5 mH applies to half a winding or the whole - unipolar = driving half-winding. A whole winding might be 10 volts, 10 ohms, 20 mH.

The driver datasheet indicates there is a shutdown current limit circuit, about 2 amps max and a PWM limit which is adjustable. Two motors would be 2.4 amps or more

With two motors, and 12V supply it may be that the PWM limit is only allowing half the proper current to each motor - one is likely to malfunction, probably the one with the longest wires = Y2, it may work until it heats up and its winding resistance increases.

The original post has not told anything more than in first post, nothing about how fast he is driving motor, connections, PWM current limit.

The advice to use a driver for each motor seems the best, particularly if part stepping is being used to get better plotter resolution.

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#29
In reply to #26

Re: Stepper Motor Failing--Electrical Interference?

12/21/2016 4:26 PM

In my estimation, except for tiny motors, 12 volts is too low a voltage.

I stick with 24 volts as a minimum...Its more important to keep below the max current, and have the higher voltage to get more power which = more torque.

Yours are 5 volt 1 amp. For continuous operation, steppers are pulsed, not continuous! So higher voltages are allowed within reason...

I am sure that someone here can provide tables to allow you to drive for max torque!! At first, keep an eye on temperature....

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#31
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Re: Stepper Motor Failing--Electrical Interference?

12/21/2016 4:35 PM

Too bad there is no category : very good answer, or excellent answer. WTG Andy!!!

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#32
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Re: Stepper Motor Failing--Electrical Interference?

12/21/2016 7:16 PM

As I'm sure you know, the reason why higher voltage is needed (especially at higher step rates where there are only milliseconds between switching a winding on and off) is that the inductance of the coils means it takes a while to get enough current flowing to generate the required torque.

The higher voltage means that the current can build up more quickly.

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#34

Re: Stepper Motor Failing--Electrical Interference?

12/23/2016 2:06 PM

Steppers are prone to miss step and stall for a variety of reasons....accelerating too fast- and at higher speeds are harmonic sensitive,

harmonic can be mechanical ( I believe this is most likely the problem as you are using 2 motors on 1 shaft) and both motor step signals

do not happen at the same time....1 motor steps and temporarily sees the other as an additional load...you would be better off to use a

larger motor and driver, or reduce the load by pulley reduction and deal with a slower speed on that axis with the smaller motor...

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#36
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Re: Stepper Motor Failing--Electrical Interference?

12/23/2016 2:26 PM

I have seen dual motors used before, with apparently no problems, provided they are identical, but I have never sone it myself.... Your post is good and I believe accurate, if there are any differences between the motors.

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#37
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Re: Stepper Motor Failing--Electrical Interference?

12/24/2016 8:02 PM

Hi Andy, what I was thinking is the step motors cog, i.e. step, stop, step, stop, and do this at some clock freq, controlled by the 'arduino', and these clocks are not synced so both motors step at the same time, so the clocked motor sees the stationary motor as an additional load and stalls...might work to use the same clock on both drivers...if both are running in the same direction...if they're direct coupled ti opposite ends of the shaft, the timing through the driver running the motor in the opposite direction could differ and again cause a stall...

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#38
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Re: Stepper Motor Failing--Electrical Interference?

12/24/2016 8:37 PM

The motors are connected in parallel - to the same driver via the same bits of wire! How could they possibly not step at the same time?

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#39
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Re: Stepper Motor Failing--Electrical Interference?

12/25/2016 9:22 AM

If they are paralleled on the same driver you probably have harmonic ringing between the coils of 1 motor feeding back to the other motor, due to the imperfect matching of the coils...

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#41
In reply to #38

Re: Stepper Motor Failing--Electrical Interference?

12/25/2016 1:43 PM

If one is not allowed to, by being held between positions a little maybe.....because the toothed wheels are not positioned correctly.

Se my previous post.

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#40
In reply to #37

Re: Stepper Motor Failing--Electrical Interference?

12/25/2016 1:42 PM

I have negated the OT someone gave you.

You set me thinking, I wonder if the small toothed wheels mounted on the motors were wrongly set, so one of the other motor is not at a set position, maybe what you fear (assuming I understood you correctly) could be happening.

Assuming not shafts with flats on them, loosening the set screws on one and moving the toothed belt a touch then tightening them up, should do it!!

With flats on the shaft, one or both motors may need to be turned a tiny amount....smaller screws with washers might allow some small movement!!

I hope I made myself clear.....

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#35

Re: Stepper Motor Failing--Electrical Interference?

12/23/2016 2:17 PM

Afterthought: alter your software so the motors sequence is switched in software and you'll probably find the other one drops out...

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#44

Re: Stepper Motor Failing--Electrical Interference?

12/27/2016 12:24 PM

Switch to an L/R driver and I'd bet the problem goes away...

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